justjuiceit4:
The reason the dealership uses lower octane gas is to reduce costs. In addition, the dealership expects that the car will be driven normally. When you drive a car normally, you don't use the same level of energy as you would, if you drove it like you stole it. So, low octane gas is okay for normal everyday driving.
For those, with G-35 Coupe, who drive them hard, please, and please, use what the manuals have suggested. This is not about whther one os good or not. It is about the thermodynamic properties of both gas grades. Each gas grade will produce some level of resistance to combustion, which translates into energy production in your combustion chanbers. The higher the combustion resistance, the more gas will need to be burned to make up for the expected combustion levels set in your ECU.
In the same vein, The lower the combustion resistance, the less gas will need to be burned to make up for the expected combustion levels set in your ECU.
And, in fact, moding your G-35 Coupe with good and well established air intake like Injen, stillen, JWT Pop charger, is a very good thing for your engine, so long as dirt and dust don't make it through the filter elements. You actually have far less resistance in the combustion chamber, and more energy produced, per each mile per gallon.
This isn't necessarily an opinion. This is thermodynamics.
I got into auto thermodynamics when I noticed that the black hood bra that makes the front of most cars look good, seemed to be the culprit behind a failed radiator in my little car (Nissan). Well, I took time to study why that occured, and what I doscovered was amazing. However, I must warn that this is not he same for all cars.
Wel, I realized that over time, those hood bras accumulate dust from everyday driving. Eventhogh the hood bras are made of leather, there a re still portions of the bras, usually at the seems, or in the small stitched nettings, that accumulate and store the dust in cotton like strands. With rain, the dust moves even futher into those seems, and with the sun, the dust is baked into the material. Over time, this swells the leather parts of the hood bra, and it starts restricting airflow to parts of your radiator in small amounts. And, then, one day, when you least expected it, your radiator that should have lastred 6 years or more, will suddenly quit. Radiators need all the airflow thay can get. This is a serious heat transfer issue.
What do you think?
Re-Tuning G35 engines to run on lower Octane
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!979TransAm
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Re: (Jacko3)
Guys Remember don't get it twisted, too high or too low of an octane rating can hurt performance. Don't think higher octane = more power and just better. Most cars have are tuned to an optimum level of octane, Hence your manual recommends you run 91.
Re: (!979TransAm)
I think what you are saying is that - to benefit from the potential engineered into your engine, you should run the factory specified octane gas. Running lesser octane results in lesser performance. Lesser performance is not a problem for many.!979TransAm wrote:... Don't think higher octane = more power and just better. Most cars have are tuned to an optimum level of octane, Hence your manual recommends you run 91.
On another note, the news just reported that estimate gas prices are expected to top 4 bucks a gallon by this spring. So, there may be more people running 87 octane for their daily needs.
Re: (rn79870)
rn79870:
You are exactly right! All your engines potential is already stored as discrete data in your ECU.
You are exactly right! All your engines potential is already stored as discrete data in your ECU.
Re: (Jacko3)
You know when I would take my G-35 sedan into the dealer for service (and that front brake recall.) I put in 87 octane in the loaner upon return. I asked the service rep before I did it and he said that he doesn't like it but everyone else is doing it so he's not going to stop me.
BTW if any of you are in Miami and you use South Motors Infiti I suggest talking to Steve over that other guy (whatever his name is.)
I never noticed anything different come to think about it. But again I am talking about my Baby. I must admit there are times I want to just get rid of it and then, like last night I drove it on mostly vacent streets to run an errand and I am once again reminded why I got it.
Back to subject: So you guys are saying if I put 87 octane in it won't hurt it as long as I don't put the engine hard? Forget the Octane boosts as a waste of time? Synthetics are good? And just hope for a huge new oil redeposit discovery real soon?
BTW if any of you are in Miami and you use South Motors Infiti I suggest talking to Steve over that other guy (whatever his name is.)
I never noticed anything different come to think about it. But again I am talking about my Baby. I must admit there are times I want to just get rid of it and then, like last night I drove it on mostly vacent streets to run an errand and I am once again reminded why I got it.
Back to subject: So you guys are saying if I put 87 octane in it won't hurt it as long as I don't put the engine hard? Forget the Octane boosts as a waste of time? Synthetics are good? And just hope for a huge new oil redeposit discovery real soon?
Re: (Davgreg)
87 will work just fine if it is a daily driver and if you don't routinely push it too hard, like very high RPMs. Regular dino oil is also okay if you drive normally and don't stress the engine routinely. If not I would advice you to use a higher octane grade gas and a better engine oil--synthetic. But over time, expect a drop in vehicle capability, and a build up of all kinds of acids, sludge, and othjer harmful deposits that degrade many engines.
Of course, if you plan to keep the car for 6 years, I think regular dino oil and 87 octane gas is okay.
But for me, I am totally crazy and hard on my car, which apparently degrades it as well. But that process is significantly reduced and inhibited as a result of the types and quality of fluids I use. If U sed dino oil and 87 octane to drive the way I do, I should be expecting big repair bills by age 4 of my car.
