friends 318 build

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stroked 340

stroked 340

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Ok,a friend is getting ready to make some improvements on his '76 318 he already has the comp.477/.480 cam installed and will be using a Mopar m1 dual plane intake gasket matched to the 587 heads running 1.88/1.60 valves..my question is how much should he have the heads milled to raise the compression??...

Also what do you think he'll run..this 318 is in a '70 dart 904 w/full manual valvebody 8 3/4 with 3.91's he'll also be running a 600/650 carb and headers with 2 1/2 pipes..
 
Stroked 340, there is a formula for this, I got it from my bible, The Auto Math Handbook.

It's based on 'displacement ratio' which is cyl. volume divided by chamber volume and is always one point less than comp. ratio. So for example, if you have 9.5:1 comp ratio, your 'displacement ratio' will be 8.5:1

Clearly you'll need to have a new target disp. ratio and would also need the original comp. ratio to figure it out.


new disp. ratio - old disp. ratio
________________________ x stroke

new disp. ratio x old disp. ratio


I did a quick calc. using theoretical ratios of 10.25 and 8.5 for the old. I came up with . 066" to mill. Seems like a lot, but that's a 2.25 point jump.

I'll guess he's going to run 13.2.

Hope that helps.
 
A '76 318, going with the larger chambers? I'd lose the M1 and get Either a stock iron intake, or something like the RPM (non air gap)... Verify first what you have for piston to valve clearance. Then mill as much as you can, taking off whatever you need from the deck, and then the intake itself and the intake side of the head cut to get the intake to fit. I think you will have a hard time getting a true 9.5:1static unless you really cut it, and less than that will feel sluggish with that intake combo.
 
Is he changing the pistons? If not, thats a mistake. Have him throw some KB167's in there. He's using alot of lift from what it looks like. The pistons will help with compression. Id shave no more then .002 of the heads, and use a thin head gasket. Then the airgap will be fine with a 650 carb.
 
KB 167 pistons at zero deck and .020 milled off the heads with thin head gaskets should get it to a good CR and still be streetable. If anymore than .020 is milled off the heads, the intake side of the heads will need milled too for the intake to fit properly.
 
Shortblock is staying as is stock,just putting the 360 heads on it,so .020 off the deck side should do it??...
 
I'd go .060. but it is build dependent and head cc dependent.
 
.020 will add about .3 points. The problem is, you have a shortblock that with the smaller chamber (still open design) only got to about 8.2:1. Drop that to about 7.8:1 by adding larger 360 chamber heads, mill .020 and you're all the way up to 8:1, with a fairly large cam (for a 318) and the large plenum (way too big for the 318). I would estimate it not making even the 99mph figure. I'll go with 14.80s at 94 or so.
 
Throw a 360 scat crank in it. 349 cubes and the pistons come right up. Compression problem Solved! Course, it's not that simple. Probably have to trim the counter weights to clear the piston skirts. BJR has a much longer post in the teck archives on how to do just this.
 
I think You should mill the heads .035 and I think you will be fine. run high 13's.
 
sell the 360 heads and put on a set of magnums then get a magnum intake..

better flow, and a smaller chamber =more CR

you can get rebuilt ones at a decent price or a JY..

CMengines.com sells rebuilt heads..

other then the pushrods and lifters with the oiling hole in them, I think you will be way better off then milling the 360 heads...
 
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