what heads sould i use

[lazerboat]

well here is what im faced with I am building a 318  with stock short block , and just bought a set of ported and polished J heads , but i  have a set of 308 fast burn heads. what would be better more compression or better flow    I plan on putting   a mild cam headers  four bar. carb  , and droping her in my 66 a100 panel van  2700 pounds  with a 727 and 355 suregrip any insite would be great  and whats a good cam for my combo  thanks

[moper]

Have the 308s milled on the deck and intake surfaces .030, set the deck height so the pistons come out .010 from the block, and run them. Large valves and larger ports will be worse on that engine.

[Chryco Psycho]

properly ported the 308 is by far the better head with more compression & better flow , you can also use the smaller 318 / 302 casting heads

[lazerboat]

so if i use  the 308 and have a pos .10 on deck hight  mil the heads .30 will there be any valve clearence isues what compession should i expect  I have a 71 block  and what cam should i use , so what would the ported j heads be good on like a 11/1  + engine       thanks for all your help

[dodge freak 2]

Are you sure you have positive deck height / mine is in the hole a bit.

Sell the J's on ebay and use the 308 heads. I have the MP castings without the air holes on the exhaust ports and 2.02 intake valves on my 318. Had them milled .030 and I swear with my 3.91 gears the motor seemed to make more power everywhere- even at low rpms.

Have a custom grind 224 @ .050 cam with 111 lbc and it idles at 700 rpms and revs clean to 6500 daily, lol

[moper]

You need new pistons to get them tall enough to come up.. and the way they do that is milling the block's deck surfaces. In any event, no, no piston to valve issues when a performance piston is chosen. Compression will be around 9:1.

[the_engineers]

Moper, you're not saying the pistons should stick out of the block by .010, are you?  I think this is how it's being interpreted.  Should be "pistons are .010 below the block"...

...set the deck height so the pistons come out .010 from the block...

[Chryco Psycho]

Stock 10:1 340 piston were .010 above the deck from the factory

[mojavered]

Is this also called, proud or proud of the deck? It seems kind of "racey" to me and something you would only want with higher compression.  Then again, I guess that it does not really matter what the compression is. 
Can someone please explaing the pros and cons of having the piston sit above the deck?  Also, what applications would you want to use this or not use this in?  Thanks.

[Chryco Psycho]

there is no real advantage to have the piston above the deck other then to create the desired compression & quench
 the factory piston was above the deck for the 10 :1 ratio used from 68-71 , in 72 they dropped the compression

[mojavered]

Would that be true on the 340 only, or BB as well?  I just mean the piston height?  I know that they started dropping compression in the early 70's

[Chryco Psycho]

the 340 was the only factory engine with the piston above the deck to get the compression they were after