The quaity fluids I use allow me to get the same 6 years out of my car, driving it hard, as you would using the regular type fluids, driving your car normally.
Driving habit counts.
Of course, if you plan to keep the car for 6 years, I think regular dino oil and 87 octane gas is okay.
But for me, I am totally crazy and hard on my car, which apparently degrades it as well. But that process is significantly reduced and inhibited as a result of the types and quality of fluids I use. If U sed dino oil and 87 octane to drive the way I do, I should be expecting big repair bills by age 4 of my car.
The quaity fluids I use allow me to get the same 6 years out of my car, driving it hard, as you would using the regular type fluids, driving your car normally.
Driving habit counts.
Re: (redhed)
That's the truth. The stock 3.69's are way to low for freeway driving. If we could get another 10%, say 3.30s as an aftermarket option, I'd seriously look into it. It isn't just the mileage, I hate seeing the tach over 3k when cruising. My ex-Maxima was 400+rpm lower at freeway speeds, and the mileage was always in the 26 to 30 range (depending whether I went inland - hilly, or up/down the coast - flat land.)redhed wrote:about the only thing that would truly decrease fuel consumption on the G would be a taller overdrive ratio and/or taller rear axle ratio. the engine runs too many rpms on the interstate cruising...jmo.
Re: (rn79870)
If you're worried about gas you probly have the wrong car. High performance does have a cost.
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Sentientbydesign
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Re: (Jacko3)
Jack,
Let's clarify something before too may people read what you stated and believe it.
The higher the octane rating, the higher the fuel's resistance to combustion. Not the other way around. The idea is that we don't want the fuel to start combusting before the compression stroke is completed. If it does, then it will essentiall push against the rotationally "correct" direction of the crankshaft producing a knock.
Lower octane fuel will combust without spark in some situations, especially when cylinder temperatures are very high. It's kind of like if guy gets too excited with a hot woman and *coughs* too early. Sorry kiddies.
Also, these numbers that you're proposing for longevity of the vehicle are all speculative. I appologize if I'm being obnoxious, but there are a lot of non-members and noobs who read this information and misinforming people is a major fear of mine.
I recently read that the engineers designed the VQ for the G to last at least 200k miles. I don't know the validity of that claim, but if we assume it is correct for speculation purposes (I'm a math major, we have to assume all of the time to find answers), then that would make the longevity of the car somewhere in the 10-15 year range depending on miles driven per year, driving style...etc. I personally think the electronics on the car will die before the engine stops.
If I remember correctly rn79870, there is a JDM option to make the final reduction gearing different (in the differential). PLEASE check it out and let me know if that's what you're looking for. I'd be up for that mod too.
Teflon, that is completely untrue. We are not trying to get Civic numbers for fuel economy. Just something closer to the EPA ratings. I'm close to 2 MPG lower than the EPA city average. I'd be content with 19MPG in the city and somewhere around 25 on the HWY.
Modified by Sentientbydesign at 11:08 AM 2/1/2008
Let's clarify something before too may people read what you stated and believe it.
The higher the octane rating, the higher the fuel's resistance to combustion. Not the other way around. The idea is that we don't want the fuel to start combusting before the compression stroke is completed. If it does, then it will essentiall push against the rotationally "correct" direction of the crankshaft producing a knock.
Lower octane fuel will combust without spark in some situations, especially when cylinder temperatures are very high. It's kind of like if guy gets too excited with a hot woman and *coughs* too early. Sorry kiddies.
Also, these numbers that you're proposing for longevity of the vehicle are all speculative. I appologize if I'm being obnoxious, but there are a lot of non-members and noobs who read this information and misinforming people is a major fear of mine.
I recently read that the engineers designed the VQ for the G to last at least 200k miles. I don't know the validity of that claim, but if we assume it is correct for speculation purposes (I'm a math major, we have to assume all of the time to find answers), then that would make the longevity of the car somewhere in the 10-15 year range depending on miles driven per year, driving style...etc. I personally think the electronics on the car will die before the engine stops.
If I remember correctly rn79870, there is a JDM option to make the final reduction gearing different (in the differential). PLEASE check it out and let me know if that's what you're looking for. I'd be up for that mod too.
Teflon, that is completely untrue. We are not trying to get Civic numbers for fuel economy. Just something closer to the EPA ratings. I'm close to 2 MPG lower than the EPA city average. I'd be content with 19MPG in the city and somewhere around 25 on the HWY.
Modified by Sentientbydesign at 11:08 AM 2/1/2008
Re: (Jacko3)
As for underdrive pulleys, as long ast teh cranck shaft is internally harmonically balanced, as some cars do, to maintain a safe level that turns your water pump, power steering fluid, and other pumps, becasue of the smaller size of the pulley set, you will need to drive the car much faster and harder, at higher RPMs. A traffic stop or a long traffic jam with an underdrive pulley is not a great idea. What you loose in pulley size, you have to gain in engine speed. I would actually advice anyone with an underdrive crank pulley to raise their engine timing by about 2 - 3 degrees and no more than 950 rpm at idle. This is to account for periods of idling when the fluids are not moving fast enough as a result of the underdriving.
