How did GM manage to raise the LT1s compression ratio up to 10.25 and not have a detonation problem even with using lower octane gas? Did they sacrifice timing curves? I'm wonder about this because I'd like to rebuild my 1980 K10 350 engine which has somewhat a low compression up to about 9.5 to 1 and still be able to use low octane fuel. Thanks for any input

Mike

 

by decreasing the size of the combustion chamber. deck the block and mill the heads. sick

 

The LT1 uses reverse cooling. This sends cooled water to the heads first and then to the block. This keeps the heads cooler than normal and allws higher compression without detonation. Also the heads have fast burn combustion chambers, which also control detonation better. The engine will perform best on premium fuel, but is capable of running on lower octane gas because of the knock sensor, which retard spark timing when detonation occurs. However, this makes the engine sluggish, especially if regular fuel is used.

If you build your engine using Vortec heads, which are similiar to LT1 heads, but without the reverse cooling feature, 9.5:1 compression should be no problem with midgrade fuel, but you may have to retard the timing if you run regular. If your car already uses a knock sensor, then you should be able to run on regular.

But keep in mind that with the current price of fuel, it makes little difference on what grade you use. In my area regular is $3.30 a gallon, and premium goes for $3.50 a gallon. A 15 gal. fill of regular costs $49.50, while a 15 gal. of premium costs $52.50. When comparing prices, $3.00 compared to $49.50 is not that much of a deal. Also consider the fact that when burning premium, the fuel mileage will be better because of more advanced spark, making the difference in cost even less.

 

Thanks Pete, as always you manage to clear the air for me. So fast burn heads are the same as vortec heads? And do you recommend these over edelbrocks?

 

From what I was told, and it may be a lot of BS, Edelbrock and GM cooperated on developing the fast burn heads. The Edelbrock are more expensive but they are aluminum instead of cast iron, and I belive they are available with the old small block bolt pattern, so you won't need to change the intake amnifold. Another feature is that aluminum heads can support more compression because aluminum is a better conductor of heat than cast iron, and the combustion chamber stays cooler.