Does anyone know right off what my compression would be if i put my 305 (58cc) heads on a 350 with flat top pistons? Thanks

 

With flat tops? around 11:1 if you deck the block. Mine was too high, so I used a die grinder and ported out the combustion chamber a bit until 64cc = 10.0:1 on the nose.

 

Although a smaller combustion chamber will increase the compression ratio, using heads designed for a smaller engine can hurt power. Power is made in the heads. The engine needs to breath. The more air you can get into the engine, the more fuel you can burn. The more fuel you can burn, the more power you can make. Using a head that flows enough air for a 305 engine normally means it isn't going to flow enough air to feed a 350 or larger engine.

Although some people have good luck and are quite happy using 305 heads on a 350, they're not your best option for building power with heads. No matter what else you do to an engine to make power, cam, intake etc, it still boils down to the heads as the power makers.

 

http://www.wheelspin.net/calc/calc2.html

You can do it yourself using this online cr calc.
Typical felpro gasket is 4.166" dia and .039" thick
Typical replacement flat tops are 5cc relief volume and either nomonally .025" or .045" below the stock deck at TDC.

Not all "58cc" 305 heads are actually 58cc.
You need to cc yours and see. You'd be suprised.

 

305 heads range from about 60cc down to 52cc

 

I'd agree with the flow data idea. More flow = more power. I just read an article on here last night about head castings, and if I read it correctly (it was late) some of the 305 heads came with 1.84" int. valves as compared to stock 1.94" on the 350. Both shared the 1.5" exh. The size of the valves has much to do with head flow- basically. That's why many people upgrade the the 2.02" int and 1.60" exh.

Go here for any calculations you should need. These are very simple programs and small files. http://www.turbofast.com.au/javacalc.html
they're intended for boosted figures but your questions are of static compression ratios, as opposed to the increased dynamic CR of adding boost.
If your intent is to raise compression, that raises cyl pressures. Which causes more stress on parts. Are the heads the only thing being upgraded?

 

Actually they are not an upgrade. I would just be taking them off my 1992 Z28 305. I am rebuilding a roller block 350 and was just curious to see the responses. Plus, the AFR's i want are like $1800. Thanks 4 the replies.