It is true that fluids moving too slowly actually enhances the life span of the water pump anf power steering pump, as a result of underdriving. However, these equipment have fluids that were designed to move at certain speeds within these equipment. Thus, when these fliuds fail to meet their expected flow rates, they allow the ofrmation of acids and chemical that may actually attack the internals of the equipment that pump them throughout the vehicle. It is the same thing as letting a new car sit still for days without driving it regularly. Over time, the car degrades and soon you will need new equipment becasue the fluids in the car have begin to attack and deteriorate the equipment that pump them throughout the car.
The other alternative is to buy a pulley set that does not require underdriving. so, all you worry about is the internal harmonics of the crankshaft. A crankshaft that looses its harmony or harmonics will destroy the bushings and seal that keep it tightly set in the grooves that connect it to the pulleys. When you have no internal harmony, then, you have internal vibrations. This can be fixed but you are looking at many hours of removing covers, pulleys and worn bushings and seals.
These are my opinion basedon what i have been able to garner out there!
It is true that fluids moving too slowly actually enhances the life span of the water pump anf power steering pump, as a result of underdriving. However, these equipment have fluids that were designed to move at certain speeds within these equipment. Thus, when these fliuds fail to meet their expected flow rates, they allow the ofrmation of acids and chemical that may actually attack the internals of the equipment that pump them throughout the vehicle. It is the same thing as letting a new car sit still for days without driving it regularly. Over time, the car degrades and soon you will need new equipment becasue the fluids in the car have begin to attack and deteriorate the equipment that pump them throughout the car.
The other alternative is to buy a pulley set that does not require underdriving. so, all you worry about is the internal harmonics of the crankshaft. A crankshaft that looses its harmony or harmonics will destroy the bushings and seal that keep it tightly set in the grooves that connect it to the pulleys. When you have no internal harmony, then, you have internal vibrations. This can be fixed but you are looking at many hours of removing covers, pulleys and worn bushings and seals.
These are my opinion basedon what i have been able to garner out there!
Re: (Sentientbydesign)
Sentientbydesign:
This is what I said basedon your ealier comments, "Lower octane gas will resist combustion far more than higher octane gas. The thermodynamic effect is that you will use or require more energy to overcome that resistance with lower octane gas than if you used higher octane gas. When I speak of "energy", I am talking in thermodynamic terms. Most people have no clue about therrmodynamics or the thermodynamic properties and calculations that go into auto design."
Please read what was written on howstuff works on octane ratings. http://auto.howstuffworks.com/question90.htm.
On that website, these are the first words on the first paragraph:
"The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting."
An octane rating that requires little or no compression to ignite as in low octane rating, is resisting combustion from the spark plugs. Thus, I further said, "The thermodynamic effect is that you will use or require more energy to overcome that resistance with lower octane gas than if you used higher octane gas."
What you said was right except for the fact that you did not add combustion by a spark plu. But my explanations of this effect, is also right. The point is, use a high octane rated fuel in your G-35 Coupe.
This is what I said basedon your ealier comments, "Lower octane gas will resist combustion far more than higher octane gas. The thermodynamic effect is that you will use or require more energy to overcome that resistance with lower octane gas than if you used higher octane gas. When I speak of "energy", I am talking in thermodynamic terms. Most people have no clue about therrmodynamics or the thermodynamic properties and calculations that go into auto design."
Please read what was written on howstuff works on octane ratings. http://auto.howstuffworks.com/question90.htm.
On that website, these are the first words on the first paragraph:
"The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting."
An octane rating that requires little or no compression to ignite as in low octane rating, is resisting combustion from the spark plugs. Thus, I further said, "The thermodynamic effect is that you will use or require more energy to overcome that resistance with lower octane gas than if you used higher octane gas."
What you said was right except for the fact that you did not add combustion by a spark plu. But my explanations of this effect, is also right. The point is, use a high octane rated fuel in your G-35 Coupe.
Re: (Sentientbydesign)
I would also like to ask how can advicing others to use high octane rated gas in the G-35 coupe as the manual suggests be misleading? I am just as good in math. In fact, i love math. You said you use low octane gas, and I am saying that low octane gas is just as good in different conditions than others. However, I made it clear that the G-35 Coupe requires a high octane gas, and it should be used just as the manual says.
I think we are both saying the same thing but in different ways. I also love fluid mechanics and thermodynamics. So, I use them to explain things when I can.
I think we are both saying the same thing but in different ways. I also love fluid mechanics and thermodynamics. So, I use them to explain things when I can.
