Re-Tuning G35 engines to run on lower Octane

[rn79870]

C-Kwik You make a good point about changing gears. With a 5 speed the options are not what they would be with a 6 speed. At least it is a very smooth engine. Thanks

[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.

Well, when TPS reaches max voltage, it is WOT. Not so much making an argument here, but clarifying that there isn't necessarily a seperate sensor. At least I've never seen one in a Nissan.

As for duty cycles, they don't max out as in going to 100%. It would run way rich if it did (Not sure if that's what you meant or not but it wasn't too clear and one could misinterpret your post as such). It would follow the ECU's map tables perhaps to push duty cycles for to it's max cycle in the table for it's given RPM, TPS and perhaps MAF data. I doubt it would ignore the MAF data as it would provide the ECU with info regarding the absolute pressure and some Nissan service manuals (perhaps Chilton's manuals) that I've read indicate that the MAF signal was still used.

[rn79870]

As for duty cycles, they don't max out as in going to 100%. It would run way rich if it did (Not sure if that's what you meant or not but it wasn't too clear and one could misinterpret your post as such).

Not in the sense that they are injecting fuel 100% of the time. The signal is digital. They have an off cycle regardless of WOT, but the on cycle time (the length of time fuel is being injected) is increased at WOT. Or, the injector doesn't increase fuel flow, it just flows fuel longer for WOT operation.

Thanks for pointing out the confusion in my post.

[redhed]

jacko,

if you are constantly flogging your G, you have much more to worry about than your engine.

synthetic engine oil and 91 octane will do nothing to save your transmission, rear diff, half shafts or brakes! all of those will probably give out before a G VQ v6 that's lubricated with dino oil, or fed 87 octane!

[redhed]

my g ('06 coupe automatic) runs about 3200 rpms at 80 mph...i have the 17 inchers...

[Sentientbydesign]

jacko,

if you are constantly flogging your G, you have much more to worry about than your engine.

synthetic engine oil and 91 octane will do nothing to save your transmission, rear diff, half shafts or brakes! all of those will probably give out before a G VQ v6 that's lubricated with dino oil, or fed 87 octane!

You can actually run high quality synthetic in all of those areas to help increase their lifespans. NISMO makes a diff cover that dissapates heat better than stock too and that could help things.

One day, IF I ever start doing serious mods to my G, I will look into studier half shafts.

[justjuiceit4]

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.

Well that is an obvioius statement, I did not figure that I had to mention it since I mentioned this in the next paragraph with rental cars. I have test-driven over 1000 cars and a lot of the dealers I have been with say "go ahead and open her up!" Worst thing they could ever say to me! I somewhat disagree with the low octane is okay for normal driving, because with the 3000GT, even "more conservative" driving let to a noticeable decrease in performance. With most sport cars such as the 350Z, WRX, etc people test-driving them will want to see the performance of these cars....as opposed to something such as a Rio. Dealers that sell higher performance cars that can make a noticeable difference with higher octane, should use higher octane......some people will buy a car based on seat of the pants and not what a magazine says the car can do.

Insteresting enough, I drove the supercharged Ion Redline when they first came out at a ride and drive. I was suprised that the hp/tq levels were rated so low, as the car felt much faster, so I talked one of the engineers at the event. He told me that advertised hp/tq they claim is obtainable with 87 octane, hot day, higher than sea level altitude. Saturn/GM did not want to get into a simular sitution Mazda did with the overstated hp of the Miata and RX-8. He did mention that after 2-3 tanks of premium the engine power would noticeable increase. Obviously the test car had premium in it and it was a cool day close to sea level.

Modified by justjuiceit4 at 7:12 PM 2/1/2008
Modified by justjuiceit4 at 7:49 PM 2/1/2008

[Jacko3]

You make some point. However, I also flog my other little Nissan which has over 210K--the car is still kicking strong--I raced a 4-banger 1992 Honda with after-market exhaust----the honda was disappointd that my little Nissan could make it look so bad.

