i have a 305 i built about a year ago thats in my 82 camaro with flat top pistons, a mild cam and a 500 cfm carter carb and my uncle has a set of 76 cc 202 heads, i was looking at a set we have in the garage, and the valves seem to be about 3.75 inches from the far side of the intake valve to the far side of the exhaust valve, while the bore of the 305 is 3.75 inches, do you think that the valve will hit the cylinder wall, also i am also going to swap cams in it, i have a 2.73 gear in the rear, a 3 speed auto th350 with a 2500 stall, what cam would you recomend (oh yeah i am also going with a Eldebrock performer manifold, 1000-5500 rpm range) what cam would you recommend for about 1000-5500 rpm or around that, thanks for your help

 

Combustion chambers too big and valves too big.Use either a set of 305 w/ 1.84 ints. 1.50 exh.[do a pocket port],a set of 305 torquers [world heads] or a set of GM alum. with 1.99/1.50 58cc chambers off a 350 sbc.

 

You could probably use them if you dont go with more than a .450" lift @ .050 , but the cc's are pretty big for a 305, your compression will take a nosedive

 

Considering that the bore of a 305 is 3.736", and that the valves aren't exactly centered over the bore, i.e. they're at some point where the edges of the bore are closer together than the diameter, I'd say you're likely to run into problems with the valves hitting the bores.

With 76cc heads, I believe your CR would be in the very low 8s at best, maybe even down in the 7s. It's only about 9.3 with 58cc heads, and about 8.5 with a 12cc dish (70cc chamber volume total).

All around not a good idea.

 

the valves wont hit the bores , they (the valves) dont go that far in, thats why you zero deck a block , to make sure the piston is even with the top of the deck, and you can also have a positive piston height (where the piston sticks out of the block) on pop up pistons. an 11.1-1 pop up like the original LT1 motors has a slightly positive piston height and only gives about a 9.5/9.8-1 comp ratio on a 76cc head. you can use them but they would probably hurt more than help due to the cc size. find a set of cast iron tpi heads from like a 90 tpi 350, they have 64 cc chambers with 1.94 valves but have better runners than the 305's.

 

Zero-decking a block has nothing whatsoever to do with the issue at hand, which is that the valves won't even be over the bore, but rather over the deck. If the bore is too small to accept the valves, then it really doesn't make any difference what kind of pistons you use, the valves are going to hit the block. Bummer. Valve train parts really don't like that very much.

 

Well if its 3.75 from one side to the other of the valves, and since the bore is 3.74 (rounded) its not gonna work, just like RB said. The compression loss will also be as pathetic as he said, if you use a normal Fel-Pro gasket and those heads, the ratio will be a dismal 7.6:1
I dont think that even the smogger cars of the 70's were that low, although close.

Zero deck the block. Yea that works to help the valves... to hit something solid faster.

 

yeah i heard the same thing later that night from a friend, i have a 350 4 bolt main in the garage i guess i will put some money in it and put it in my car, it has domed pistons, it came in a jet boat, im not sure of the dome on them but its about .125" i think. me and my dad have rebuilt it many times and decided to move up to a 400 in the boat, so now we have the 350 with 2 chipped pistons, so ill just replace the pistons, put the heads on it, 76 cc chamber, a eldebrpck performer manifold, and top it off with my 500 carter carb, what do you recommend as a cam size for that. i was thinking a 488 exh lift, 488 int lift, 234*exhaust duration, 224*intake duration cam from summit, for about 1500-5500 rpm, which the 4bolt main with stage two rods can more than handle. and also is there any chance of this passing e-check? do you think i can run pump gas? thanks