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ibleedmoparts

ibleedmoparts

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If i take a 68' 318 w/9.2:1 compression ratio put a #302 head on it, how much milling would be required to hit 10:1? maybe a dumb question but you guys know more than me about that stuff, you guys are the best and true life savers.

Floyd
 
The Milling of a head ik kind of a Myth.If you mill a head lets say .010 or even .060 how much smaller is your combustion chamber going to be?You need to swap out the pistons or find closed chamber heads.
Jim
 
Very incoooooooorect!!!!!! Depending on the amount of compresion rise your looking for, pistons are the big gainers in this.
 
What is incorrect?Pistons will be the big gain.I think you will raise the compression about .5 with closed chambered heads.So maybe from 9.2 up to 9.7 Every machine shop-engine builder I have talked to say milling a head will do very little to nothing for you.
Jim
 
Are the 302 heads closed chambered? I hear good things about them...I mean i'm only looking for about .5-.8 on top of that 9.2...thats why i asked about milling, any ideas rumblefish?
 
Milling an open chamber head will raise compression more then milling the same amount off of a close chamber head. But either way a piston swap can have a much greater effect like stated above.
 
Small block closed chamber heads
Casting # 341 1962-67 318
# 080 1964-65 273
# 178 1966 273 early
# 234 1966 273 late
# 920 1966-67 273-318

I have no number 302 it must be a newer head. Jim
 
See, heres the trick, re-read the OE post and notice that the engine is a '68 and the 302's hae the smallest chamber over that years heads.

Even if there no cc difference in the heads, he's looking for a .07 gain in compresion.

I agree, he may not get there, depending on the deck surfaces thickness, but what he needs is a look into the cc's of each head and exactly how much each head chamber can be milled and at what rate the gain is.

For the 318, reduce the chamber volume, remove .0053 from the head surface per 1cc of head chambered volume.

for each .10 removed rom the head, 0095 must be removed from the intake face of the head.

mill .0371, for a 7cc reduction

mill .0424 for a 8 cc reduction

A 7 cc reduction is a .7 gain in compresion to 9.98.
A 8 cc reduction is a .8 gain in compresion to 10.11

This math was done on a desk top dyno comp calc with a 318 engine. The rest was quickly done and is not 1005 ACCURATE, BUT JUST NUMBERS THROWN IN TO GET A 9.19 ratio to start with for a ref. point.

I then reduced clyinder head cc's to 67 cc's to get the 9.98 and then to 66 cc's to get 10.11.

If 7 cc's need to be removed from the head, the 7 X .0053 is .0371 needed to be removed for the 9.98 or .0053 X 8 is the .0424 for 10.11 - 1 ratio
Can a cyinder head take a .0424 milling?

OH, allmost forgot to mention....this math should be redone with the proper values/measurements of the parts involed.
 
Whew, that took a bit to do and was watching TV. Sorry, bu the sci. Fi. freak in me took over....he he he he

Jim, the machinest is correct in away. Any big gain will be through pistons.

Between the head milling and decking the block, you can really get the ratio up. But the block milling is not cost effective for the common Joe like us. Just the head is.
 
Not sure about the #'s myself but I think milling the 302's and running a thinner head gasket would get you in the ballpark.
 
IF the engine has not been messed with, his head gasket being stock that is, he all ready has the thin gasket on top and would need to find another one to replace it with or mill an extra amount that is the difference of the gasket thickness.
That can be an easy .020 extra head milling. Eeeeek!!!!
 
I've cut .100 and more and raised the compression over 2 points on a engine, as a rule of thumb every .040 will raise the compression 1 point. JMO
 
For what it's worth the 302 closed chamber heads I just had cc'ed came out at 59cc. I think there is a pretty large variance in the head volumes. Make sure to check yours and compare it to what you have on there now. Between that and checking the depth of your pistons in the hole you can decide how close you will be to your goal. You may be able to get close to what you want with just the heads and the thin gasket but maybe not all the way there.
 
