Compression Issue (thin head gaskets??)

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805moparkid

805moparkid

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hey guys were building this 318 for the bosses wifes truck...

and will with the head cc's and piston in the hole were looking at a measly 8.5:1 comp... this is with a 4.04/.040 head gasket...

this 318 is only .040 over so 3.95 bore...

any body know of a .020 thick head gasket with a close size to that bore? nearest i found were cometic in 4.04/.040 thick giving me a 7.8:1... would like closer to 9:1

heads are 70cc
slug is .070 down
4cc for valve reliefs
3.950 bore

may just have to mill the heads...
 
Look for 302 heads, they have a smaller chamber. You could try 66-67 273 heads too, I believe they're 57ccs from the factory. You won't have to look for shorter pushrods then. Mopar had a gasket set that compressed tp .028, but I think they're hard to come by. The other thing to try is a shim type of gasket. They're steel and Cometic might be able to help you. Try asking for a 273 head gasket for the smaller bore.
 
805moparkid said:
yea i found those but ita a 4.140 bore lol... its just a 318 with 3.95 bore... what i would gain in thickness i would lose in diameter...

looks like were gonna mill these things... how much can you safely go on these?
Click to expand...

Yeah, I can read. Those are the thinnest you can get with the smallest diameter without going to some high dollar gaskets. .150" difference. .075" on each side. You really beeotchin about that? lol Mill the heads if you don't want to use the thin gaskets.
 
the mopar ones P4120094 and the MR Gasket 1121 are the same head gasket...
 
I have the same Mopar head gaskets on my engine. When I first got them I thought there was only one head gasket in the package. Then I saw where there was two. They are thin....lol

Go with those gaskets and 302 heads.
 
It don't cost much. I always have my blocks zerodecked some of the smallbocks pistons are way down in the hole
 
70aarcuda said:
the mopar ones P4120094 and the MR Gasket 1121 are the same head gasket...
Click to expand...

They used to be. Mopar changed companies in the later runs. We have several of both sets at the shop and they are quite different in both material, color and details.
 
mr.318 said:
It don't cost much. I always have my blocks zerodecked some of the smallbocks pistons are way down in the hole
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Yeah, some are like .175" in the hole. You have your blocks decked that much? That's nuts.
 
StrokerScamp said:
They used to be. Mopar changed companies in the later runs. We have several of both sets at the shop and they are quite different in both material, color and details.
Click to expand...


the ones i have are the same...
 

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yea were gonna mill the heads... the shop was supposed to give us an idea on comp but never did... so i cc'd everything and it was bad lol...

so looks like .080 off the heads... can you do that on these?? also i know they need to have the intake milled
 
805moparkid said:
yea were gonna mill the heads... the shop was supposed to give us an idea on comp but never did... so i cc'd everything and it was bad lol...

so looks like .080 off the heads... can you do that on these?? also i know they need to have the intake milled
Click to expand...

How large were the chambers?

.0053 per 1cc with a 318 open chamber head

ive milled .045 and a friend milled .060 no issue.
 
What compression are you aiming for? If this is a street driven truck, you don't want to go much over 9.1. What good will it be when they wanna tow or haul with it? They'll have to run race gas if the engine is under constant load.
 
KB-167 pistons should get the compression up. Easier than milling heads/decking block.
With a 302 head you should get decent quench with a .040 head gasket.
 
x2 agree

cometic will make you .020 MLS gaskets they are about $150

so the piston kit with KB-167s will give you way more bang for the buck.
put in the pistons, zerodeck the block and have at it. your stock .040 head gaskets will give you good quench distance. you could have the heads milled slightly also. just to get them flat/straight and you shouldnt have problems with valve clearance on the pistons or pushrod lenght etc like you would if you have the heads cut a bunch.

http://www.popularhotrodding.com/enginemasters/articles/mopar/0667em_mopar_318_engine/viewall.html

also those pistons come in a full kit that has good rings. i'm not sure but if they are like the BB versions, the top ring needs a very specific end gap also

http://www.summitracing.com/parts/UEM-KB167KTM-040/
 
p.s. a nice all around cam is one of hughes whiplash cams since it's for the bosses wife :D

[ame="http://www.youtube.com/watch?v=xrqvMTafr_c"]'69 Cuda 340 TTI Headers and 3" pipe w/ Dynomax Race Magnums (Ultraflos). - YouTube[/ame]
 
1wild&crazyguy said:
.080 is like 16 cc's.lol
Click to expand...

need to go from 70cc to about 60cc with the 4.04/.020 thick gasket... sorry more like .060 off...

red67gts said:
deck block .045 and cut heads .040
Click to expand...

short block is together

StrokerScamp said:
What compression are you aiming for? If this is a street driven truck, you don't want to go much over 9.1. What good will it be when they wanna tow or haul with it? They'll have to run race gas if the engine is under constant load.
Click to expand...

9:1 is goal

moparlover said:
x2 agree

cometic will make you .020 MLS gaskets they are about $150

so the piston kit with KB-167s will give you way more bang for the buck.
put in the pistons, zerodeck the block and have at it. your stock .040 head gaskets will give you good quench distance. you could have the heads milled slightly also. just to get them flat/straight and you shouldnt have problems with valve clearance on the pistons or pushrod lenght etc like you would if you have the heads cut a bunch.

http://www.popularhotrodding.com/enginemasters/articles/mopar/0667em_mopar_318_engine/viewall.html

also those pistons come in a full kit that has good rings. i'm not sure but if they are like the BB versions, the top ring needs a very specific end gap also

http://www.summitracing.com/parts/UEM-KB167KTM-040/
Click to expand...

short block is together, and 150 dollar head gaskets on a stock engine is stupid...

again take note this is not my build... just trying to get info...
 
If you go through all this trouble to gain 1/2 point of compression, you may gain 6 HP in the 318. Is 6 HP worth it?
 
IQ52 said:
If you go through all this trouble to gain 1/2 point of compression, you may gain 6 HP in the 318. Is 6 HP worth it?
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the 8.5 would have been with the small bore head gasket... i ran all the other heag gaskets thru the calc. and got a 7.8:1 best...

so were looking for at least high 8's....

as far as hp we could careless... its the tq... its for a 46 dodge
 
If 9.1 is the goal then there are three ways. Use KB167s or use magnum heads with the stock pistons, or find some 302 heads and use them with the stock pistons. I didn't include milling because that just ain't right. lol
 
Mill the heads, i would.

mill .053 off of them, then mill .030 off the intake face of the heads, test fit intake and more them likely ...mill another .020 off the intake itself.

Ive milled all kinds of heads to get where i need to be, milled my j's down to 60cc...no issues doing that. some people dont see it from any view but theyre own, no sweat bro.
 
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