Re: (Sentientbydesign)
It isn’t the gas as much as the engine revving so high. It would be a much more comfortable freeway car if it were turning about 400 RPM less… I could really care less about racing my G. I get on it every once in a while entering a freeway, but I’m off it by the time the speed becomes illegal. With the low gears, I need cruise control to keep anywhere the legal speed, it just wants to keep revving.TeflonG35 wrote:If you're worried about gas you probly have the wrong car. High performance does have a cost.
You’re correct in theory, but not as correct in practice. With my Mustangs (sorry for this example), we set initial timing to 15 degrees (up 5 from factory). The ECU would add another 20-21 degrees of advance gradually through about 3000-3200 RPM, for a total advance of 36 degrees BTDC. The spark happened 36 degrees south of TDC on the up stroke. (that’s about 1/5th. of the way down). By the time the fuel started burning the piston had traveled that 36 degrees and was on the down stroke. The higher octane actually slows the combustion of the fuel ever so slightly – which is what you basically said, and allows the more argessive timing. Lower octane would combust earlier and work against engine rotation – which is what you said too.Sentientbydesign wrote: The idea is that we don't want the fuel to start combusting before the compression stroke is completed. If it does, then it will essentiall push against the rotationally "correct" direction of the crankshaft producing a knock…
I’ve still got a $400 Snap-On timing light that allowed checking the rpm, initial and the total advance when setting timing. The link shows one, but mine is red.http://buy1.snapon.com/product...p.asp
I’ve got no idea what initial or total advance on a VQ35HR is, but if someone knows, post it please.
I’ve been looking and all I can find is gear sets that go the other way – to 4.11. There is a driveline specialist in the next town over that may shed some light on this. I’m afraid that the cost of the change would offset any gain. I’ll be investigating the JDM option and probably posting a question in the Z forum too. I’ll post the results if I find anything interesting.Sentientbydesign wrote:…If I remember correctly rn79870, there is a JDM option to make the final reduction gearing different (in the differential). PLEASE check it out and let me know if that's what you're looking for. I'd be up for that mod too.
Re: (Jacko3)
Sentientbydesign:
As far as I am concerned, you do understand cars better than I do, mechanically. You have been mostly right, but then, I enjoy explaining phenomenons using physical science atributes such as energy, workdone, viscosity, acidity, alkalinity, etc (stuff like that). So, what you do well to explain mechanically. I try to do the same in other ways. There are more than one way to skin a banana.
I am also a very intutive driver--totally connected to every piece of the car and its behavior. When I step into any car i have not driven before, my first goal is to connect with the car. This can take a while. When i have achieved connection to the car, then, I will certainly put it through its paces.
But thanks for all your guidance on many matters. I hope you are having a wonderful day so far.
As far as I am concerned, you do understand cars better than I do, mechanically. You have been mostly right, but then, I enjoy explaining phenomenons using physical science atributes such as energy, workdone, viscosity, acidity, alkalinity, etc (stuff like that). So, what you do well to explain mechanically. I try to do the same in other ways. There are more than one way to skin a banana.
I am also a very intutive driver--totally connected to every piece of the car and its behavior. When I step into any car i have not driven before, my first goal is to connect with the car. This can take a while. When i have achieved connection to the car, then, I will certainly put it through its paces.
But thanks for all your guidance on many matters. I hope you are having a wonderful day so far.
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Sentientbydesign
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Re: (Jacko3)
*blinks repeatedly*
Does anyone else see the problem here? I feel like I've got a paradigm shift and I'm looking at this situation from an alternate universe.
Jacko3
Lower octane fuel WILL NOT resist combustion more than higher octane fuel.
The octane rating is exactly opposite of what you stated.
That's my main issue with your statement.
rn79870
I'm a little confused. By advancing the timing, the cylinder sparked before completing the compression stroke? And in doing so, you get combustion to start before reaching TDC?
Also, you are correct regarding the final gear reduction. The "upgrade" that I found was a slight increase in the final gear (just looked again). Great for drifting!!! lol.
Does anyone else see the problem here? I feel like I've got a paradigm shift and I'm looking at this situation from an alternate universe.
Jacko3
Lower octane fuel WILL NOT resist combustion more than higher octane fuel.
The octane rating is exactly opposite of what you stated.
That's my main issue with your statement.
rn79870
I'm a little confused. By advancing the timing, the cylinder sparked before completing the compression stroke? And in doing so, you get combustion to start before reaching TDC?
Also, you are correct regarding the final gear reduction. The "upgrade" that I found was a slight increase in the final gear (just looked again). Great for drifting!!! lol.
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telcoman
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Re: (Sentientbydesign)
Here is some more light on this subjectSentientbydesign wrote:*blinks repeatedly*
Does anyone else see the problem here? I feel like I've got a paradigm shift and I'm looking at this situation from an alternate universe.
Jacko3
Lower octane fuel WILL NOT resist combustion more than higher octane fuel.
The octane rating is exactly opposite of what you stated.
