Highest Octane For Stock ECU??

the_student

Yeah, most of us Californians usually have 91 around. In San Jose, there is actually one station with 100 octane that you can mix with 91 and get around 95/96 octane.

JoeD

Yes, my friend's 76 station in Redwood City offers 100-octane unleaded at the pump, too. However, on practically any stock car, it will hurt performance rather than help.

It's only in the case where a car is dyno-tuned to run on a specific grade where there will be an improvement. Only then in the hands of a competent tuner will you reap the benefits of "more octane."

the_student

I assume that US versions of the 370Z were optimized for 93-octane. And since here in Cali we usually have 91, would you say if we are able to mix 100 and 91 octane to achieve a 93 octane level, that the cars will perform more to their peak performance? It would be a relative increase in performance from filling the tanks with 91...in theory.

JoeD

Doubtful.

The only production-car I can think of which was optimized for anything but 91 is the Veyron. Everything else is made to run on 91-octane, as California is the biggest car-market in the country.

Mix any octane of fuel you want in a 370Z...there will be no varience on a dyno greater than what there would have been even if you didn't change the gas from pull-to-pull.

ZzzZz

I doubt they'd cripple cars for just California's sake. Yes, the cars are all sold "50 state" emissions equipped, but I'd bet money that the ECU compensates for the lower 91 octane, thus making the minimum requirement, but can handle advancing timing when the octane's higher.

Even though its not exactly a US-Spec, here's an example of what could be going on for our 370s:

Stock UK Spec EVO VII (Vishnu Performance)
EVO VII dyno run 91 vs 93 octane - NASIOC


Or for US-Spec, look no further than the 350z!
350z 91 vs. 100 octane

rudi

In the manual for the Australian version, it states: Use UNLEADED PREMIUM gasoline with an octane rating of 98 (RON)

I have alway used BP Ultimate which is 98 RON in both my 370 and S15

Mercennarius

I'd venture to say you're wrong. Many cars are actually produced in two variants for the US...the federal spec and california spec. The ECUs are modified to run on Calis piss poor gas and stricter emission requirements. Sometimes cars are sold in every state BUT California(TT Supra etc.).

Though I will agree that running higher octane then is needed will net you zero gains...in fact often times it can hurt your overall performance. Optimally you want to run the lowest octane your engine can run on without detonating as this will give you the most power and mileage. As soon as your engine detects knock it pulls back timing/adds fuel to the map to run a more conservative and safer tune to prevent future detonation.

As for the original posters question, your ECU does not read octane levels it only sees what the O2 sensors and knock sensors tell it. You can run as high of octane as you want but it would be pointless to run anymore then you need and may do more harm then good. Just run 91-94 regular pump gas...anything less and you're engine will likely run a safer tune and anything more would be a waste on a stock car. I'd be more worried about the quality of the gas, stray away from older gas stations as they tend to have more sediments deposited in the bottom of their tanks that can get in your gas. The difference in brands is negligible.

Trips

Good Post... thats the bottom line, there is need to over octane a stock car unless it's highly modified only then will you see a difference.

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ZzzZz

That's the question though, where is the sweet spot between 91-94? Why pump 94 when you can save money with 91 right?

Was never suggesting 100octane+ is beneficial for a stock 370z.

Driftomodachi

From what I have heard, 100 octane in Japan is like the 91 octane here and 91 octane there is like the 87 octane here. And since the z is a "world car" the ecu should compensate and performance should improve with the highest octane the car was designed to run on which is 100 octane.

Not sure how true that is

DEpointfive0

The US doesn't use Octane, we use AKI, average knock index. You cannot compare it to the rest of the world

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Jordo!

We do refer to octane, but it's rated a bit differently -- RON+MON/2 = AKI, whereas most of the rest of the world uses RON.

You can get a close approximation on RON vs AKI tho'; typically .95*RON = approximately equivalent AKI.

Example: The Z recommended octane is 91 AKI and 96 RON

96 RON*.95 = 91.2, very close to the AKI value.

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DEpointfive0

Yeah, that's close.

If the RON is 100 in Japan, 95~ AKI

My money would be something like 94 on America's AKI system because that's probably the highest you CAN find at a normal pump in the US (I think I've seen 94 at the pump in Ohio, or Illinois, or Michigan)

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Driftomodachi

I'm sure Nissan considered all this when they put parameters on the ecu so that it could be a world car.

So can a z34 run "100 octane" or whatever it's called from the local 76 station pump here in So Cal and will it improve performance?

When I had my 240sx with an sr swap it ran ok on 91 but felt much livelier when I put in 100 but the vq is a different motor. Sorry for the noob question just trying to learn. It's funny google actually pulls up better results than the forum but I haven't found a thread that confirmed anything

DEpointfive0

I doubt it. And you'd probably "gain" only if you reset your ECU too

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