Those of you that think that using 87 octane only slightly reduces the power, go dyno your car with 93 octane. Run that empty, then re-fuel with 87 octane and dyno it again once the ecu has had time to adjust.

I am willing to bet you will drop around 20 rwhp. Thats significant in my book.

Your mileage will suffer too, taking away from any savings you would have gotten.

The ecu changes the timing and a/f ratio, and basically your car will run rich with retarded timing, causing power loss and worse mileage.

If you don't want to do the dyno experiment, do the mpg experiment. Make sure to fill up with 87 octane, run it almost all out, then go back to 93, and on the second tank full, see how much more you get on a tank full, now that the ecu has had time to adjust back.

I had someone I know, who used 87 in her 97 Maxima SE, try this. She told me she is getting 50 more miles on each tank with the premium, and that her car runs a lot smoother, taking less gas to go. She now runs premium all the time.

If the car is designed to run on 87 octane, it is better to run cheap gas.

Our Z's are designed for 91 or higher though, and they will suffer from using cheap gas.

 

You would have to try it and see what your mileage looks like.

It might, depending on the environnemental conditions and your driving style. The potential is there. But someone who is real easy on the gas pedal might not benefit from it.

I run my Z exclusively on Shell VPower.

 

Now you are not making sense Kolia.

If the manual says 91 octane, why use 93 or 95? Unless the car is tunned to higher octane gas, not only won't you see benefits, but you might actually lose power since higher octane gas burns differently. Plus, our car is equipped with an array of emission control devices and sensors that work within very strict parameters. And since it burns differently, Higher octane gas will have this system work differently, putting strain on the cats, make car run lean, or rich, or whatnot, etc... The car doesn't adjust only to the combustion chamber

also on shell website it says "Octane ratings for premium gasoline vary across the country. The octane level of Shell V-Power is anywhere from 90 to 93 octane, depending on the region." It’s important to point out, however, that octane is not the only factor to consider when choosing a fuel."

 

I guess everyone here answer the question will one tank of regular gas be bad for the Z? And the answer is NO! But good discussion about increase in gas prices that effect the decision whether to use regular or premium? If prremium is 20 cents more that regular add around $2.00-$5.00 more on top of the $30.00 fill up. It should not make a big difference. Save that slice of pizza or McDonalds and Z will thank you!

 

https://my350z.com/forum/showpost.ph...8&postcount=56

 

Yeah, I remember that thread

the guy had had a 18rwhp gain by going from 91 to 100 octane in a 5 minute interval.

BS, there is something wrong somewhere or we are missing some elements... or explain to me WHAT would cause the engine to put out extra 25hp.

Talking to gas emission engineer. putting 100 octane gas in a modern car designed to run 91, will have your catalyst fail in less than an hour. A friend of mine had catalyst fail after 2 laps using japanese grade 100 octane gas.

 

Was the race fuel leaded? If it was (it most probably was) then sure, the cats will die. Some race fuel are unleaded.

With the advent of closed loop ECU, today’s engines are very dynamic indeed. Multiple parameters can and are adjusted by the computer. Ignition timing is one big factor, but injection sequence and cycle time will also vary with rpm, barometric pressure, ambient temperature, load (via Throttle sensor), O2 sensors feed back and knock corrections. Remember variable intake timing (and exhaust on the Track and 35th)

The base tables of engine management extend way beyond normal operating conditions. Plus, most ECU can log and learn from events. That is why we reset are ECU from time to time. This is also why we can go FI while keeping the stock ECU (MAF based ECU is a mandatory factor for that)

We must also keep in mind the thermal efficiency a typical 4 stroke engine is around 20%. That is, only 20% of the energy stored in the fuel actually drives the wheels. What ever gains we make moding our engine is actually less loss. The power potential are huge (F1 engine with 3l capacities run over 900hp on 105 octane “street” fuel –see FIA regulation on that)

So, when I say that the potential for bigger HP from running 100+ octane is there, it’s no BS. What I do not know is if our engine will actually take advantage. I believe it will. But I’m in no position to prove it.

 

no, Japanese grade 100 octane gas is absolutely unleaded.

so like this person told me, unless a competent, knowledgeable fuel/emission engineer tells me otherwise. I'll stick with I've been told.

 

Well...dyno's don't lie...people do.

Even assuming the dyno's can change ~5rwhp between each pull...that's still at least 5rwhp from switching to a higher octane.

 

It's quite alright with me.

Would the opinion of a automotive/motorsport technical designer with 2 years experience in F1 car design count?

 

Well, people dyno

anyway. I have used 93 octane gas(canadian grade, lol) several times.... and been to the dragstrip several time to prove the point.

My ET was exactly the same, my trap speed was exactly the same and my friends Z who always used 91 octane is exactly as fast as me.

a 5rwhp difference would have been noticeable..a an 18 rwhp is rediculous

Kolia do you have a degree in something pertinent with Fuel, fuel systems, emission control systems and engine control units?

If the engine/car can adapt SO QUICKLY to higher octane gas, by the same mechanisms(and logic) then using lower octane gas would be perfectly fine as well, as the engine would adjust instantly. I do not follow

 

Comparing E.T.'s is not accurate what-so-ever. It varies on shifting techniques, launching techniques, RPM's at which you shifted, etc. Dyno's at least have a 5rwhp varied result between pulls. You pretty much can nail the same technique on a dyno...alot easier than on a 1/4 mile run..

