Re-Tuning G35 engines to run on lower Octane

[rn79870]

As to other options...I see Infiniti (Nissan) has a VQ25HR engine, yet I've never seen any car advertised with this engine. Does anyone know what it is used for?

[rn79870]

I used to keep very accurate fuel logs (not with my G though). I logged mileage, amount of fuel used, costs and brand, even the station location.

I added one of those PTFE oil treatments that was suppose to "slicken" up the engine, add horsepower and increase mileage. The fact is that it did work and did increased mileage by about 10%. I assume it added a little power too. The problem is that once I changed the oil (3000 miles later) the mileage went back to pre-treatment figures. Adding that stuff to every oil change wouldn't have been cost effective. Scratch another option.

[!979TransAm]

Sentient-Girl (What does the design mean in your name? Decorator?? just curious really) If you want to talk about upping fuel economy and holding performance lets.

First place would be gearing of course. Maybe see a slick 2 OD transmission or just a plain change in rear end gearing. An interesting mod I have seen was a product that attaches to the rear of the gear box and adds an over drive over the gears, splittting gears down making a 5 speed a 10 speed virtually. Performance wise great idea because it keeps the engine wound up in the power band. Been shown to give the car 2 tenths in the quarter or more. Economy wise you would see a good improvement in mileage with splitting the gears.

Keeping the motor correctly tuned and all service maintained of course will enhance mileage. Open up the exhaust to let it breath, add a cold air intake, consistent cleaning of the air filter, make sure your tires are at proper inflation (couple pounds over can help mileage). Easiest thing is to control your acceleration and not use cruise control. Don't focus on controling constant speed but rather constant RPM. Change in RPM waste power.

There are lots of factors that go into use of the right octane fuel, not just static compression. Proper camming that keeps the dynamic compression down and proper timing are large influences. Proper tuning and Good running cooling system are also important to further avoid detonation.

You can run 87 octane in your motor because you have an ECU that monitors all of this. (Quick thought maybe a grounding kit would improve mileage as well if it focuses on making the ECU more efficient.) Run that 87 if you like but I'd also suggest running better quality fuels than wawa or royal farms.

Little side true story, Had an old beater 91 honda that I found got better mileage on mid grade at the cost of a few more pennies. The mileage I picked up outweighed the extra cost. I went to premium and the change was minimal (not worth the extra money for that car)Proper octane can Also make a car more effecient.

Maybe some one should give us a write up. drive a tank with each grade of fuel and log differences. Main variable being your driving consistent could be tough

[rn79870]

Sentient-Girl (What does the design mean in your name? Decorator?? just curious really)

I might suggest that you look up Sentient in the dictionary, then look at his occupation. It will all make sense then.

Maybe some one should give us a write up. drive a tank with each grade of fuel and log differences. Main variable being your driving consistent could be tough

Perhaps we should be sending this issue to Myth Busters. Let them do the testing. Would make for an interesting show.

Submitted to Myth Busters...http://community.discovery.com...89059Modified by rn79870 at 11:36 AM 2/3/2008
Modified by rn79870 at 11:37 AM 2/3/2008

[joe603]

Face it, we're borrowing fuel from future generations, and fuel is not a renewable resource. Why be selfish.

I disagree with this...there is enough dino fuel to last thousands of years at our current usage. The catch is that it gets more expensive to extract the oil from other mediums. I've read that coal shale alone has enough oil to last over a thousand years at projected usage rates. It is not renewable, but we'll never use all of it. Plus, they are developing alternative use fuels, like hydrogen, that will also never deplete (to a point). So I would say that we're being selfish by taking all of the oil that is inexpensive to obtain from future generations...its up to them to develop techniques to extract fuel from other sources economically.

[kmech_7]

look man i dont want to hear ever that you pay too much for gas in NJ. thats BS!!!!!! i pay the most for gas in the country! i live in San Diego. if you dont believe me just look online at the price spread across the country. i pay about 50-90 cents more a gallon ALWAYS!!

yet i always put premium in my car and a booster. on a military E-5 paycheck this is hard to do......but if i can do it twice a week or more.......

[kmech_7]

i can tell the difference in the octane because if i put the cheap stuff in my car the engine will start to knock. i have to run at about 95 to keep it purring like a kitty. you can reallly tell with a s/c engine. if you do that it will be apperent

[!979TransAm]

Yeah good idea mythbusters could drive a car around a track for hours. Course it would have to be a motor that recommends higher octane but the owner uses lower.

