ok ive contenplating on with gaskets on wanna run on my 305 tbi. i wanna increase the compression. im about to put on World s/r heads (67cc,171cc)but just couldnt decide any opinion would help!

heres a few im looking at:
http://store.summitracing.com/partde...=1#Application

http://store.summitracing.com/partde...3&autoview=sku

http://store.summitracing.com/partde...3&autoview=sku

 

changing your headgasket makes such a small difference in compression ratio - a dyno would be hard pressed to notice a difference. What's your current compression ratio? Aluminum or Iron heads? Your best bet to increase compression ratio is to shave your heads, how much depends on a lot of things, like current valve clearance and dome/dished/flat-top pistons (piston to head clearance). Unless you currently have a .070" gasket or something silly, your butt-dyno wont even feel a difference in a 030" gasket difference.

going from .041 x 4.166 to a .015 x 4.1 gasket would do something like 8.316:1 to 8.858:1 - which is really next to nothing and would cost you a lot of money, because you have to do a lot of maching work to put in a shim gasket to the block and the heads. You're better off to shave your heads at that point. You should be aiming for closer to 9.5:1 to 10:1 compression ratio with iron heads (you'll have to fill up with premium gasoline). If you have aluminum heads you can aim for closer to 11:1 compression (again you'll have to run premium gasoline).

This assumes everything else is ready for the increased compression - ie. good strong block and you're getting a new head bolt set right?

cheers

 

Well that's strange... I switched from some thick **** victor headgasket to a .015 shim gasket and noticed an improvement. Engine has a bit more pop and I started running high 11's. Oh yeah, didn't have any extra machining done. Just popped the heads off, cleaned up everything and put the shim gaskets in. Been in there over a year now without problems.

 

the heads are iron i do have new head bolts to go on the pistons are stock flat top rite now the block is in good shap the current compression is around 9.3 or so

 

I hate to grave dig but it beats starting a new thread for a simple question. You say you didn't need any machine work to throw shim gaskets on. Would I be able to use them without machining if its a stock block never been touched and brand new aluminum heads?

 

Would be fine. Just make sure the deck is square.