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[ANSWERED] 17 z06 running on 91 octane

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[ANSWERED] 17 z06 running on 91 octane


Old 03-01-2018, 08:07 AM
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Originally Posted by Pacembellum View Post
figure a c7z on 91 is only making 630 crank, now figure it's hot (abive 86 degrees) and pulling timing...down to 600 crank. C6z was underrated and not as temp sensitive and 275lb lighter, i could believe it at keast "feeling" close.
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Old 03-01-2018, 10:42 PM
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Originally Posted by Patman View Post
Temperature also plays a factor in octane requirement. In cooler weather you can get away with lower octane, my wife's BMW calls for 91 octane but in the cold winter months I usually put in 89. And I recall with my old C5, which was tuned, it would audibly ping on 91 in the summer but it wouldn't ping at all in cooler weather (I mostly ran 94 octane in it during the hot months)
We have a work truck, a 1999 Mercedes ML-320 tha calls for 91 octane. I'v filled it countless times with 87, never a ping, just less power but not even tha noticeable. Now before a one says I will ruin my engine, it has 193,000 miles on it and does not burn any oil and there is no valve noise. All about the electronics monitoring timing.
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Old 04-07-2018, 12:13 AM
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Tadge said "Even in high torque/Hp operation, there will only be slight performance degradation and the ECM"

Jbsblownc5 dynoed his 17, about 65rwhp difference between 91 and 93. I would say that's a good amount? What is it in 1/4, maybe half sec?

Wasn't aware that 2017 requires 93 when I purchased the car, M7 won't overheat on track that's great but I don't really track it, I do drag race it. and 1/2 sec slower than previous Z06 that's a huge difference. Usually cars get a little more hp on the newer models. Doesn't it suck when the 65 rwhp is always on your mind when you pull up or see previous years Z06s on the highway etc?

(Any other 2017 dynoed their Z, is it also around 65rwhp difference? )


Last edited by okaythen; 04-07-2018 at 12:13 AM.
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Old 04-07-2018, 12:18 AM
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Originally Posted by _zebra View Post
another thing people don't mention is altitude. the general rule of thumb is for every 2500' of elevation, you can go down a point of octane with minimal difference in performance due to the air density decrease.
granted, at 2000', las vegas ain't high enough to warrant 91, but other areas in the mountains do. that's how they try & make the argument for that trash 85. unfortunately, it seems tons of places west of the mississippi just don't want to source 93
So if the altitude is 2500', to have 93 for the car do you need to actually need to get 94?? (since there is 1 octane drop) and the same for 91?

Like OP I am also in Vegas, it's mostly 91 here and since it's not quiet 2500' here but if it's really hot ( or I get a bad tank of gas). It's lower than 91 I guess and could cause knocking? Never think about it that way before, and not sure how do you hear the knocking since at full throttle the car is not quiet.

Last edited by okaythen; 04-07-2018 at 03:06 AM.
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Old 04-12-2018, 05:48 PM
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As your altitude increases, the octane requirement goes down for normally-aspirated engines because they can't pull full manifold pressure above sea level density altitude .

For a supercharged/turbocharged engine, the octane requirement stays essentially the same as altitude increases because the blower is usually slightly larger than needed at sea level, and does allow the engine to pull sea-level manifold pressure up to a certain point called the "critical altitude". Above that point, even a blown engine starts to lose power.

It would be interesting to know what the critical altitude of a LT4 is.
Does anyone know?

Last edited by Gearhead Jim; 04-12-2018 at 05:51 PM.
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