And comparing runs to another Z driven by another person...completely inaccurate.

 

I have a DEC in Aerospace Design (I’m from Quebec). I kinda drifted toward automotive over the years. And I have worked at Ferrari F1.

It would be hard to explain in details in only a few posts. I have documented myself on engine management and various technologies used in the automotive industry. I’ll try.

A note on knocking. We are not talking here of full detonation. Knock will first appear as spontaneous ignition of unburned mixture during the sparkplug induced combustion. In essence, we have spark ignition, combustion of the mixture starts, pressure and temperature rises and WHAM! The remaining mixture explodes. Retarding first ignition will have the combustion occur during the downward movement of the piston, reducing the peak pressure in the cylinder and preventing detonation. Can you see now why we lose power when ignition is retarded?
Normal combustion is relatively slow (6m/s). So the faster the engine runs, the earlier ignition must occur so the flame can “catch up” with the piston and reach peak pressure at the correct time.

Strictly performance wise, you would have to clear the ECU’s memory to be certain you benefited from higher octane fuel. Going back to the ECU’s learning process, it will record events like knocking and adjust timing (retard) to prevent it. Then, whenever the same knocking inducing conditions are approached, the ECU will retard timing BEFORE knocking happens to prevent it. It will no longer wait for the actual signal from the knock sensor (it takes more than one event for the ECU to start bypassing the KS signals).

So, if you run regular gas always, the ECU will have learned to prevent knocking by killing power before knock happened. Put nice gazillion octane fuel in the engine at that time, it will still retard timing as a preventive measure.

When you say that most people won’t see the difference, you’re right. Because the ECU would not unlearn his knock retardation table and ordinary people do not drive WOT all the time.

We will feel a difference if the engine needs to use knock correction with 91 octane at high rpm. Then power is “artificially” killed by the ECU at these rpm. According to my observation of Subaru ECU readouts, stock ECU usually have to do some knock correction at high rpm, even on fully stock engine AND premium fuel.

 

Like everybody else says, I think you've got nothing to worry about, When I first got my Z, I accidentally filled up about half the tank with non-premuim without thinking (force of habit- My old car was a '93 Integra that took non-premium). I just stopped and filled the rest with premium...no problems.

 

@Kolia, I know exactly where you are from, lol. Funny, I thought you knew me as well... might want to got take a look at bmw quebec chapter website.

What you are saying makes more sense. You might see some benefits (hp) at WOT and near redline in some odd situations... but NEVER 18rwhp accross the entire powerband like that freak dyno posted(which btw, has 0 gains at redline, even more freaky). Also, you are not depicting the whole picture. You are completely ignoring the emission control system. Which monitors and is dependent on the whole combustion process. If you reset ECU, it will revert to whatever setting the car was originally intended for... 91 octane.

@ Nis. You haven't been to dragstrip much. I can have 10 passes within a .1 mph speed. Dragstrip is real life situation, unlike dyno, and is an extremely accurate indicator of horsepower. Also, I've been running with this Z friend for over 2 years and more than 100 passes. It's the best realife benchmark you can have.

 

10 passes within .1 mph? Wow...you must be a great driver.

I call BS...i've been to the track quite a few times and times can vary by more than one full second...much less .1 with the traps...

Maybe 2 runs that were within .1 (which...is still...outrageous), but definitely not 3, and I would estimate that it would NEVER happen again in your lifetime.

 

I think we can conclude high octane does have a potential fuel economy benefit. It is slightly denser than lower-octane gas, meaning there's a little more energy in a gallon. But the small difference is hard to measure in real-world use, and that same density can contribute to undesirable buildup of waste products inside the engine. 87 octane won't hurt the engine and the loss of horse power is hard to measure in normal use. Use what ever gas you want and don't worry.

 

it's the opposite, as a norm, the higher the octane, the lower the energy per gallon. Higher octane fuel, has higher POTENTIAL energy. which is totally different. If there is no knock, then increasing octane is totally rediculous and irrelevant.

Engines perform best when using fuel with the octane rating they were designed for. Final. This discussion is rediculous also

@nis don't believe me then.

 

For a quick fix: put in a gallon of toluene when you can (based on my car, you probably have 1.5 gallons of air in your tank after you fill it).

just posted on this topic....

"running higher octane (doesn't matter what the number is, just higher) will result in your car running closer to max potential. this is because you *do* have timing adjustments on your engine - probably every Nissan does. It's the ECU and it will definitely retard timing to preserve the engine. using better gas will reduce retardation under certain conditions.

in a stock NA engine, high octane doesn't GAIN power, it simply prevents potential LOSS of power.

question is "is it worth the extra money for the nicer gas?" that's for you to decide. in day to day driving, it's probably not worth going over 91. but running 87 all the time will result in your engine always retarding the timing."

KOLIA - wondering what your take on the toluene is. did it on other cars - VR6 and Conquest TSI - not the Z. seemed to work, esp on the TSI.

Also I didn't know the ECU remembers where it retards timing. Does that mean you have to reset ECU (unplug battery) each time you bump the fuel quality up significantly?

peace
aki