Compression Ratio Primer
Thread Starter
Race Director
Joined: Mar 1999
Posts: 10,258
Likes: 1
From: Calif.
Compression Ratio Primer
OK this might be old ground, but...
I have run 10:1 compression on pump gas with iron heads in an older engine of mine. This engine was built with a "zero" deck, meaning the pistons were just barely in the hole at TDC. With that engine's .039" head gasket, all the cylinders had a quench well within Lingenfelter's specs of .040"-.045"
The question is this. Aluminum heads can sometimes allow you to run between .5 and 1 full point more compression. In theory, I can build my new aluminum-headed 406 with a .040"-.045" quench and probably get away with an 11:1 compression ratio, yes?
The car is street driven only to and from the track these days--when it has an engine--and because of this I wouldn't havve a problem supplementing the 92 octane pump gas it usually gets with a few gallons of 100 octane unleaded.
Nothing's cast in stone yet--just tossing it out for discussion.
I have run 10:1 compression on pump gas with iron heads in an older engine of mine. This engine was built with a "zero" deck, meaning the pistons were just barely in the hole at TDC. With that engine's .039" head gasket, all the cylinders had a quench well within Lingenfelter's specs of .040"-.045"
The question is this. Aluminum heads can sometimes allow you to run between .5 and 1 full point more compression. In theory, I can build my new aluminum-headed 406 with a .040"-.045" quench and probably get away with an 11:1 compression ratio, yes?
The car is street driven only to and from the track these days--when it has an engine--and because of this I wouldn't havve a problem supplementing the 92 octane pump gas it usually gets with a few gallons of 100 octane unleaded.
Nothing's cast in stone yet--just tossing it out for discussion.
Pro
Joined: Jun 2001
Posts: 683
Likes: 0
From: Calgary
Re: Compression Ratio Primer (Jack Sweet)
I am building a similar combo as well. From everything that I have read so far 11:1 is streetable with pump gas as well as a few conditions are met. Zero deck , 160 degree thermostat with good pump and rad (edelbrock victor and maybe big block rad), a good supply of cool air to your carb (underhood air will not do!), and an air gap style manifold (or at least block off the exhaust heat riser). There are probably a couple more things that you can do but it is getting late and I can't think of them.
Thread Starter
Race Director
Joined: Mar 1999
Posts: 10,258
Likes: 1
From: Calif.
Re: Compression Ratio Primer (Jack Sweet)
Thanks. I thought it was/is theoretically possible but I just wanted to hear it from another source. That opens up the piston choices even wider. Now if I can just get the World's Slowest Machinist to get busy with my engine.
