JimmyJames

The 240 I'm looking at right now has only been powered by 93 Octane gas. I understand 93 Octane is a better grade fuel than Unleaded, but can it have any negative impact on the engine? Does is even make a difference since the engine is normally aspirated? Thanks

D1drifter

Unless he raised the compression the N/A KA motor, hes waisting money on getting the higher octane gas. Sure its higher grade, but the higher octane is more useful on turbo or supercharges engines. Higher octane only means the less likelyness of early detonation.

Maeda

I believe the engine is supposed to be running on 91-93 ONLY. The ecu retards the timing with anything less.

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MorganS13

actually 91 octane is recommended for maximum performance, but the car will usually run fine on 87 because the ECU is retarding the timing to account for this and you are losing a little power (i have no clue how much, it is probably negligible). on the otherhand, you are not really gaining anything by running 93 over 91 since i'm pretty sure the 240 ECU's do not advance the timing to take advantage of anything over 91. most places around here have either 87, 89 or 93, so i just get 93 on the certain days when its on sale for the same price as the other grades. sure 93 is overkill on most N/A cars, but i know my car and several other people cars have a noticable improvement with 91+ compared to 87 (smoother power delivery and idle are the most obvious).

Ghettokracker71

Hence why on the gas door there is a sticker that says to use premium grade fuel for maximum performance....

MorganS13

SHH!

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zero.counter

On the S14, I have used 93 for the last year since I got it with the exception of being cheap for a couple of weeks. I would over-rev in some situations when using 87 octane and set off the knock sensor. I learned my lesson after having tested the situation by using 87 and getting the error, then switching to 93 without any issues. I am not worried about performance, but moreso detonation due to cheap fuels and costly downtime. Read the sticker on the inside of the gas door...

Maeda

Finally somebody that believes me. Personally I run the highest octane I can afford. Detonation should scare everyone and their mother.

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misnomer

I run 87 most of the time. I used to run 91, but never noticed a difference in performance. Never had a problem with detonation (I am pretty high altitude, however). Most resources I can find also say it's useless to buy higher grade gas than your car requires. I'm personally a bit more concerned with cheap fuels and modifier deposits than the octane rating of my gas. If you're that concerned, bust out your owners manual and see what it asks for. IIRC, my '92s manual just says 87. . .

I am of the opinion that higher grade gas is really only needed for high compression or forced induction.

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IKu

do you have proof the ecu retards timing? i really doubt this is true; how does the ecu know what octane level it's running? octane level doesn't affect the energy level of the gasoline, not directly at least. i'm not saying you're wrong, but some proof would be nice. =)

Burmonster

The ecu doesnt read the octane leve, it reads the knock sensor in your engine. Lower octane causes detonation, which is sensed by the knock sensor, and then the knock sensor signals the ecu, telling it to retard the timing.

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twitchy

how does the ECU know what octane you use?

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NISMO_drift

read the post directly above you ^^^^^^

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IKu

well... it's true lower octane is more likely to detonate, but do you know if 87 or 89 octane will detonate in our cars? i've used 87 for a while, and i don't *think* my car has knocked, but perhaps the ecu retarded timing before i knew it, at least according to what you are saying. so do you have any proof that there is indeed knocking? or that the ignition is retarded when someone uses 87 octane?

Mikes14240sx

ASSUMING that your baseline timing is within spec I doubt you'll be harming the engine running 87.