So, given the lower quality of that car, I think the G-35 Coupe can handle more stress than that. BTW, maybe after 5 years, who knows, I might sell the G. I really think the G was designed for flogging. I really do have a hard time driving it gently. Car seems to behave in a way I like, under stress or hard driving. There is a difference b/w hard and aggressive driving and abuse. I don't abuse my car. I drive it hard.

With new mods, the G-35 loves to revv like hell. The Stillen exhaust is like music to my ears. What am I to do? Before mod, 4th gear had a time getting to 65 miles per housr. With new mod, 75 - 80 miles per hour in 4th gear seems normal. The mods make a difference on the G-35.

What do you think? Why did Infiniti restrict the G-35s performance by that much? Any answers? Why did they wait for the customers to pay to open up the car? I am still scratching my head for an answer on this one?

[Jacko3]

Like Telcoman had earlier said, I went out to check my RPM at 80 miles per hour--Telcoman was accurate, 3000RPM at 80 miles per hour. Of course, this is with mods.

[bublightyear]

I'm glad someone else was thinking it too! Gas prices suck but I bought my G35 cause it looks awesome & goes really fast . If I was concerned about gas prices (I drive sometimes 150 miles a day) I would by another car.

[smockers83]

At least your lowest fuel octane is 87.

In Utah its at 85 for some reason...and still hella expensive

That's because of the elevation--octane ratings can be reduced with elevation.

[Sentientbydesign]

It seems like there are a lot of G owners who are proud of their poor fuel economy. As if it set them apart from all of those "other" cars.

There is nothing wrong with those of us who want high performance and fuel economy. Are we going to get it? Probably not as much as we'd like, but that's the goal. If I can mod my G to get 2-3 MPG more than yours and only sacrafice 10-15 hp. I would do it in a heartbeat (assuming the mods making the fuel economy were't ridiculously expensive).

As far as Jacko's question. I really believe that Nissan got in hot water with the US buyers when they figured out that most of the Infiniti line-up were just rebadged slightly higher quality Nissans. They made a change to make sure their luxury and regular lines were different. So, yeah they could have made the G just like the Z, but the idea was to maintain some difference between them. Mainly the level of luxury (though I don't find the G to be very luxurious). Also, the general public wouldn't have appreciated 30-40 more HP at the cost of an extremely loud "Luxury sports coupe".

[rn79870]

...There is nothing wrong with those of us who want high performance and fuel economy. Are we going to get it? Probably not as much as we'd like, but that's the goal. If I can mod my G to get 2-3 MPG more than yours and only sacrafice 10-15 hp. I would do it in a heartbeat (assuming the mods making the fuel economy were't ridiculously expensive).

I couldn't agree more. Wait until gas is 4 bucks a gallon, and it costs close to 80 bucks to fill up the tank. I don't need 306 HP, in fact, I would have bought the car if it had 275HP. I could really care less whether a Civic beats me from one stop light to another.

I like Infiniti because it is a logical upgrade for a guy who likes Nissan products. It looks good, it is comfortable, it has quality about it, and it fits.

I would give back 25 HP for a 3 mpg gain. Face it, we're borrowing fuel from future generations, and fuel is not a renewable resource. Why be selfish.

[redhed]

sure, but my point was that the engine probably is one of the least stressed parts of the powertrain...especially when fully warmed up.

[redhed]

jacko,

it is a little dangerous to automatically assume that the G can take lots of abuse simply because it's positioned as a premium car. one would hope that 40k would get you a better/more durable powertrain than a 25k car...but that's not necessarily true.

[telcoman]

I couldn't agree more. Wait until gas is 4 bucks a gallon, and it costs close to 80 bucks to fill up the tank. I don't need 306 HP, in fact, I would have bought the car if it had 275HP. I could really care less whether a Civic beats me from one stop light to another.

I like Infiniti because it is a logical upgrade for a guy who likes Nissan products. It looks good, it is comfortable, it has quality about it, and it fits.