RN - Webster says, "sentient - Finely sensetive in perception or feeling." Either some kind of tree hugger or mother teresa? Clue me in. Must you disect every joke. I'd call you a negative nancy but I don't think you can look that one up in the dictionary. So I'll explain, the negative quite obviously refers to your bad attitude where as by saying nancy I am calling you a woman/girly man. This relates because woman are renouned for their nagging capabilities. Again I poke. I presented information, but because you didn't say it you seem bitter or peeved. Forgive me if I push your buttons.

Kmech- Raises a good point, the higher output motors are just more noticeable when detonation occurs, just because you don't hear it/feel it doesn't mean it isn't there. Any for most here it doesn't make sense to skimp 30 sense a gallon when you plop down $1000 for an exhaust or money on other mods/maintenence.

[rn79870]

RN - Webster says, "sentient - Finely sensetive in perception or feeling." Either some kind of tree hugger or mother teresa? Clue me in. Must you disect every joke. I'd call you a negative nancy but I don't think you can look that one up in the dictionary. So I'll explain, the negative quite obviously refers to your bad attitude where as by saying nancy I am calling you a woman/girly man. This relates because woman are renouned for their nagging capabilities. Again I poke. I presented information, but because you didn't say it you seem bitter or peeved. Forgive me if I push your buttons.

I'm sorry too dude, I didn't realize English was your second language.

[!979TransAm]

It's cool most people can't tell so welcome to the majority.

[Sentientbydesign]

Per Dictionary.com (Merriam Webster online has LAME definitions)

Sentient:

1. having the power of perception by the senses; conscious. 2. characterized by sensation and consciousness.

Sentient By Design is a Double Entendre

It's a emphasizes a disbelief in Evolution as it stands and I am a graphic designer. I work for University of California, Riverside. Hope that clarifies things.

My personal opinion is that the G35 despite all the R&D spent on designing zero lift aero and having a finely tuned air pump, were somewhat misguided.

The entire intake setup is ineffecient. The plenum as we all know gave a bias to the rear cylinders and choked the fronts. The airbox and tubing to the throttle are a joke. I see why manufacturers use those flexible accordion style tubes, but they create massive turbulence.

Most of the aero design was done to reduce lift, but in doing so it created drag. Nobody thought to divert air around the tires which are probably the single largest drag maker (not including the radiator and body panels).

I propose that $200-$300 could make significant improvements to fuel economy AND accelerration.

And the point of the mods wouldn't be to pay for themselves, but simply to reduce our impact on non-renewable resources. (They would pay for themselves in about a year's worth of driving though).

Oh and Kmech_7. I feel ya. Californians pay more for gas than anyone else in the continental US. You'd have to hop across "the pond" to get higher prices. Even with the recent drop, we're still mostly over $3.00/gallon.

[kmech_7]

i just filled up again today and paid 3.45 a gallon

[rn79870]

Join Costco. 91 octane is $3.15 today in North (San Diego) County.

[!979TransAm]

Sentient I apologize, seriously that is a cool name. And I would also have to agree with you on how simple design changes could make a good difference with the car. BTW your mention of wheels causing turbulence, Aren't there a few sports cars with wheels designed to act as fan blades and suck air from the engine campartment and over the brakes to help cool them? I have heard of it somewhere....

[telcoman]

look man i dont want to hear ever that you pay too much for gas in NJ. thats BS!!!!!! i pay the most for gas in the country! i live in San Diego. if you dont believe me just look online at the price spread across the country. i pay about 50-90 cents more a gallon ALWAYS!!

yet i always put premium in my car and a booster. on a military E-5 paycheck this is hard to do......but if i can do it twice a week or more.......

Kmech_7

Thank you for your service to our country

This morning regular 87 octane at BP is $2.77 here in NJ. One of the reasons gas is cheaper in NJ is we have one of the lowest state tax rates on gasoline in NJ. We have high property taxes and toll roads. I have to assume you either live on base or very close to it? My commute is 100 miles per day or 24k miles per year. Fuel and toll costs are a considerable non deductable cost for me.I've always loved driving a stick shift. My first one was a 1940 Pontiac 4 door sedan with running boards and a 3 speed on the column. Its two options were an AM radio & a heater. It also had sort of a push button starter that was located just above the gas pedal & you pushed it with the tip of your foot.My G is the best vehicle I've ever owned and for me it runs just fine on regular 87 octane. The altitude here in central NJ is under 500 ft above sea level. It is hard for me to understand why you would want to use a supercharged vehicle for transportation? I see nothing wrong with experimenting with automobile engines as a hobby and taking them to the track if you can afford the expense. To convert a day to day vehicle spending thousands of dollars & then having to use premium fuel to get it to run properly doesn't make sense to me. But then again, I'm an old farht so what do I know?The whole point of this thread was to inform some of the younger first time vehicle owners that it is not necessary to spend the extra money for premium gasoline if they do not wish to do so. Their engines will not self destruct or blow up. If saving a few dollars is more important than a 0 to 60 time it is certainly okay to do so. Between the special interest oil companys and some of the the automobile companys they all have their own agenda to try and make as much money as they can.For someone in their early twenties taking that extra few dollars a week instead of spending it on premium fuel & putting it into a IRA or 401 k plan will yield ten's or perhaps hundreds of thousands of dollars when they become an old farht like me. Something to think about.

