Milling heads and intake on '83 318: How much to mill?

[83Imp]

I have an '83 Imperial that I am working on. It is undergoing an EFI-ectomy and will have a Performer intake, DemonSizzler-built Thermoquad, headers, mild cam, and electronic ignition. From what I can tell, the motor is original and has never been touched.

What I would like to do is to pull the heads to have a valve job done and mill the heads a little to raise the compression to around 9:1 or 9.5:1. I'm not sure of the stock compression ratio on the '83 318.

1. How much would I have to have the machine shop mill the heads to get between 9:1 and 9.5:1?

2. How much would I have to have my intake milled so that everything matches up after the heads are milled?

3. How does this affect pushrod length (if any)?

Thanks!

[cageman]

well, it is a hydro cam, so you have some leeway, but as for the intake, I guess you should see how far down the hole the pistons are and figure out what the heads are and shave them, then set the intake on and see how she looks, as for angles and such
I pulled an intake off of an 81 imperial and it too had a 318, but the intake ports match my 360 J heads, I hope it is a good intake for racing.
What part number are your heads, I am curious as to what they are.
Thanks

[michaelmopar]

Originally Posted by 83Imp

I have an '83 Imperial that I am working on. It is undergoing an EFI-ectomy and will have a Performer intake, DemonSizzler-built Thermoquad, headers, mild cam, and electronic ignition. From what I can tell, the motor is original and has never been touched.

What I would like to do is to pull the heads to have a valve job done and mill the heads a little to raise the compression to around 9:1 or 9.5:1. I'm not sure of the stock compression ratio on the '83 318.

1. How much would I have to have the machine shop mill the heads to get between 9:1 and 9.5:1?

2. How much would I have to have my intake milled so that everything matches up after the heads are milled?

3. How does this affect pushrod length (if any)?

Thanks!

*Stock compression on a 83 318 varies from 9:1 -9.1:1
*140 h.p. w/ EFI 9.1:1 compression w/ Head# 163,593,302,308,576 all were 64.5 cc. [1.78/1.55 in/ex cam 390/420- 140hp & 150hp]
*150 h.p. 9.1:1 w/ 1-4bbl thermoquad same head numbers and cc volume.
*165 h.p. 9:1 w/ 1-4bbl thermoquad w/ head# 051,593,308,576 all were 65.5 cc. 1.88/1.55 in/ex 390/420.[all hp and compression are based on a "in the hole" of .041 and a .030 compressed gasket and flat top pistons.]
*In order to raise compression to 9.5:1 you would need to follow this formula on above heads. the 051,596,308,576,593,163- as follows for every 1cc reduction in cc volume you will increase compression by approx. .14 points to get this mill .0048 of of the head side and then same time mill .0063 from the intake side[Milliing from the intake side of the head allows the intake manifold to line up properly](this is the head not intake manifold)
*For head #302 mill .00625 from the head side and .0063 from the intake side for the same .14 point raise in compression.
*As long as you dont go to much it will not affect the preload to much but i always recomend adjustable rocker arms to be safe.

[TK]

the 80's 318's i have cc'd were more like 7.9 to 8.3 to one in stock form (i evn found one with 7.6). a 318 makes good power in mild form with 8.5 compression, so, for starters, you need to cc the heads to figure out how much to take off.
i would not go over 8.5 to 1 for fuel reasons

[dwc43]

165 hp is pretty sad if that's all you got from that combo. A '69 318 2bbl was 210 hp at the crank.

[DartGT66]

Rated by whom?
Numbers teh factory published were mainly "blueprint" numbers, and the real world numbers can vary quite a lot. Combustion chambers are usually way bigger, deck heights may be bigger and so on. The way they rated nad measured horsepower changed in '72, if I remeber correctly, the output of a stock 318 fell from 230 to 150 without any significant changes in the engine. The old rating of 230 was pretty high. If you have ever driven a 273 commando that was rated at 235 hp and compare it to a 2 bbl 230 hp 318, it makes you wonder how much difference does 5 hp make. They are like from different planets performance wise. There are other numbers pretty similar, like the ratings of a 2 bbl 383, compare that to the rating of a 340 and wonder which engine would produce a quicker car.

