emptnest

I run a stock LT1 C4 in HPDE. At one of my recent events, fuel was available for purchase in various octanes above the conventional 93 that I normally purchase. I believe they had 98 ethanol free unleaded, 100 unleaded, and 110 leaded.

I was tempted to try the 98 ethanol free unleaded, but not knowing anything about it, I just stayed with conventional 93.

Lets assume away the 110 leaded.

Would any of the higher octane unleaded cause problems with the stock LT1? Can the engine programming self adjust on the fly to take advantage of the better fuel?

What say the experienced gear heads here?

Joshboody

Doubt there's any advantage over 93oct. I don't know the LT1 well, but LS1 I have almost max timing on 91oct in most conditions including HPDE. The temp adj are fairly aggressive.

edge04

don't bother, waste of money if your tune is not set for that

C5 Hardtop

I've had excellent results mixing 110 octane in a '99 Camaro I drag raced. It had the LS1 engine. I don't recall if it was leaded or not. It was for sale at the track.

The trick is to mix high octane with 92 (Seattle, WA) octane to bring up the octane level in your tank by just a few points.

I saw about 0.15 to 0.2 gain in ET and it was repeatable. I added a gallon of 110 with an existing 1/4 (ish) tank. Experiment to find what your car likes.

If you add too much, the engine will lose a bit of power because the gas burns at a different rate and that changes the timing. That offset doesn't seem to be compensated for with the engine management software.

Rookieracer

Octane is a rating to describe the fuel's resistance to auto ignition.
The power comes from the fuel's BTU content. Or energy content.

Higher octane racing fuels generally have a higher BTU content as well. So there is more energy in the fuel that can be released and used to push the piston down.

Regardless of whether you choose to re-tune the spark curve to take advantage of the higher octane, the 98-110 fuels will have a higher energy content which will translate into more power without a re-tune, just not as much.

A word of warning, in many cases the higher octane fuels have a slower burn rate than pump gas, so going to the 110 fuel from 93 might actually rob some power without the compression and tune to support it. Once again "more" is not necessarily better.

I think you would be pretty happy with the 98.

arturox2

Interesting Tadge comments regarding higher octane use in the Z06 located here:

https://www.corvetteforum.com/forums...t-r-nismo.html

Joshboody

BTU is energy density, directly related to AFR... determines fuel per O2 needed. Only way to increase energy released (for same AFR) is add O2, which some fuels contain it.

Disclaimer: I'm no chemist though.

CHJ In Virginia

Higher octane fuels will not generate any power gains without engine being retuned to make use of extra octane. DO NOT use leaded 100 or 110 in your car unless you have removed the catalytic converters. the lead will plug the cats and you will have an expensive repair on your hands.

Bill32

I run 89 in my 92..............and still catch up and pass the C5 &6's.

93Rubie

Not worth the money on a stock engine or even a modified one (depends on the modifications and use). I run 93 when I can and 91 when I cannot. I've done data logs on 90+ degree days and NEVER saw any spark retard or knock counts. Which means I am making as much power as the engine can as it sits on that day. BTW, at WOT a stock LT1 pushes 36 degrees or so of spark advance.

93Rubie

Only if they are not as skilled a driver as you or they are taking it easy. That or your car is highly modified. A stock C5 should walk away from a C4 with equal car prep and drivers. I've ran down and from plenty of faster cars but truth is truth.

Bill32

More tongue in cheek than anything, unless you're running close to the track records, work on the driver to improve lap times, not the horsepower.

I do use 89 on he track, BTW.

db2xpert

If your ambient temp is high 90+, then mixing in some 98 can be some insurance against knock ignition retard. More a case of not losing the HP you have, rather than a gain.

You might or might not gain a few HP with a retune.

arturox2

Per Tadge Juechter in his "Ask Tadge" response to the GTR vs. Z06 question:

"Generally speaking, higher octane enables more aggressive spark calibration and higher power. While the Z06 is certified for 91 octane fuel, adding octane boost will offer greater resistance to spark retard and detonation under thermally challenging conditions (reduced likelihood of power reduction when intake temps go up). Racing fuel (100 octane) available at the track improves this robustness even further. We will be recommending that customers who track their car, especially at higher temps, use the highest octane fuel available."

LateBreak

That's on the new LT1 arturox, but on a C4 LT1 you'll lose power with too high of octane. Run pump 91-93 and you'll be fine.

arturox2

Thank you.