BCNUL8R

iTrader: (2)

A friend of mine is just finishing up a 512 cubic inch bbc he said it was a race gas engine. I asked him what the compression was and he said it was 11.3 to 1. I told him that my 408 was 11.4 to 1 and it ran fine on 91 octane. I also talked to him about static compression and dcr really being what determines how much compression you can run on pump gas. He told me that it was different with carb motors and injection due to better fuel atomization with injection. He wouldn't give me the cam specs because we plan on racing when both our cars are done so I don't know what the dcr is on his engine.

What's your take on this?

p.s. I will have a 150 shot for some extra insurance

Wnts2Go10O

iTrader: (12)

what motor and fueling method doesnt determine what it can run on. what would determine the need for one fuel over another is more a mix of the chambers, the timing, and static and dynamic compression. my take is, the older technology isnt as efficient (in all aspects((except oiling)) including cooling) and could very well need things the ls series motors wouldnt. it doesnt matter whether youre using the engine to pull in fuel or if youre spraying it in.

BCNUL8R

iTrader: (2)

That's what I tried to tell him, but he is alot more experienced than me so I didn't want to argue something I wasn't sure about.

Now I'm thinking he might be lying about his compression ratio since he has told some of my other friends that his main goal with this car was to beat me.

Wnts2Go10O

iTrader: (12)

he needs a 512 to beat you?

anyways, seems to me he doesnt really know wht will effect it. timing and compression sure, but fueling? not unless your running nitro which makes its power from detonation.

BCNUL8R

iTrader: (2)

I think it's going to come down to traction. I don't have the optimum suspension by anymeans with the IRS, but he would have been better suited to spend some of his money on suspension instead of putting it all in the motor. He spent everything on the motor and is running stock suspension with a 9" rear end no mini tubs or anything. His car is a 67 firebird which originally came equiped with a 6 cylinder overhead cam engine.

383backinblack

i dont know if you'd see a difference on a n/a engine, but i know on a blower motor, you can actually run more timing and/or less octane with a blow through carb than you can with injection, because of the wet manifold. The heat of vaporization of the fuel in the carb/intake can have a SIGNIFICANT cooling effect on the intake air temperature........it all depends on about 1,000 factors.

In some cases you will actually see ice form on carburetor venturi's from the extreme temperature change which is in part effected by a combination of the pressure drop through the carb (which is what makes carbs work) and the fuel being present, and atomized throughout the intake tract, where as injected motors are typically dry manifolds.

so basically, what he told you is the opposite of the truth lol......you can usually run a few more PSI of boost on the same motor with the same tune on a blow through carb than with Fuel injection

Old Geezer

iTrader: (3)

BCNUL8R

iTrader: (2)

Sorry. I didn't really know where to put this, but wanted some technical info to back my claim that a carb didn't require a higher octane fuel when compared to an injected motor given the same compression ratio.

I don't claim to be an advanced tech guru at all I'm only in my second season of racing ever in my life.

Thanks to the others that replied I'm always looking to learn from those with more experience and knowledge than I have.