That's my main issue with your statement.
rn79870
I'm a little confused. By advancing the timing, the cylinder sparked before completing the compression stroke? And in doing so, you get combustion to start before reaching TDC?
Also, you are correct regarding the final gear reduction. The "upgrade" that I found was a slight increase in the final gear (just looked again). Great for drifting!!! lol.
http://en.wikipedia.org/wiki/Octane_rating
While everyone digests that, I think I'll just go change my oil again.
Telcoman
Re: (Sentientbydesign)
Yes, If initial timing is set to 10 or so degrees before top dead center then at idle, the plug is fired before the piston reaches the top of the compression stroke. As the rpm increases, so does the total timing. Pre ECU this advance was adjusted by messing with the springs and weights in the distributor. Post ECU, the computer does it for you. Full advance is somewhere around 30 to 40 (40 being more high performance than 30) degrees depending on the engine/manufacturers specs. So at some speed above 3000 RPM, the spark is actually occurring 30 to 40 degrees before the piston reaches the top of the cylinder. (depending on engine specs.) They used to add lead to gasoline to slow down the burn (IE higher octane) but that hasn't been the case since 1975. Now, they use something called isooctane. (which is something a chemist could probably explain, I can't).Sentientbydesign wrote:I'm a little confused. By advancing the timing, the cylinder sparked before completing the compression stroke? And in doing so, you get combustion to start before reaching TDC?
Low octane gas burning faster therefore, the timing is retarded so that the piston is closer to the top of the compression stroke when the plug fires. Higher octane fuels have greater anti-knock abilities.
This site may help you visualize the process.http://auto.howstuffworks.com/ignition-system1.htm
Re: (telcoman)
Interesting cite telcoman...
From the wiki article...In this example, the engine maximum power is reduced by about 4% with a fuel switch from 93 to 91 octane (11 hp, from 291 to 280 hp). If the engine is being run below maximum load, the difference in octane will have even less effect.
So, let's extrapolate that a performance reduction of probably 5 to 6% will occur for running 87 octane vs. 91 Octane. For a loss of 15 to 18 HP in a VQHR. Again, it you are not driving hard, you'd never notice it. If you are, you would.
From the wiki article...In this example, the engine maximum power is reduced by about 4% with a fuel switch from 93 to 91 octane (11 hp, from 291 to 280 hp). If the engine is being run below maximum load, the difference in octane will have even less effect.
So, let's extrapolate that a performance reduction of probably 5 to 6% will occur for running 87 octane vs. 91 Octane. For a loss of 15 to 18 HP in a VQHR. Again, it you are not driving hard, you'd never notice it. If you are, you would.
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itgogitrev
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Re: (rn79870)
Quote »That's the truth. The stock 3.69's are way to low for freeway driving. If we could get another 10%, say 3.30s as an aftermarket option, I'd seriously look into it. [/quote]I'm still new to Nissans and Infinitis, but I have a vast amount of knowledge in VWs/Audis. In some of the cars that I helped build, I installed different final drives for turbo's 2.0s. The stock one was a ridiculously high 3.94:1 and it was useless for 2.0Ts that were boosting past 15 lbs. I swapped in 3.65s from VR6 Corrados and 3.39s from Jetta/GTI VR6s.
Are Infinitis as interchangable? Is it possible to swap the final drive from an M45 (a 3.36?)
I've calculated that a G35 6MT with a 3.36 gear ratio would do about 75 mph @ 2570 RPM. From what I could gather, the stock 3.69 does 75 mph @ 2800.
Are Infinitis as interchangable? Is it possible to swap the final drive from an M45 (a 3.36?)
I've calculated that a G35 6MT with a 3.36 gear ratio would do about 75 mph @ 2570 RPM. From what I could gather, the stock 3.69 does 75 mph @ 2800.
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telcoman
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Re: (itgogitrev)
At 80MPH my tach is at exactly 3000 RPM in 6th gear. When I drove a G35X loaner automatic at 80 MPH the tack was at 3250 RPM in 5th gear.itgogitrev wrote:
I'm still new to Nissans and Infinitis, but I have a vast amount of knowledge in VWs/Audis. In some of the cars that I helped build, I installed different final drives for turbo's 2.0s. The stock one was a ridiculously high 3.94:1 and it was useless for 2.0Ts that were boosting past 15 lbs. I swapped in 3.65s from VR6 Corrados and 3.39s from Jetta/GTI VR6s.
Are Infinitis as interchangable? Is it possible to swap the final drive from an M45 (a 3.36?)
I've calculated that a G35 6MT with a 3.36 gear ratio would do about 75 mph @ 2570 RPM. From what I could gather, the stock 3.69 does 75 mph @ 2800.
Telcoman
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itgogitrev
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Re: (telcoman)
Yep, my plots tell me that 80mph comes at 3000 RPM.
A 3.36 would drop it to about 2730 RPM.
A 3.36 would drop it to about 2730 RPM.
Re: (itgogitrev)
I'm over 3k at 70. with the 5AT. 45 is 2k and 80 is around 3.5k
What is the 6th gear ratio with the 6MT?