Again, Thank you for your service to our country & don't forget to vote tomorrow.

Telcoman

[rn79870]

Interesting (as usual) reply telcoman.

With close to 50k on your car, I'm sure any problems would have become apparent by now. If the extra performance isn't important, then 87 may be the ticket.

[Sentientbydesign]

Transam,

Yes I have seen a few cars with the fan blad setup. I actually had a few classes with an up and coming mechanical engineer who had CAD drawings for just that purpose. The main flaw in his design was that the wheels could not hold the weight of the car, but his design allowed for variable blade angle and even reversal if there was a benefit. The idea was to cool down the brakes and to add a slight "push" when going around corners. I thought it was more of a fun concept than realistic.

My thoughts regarding the wheels were actually more inline with the McLaren F1. It has diffusers in the rear and diverters in front of each wheel/tire.

That combined with a smoother underbody would yield some awesome gains.

So yes. Telcoman is correct. You can run lower octane gas in your car. Most of us advise against it for one reason or another, but it's not going to kill your car, just possibly degrade performance and fuel economy.

[Q45tech]

Saving 30 cents per gallon seems useful, but what do you do next year when prices increase by 30 cents.

The most effective method is to reduce miles driven as that is 100% fuel saving.......................even a 50 mpg car doesn't help if gasoline rises to $6 per gallon.

Most [many] people will ultimately need to take a second job to pay for gasoline................ or electricity to power car or pay the increment on a hybrid.

[Sentientbydesign]

Saving 30 cents per gallon seems useful, but what do you do next year when prices increase by 30 cents.

The most effective method is to reduce miles driven as that is 100% fuel saving.......................even a 50 mpg car doesn't help if gasoline rises to $6 per gallon.

Most [many] people will ultimately need to take a second job to pay for gasoline................ or electricity to power car or pay the increment on a hybrid.

Thanks Q for making us all sad now

[!979TransAm]

yeah thanks for reminding us all there is really nothing us single consumers can do about the cost of gas.

Sentient- Wheels spoilers would be a good addition, then foilers on the behind the wheel.... Thats what they put on the trans ams (foilers as an option) In 79 the Trans Am was the first car to beat the corvette in drag coeffecient that GM allowed. Coefficient was something like .78. sorry for the trans am facts

[Davgreg]

Hey All remember me? the guy who asked the question in the first place?

I think what I was trying to get at was if we could modify the G35 or use just use lower octane in the engine.

For city driving there is no need for all that performance. But when you want it then well... That's why we got one.

You want to pay $3.50 a gallon to go stop light to stop OK suit yourself. Me I want to maybe save the cash as well as my car.

I want it to last a while and I want to be able to to enjoy it. If Mr. Civic needs to beat me, then fine, he may. I know (and so do you) who's gonna win that race anyway.

Object is to keep my car and keep some cash while I am at it. The wife drive like she's 80 anyway and I was just curious if I could lower the octane without running up a costly repair bill down the road later.

P.S. for those of you who think I do not use my G correctly, I will say this: The Cruise Control taps out at ninety-one MPH and you cannot modify that

[rn79870]

Saving 30 cents per gallon seems useful, but what do you do next year when prices increase by 30 cents.

The most effective method is to reduce miles driven as that is 100% fuel saving.......................even a 50 mpg car doesn't help if gasoline rises to $6 per gallon.

Most [many] people will ultimately need to take a second job to pay for gasoline................ or electricity to power car or pay the increment on a hybrid.

You make a good point. I have a friend who just got back from 2 weeks in the UK. Gas was the equivalent of $8.00 (in US dollars) for a gallon. Cars (rental) typically had 1 liter engines and he guessed about 50 HP. When gas hits 8 bucks a gallon here, and it takes $160 dollars to fill the tank. (Multiply that by 4 to 6 times a month) you're right, a second job will be necessary just to buy gas.

[Sentientbydesign]

Could you ellaborate on the airfoil. The term seems very familiar, but doing various google searches yielded no real answers.

