Thread: how many cc's do i need

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i have a 1956 pontiac with a really healthy 350 with a crane cam
dual plane airgap intake with a edelbrock 650 full length ceramic headers followed with a couple cheerbombs.
this car gets played with alot and goes several times to the track..i currently have dished truck pistons and a set of 305 heads...i know i was low on cash so i threw a fresh set of 305 heads i had laying around... it actually works good considering i know 305 heads are chockers and it pulls like hell at 4-5 grand but idles off and hesatates at times.i was told by a fellow racer that i dont have enough compression and should be running at least 10:1 to make it work at the cams potential cause it has a late exhaust timming to bleed off some compression and that those 305 heads are really holding it back...a performance machine shop in the area has a set of bare dart S.R heads that have been angled milled and have i think they are 49 cc combustion chambers but he said they would breath good as well as giving me 10:compression and he want $600 bare for the pair....would that be right
http://www.cranecams.com/index.php?s...51&lvl=2&prt=5

a 49 (cc's) will rasie your compression for you but it mite rasie it a little to high what is the compression on your engine now and how many cc's do you have now

i'm running the stock 350 dished piston with 305 heads i think they are 64cc i think

That's a pretty long cam - 2800 - 6000 RPM and .480 lift. It should have a pretty nasty idle. It needs at least 10:1 compression.

The reason the car is nosing over at 5000 RPM is the heads are choking it to death. Carb, manifold, cam and heads need to work as a system, and you've got gridlock in the heads.

Summit sells those Dart Iron Eagle heads for $589 bare, so your guy is right in the ballpark. I'd guess they go for about a grand fully loaded. They've got 2.02/1.60 intake and exhaust valves and good intake/exhaust runners, so they should breathe fine.

With the dished pistons, I don't know if the 49cc heads will get you the compression you want. The builder should know. Tell him what you've got and ask him. If 49cc kicks it up too high, think about 60cc Edelbrock heads (60719 or 60999). They're aluminum (more tolerant of high compression) and about the same price ($999 at Summit).

305 heads have a 58cc chamber. This is why they are not recommended to be used on 350s or 400s other than the fact that the small valves and ports just can't support the bigger cubes. With flat tops you would be over 11.5:1. Piston dish is usually 21cc so esimating your deck height and head gasket thickness as average for a never redecked 350 and you are at 10:1 right now. The heads are killing you. You are running out of flow long before you run out of engine.

Those 49cc heads will put you at 11.2:1. Try buying gas for that with an iron head. Those Edelbrock 60cc heads should net you 10:1 with the dished pistons and give you the flow you need. The Iron Eagle heads are also a great choice. The 64cc heads will land you around 9.6 but could be lowered to 9.5 with a thicker head gasket. This is as high as you will be able to run on pump gas and still run a decent distributor curve for power. (9.25 would be better. A rule of thumb for using aluminum heads is you need one more point of compression to make the same power as an iron head of the same cc. This is due to the much greater heat transfer out of the chamber into the cooling system of the aluminum head. I think you would end up with a stronger engine overall with the Iron Eagle 64cc heads and a milder cam that comes on around 1800-2000rpm .

If you insist on keeping the big cam buy the 60cc Edelbrocks and go for the 3000rpm stall converter or 3.73 and up (numerically) rear gears to get that heavy Poncho launched. Also put a 750 on that Air Gap so the new heads can breath.

Tom

yea my motor origonally came outta a truck and i had it totally rebuilt.. but it does still have the dished truck pistons that look like ashtrays....it hasnt been decked....i found out that these head are actually 52cc combustion chamber sportsman sr heads is that tosmall of chamber

Without going back and refiguring you would still be in the range of 10.5 which is still too much for 93 octane pump gas in an iron head. If the chambers were mirror polished you might get away with it but bottom line is that these are not the heads for your street engine.

Tom