What is the 6th gear ratio with the 6MT?
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!979TransAm
- Posts: 47
- Joined: Tue Jan 22, 2008 9:07 am
Re: (itgogitrev)
Thank you Telco for straightening out the octane thing. Your ecu can compensate for lower octane fuels but by doing so you could lose effeciency.BUT your ecu does so by changing timing WHICH can NEVER change static compression(the cause for the need of high octane). Adjustment of the timing is merely a bandaid, Guess what? a Bandaid is not a permanent fix, AKA "use lower octain when the correct octain is not available. For the G37 the manual specificaly states that the owner should only use the minimum necessary to get him to another fueling station where the correct gas grade is available."
And what rn interuprated was half right. You may not notice the difference just because you are not running the car hard, but the difference is still there daily driver or race car.
Bottom line: Use the wrong octane level and it will slowly effect your car. Not my car so do what you want. The manufacture would not just strongly reccomend to use 91 for their health.
And what rn interuprated was half right. You may not notice the difference just because you are not running the car hard, but the difference is still there daily driver or race car.
Bottom line: Use the wrong octane level and it will slowly effect your car. Not my car so do what you want. The manufacture would not just strongly reccomend to use 91 for their health.
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Sentientbydesign
- Posts: 5993
- Joined: Wed Feb 02, 2005 8:21 am
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05 Subaru Legacy GT Stg 2 - Sold
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04 WW Evo VIII - 302 AWHP - Ex's
96 I30 - Sold - Contact:
Re: (itgogitrev)
That's a very interesting idea. Not sure if they are interchangeable, but it would be a great way to save on gas.
On the flipside, all of us who like to push our Gs would suffer after doing the swap, but then again, we can't have it all.
On the flipside, all of us who like to push our Gs would suffer after doing the swap, but then again, we can't have it all.
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C-Kwik
- Moderator
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- Joined: Thu Aug 01, 2002 9:28 pm
- Car: 2013 Chevy Volt, 1991 Honda CRX DX
Combustion inside a cylinder is not an immediate release of energy. It is spread out over mostly the power stroke and partly over the compression stroke of the piston. Rather than a single explosion , it burns as the piston moves down continuously releasing energy while the piston moves down.
When detonation occurs, the energy release is much more violent and immediate. A good analogy is if you were to push Car A with Car B. Lets say you butt Car B up to Car A then using 100 lbs of force push car A for 20 seconds. You've essentially put 2000 lbs of force into moving car A. Now lets imagine you put all 2000 lbs of force into car A into a single second. You'll be replacing some bumpers very shortly.
While the process of detonation is much more complicated, the end result is similar. Detonation releases a lot of energy in a very short period of time, which could ultimately lead to engine damage.
The cause of detonation is pressure. Heat is a contributing factor, but pressure is the primary trigger. The rate of burn of a fuel is not relevant as the process of detonation is not the same.
"Nitromethane is burned as a fuel in drag racing autos, but also can be made to detonate, a special kind of burning in which the material undergoes a much faster and far more violent type of chemical transformation. With its single nitrogen dioxide (NO2) group, it is a simple representative version of explosives with more NO2 groups."
The above is an exerpt from an article about a recent discovery about detonation. Additionally, it states:
"Though it is an optically transparent, electrically insulating material, it undergoes a shocking transformation: It turns into an optically reflecting, nearly metallic state for a short time behind the detonation shock wave front.
But further behind the wave front, the material returns to being optically transparent and electrically insulating."
Source: http://www.sciencedaily.com/re...2.htm
The results of detonation and much of the conditions under which it occurs are known, but the process is still not fully understood.
However, the rate of burn a fuel experiences is not necessarily a reflection of it's propensiy to detonate. I've seen no scientific data to say otherwise and this article clearly shows there is a very different process going on that doesn't occur during normal combustion.
As for what knock isn't, it is not the pressure and resistance placed on a piston still moving up during the compression cycle if combustion starts before top dead center. All modern motors advance timing (usually between 10-20 degrees BTDC for each piston. This is to compensate for the fact that during normal combustion, it takes time for the flame kernel to grow to a size where it is releasing energy in a sufficient amount to be efficient and perhaps usable. Essentially, a small flame in the combustion chamber can not push down very hard on the piston so starting the combustion at TDC would mean that for part of the power stroke, the amount of force pushing down on the piston would be quite small. So the idea behind advanced timing is to grow the flame size prior to the power stroke so that it provides the most energy during the power stroke.
The problem is that detonation can occur even after combustion starts. Basically, as the piston moves up, there is a certain rate of compression going on. However, as fuel starts burning during compression, it expands the gasses due to the increase in heat, causing a bigger increase in pressure than the compression the piston provides by itself. So too much timing advance can be a bad thing. To help remedy some of this, a higher octane fuel can allow for some additional timing advance by allowing a higher pressure threshold before detonation is experienced.
