Posted By: derekeh
Raising compression on a 318 - 12/28/08 05:41 AM
I recently bought a 318 that had just been rebuilt. Has been bored .040 over. The pistons are flattops that are about .1 down in the hole at top dead center. The head gaskets are .05 thick. The heads are 1976 318 heads with the numbers 4027163 on them. Id like to get the compression up in the 9's if I can without altering the short block. I do have a set of 302 heads if they would help.
Posted By: 70AARcuda
Re: Raising compression on a 318 - 12/28/08 06:02 AM
here is your best deal on head gaskets..the old mopar performance thin .024 are no longer available...
http://store.summitracing.com/partdetail.asp?part=MRG%2D1121&autoview=sku
Posted By: calrobb2000
Re: Raising compression on a 318 - 12/28/08 06:09 AM
hi
yes definatly go to the 302 heads and shave at least .020 off , more than .020 and you will also have to cut the intake face also .
use the thinest head gasket you an find.
usig taller pistons would also be good .
Posted By: dulcich
Re: Raising compression on a 318 - 12/28/08 06:51 AM
With the 302 heads and .024 gaskets you will be about 8.8:1.
I wouldn't spend the coin on rebuilding another set of heads, and would just run it as-is. Even with this set-up the pistons are always going to be a mile down in the hole.
Put headers, small cam, and two-plane intake on it and don't worry about the compression if you can't swap the pistons for now. Finding the heads and getting them rebuilt and swapped is way, way, more work and time and money than swapping pistons, and the 302's aren't any good for flow without a lot of port work and bigger valves anyway.
The best thing to do is re-piston and then add some good heads as time and money allows.
-dulcich
Posted By: derekeh
Re: Raising compression on a 318 - 12/28/08 01:36 PM
I have quite a few 360 heads lying around also. What would be a good piston to use and would it require rebalancing?
Posted By: FuryUs
Re: Raising compression on a 318 - 12/28/08 01:44 PM
360 heads are going to kill the compression. Don't go that way if you want compression unless you're making changes tot he short block to get the pistons up in the bore.
Posted By: derekeh
Re: Raising compression on a 318 - 12/28/08 02:15 PM
Thats why I asked what would be a good piston to use
Posted By: MoparJoe
Re: Raising compression on a 318 - 12/28/08 03:25 PM
KB399's will work good with 360 heads in a 318, you can't swap to magnums/edelbrocks/302's later if you use them since they are domes. A KB 167 will work too, it's a flat top and has around 9.2 comp with 360 heads.
I'm have a 318 going together with a set of 399's, planning on making a mild street motor with 308 heads and a hyd roller.
Posted By: RapidRobert
Re: Raising compression on a 318 - 12/28/08 04:04 PM
If you do end up altering the short block & ch pistons make your selection(piston/gasket/heads) which will give you proper quench if not as said thinner gaskets/302 heads(or magnums) is about all you can do & you might adv the cam. I'm in the same position my 360 build is .110" in the hole so I might continue to look for a 3.79 crank or a 4" er if the pistons will stand enough milling but thats not looking too promising or maybe a custom cometic head(& intake) gasket(s)
Posted By: forphorty
Re: Raising compression on a 318 - 12/28/08 09:20 PM
if the engine was recently rebuilt, why not run it as is? sure, it will be less than ideal, but changing pistons and heads will be almost like starting over. i think i would put the engine in and enjoy it while saving to build the engine you really want. keep in mind, if starting from scratch, a 360 can be built as cheaply as a 318.
Posted By: JBurch
Re: Raising compression on a 318 - 12/29/08 06:01 PM
Just a thought, another way to raise compression would be to angle mill a set of heads. Careful pre-planning is the word of the day, though the results would be worth while. Don't go crazy on cam lift and no knotching of pistons required.
Other wise re-piston with some KB 167's and the thinest head gaskets you can find.
Good luck!
Jim Burch
Posted By: derekeh
Re: Raising compression on a 318 - 12/29/08 08:59 PM
Ill probably just leave the engine alone then. Someone just gave me the 302 heads and I was looking for a cheap way to get the compression up. My idea was a home porting job on the heads and getting bigger valves put in. But if its not worth doing Ill just leave the engine as is. It has a bigger than stock cam but Ive been unable to find out what kind it is
Posted By: Wedgeman
Re: Raising compression on a 318 - 12/30/08 12:13 AM
Yep ! Go with KB's 167 piston......throw magnum heads on them and you'll have plenty of fun in the streets !
Dan
Posted By: derekeh
Re: Raising compression on a 318 - 01/01/09 03:24 PM
I have a set of magnum heads but they are for another engine lol. I have some 360 heads that ill just put some JB Weld in the combustion chamber to help up the compression. Always has worked before