[rn79870]

Hey All remember me? the guy who asked the question in the first place?

Yea, see what you started... I think the answer is that if you don't push your G, you can use lesser octane fuel.

Quote »P.S. for those of you who think I do not use my G correctly, I will say this: The Cruise Control taps out at ninety-one MPH and you cannot modify that [/quote]Most car CC's top at 90. You'll learn that if you drive I-5 through the central valley of California. The 1st. hundred of miles of which lacks even the slightest curve, and hardly any on/off ramps. Then there is a slight up hill, a slight curve and another 100 miles of the same. Even the 18 wheelers cruise at 70+

[C-Kwik]

The entire intake setup is ineffecient. The plenum as we all know gave a bias to the rear cylinders and choked the fronts. The airbox and tubing to the throttle are a joke. I see why manufacturers use those flexible accordion style tubes, but they create massive turbulence.

Perhaps it is inefficient and unbalanced. But when keeping things like fuel efficiency, noise, performance and an acceptably broad torque curve in mind, coming up with a well balanced system is not always easy.

Most of the aero design was done to reduce lift, but in doing so it created drag. Nobody thought to divert air around the tires which are probably the single largest drag maker (not including the radiator and body panels).

How so? I'm curious as to what kind of data you've had access to that allows you to determine there is such a problem with drag in the tires...at least anymore than other cars on the road.

I propose that $200-$300 could make significant improvements to fuel economy AND accelerration.

What improvements would you make then?

[Sentientbydesign]

I didn't say that the drag on the G's tires were worse than any other car.

I have just been doing a lot of research on reducing drag in general and the data I've come across indicates that the tires produce a large chunk of drag that can be "easily" overcome with air diverters.

I also don't see how restrictions in the intake can positively effect the torque curve or fuel efficiency. It's a gas/air pump, not a radiator.

I'll post the mods when I've developed something useful. Until then, it's all just planning.

[C-Kwik]

I didn't say that the drag on the G's tires were worse than any other car.

I have just been doing a lot of research on reducing drag in general and the data I've come across indicates that the tires produce a large chunk of drag that can be "easily" overcome with air diverters.

Well, I'd have to question how you would use such "diverters" without having impacts elsewhere in the vehicle. Bearing in mind that a bunch of smart guys at many different auto manufacturing companies haven't come up with a solution that would appear to have been implemented on the majority of cars on the road. Consider that some of the smallest aerodynamic nuances make enough of a difference that several nuances together can have a measurable impact on the overall aerodynamics of a vehicle.

I also don't see how restrictions in the intake can positively effect the torque curve or fuel efficiency. It's a gas/air pump, not a radiator.

Well in a bit of a haste, I neglected a few things in my prior post. Namely space and vibration. The bellows in the intake tube for example, are there to reduce vibration and noise that could be heard and felt and perhaps cause premature failure of some of the intake parts as the engine moves around on it's mounts. Certainly, there can be some gains from a smoother intake, but additional resonance noise, vibration, and noise may become unacceptable. Unfortunately for the performance enthusiast, OE vehicle feature many compromises to cater to the masses.

But its not just limited to the intake tube. While it would seem that there are upgrades to try and balance out the flow in the intake manifold of the RWD VQs, these performance mods likely have little thought going into the big picture that vehicle engineers must consider. Sure, there are things that could be done better. But many compromises are generally made to achieve a certain interpretation of better.

I'll post the mods when I've developed something useful. Until then, it's all just planning.

I'm all up for new ideas and thought. And I certainly wish you luck on these. But I'll remain skeptical until I either see these mods or have some meaningful discussion about them.

[adren77]

I am surprised nobody mentioned this since u are all car gurus.

There is one way that modern cars can be tuned to increase the efficiency of the engine at the expense of reducing power. The key is the continuous variable valve timing. I will try to explain how this can be used to increase engine efficiency.

Some of you mentioned thermodynamics. If you have taken an introductory class, you would have studied the OTTO cycle. SI Internal combustion engines are based on Otto cycle. Engine operation can be modified to modify this Otto cycle, such to become more efficient. During the Otto cycle, a large part of the energy is wasted through the exhaust stage. Why? The reason is that when the piston reaches maximum volume during the power stroke, there is still "high" pressure inside the combustion chamber. Pressure difference across the piston is what makes it move right? So this "high" pressure inside the cylinder means that there is still potential for the piston to keep moving (extract more mechanical work). However, since the piston is at maximum stroke (cylinder at maximum volume), the piston cannot keep moving and the pressure is relieved through exhaust. So, what I am saying is that by making the power stroke LONGER than the compression stroke, you can utilize this high pressure and get MORE work and less energy wasted through exhaust stroke. So how does an engine make the power stroke longer?