I would give back 25 HP for a 3 mpg gain. Face it, we're borrowing fuel from future generations, and fuel is not a renewable resource. Why be selfish.

rn79870

I agree with you also. I don't need all of the HP that Infiniti has which is one reason why regular 87 octane is fine for me. I purchased the Infiniti because I felt it was more comfortable, and handled better than the Acura TL that I was comparing it with. I also wanted Sirius Radio and the Acura only offered XM.The rear wheel drive 6 speed Infiniti I felt was a superior vehicle. I don't give a crap if a Civic beats me at a stoplight either

Telcoman

[!979TransAm]

Go buy a Maxima if you want fuel economy

[Jacko3]

rn79870:

I have to agree with you about the fuel issue. I am as guilty on this fact as any other criminal out there. I struggle everyday with my conscience between choosing excitement with the G versus conserving fuel. That is why I have the 2nd car.

I have never felt such huge a temptation to drive any other car like I feel with my G-35. I feel like a criminal driving it the way I do. And after each exciting driving session, I go into a guilt trip such as, why did I go that fast?, why did I burn that much fuel when i could hev driven a little slower?, why did I scare that old lady with the loud noise of my exhaust?

I keep going through these emotions with this car. Beleive it or not, after about 30 minutes to an hour, the demon of the G-35 overwhelms me again, and off I go to get another round of excitement. Can anyone give me a good advice on this matter? I never knew that a car could become addictive.

[Jacko3]

Sentientbydesign:

You are saying exactly what my mechanic told me. So, next month, I am changing the transmission and differential to synthetic, since I wil be driving the car a little harder than normal. Of course, if I plan to keep the G-35 for 10 years, I doubt it will make it. Right now, I am hoping it makes it to 6 years. After that, I am sure infiniti would have something better than the G-35 by then. What do you think?

[Jacko3]

SentientbyDesign:

I agree with you about the loud noise of the G. When the OEM exhaust was removed, it had a muffler. Well, when I saw the Stillen exhaust, it had no muffler except for the big oblong can at the end of the tail pipe. Seems like the G has been muffled to choking point by infiniti. I wish they made options for muffled and non-muffled versions of the G-35.

[Q45tech]

A little thermodynamic engineering will show you that that for MPG, fuel btu is the important factor not octane.

To stretch gasoline supplies and to reduce carcenogens [benzene/aromatics] current gasoline has been diluted with ethanol and and others where the 125,000 btu per gallon [early mid 90's] has steadily declined to less than 112,000 and some is sold at 107,000 btu.

This is a 15% reduction in possible MPG just fom fuel alone.

[rn79870]

Go buy a Maxima if you want fuel economy

That whooshing sound you heard in the sky, it was the point we are making passing over your head.

[rn79870]

A little thermodynamic engineering will show you that that for MPG, fuel btu is the important factor not octane.

To stretch gasoline supplies and to reduce carcenogens [benzene/aromatics] current gasoline has been diluted with ethanol and and others where the 125,000 btu per gallon [early mid 90's] has steadily declined to less than 112,000 and some is sold at 107,000 btu.

This is a 15% reduction in possible MPG just fom fuel alone.

Is that why the EPA revised fuel ratings for 2008?

[SVTCOBRA]

3 pages!!!!

Either put premium or racing fuel in it or sell it.....

[!979TransAm]

That whooshing sound you heard in the sky, it was the point we are making passing over your head.

haha actually I'm suprised what I said whooshed over your head. My simple point being as many point to, You drive a luxury vehicle, If you can not stand to pay 30 cents more per gallon for you engine to run PROPERLY you can not afford to drive such a car. Jump up and grab that one from the sky please

Compare the performance and mileage to sports cars of old the G-35 is still a great step up.

To solve all of the troubles here maybe Infiniti will recognize your cries for economy and create a tuned down sedan and leave the performance for the coupe.

