Im a little uneducated in this area, but heres the deal Im trying to get up to 10:1 to run a new cam,carb,intake combo Im at 9:1 right now. I did some searches and there was some info in there about maybe changing gaskets would do a little for you. I guess what Im asking is are there any other ways to raise it besides getting the heads decked?

 

change the heads and pistons and zero deck the block. swapping gaskets is a poor way to increase compression. look at what sort of quench area you have, or want and get your parts to make that happen. try looking at the big picture or the combination of parts involved instead of trying to work around doing it the cheapest or easiest way.

 

yea unfortunately he's right. You won't gain much from the head gasket. You're talking about head work or head swap if you want any appreciable gain.

 

If your actual cr is 9:1 now, and you now have typical replacement composite head gaskets ( felpro) .039" thick and you were to change to a thin steel shim style head gasket (4.10" bore .015" thick) your new cr would be 9.58:1
Not a bad boost for the $$$ of these gaskets .

Are you guesstimating your cr or have you measured all the variables required to calc accurately? if your piston top sits below the deck at TDC you'll improve your quench clearance as well. about .040" total is best.

 

What heads do you have? Changing heads is the best way to boost compression on an existing and running shortblock. I went from about 9:1 or so to a hair under 11:1 just by changing from 882s to 601s.

 

well its the 350ho crate engine and its supposed to be 9:1, but like i said im totally uneducated in this area like i dont know what quench is can someone help me out on that and explain it? I was going to have to take the heads off so that they can be machined to be able to run 1.6 rockers but I was just wondering about getting the heads decked,milled (uncertain of the correct terminology for this) while at the same time, but heres what the heads are:
Vortec Cast iron- 64cc Chambers,170cc intake runner, 1.94" Intake valve, 1.50" Exhaust Valve
and heres the combo im trying to run
xe274,750dp,rpm air gap,1.6 rockers, new valve springs
I was told this was a good combo as long as youre running 10:1,
it was either this combo or a similar combo except running the xe274 running the lt4 hotcam, and on that one I dont know what recommended compression should be? Im just kinda stumped here about the whole compression subject, any help would be greatly appreciated.

 

Well, quench refers to the flat area of the compression chamber. Assuming your pistons are .000" in the hole, then the thickness of your head gasket is the distance from your head to your piston at TDC. Now, you don't want that measurement getting too close or you can potentially have piston to head contact.

If you are getting the heads machined anyway, it shouldn't be too bad to have them milled as well (might help you to get it done anyway - it would take care of any warping that might have occurred)

This is the "right" way to increase compression BUT if your piston to head clearance known (you can measure this while the head is off) say it's ".020 in all cylinders, then you might be able to get away with a thinner gasket. I think for proper quench the ideal piston to head is .040" to .050. (having a nice tight quench increases turbulance and gives you a better mixture/combustion)

 

thanks for clearing quench up for me it all makes sense to me now, I think I will just have the heads milled while theyre at the shop, but after doing this to the heads are there any other things or problems that may arise that I must take into consideration? just trying to get all the info I can, newbie bear with me.

 

I'm no expert on milling heads, but you shouldn't have any trouble. Usually you're talking about just tens of thousandths so stuff like lining up exhaust primaries and accessories will not be an issue. Intake manifolds are usually slotted around the bolt holes to accomodate differences in heads. etc. etc.

I'm not feeling that technically savvy at the moment to figure out how much volume you lose per thousandth of an inch. Well... maybe I am. figure the compression chamber area is roughly 2/3 of the cylinder area. let's assume ".010 inches milled. On a 4" bore you're talking about ".06 cubic inches for half the area which is about to 1.4 CC. Feel free to let me know if I'm way off

I've read that you can mill vortec heads .040", and some other heads as much as ".100. So figure you should be able to drop 4-6 cc's with no issues - which equates to half a point of compression.

speaking of which.... those heads must have a pretty good dish in them to only have 9:1 with 64cc heads - I figure about 14cc dish?