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Old 01-23-2013, 03:49 PM
oldbogie oldbogie is offline
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Quote:
Originally Posted by 73nova350 View Post
looking into new set of heads not sure what is best, i have a sbc 350 comp cams 280h cam package 280 advertised duration 480 lift long tube headers edelbrok rpm air gap man edelbrok 600 carb 390 posi rear right now i have the stock iron heads on there except added 194 valves. any suggestion on what heads would be best. looking to go with aluminum
This engine sounds rather missmatched with a long duration low lift cam a small CFM carburetor, Edlebrock Performer RPM intake.

Stock 350 iron heads that you had 1.94 intakes put into, what is this? Unless the heads were off a heavy duty/industrial engine they came with 1.94 intakes. What is the head casting number?

In selecting the chamber volume for new heads you need to understand the pistons you have. Most pistons have a circular dish, these are not very good for performance nor efficiency regardless of the head used. Other choices that can be there are D dish, flat top, or dome but these don't typically show up in OEM motors so unless this has had some custom bottom end work it's not likely to have these kinds of pistons. So far as pistons go in the 350 flat tops or D dishes work the best and are generally seen with a small chambered head say 58 to 64 ccs. Chambers are best when shaped and generally proportioned around the characteristics of the L31 Vortec. there are aftermarket large chamber heads that use much of the L31 technology but these are really for blower motors or big inch small blocks, not that they couldn't be used in a 350 with domed pistons. Another critical item is the thickness of the head gasket and the clearance distance between the piston crown to the block's deck. These two things control the squish/quench clearance where in combination you want to hit about .040 inch. With a small chambered aluminum head with an unmilled deck, where you can get into trouble is with a thick gasket often specified with an aluminum head, in tis case with a .025 inch deck clearance and a .053 gasket you can end up with a .078 clearance which greatly reduces the effecctivness of squish quench. So you've got to keep an eye on these dimensions and look out for a thin head gasket that is also compatible with the aluminum head. The issue here is that the aluminum head expands and contracts more than either the iron block or steel gasket, so it rubs on the gasket which wears grooves into the softer aluminum. The best and longest lived gasket needs to be made to accomodate this, multi-layerd steel, graphite faces, and composition build ups are used and have different thicknesses, a simple steel shim would become a problem in street or mixed street strip service with the aluminum and iron sandwich. You can get away with a steel sim in this type build up for race only where the heads are just considered an expense item to get into the winners circle, which means it works, but not forever. A zero decked block is probably easier to work from for the street ot street/strip as it allows a thicker mulitlayer or composition gasket to be used which is easier on the head's mounting face so the sealing and the head lasts a long time.

As you can see there are a bunch of things to keep track of all the while realizing there's more than one way to skin this cat.

Bogie
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