[telcoman]

haha actually I'm suprised what I said whooshed over your head. My simple point being as many point to, You drive a luxury vehicle, If you can not stand to pay 30 cents more per gallon for you engine to run PROPERLY you can not afford to drive such a car. Jump up and grab that one from the sky please

Compare the performance and mileage to sports cars of old the G-35 is still a great step up.

To solve all of the troubles here maybe Infiniti will recognize your cries for economy and create a tuned down sedan and leave the performance for the coupe.

Am I the only one that has noticed that my G runs and performs better on some days compared to other days?Temperature, humidity, altitude are factors that effect engine combustion and I think some are mistaken that octane alone affects engine performance? We had rain and high humidity in the 40's on Friday and clear weather in the 40's and low humidity on Saturday. My G felt and ran much better on Saturday than it did on Friday using the same tank of fuel. (87 regular). Some have posted that their G ran better with premium vs regular but never mentioned weather, altitude or humidity when comparing the two types of gasoline. All I know is the profit mark up on regular 87 octane is pennies and the profit on premium is considerably more. So if it makes one feel better to spend extra money on premium go ahead. For most of us, in five years or so we'll all be driving another vehicle so for me I'll have an extra thousand or so in my pocket to put towards a new one. Add another couple of thousand that I'm saving doing my own oil changes and other simple maintenance items and perhaps I could afford an M next time?

Telcoman

[SVTCOBRA]

My cars love the cooler weather!!! Feels faster.But, my tires do not. They just want to spin.

Humidity may be clogging up your paper air filter.

[Sentientbydesign]

haha actually I'm suprised what I said whooshed over your head. My simple point being as many point to, You drive a luxury vehicle, If you can not stand to pay 30 cents more per gallon for you engine to run PROPERLY you can not afford to drive such a car. Jump up and grab that one from the sky please

Compare the performance and mileage to sports cars of old the G-35 is still a great step up.

To solve all of the troubles here maybe Infiniti will recognize your cries for economy and create a tuned down sedan and leave the performance for the coupe.

No, Transam-boy, it's still whooshing over you head. We are all very sure about why we bought our Gs. Most of us did it for performance. Some of us did it for looks. But telling us that we can't want performance and better fuel economy just shows that you haven't paid attention to the contents of this thread nor that of any of the other 3 or so threads regarding this issue.

Plainly stated, the G35 has many fuel economy holes that can be filled WITHOUT sacraficing performance. Actually, a few of them might actually improve performance over stock. We as Americans have this ignorant notion that we must sacrafice one thing for another. Well let me be one of the first to tell you...You can have your cake and eat it too. It's all about how you hide that missing slice!!!

I'm too poor to implement the modifications mentioned, but when I do, you'll either be seeing threads with how-tos or you'll be calling me to order parts. And when that does happen, I'll be sitting at home thinking about this thread and people like you and

There's absolutely no reason we should have to continue making the same dumb mistakes that automakers have for the past 40+ years.

[Jacko3]

Telcoman and SVTCOBRA:

I have experienced the same things as well. I thought I was the only one with those same experiences. Can anyone tell us about the humdity, temperature, wheel spin, and the rest? Thanks!

[telcoman]

Telcoman and SVTCOBRA:

I have experienced the same things as well. I thought I was the only one with those same experiences. Can anyone tell us about the humdity, temperature, wheel spin, and the rest? Thanks!

Collectively we all have our experiences with our automobiles. None of us are expert chemists, fluid mechanics, physicists, etc. I only write based on my 40+ years of driving expericence. IMHO for normal day to day driving I believe spending the extra money for premium 93 octane is a waste of money.Part of the reason the American Automobile Industry is where it is going slowly down the tubes is because the management thought they could make more money by refusing R&D and new inovation. The Germans and Japanese thought differently. The oil companies have a huge stake also.I drive my high performance vehicle but I don't need 300 HP. My old 92 Lexus 5speed got 32MPH on the highway. If I could get an Infiniti 6 speed that got the same mileage I'd buy a new one tomorrow. I wouldn't care what the HP was & I'd still use regular 87 octane.

Telcoman