Upping the comp. Which pistons???

[drobertson]

I'm rebuilding the 318 in a 1973 Charger. The stock comp. ratio is 8.6:1, and I want to raise that. The motor will be stock except the summit racing street-strip camshaft, 4 bbl intake, 600 cfm edelbrock carb, and dual exhaust. The pistons I'm looking at are these- http://www.summitracing.com/parts/uem-kb399ktm-030 . The motor will be bored 30 over, and these should work. I was just wondering whether the compression with these pistons would be too high to run on 91 octane fuel. The cam is http://www.summitracing.com/parts/sum-1789 . Stock 318 heads will be used, but I have some 1976 360 heads I can swap onto if needed. Thanks!

 

[idrivemopar]

That is almost the same specifications on cam and pistons I have in my 340, and my compression is about 9.5 to 1, runs great on pump gas, high octane of course, and gets up and boogies down the road.

 

[drobertson]

That is almost the same specifications on cam and pistons I have in my 340, and my compression is about 9.5 to 1, runs great on pump gas, high octane of course, and gets up and boogies down the road.

Sweet. I'm just worried about the pistons hitting the valves while it's running.

 

[idrivemopar]

That I could not tell you, depends on decking and head clearance, and piston height, I am sure someone here will chime in, but, I had a local guy do my build because I didn't have enough room to work on it. Also, make sure you get the heads done with hardened valve seats for unleaded gas, and you will also have to use a zinc oil additive or zinc oil for flat tappets.

 

[drobertson]

Yeah the heads I've got have already gotten hardened valve seats. Since these dome pistons have two valve reliefs, I think I'll be ok. Anybody else got tips?

 

[Seventy]

There is another similar post on here somewhere where I went into more detail, BUT...

If I were building an HP 318, I would find a set of 302 casting 318 heads (any mid 80s to early 90's 318 powered var, diplomat, new yorker, etc), you can buy them CHEAP, like $30 a set, lol..

Install 2.02 1.60 valves in them and do some porting, they take porting well, match them to a 360 felpro intake gasket. I have the part numbers if you need them for the valves..

Then I would use these pistons http://www.summitracing.com/parts/slp-h814cp60/overview/make/dodge
with them and the above heads (maybe cut 50) you will have great compression for pump gas...

choose some nice head gaskets and for a cam I would go with a 430/450 (dont remember the exact lifts) purple cam (not a fan of single pattern cams, technology has come a long way)...

If you are looking for a good running stout +30 318 you wont find better for the money...

Pretty simple, work a set of 302 heads, purple cam, flat tops with good deck height and go to town, easy 300+ hp small block with the right intake and porting. Do yourself a big favor and get rid of them old heads, the chamber in the 32's is about all you could ask for, do some research they work well. Just swapping them out for the old heads would get you night and day...