I'm considering having a 383 built. Target compression is going to be about 10.8:1 to run on 91 octane with aluminum heads (AFR 195 most likely). The question is, is it better to have the engine built use 74cc heads to hit the 10.8:1 or to have the engine built to use 64cc heads to hit 10.8:1, and why?

TIA,

 

An engine with flat-top or dished pistons is more efficient than an engine of the same compression with domes.

Think about flame travel.... if you had a flammable golf ball and a flammable sheet of the same material of equal volume, and you lit each one with a spark right in the middle, which one would burn more quickly and completely?

A 383 with zero deck, standard thickness head gaskets (.039"), flat-top pistons with 6cc valve reliefs, and 64cc heads, will get almost exactly 11:1 CR. That's what I'd suggest you do.

 

you're the man! thanks!

 

AFR 195 heads come in either 68cc or 74cc... so I think you need to consider that also, I mean you could have them milled down, but I wouldn't really want to mill down a new set of heads myself.

My engine (385 Stroker) is built with Flat Tops with 6cc Valve Reliefs... with a 64 cc head they are supposed to be 11.0:1, with a zero decked block (now I don't know what size gasket that is with, I'm assuming .039") so with the 68cc chambers in my AFR 195cc Street Heads, and the reccomended gasket from AFR (.041" thick 4.125 bore) I believe I am in the 10.5:1 - 10.6:1 range, which seems completely do-able with 91 Octane Gas and some tuning, considering these are aluminum heads.

Make sure of the chamber size in the heads, I believe you will find out that they are 68cc's and not 64cc's. Either way I suggest Flat Tops and the 68cc heads, looks like it would be a great selection, probably put you right around 10.6:1. I would stay away from dome'd pistons.

 

Thanks for the info. You're right, 68cc or 74cc.

However, you can order them milled before the ports are cut (for a small fee) so you don't have to mill the intake. I was going to go with 74cc milled to whatever cc I want. My understanding with the AFR heads were that the 74cc had a better chamber (was it because of valve shrouding?) than the 68cc.

 

For a small motor like a 383, you need the chamber size to be small. Getting the compression where it needs to be in the optimal manner will far outweigh any valve shrouding effects.

Now if you had a large motor, that needed every last CFM of flow it could get, then it might be worthwhile to go with the larger chambers.

Or, you can use the small chamber, have it milled from the factory for slightly smaller than optimum chamber size, and lay back the perimeter of the chamber walls to a head gasket for your small bore size; any valve unshrouding of the chamber farther than the bore, wouldn't matter anyway.