I am building a 400sbc and am using a set of stock pistons and rods I can get for $50. My problem is that I read that with these pistons and 64cc heads I'll only get 9.1-1 compression. I was looking for 10.0. Would smaller heads be practicle? What other way could I raise comp.? What are chevy 202 heads. Is that a very generic term or is it a specific casting. Volume? Thanks for the help.

 

Depending on your cam timing 9.5 to 1 might be the max you can go with cast iron heads on pump gas. I would not push it much. You can raise it by using the thinest head gasket (about .039") or getting the block decked to Zero deck height.


202 heads are various castings with 2.02 inch valves. They usually have bolt holes and two small bumps on the end that look like Ms. They are castings 186, and 291 I think.

 

Yeah, that's about right. Assuming a .030" overbore, .025" stock deck height on the pistons, and a .039" head gasket. You go from about 8.4:1 to only about 9.2:1.

LIke JCB says you can deck the block for zero deck height on the pistons which will bring you up to about 9.6:1, plenty good for moderate performance use.


[This message has been edited by Damon (edited November 19, 2001).]

 

IMHO about the stupidest thing you could possibly do would be to permanently and irrevocably destroy an irreplacable block by decking it that much, just to save a set of used stock pistons. That's just about the worst possible decision you could make, based on about the most warped logic there is.

Get a set of real pistons and throw that stock crap in the trash where it belongs. In my 400 I have a set of TRW forged ones with 12.5cc dish (much smaller than the stock dish) and a set of 186 casting double-hump heads, which give about 10.4:1 CR. I'd recommend something along those lines.

The various "double-hump" castings have chamber volume of about 64cc.

Stock rods can be OK; get the rod bolts replaced however. Use ARP or other high-quality ones.

You can take any randome set of SBC heads and stick 2.02" intaks valves in them. That is not a measure of desirability in heads at all, it's a "buzzword" that suckers in uninformed novices. A set of good castings, whether stock or aftermarket, is the basis for a good running engine; if the castings flow, then you get benefit from larger valves. If the castings have small ports or are some one of the ones that are thin in critical places (prone to cracking, which renders them scrap iron) then it isn't really important what valves somebody graunched into them.

If you're going to seriously build a 400 and expect to get out of it what it's capable of, start with the heads; then once you get the best possible of those, pick a set of NEW pistons to go with them that give the desired CR without compromising on your head gasket choice or anything else. DO NOT try to cheap out with a bunch of used trash in the bottom end, then stick 305 heads or something on it in some misguided attempt to raise the CR; you'll join the ranks of the people who lose to Mustangs in spite of having motors that have the potential to kill them all.

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"So many Mustangs, so little time..."
ICON Motorsports

 

Well, hindsight.. rb is somewhat right. Don't try to save money just to use the pistons. The cost for the block work will cost more than another set of pistons can be obtained for.

But, the point being, a fractional increase in compression is not worth it in most cases and certainly not for pump gas.

 

EVERY DAMNED 400 BLOCK I HAVE EVER WORKED ON OUT OF A JUNKYARD OR BOUGHT USED FROM SOMEBODY HAS HAD WARPED DECKS. EVERY DAMNED ONE!

You're gonna have to deck it regardless, if you would like your head gaskets to seal up, that is. What's the difference if you take off .010 or .020 or .025? I would not call that "ruining a good 400 block" by any stretch of the imagination.



[This message has been edited by Damon (edited November 19, 2001).]

 

Fixing an imperfect block during machine work (presumably including boring, which is most often required anyway) is one thing; sodomizing one for the express purpose of salvaging used stock pistons while at the same time not doing normal maintenance to the block such as boring (which obviously would make you need new pistons anyway) is the height of stupidity and self-inflicted injury. My objection isn't to decking a block as such, it's to the reason given for doing it. Decking a block .005" or .010" to clean up warpage is alot different from zero-decking one to increase the CR so you can use stock pistons. That is what I call ruining a block. The difference is that once you zero-deck a block, if the block warps again or your next piston is a bit taller than the last, it's trash; but if you select pistons correctly and do the minimal amount of decking as a maintenance procedure, your block still has life left in it.

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"So many Mustangs, so little time..."
ICON Motorsports

 

But it costs the same no matter how much you take off. Once a block has been seasoned from tens of thousands of miles of street use it's not gonna warp any further unless you REALLY abuse it (overheating it). The 400 is a peculiar bird becuase it likes to warp up real good, but once it takes a set, it's pretty inert from there out.

Besides, how many rebuilds do you get out of a block? The origninal one, the one that you pop it 30-over, then the one at 40-over and then the 60-over one where you strike water or the cylinder cracks 3 months after you put it in the car. You only get really 2 good rebuilds out of most 70's vintage stock lightweight castings. What are you saving it for?

I won't argue with you on this point further. I don't see the big deal. You do. Honest difference of opinion. Leave it at that.

p.s.- I don't appreciate being called stupid any more than than the next guy.