In the case of the VQ, you have a high compression motor designed and tuned to run on higher octane fuel. Since the compression is static, the only way to use lower octane fuel is to reduce the timing advance. What happens here is that you get a less than ideal flame front as the power stroke begins and less peak pressure. The latter is significantly important in a high compression motor as the biggest benefit of higher compression is that the expansion ratio on the power stroke is greater. The higher expansion ratio allows for more of the heat and pressure to be converted into mechanical energy rather than being dumped out of the exhaust as pressure and heat and being transferred into the cooling system as heat. Starting with a lower peak cylinder pressure means there is less energy to be converted into mechanical energy.
Backing the timing can allow the motor to run safely on lower octane fuel, but it degrades the power output and efficiency. How much can vary quite a bit. Perhaps the best thing you can do is try both and see if the efficiency and power loss is outweighed by the cost of fuel. The knock sensor should pick up even the lightest events of detonation and keep timing retarded enough to prevent any engine failures.
Like some other higher performance vehicles, the VQ may on a continual basis, attempt to keep the vehicle running on the threshold of knock. This is suggested by the report by a magazine that put 100 octane fuel in a Z in an early test. HP did go up slightly. It's likely because the ecu advanced the timing until knock was heard and then ran timing at or just below that level. I can't recall which cars, but there are some cars that do this and the manufacturers were very vocal about it. I expect in an effort to continually increase performance and efficiency, and with continually increasing engine control technology, we will see this type of technology in more and more cars.
When detonation occurs, the energy release is much more violent and immediate. A good analogy is if you were to push Car A with Car B. Lets say you butt Car B up to Car A then using 100 lbs of force push car A for 20 seconds. You've essentially put 2000 lbs of force into moving car A. Now lets imagine you put all 2000 lbs of force into car A into a single second. You'll be replacing some bumpers very shortly.
While the process of detonation is much more complicated, the end result is similar. Detonation releases a lot of energy in a very short period of time, which could ultimately lead to engine damage.
The cause of detonation is pressure. Heat is a contributing factor, but pressure is the primary trigger. The rate of burn of a fuel is not relevant as the process of detonation is not the same.
"Nitromethane is burned as a fuel in drag racing autos, but also can be made to detonate, a special kind of burning in which the material undergoes a much faster and far more violent type of chemical transformation. With its single nitrogen dioxide (NO2) group, it is a simple representative version of explosives with more NO2 groups."
The above is an exerpt from an article about a recent discovery about detonation. Additionally, it states:
"Though it is an optically transparent, electrically insulating material, it undergoes a shocking transformation: It turns into an optically reflecting, nearly metallic state for a short time behind the detonation shock wave front.
But further behind the wave front, the material returns to being optically transparent and electrically insulating."
Source: http://www.sciencedaily.com/re...2.htm
The results of detonation and much of the conditions under which it occurs are known, but the process is still not fully understood.
However, the rate of burn a fuel experiences is not necessarily a reflection of it's propensiy to detonate. I've seen no scientific data to say otherwise and this article clearly shows there is a very different process going on that doesn't occur during normal combustion.
As for what knock isn't, it is not the pressure and resistance placed on a piston still moving up during the compression cycle if combustion starts before top dead center. All modern motors advance timing (usually between 10-20 degrees BTDC for each piston. This is to compensate for the fact that during normal combustion, it takes time for the flame kernel to grow to a size where it is releasing energy in a sufficient amount to be efficient and perhaps usable. Essentially, a small flame in the combustion chamber can not push down very hard on the piston so starting the combustion at TDC would mean that for part of the power stroke, the amount of force pushing down on the piston would be quite small. So the idea behind advanced timing is to grow the flame size prior to the power stroke so that it provides the most energy during the power stroke.
The problem is that detonation can occur even after combustion starts. Basically, as the piston moves up, there is a certain rate of compression going on. However, as fuel starts burning during compression, it expands the gasses due to the increase in heat, causing a bigger increase in pressure than the compression the piston provides by itself. So too much timing advance can be a bad thing. To help remedy some of this, a higher octane fuel can allow for some additional timing advance by allowing a higher pressure threshold before detonation is experienced.
In the case of the VQ, you have a high compression motor designed and tuned to run on higher octane fuel. Since the compression is static, the only way to use lower octane fuel is to reduce the timing advance. What happens here is that you get a less than ideal flame front as the power stroke begins and less peak pressure. The latter is significantly important in a high compression motor as the biggest benefit of higher compression is that the expansion ratio on the power stroke is greater. The higher expansion ratio allows for more of the heat and pressure to be converted into mechanical energy rather than being dumped out of the exhaust as pressure and heat and being transferred into the cooling system as heat. Starting with a lower peak cylinder pressure means there is less energy to be converted into mechanical energy.
Backing the timing can allow the motor to run safely on lower octane fuel, but it degrades the power output and efficiency. How much can vary quite a bit. Perhaps the best thing you can do is try both and see if the efficiency and power loss is outweighed by the cost of fuel. The knock sensor should pick up even the lightest events of detonation and keep timing retarded enough to prevent any engine failures.