[michaelmopar]

rated from actual blueprint build sheets from DC. I have a 88 318 and after checking compression i have found i have 9.5:1 or better and based on the blueprint sheet from dc it says that the 88 H/R puts out 175 at 9.8:1. If i run 87 octane it pings and i have to retard timing if i run 91 octance or better i can advance timing to 36 and no pinging. so i guess it depends on what block you get hold of. it sounds like there was not any quality control in the early years to go from high 7's to low 8's on compression. i tend to believe the blueprint sheet is a little closer to truth than to fiction. sometimes one may think he has an untouched block and it may have been into already. i know some years the pistons were burried in the block as much as .080 and others as much as .020. so it is either the info out there is completely wrong and i ended up with a rarity and in the fact i found a untouched motor with factory compression of 9.5:1 or better or the info is wrong and DC who spends millions on R&D dropped the ball on the facts.who knows?

[TK]

Originally Posted by michaelmopar

rated from actual blueprint build sheets from DC. I have a 88 318 and after checking compression i have found i have 9.5:1 or better and based on the blueprint sheet from dc it says that the 88 H/R puts out 175 at 9.8:1. If i run 87 octane it pings and i have to retard timing if i run 91 octance or better i can advance timing to 36 and no pinging. so i guess it depends on what block you get hold of. it sounds like there was not any quality control in the early years to go from high 7's to low 8's on compression. i tend to believe the blueprint sheet is a little closer to truth than to fiction. sometimes one may think he has an untouched block and it may have been into already. i know some years the pistons were burried in the block as much as .080 and others as much as .020. so it is either the info out there is completely wrong and i ended up with a rarity and in the fact i found a untouched motor with factory compression of 9.5:1 or better or the info is wrong and DC who spends millions on R&D dropped the ball on the facts.who knows?

all i would say is untill you cc the motor, you will never know.
the 88 hyd roller has 302 heads, according to chrysler, they are 58-66cc's. the 58cc's is a pipe dream, or a really rare find, because i have built lots of 318's with 302's and have never found one with under 62 (the cc's per chamber also vary by a couple cc's)
the piston in the 88 motors is usually about .040 to .060 with stock pistons. aftermarket flat tops, excpsecially forgies, raise it by .040 i have found.
also, the advertized compression ratio in a 88 roller 318 is iether 8to1, or 8.3to1 (two books say something different, i do know the best LA318 compression was advertised at 8.5to1)
so, the 9.5to1 compression is a find, cause i have never seen a 318 in stock form with more than 9to1 (and that was a A) untill the magnum (barf)
something else, the origonal cam specs on your roller is 240/240 391/391 (every hyd cam in the 80's WAS the same, 318 or 360)

the quality controll got worse as the years went by, not better. a 67-71 318 is almost always under .030 piston depth. and, to add, the old 210hp 318, with the lil valves 675 heads, ittybitty carb, has more power and torque than your 2bbl roller. (i have tuned and driven them both) put a 4bbl on them both and the old one will still outpower it.

so, as i said in the beginning, the only way to really tell how much to takew off the 318 heads is to cc them, but, if it were me, i would deck th eblock to 0 and not touch the heads

[michaelmopar]

so your saying a old 318 say 67 - 71 stock will outpower a roller cam 88 stock w/ only a 4bbl upgrade on both.
i'll buy that. guess DC has put out alot of pipe dreams down on paper. i bought it it sounded good. when my motor was detonating on 87 octane. timing retarded helped put in 91+ octane and it ran better advance it it even ran better. tells me that it is higher compression.

[TK]

Originally Posted by michaelmopar

so your saying a old 318 say 67 - 71 stock will outpower a roller cam 88 stock w/ only a 4bbl upgrade on both.
i'll buy that. guess DC has put out alot of pipe dreams down on paper. i bought it it sounded good. when my motor was detonating on 87 octane. timing retarded helped put in 91+ octane and it ran better advance it it even ran better. tells me that it is higher compression.

you are reading more into this than is there.

[Dart 65]

Originally Posted by dwc43

165 hp is pretty sad if that's all you got from that combo. A '69 318 2bbl was 210 hp at the crank.

Is that the corrected rating? The old rating system had them at 230 horses.

[TK]

the poly was 230, the LA was 210 (truck motors at least)

[dwc43]

You got it Tk.

[michaelmopar]

All in all there were years that dodge was very liberal in their numbers and the later models started getting real conservative. So the older 318's were not restricted as the later models were smog pumps and the like. I still say take a 88 318 roller cam and put it up against a early 70's both with the same copression, flow, and cam specs, flat tappet older, roller newer, and both with same intake and carb and the roller cam motor will out work the flat tappet motor less friction, more accurate and better ramp rates, roller cam motors are all around better performance. BUT i say it does cost more to build and for the cost it does not always make it pratical so bang for buck flat tappet is the way to go.