compression ratio increase

[firefighter3931]

I have a question about optimizing compression. My moder (assemled by previous owner) is a 446 rb w/2266 trw forged flat tops and open chamber 452 heads that are uncut. The book says 8.66:1 compression w/88cc open chmber. My cam is a crower hyd. 228/236@.050 (.480I/.502E) and the book says min 9.5 comp required for this grind. The moder pulls good up top but is missing that bottom end punch. The motor is fresh (5k) and compression is consistent across the board. How much can i mill the heads w/o getting into intake manifold fitment problems and lifter preload issues? How much of a gain does the steel shim head gasket give in terms of compression? What combination of head mill+steel(.020) head gasket will get me close without any major hassles. The rest of the combo: perf.rpm,750dp,1.75headmans/2.5exh.,orange box igniton,727/2600stall,8.75 suregrip(3.55) and 275-15 drag radials in a big pig 68 charger. Untimed as of yet but hoping for high 12's. Thanks,Ron

[wedge440]

I would go another route..(cam change)
I milled my heads .010 and had no problems with intake or lifter preload but if "I" was going to do more then .010 "I" would have the intake side milled aswell..Also, new pushrods would be needed if you didn`t have adjustable rockers...
"If" your compression is 8.66 to 1 you need to rase it nearly 1 full point to get you to the 9.5 you want.....Your "messured" compression maybe lower then you think..The only way to be sure is to check.
Thats why I say go the route of cam change...
You could also try to advance the cam you have a few degs. but "I" wouldn`t do it..
Good luck
Joe
Indianapolis,In.

[ehostler]

With how low those pistons sit (approx .09 below the deck), your only real choice is a smaller cam. If you don't want to change out the cam, you can get away with a set of Rhoads lifters.

[Doug Wilson]

Yep.

Please vote in the pole on the thread "Taking a stand". Voting on this should be important MOPAR lovers

[dave571]

Closed chamber heads would help, as they typically have a volume of 78 cc's(vs the 88 or 90 of your 452's)

If you have your heart set on keeping your 452's, the formula for intake machining is .123" off the intake for every .100" off of the heads.

You could try using the .020" stamped head gasket as well. Composites are usuially .040" thick.

[DartGT66]

Assuming the 8.66:1 is a true figure, you need to remove 12cc out of the chambers. It means milling about .045" out of the heads. Taht should not cause much problems; you may not even have to mill the intake sides of the heads. Just enlongate the bolt holes of the intake if needed and macth the ports. Typically .045" more preload shouldn't cause any problems in a mopar. It rarely is optimal from the factory, so you should propably set it anyway. Easiest and least expensive way is to use shaft shims, next is adjustable pushrods, if you feel there is a need to correct the lifter preload. But the real important thing is to measure everything first, so that you know where you are now. Measure tyhe head cc's, the depth of the pistons below the deck, verify the head gasket thickness and check the intake fit/port match. Although th .0123" for each .01" from the deck for the intake milling might be true in theory, they seldom are perfect from the factory. So you might get along with good amount of milling without doing anything to the intake side.

[firefighter3931]

Thanks for responding and another question. Would it be worthwhile to upgrade to a better intake manifold and if so, which one? Performer rpm, torker,holley street dominator ? This car is heavy with a mild stall (2600) and 3.55 sure grip and needs all the torque help it can get. Thanks, Ron

[DartGT66]

On my opinion, the Performer RPM should be just right for that kind of a combo.

[Doug Wilson]

Adjustable push rods are heavier and less rigid than non-adjustable pushrods. Everything else makes sense to me, especially measuring everything before you start.

[DartGT66]

That's true, they are heavier and personally I would use the even lower buck method of shimming the shafts. I have used the adjustable pushrods and they do work, so that shouldn't be a problem. I have also used shaft shims and even shortened the stock pushrods to correct preload! And these methods have worked too. But of course the "proper" way would be going with adjustable rocker arms and pushrods. However, that's more expensive and the little we have tested with the different rocker set ups did not offer us any performance increase over the other solutions.

[dirty dan]

Originally posted by DartGT66
Assuming the 8.66:1 is a true figure, you need to remove 12cc out of the chambers. It means milling about .045" out of the heads. Taht should not cause much problems;

Dart 66 is on the right track .
However I think .045 is to far to streach without milling the intake side of the heads.
Useing the .0123 off the intake side for every .010 off the surface
works Very well.
I have gone far beond the .045 useing that formular.
But here is the thing, If you mill off the .045 without milling the intake side how happy will you be when you can`t get the intake to seal?
And you end up haveing to remove the heads to have it done any way.
Sure you could instead cut the intake manifoild to match.
But then your intake will only fit those heads.

Short cuts can and will get you lost.
Just fuel for thought.

[DartGT66]

If the intake has sealed well before the ".123 rule" works well, that is true. And to make the milling "right, you should do just that, mill the decks and the intake surfaces AND the end rails of the block. Especially if milled a lot. However, me being cheap, I also have "other ways" to do things that I have tried and they have worked for me. (or to be honest, the correct way to do things is to get the right pistons for the job.)

[dave571]

Be cautious about how much you take off.

I took .085 off the block deck, then had to take .090 off of the intake.(I opted to take it off the intake, because that's alot to take of the other side of the head. I was concerned about the vc gskt surface getting too thin) I took .090 off(which is less than the formula suggested) because of the composite head gaskets.

The reason I say be cautious, is because I got into a situation where the valley pan gasket wouldn't work. It simply wouldn't give enough to fit. (there's a thread on this topic, if you want to look for it. I forget what I called it)

What I ended up doing, was using 2 gaskets. I cut the opposing edges off, and overlapped the center sections, with a bead of silicon between them. I even had to slot the end hold down bolt holes of the gasket to allow for the movement. .090 is nearly a tenth of an inch, and is a noticable amount to be dealing with.

[DartGT66]

Me being cheap again, I have always milled (with a file!)the end rails of the block from their ends as needed leaving the "middle" to the stock height. This way the end rails become a little longer and the valley pan fit better with heads milled a lot Another thing is that at least with some heads the vavle cover rails may become very thin and "cut" through the vavle cover gasket easy.

[dirty dan]

If you turn the intake upside down and take a die grinder and grind off a small amount of material from the bottom of each corner This will eliminate the need to worrie about the end rails.
However If you only cut 45 or 50 off you won`t have any trouble with the end rails anyway.