Like some other higher performance vehicles, the VQ may on a continual basis, attempt to keep the vehicle running on the threshold of knock. This is suggested by the report by a magazine that put 100 octane fuel in a Z in an early test. HP did go up slightly. It's likely because the ecu advanced the timing until knock was heard and then ran timing at or just below that level. I can't recall which cars, but there are some cars that do this and the manufacturers were very vocal about it. I expect in an effort to continually increase performance and efficiency, and with continually increasing engine control technology, we will see this type of technology in more and more cars.
Re: (C-Kwik)
C-Kwik:
Very nice! Had my timing adjusted by 2 degrees which raised my idle speed by a small 50 RPM (my mechanic said it alows the car to produce slighty more power). I use only 93 octane. I seem to burn more gas at full throttle, after this adjustment, but I also seem to save more gas with normal driving. Any explanation for this based on your assessments?
Very nice! Had my timing adjusted by 2 degrees which raised my idle speed by a small 50 RPM (my mechanic said it alows the car to produce slighty more power). I use only 93 octane. I seem to burn more gas at full throttle, after this adjustment, but I also seem to save more gas with normal driving. Any explanation for this based on your assessments?
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gwoods
- Posts: 3892
- Joined: Fri Jul 27, 2007 11:57 am
- Car: 2013 Infiniti M37x
1999 Nissan Altima SE limited 5spd
1992 Miata (soon to be turbo)
1965 Cj-5 with 327 v8
2012 Toyota Sequoia Limited - Location: Phoenix
Re: (rn79870)
Cheaper just to change your tires...rn79870 wrote:
That's the truth. The stock 3.69's are way to low for freeway driving. If we could get another 10%, say 3.30s as an aftermarket option, I'd seriously look into it. It isn't just the mileage, I hate seeing the tach over 3k when cruising. My ex-Maxima was 400+rpm lower at freeway speeds, and the mileage was always in the 26 to 30 range (depending whether I went inland - hilly, or up/down the coast - flat land.)
Taller tires = lower gear ratioShorter tires = higher gear ratio
I'm running 235/45/17's for this reason and at the track I run 275/40/17's
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C-Kwik
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- Joined: Thu Aug 01, 2002 9:28 pm
- Car: 2013 Chevy Volt, 1991 Honda CRX DX
I'd have to question your ability to measure your fuel consumption at WOT. If 90's based Nissan ECU's are any indication of their tuning methods, then the ECU would ignore the O2 sensor feedback and rely on the TPS and MAF signals to determine fuel requirements at WOT. Meaning, outside of a timing change somehow changing airflow, it's unlikely that it would increase the amount of fuel being injected...
Re: (C-Kwik)
When I went through the classes for an emission inspect/test/repair license (the early 90's) we were taught that the WOT sensor was triggered by the TPS (throttle position sensor). When the TPS indicated that the butterfly was at WOT several things happened. Many of the systems shut off, EGR, and A/C are two that I remember right now , The engine management system adjusted to full spark advance at 3k+ rpm and the fuel injectors duty cycles increased to max. I don't remember anything about the fuel pressure increasing, just the duty cycles of the injectors. With an increased duty cycle, more fuel would be injected. I can't guaranty how a Nissan ECU works as what we got was general innature.
This was with port injected SEFI cars at the time.
This was with port injected SEFI cars at the time.
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C-Kwik
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- Joined: Thu Aug 01, 2002 9:28 pm
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Re: (rn79870)
Be weary that a taller rear end gear directly and proportionately affects every gear. First gear will require a bit more clutch slippage and work to get started. I'd be reluctant to change the rear end gear in such a manner if you do a lot of city driving and/or have to negotiate bumper to bumoer traffic often.rn79870 wrote:That's the truth. The stock 3.69's are way to low for freeway driving. If we could get another 10%, say 3.30s as an aftermarket option, I'd seriously look into it. It isn't just the mileage, I hate seeing the tach over 3k when cruising. My ex-Maxima was 400+rpm lower at freeway speeds, and the mileage was always in the 26 to 30 range (depending whether I went inland - hilly, or up/down the coast - flat land.)
Also while taller gears generally equate to better mileage, the difference may not be as great as you might think. Particularly at highway speeds where the aerodynamic drag of the car is the biggest resistance to movement. At any given speed this aerodynamic load is a fixed constant, meaning you need a fixed amount of torque to the wheels to sustain that speed. If you add a numerically lower rear gear, it reduces the input speed, but lowers the torque multiplication. So throttle position will likely need to be increased to provide more torque. Whether it will provide an improvement will be dependent on many factors. Considering an engine's VE is not fixed and can vary with RPM and throttle position, it can potentially net virtually no gain. Especially given such a small variation in engine RPM (differences in windage and friction might not be that great). While gains might occur, I wouldn't assume it necessarily would...