Lowering compression?

[fwi]

Just want to get some of your thoughts on the best way to lower compression ratio from 13.5:1 to something more street friendly where I can run pump gas instead of 114.
It's a 447 block, Indy 1 heads, Comp cam .690 lift

 

[72Satellite440]

You could add thicker head gaskets

 

[TommyShameless1978]

You could add thicker head gaskets

They'd have to be crazy thick, though, I would think. Anyone else want to chime in on that?

Tommy

 

[greenmonsta79]

Take material out of the combustion chamber area on the heads? that's about the only way I know other than thicker head gaskets.

 

[dbowperson]

To drop that much it will probably take a combination of thicker gaskets, head work, and/or lower compression pistons. You might even have to go as far as new heads?

 

[fwi]

I am thinking probably different pistons or heads. First I have to find out exactly what is in there now.

 

[racedodge]

you could either go with an open chamber (88cc edelbrock/440source/procomp) head or if you are pulling the engine apart, just machining the domes off the pistons you do have.

 

[Meep-Meep]

The best you can do is go with a flat top piston and a closed chamber head to get your desired CR. I'm guessing you are after 9.5 - 10.0:1? Adding chamber volume with domed pistons will reduce the CR but your flame travel will not be nearly as good as with flat tops. A 10:1 domed piston engine will most likely have detonation issues, thereby requiring higher octane gas, where the identical CR engine running flat tops will skate by on lower octane.

If you do nothing else but put aluminum heads that will be similar to lowering the CR by about 1/2 point because the aluminum sucks more heat out of the chamber. Closed chamber Eddy's are 86 CC I believe, which is nearly the same volume as an open chamber iron head. I'm running 10.1:1 CR with iron heads and it's just over the limit of our crappy CA pump 91 gas. The same CR with aluminum heads I can probably get away with it.

 

[Propwash]

Eddy's come in a 88 or 84CC chamber..

I agree with tossing in some flat top's