Pump Gas in 604

[Cranky]

Is anyone running 91 or 93 octane pump gas in their 604 crate. GM only calls for 91 octane. I saw an episode of Engine Masters where they tested pump gas VS. 110 and 116 race fuels with only .8 horsepower gains and no destination. If there is no more gains than that, why are people running it?

[LRtireCHANGER]

Most people do not understand that higher octane rating does not necessarily mean more power. A fuel of a higher octane rating will resist detonation under more severe circumstances than a fuel of a lower octane rating will resist detonation. As long as you run a fuel that does not detonate in your application, then more octane rating is not necessary.........However, when talking about which fuel will make more power, we must also talk about oxygenated fuels vs conventional fuels. Oxygenated fuels have things added to them that carry extra oxygen vs non oxgenated fuels. Oxygenated fuels make more power than non oxygenated fuels. A 604 engine has aluminum heads, and a 604 is only 9.7:1 compression. In theory, an aluminum headed engine with 9.7:1 compression should run just fine on 87 octane pump gas. I would not run 87 octane. I would feel safe at around 100 octane. I would achieve 100 octane in one of two ways. 1). 50% pump 93 octane e10 and 50% avgas 2). 60% pump 93 octane e10 and 40% race 110 octane. Many people hate avgas, I do not hate avgas. I can buy Avgas locally for around $5 a gallon, and it test out at around 105 octane, when compared to pump gas. There is a 3rd option, and that is to buy oxygenated 100 octane race gas, but this is around the same price of 110 race gas. The 93 e10 that I use in my mixes gets its oxygen from the ethanol it contains.

[Jking24]

It's not really about what does or doesn't make the most power you have to consider the real world scenario when your 20 laps into a 30 lap race running wide open and the water temp is 220 and the oil gauge is pegged. How's that 87 or 91 gonna be then. The way i understand it the 604 package likes around 100 octane on gas for best overall performance from a purely hp point of view but most sanctioning body's don't let you mix fuel. When we were running them we were told if allowed to cut the race gas with pump gas to get the best results

[MasterSbilt_Racer]

I'd run pump E85 if allowed.

[ZERO25]

Go to Crate Insider and search 604 recommendations. Steve Hendren (Hendren Race Engines) gives all the specs!