Sweet guys, thats pretty interesting...For a 318 i know guys put bigger valves in there...Do you guys suggest i go that direction? Because i can score the 302 heads, i have a set of ummm--77' 360 heads, stock 68 heads and stock 72 heads...i want to use the 68' engine core because strength and compression ratio (9.2 compared to my 72' at 8.8) Love the opinions just keep them coming...i may use BJR for head work if i hear good stuff

Thanks
Floyd
 
Check out my site and make your own judgement, and I'll do what ever you want done. But I would suggest a read of the small block section as this will help keep you from making mistakes. But it's your call and I'll do what ever you want, if you send them to me.
 
Floyd, working the heads up is like working the engine up. Also, theres a saying from the past that applies to many things. In one form or another, sayings like, "Theres no replacement for displacement" and "Theres no kill like overkill" can be a draw back, a missfire or backfire in your face. In general, the sayings work, for the arena there ment to be applied in. Until you reach that arena, the one thing that beats it all is; "A well thought out plan."

And it works mainly because I don't have cubic dollors to throw at the problem or task at hand.

Give BJR all the details you can so he can "Adjust" the heads as needed.
 
The 302 is a closed chamber head that, I believe, came out in 1985. It used the small valves and has small runners. This would mean that something like the Eddy Perf RPM or Air Gap might not be an optimal choice as they are made for the big valve heads with their larger ports.

Not knowing what you want to do with the engine, other than have a 10:1 compression ratio makes it difficult to make further recommendations. Milling the head, different pistons, and different head gaskets all affect compression.

My personal combination in the Demon is a 318, 625 AFB, Performer, 302 heads, and a 272 deg .441 lift cam. It's fine for street cruising with a mildly lumpy idle. Thats my 2¢ worth.
 
I am after a good street cruiser, with a little power behind it when i need it but also running AC, i have an 833 4 speed and 3:23 rear. I'm not sold on the 318, but i have a 68', 72', 88' 318- 76 400 and a 77 360. I am just fishing the waters to see what combos are out there without going overkill and maintaining a dependable daily driver mopar. But i was curious about those 302 heads because i've heard a lot about them...and i am trying my best to learn about *** milled with *** piston and etc etc...= *** compression...I always just went stock everything because my father believes stock is the way to go, but now i have a few $$ to build my dream machine so i want to make the best decision, most informed, and best bang for my buck that will last me a while. So all of the forums opinions I value very much and appreciate. I do believe whatever i do BJR is my choice to work the heads.
 
In an earlier post you said that you have a set of 360 heads. Do you have the rest of the engine? The 360 would have a lot more potential for making power.
 
72 Demon said:
The 302 is a closed chamber head that, I believe, came out in 1985. It used the small valves and has small runners. This would mean that something like the Eddy Perf RPM or Air Gap might not be an optimal choice as they are made for the big valve heads with their larger ports.

Not knowing what you want to do with the engine, other than have a 10:1 compression ratio makes it difficult to make further recommendations. Milling the head, different pistons, and different head gaskets all affect compression.

My personal combination in the Demon is a 318, 625 AFB, Performer, 302 heads, and a 272 deg .441 lift cam. It's fine for street cruising with a mildly lumpy idle. Thats my 2¢ worth.
Click to expand...

Sounds pretty decent... have you run it at the track??? 302s stock or modified? I had a similar setup in my dart thing sounded mean -
http://videos.streetfire.net/video/1971-Dodge-Dart-Swinger_75800.htm
Never got to run it at the track though. I would guess it would run low 14s but that is only a guess sadly. I am all about making 318 power, I just wish I had more money to put into my car... maybe one day... but anyway I have a book that says the 302 has bigger chambers than the 68-74 heads... at 62.6 CC's, that is weird because I thought it was pretty small being closed chamber.
If you stay around 318 cubic inches then I would aim for 58-60 CC chambers, if you still need more compression with those CCs then you need to change you piston/block setup IMHO.
 
I like the 360 for it's extra torque making abilty's. It will do well in anything you put it in, in any arena. Great street engine. It'll drop right in as well.
 
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