Unfortunately, current engines cannot make the power stroke longer... but! Instead of making the power stroke longer, you can keep it the same while at the same time make the compression stroke shorter. The end result is the same. Think about it. The ratio of compression/power stroke < 1 in either case. Right?

So, how do you shorten the compression stroke? This is possible by delaying the closure of the intake valves; the cylinder will compress LESS air. Yes the cylinder still travels the same distance as before, but compression stroke starts after in take valves close, so delaying the time of the intake valve closure causes the compression stroke to be shorter! Essentially you are making the compression stroke shorter than the power stroke, and utilizing the high pressure at the end of the power stroke discussed previously. By doing this, you compress less air (and fuel) but you increase the efficiency of the engine because you are not wasting as much energy through exhaust. Since you are compressing less fuel-air mixture, there is less total energy inside the chamber which means you will loose power.

So now you ask, why did the engineers not think of this and utilize it since the gas prices are so high? Well actually they did!

Variable valve timing on the intake in a G35 is electronically controlled. This means it requires a complex algorithm to control it. The ECU gets different inputs such as Load and Engine speed and as output it tries to predict how much power output you desire. Obviously, if you always drive with a heavy foot, and at high RPM, you want MORE power, so the engine switches to different mode of operation... one that gives you the most power, which means compression/power stroke = 1. If you were to drive with 10% throttle all the time, and shift at 2000 rpm, you would surely notice a drastic increase in gas mileage because the compression stroke is shorter.

It is possible to create a new algorithm which will always operate the engine under condition I described above. This will drastically reduce performance but increase the overall gas mileage.

So now another smart *** guy will say, "well how come nobody thought about making a button which will let me switch between the two modes at will, that way I can always get the extra MPG when i don't need the power, and get the power when I want to race?" Well the truth is, some cars DO have it, just not your infiniti. If you think about an M5 which has a button that switches from 400HP to 510HP, that is exactly what it does. Of course it also changes other parameters such as spark timing, etc... but this is what the button does. It switches between the two algorithms which tell the ECU how to operate the Valve timing, spark timing, etc etc. to switch between the economy or performance modes.

I hope I explained this well enough. To completely understand it, you will have to look at a Pressure vs. Volume diagram of Otto cycle.

[adren77]

C-Kwik...

The belows in the intake tubes are not there to reduce the vibrations/noise.

The reason for the belows is to induce turbulence. Turbulence plays a key role in the combustion dynamics inside an engine. More turbulence inside the engine, the better! Engineers try to induce turbulence inside the engine at every possible opportunity, and intake runners is one way.

The reason why turbulence inside the engine is important has to do with the combustion characteristics inside the chamber. Turbulent air will cause the flame front to propagate faster!!! We want the flame front to propagate as fast as possible. Faster flame front = faster combustion inside the chamber => less chance of knocking to happen => means we can get higher compression ratio => higher power + efficiency. Also faster combustion means the engine comes closer to having "constant volume combustion" (just as in the Otto cycle)... which will yield higher thermal efficiency.

Turbulence in the intake will cause more drag which is a negative side effect, however in this case, it is greatly outweighed by the positive gain explained above.

[telcoman]

Some of you mentioned thermodynamics. .........

Variable valve timing on the intake in a G35 is electronically controlled. This means it requires a complex algorithm to control it. The ECU gets different inputs such as Load and Engine speed and as output it tries to predict how much power output you desire. Obviously, if you always drive with a heavy foot, and at high RPM, you want MORE power, so the engine switches to different mode of operation... one that gives you the most power, which means compression/power stroke = 1. If you were to drive with 10% throttle all the time, and shift at 2000 rpm, you would surely notice a drastic increase in gas mileage because the compression stroke is shorter.

It is possible to create a new algorithm which will always operate the engine under condition I described above. This will drastically reduce performance but increase the overall gas mileage.

adren77

Your post and explanation is interesting because this is precisely the results that I have experienced with my G using regular 87 octane. Many G owners have posted getting very poor mileage using premium fuel and driving their vehicles hard.That has not been my experience. Day to day I get between 22 and 24 MPG with up to over 28 MPG on long trips. My 50 mile one way commute is mostly on cruise control between 70 - 75 MPH. There is no need for me to push my vehicle as traffic is light in the early morning & I usually shift between 2k & 3k rpm. Most of the $ssholes that clog our roads are not up yet. So I guess the point is that we can have our cake and eat it too, it just depends on how you want to drive your G

Telcoman