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ramcharger_440
02-05-2003, 09:56 PM
I am looking to increase my compression ratio on my 440. Is this possible by milling the head? I am running 452 heads on a mild engine but the current compression ratio is 8.2:1. Looking for maybe 9:1 or 9.2:1. The bottom end is very healthy.

Also, is this advisable? What are the pitfalls, valve clearance, etc?

Thanks for your help.

dartgt340
02-05-2003, 10:13 PM
rule of thumb-.010=.1 compression. too much milling weakens deck . always check valve clearance regardless

CL440
02-05-2003, 10:51 PM
What head gasket are you running? Steel shim or composite?
Dont forget you will also need to mill the intake side of the head to compensate for lowering the head on the block. I think it is .012" off the intake side for every .010 off the face.

6 packin
02-05-2003, 10:53 PM
A half point could be had without problems. Remeber you must take the required amount off the intake to. Also deck these heads with non adjustable valve train will be trouble to. Your push rods will now be longer by the same amount. Your lifter will take up in the preload. Not to good. Run the steel shim head gasket for extra squeeze too. Give it a good coat of copper sealer before you button it up. Be all honestly raising it a point is not consevable by milling the heads. They will be paper thin. I suggest about .040 mill no more than .060 at the very most.

sundrop_440
02-05-2003, 11:49 PM
say 6packin if you had 516 heads and milled .060 could you get a full point on this engine it's alot like mine

DartGT66
02-06-2003, 03:55 AM
there is no rule of thumb about the effect of milling the heads on the compression ratio there are way too much variables; the starting ratio, the engine size and the combustion chamber style etc. Milling .040" out of an open chamber reduces the chamber size about ten cc's, and a closed chamber milled the same amount ~7cc. But let's take an example here, a 8:1 440 and 12.5:1 383 with the same open chamber heads.
Milling the heads .040" in the 383 wiil raise the CR from 12.5:1 to almost 14.5:1
The same amount milled of the 440's heads will raise the CR from 8.0:1 to about 8.6:1

cuda66273
02-06-2003, 08:41 AM
You can whack quite abit off but if you go too far the gasket sealing area gets too thin and bends the casting surface when you tork them down which can cause head gasket failure.

I've got .080 off my SB heads and we feel we're right on the edge of failure....life on the edge is always exciting:D

DartGT66
02-06-2003, 08:50 AM
I had .090" in mine =p
It was not a race engine though, but a no buck hopped mild performance engine. That 318 had a whopping 7.49:1 CR stock with composite gaskets, milling thtat much brought it to an enormous 8.66:1! It worked OK.

cuda66273
02-06-2003, 09:37 AM
The piston must have been the typical Mopar 50-80 in the hole...I zero decked mine and with the 51cc C.Chamber it makes about 11.8 if I can find a head gasket to fit the bore.:gripe:

DartGT66
02-06-2003, 09:48 AM
If I remember correctly it was .050" in the hole, and after the chamber reliefing mods they were 71cc. Even before they were 68-69.

6 packin
02-06-2003, 02:46 PM
Originally posted by sundrop_440
say 6packin if you had 516 heads and milled .060 could you get a full point on this engine it's alot like mine

Yes the 516 heads which replaces the open chamber heads results about .75 or 3/4 of a point in CMP ratio. Remeber milling a closed chamber head will NOT result as much volume reduction as the open chamber head. Mill the 516 about .030 and run the steel head gasket with a god copper coat should result in a point higher, or right at it. I know its easy to gain compression by milling.....but read what Cuda66273 says he's right. Also the issue of the push rods lengthing the same amount will result also. With the non adjustable rockers means that your lifter will eatupo the diff in preload. Which is kinda bad. A shim kit for your rockers that will help get back your loss.

DartGT66
02-07-2003, 03:53 AM
I have not measured any 516 chambers, but Dwayne Porter did and he got 84cc! So, it's not a lot fo difference comapred to the open chamber heads, and if you think about the fact that they flow worse than the newer heads, it may not be a very worthy mod.

charger_dan
02-07-2003, 05:07 PM
I picked up a set of 516s at a swap meet with the goal of raising my
compression (not uncommon w/Mopar big blocks utilizing shelf pistons).

I got them home, and started comparing their ports to a set of 906s.
There is a visible difference - especially the exhaust port.

After some research into the matter, I sold them. Too much port work
would be involved to improve airflow, and I'd rather invest in new pistons.

I read somewhere that you're better off, when building compression
into a motor, to not go crazy whacking at the cylinder head deck, but
instead to use pistons with the proper compression height. In other
words, an engine with 9.5:1 compression with a piston way down in
the bore (like mine - .110") won't be as efficient at making power as
the same engine with a more standard chamber and a piston sitting
higher in the bore (closer to zero deck).

Plus, I like the idea of maintaining stock geometry and specifications
(push rods, intake fit, etc.)

As for me, I'm saving for better pistons.

jelsr
02-07-2003, 07:15 PM
Couple of points I didn't see mentioned in the earlier posts. The 516's have 185 cc in ports and the later style, including the 915's are 235 cc. The other point is the oil hole for the overheads. This hole is approaching the deck at an angle and milling large amounts from the block deck or cyl head can cause a severe misalignment resulting in a loss of lube for the top end.

383-man
02-07-2003, 10:33 PM
I milled my 452 heads .060. My stock 383 pistons are .040 down and with the .020 steel head gaskets and the 452's milled .060 I came out right around 9.6. Ron

b-1ken
02-07-2003, 11:27 PM
I'm probably going to get hammered for this, but when I built my friend's stocker ('69 Six Pack) many years ago, I shortened the stock pushrods to fit correctly, with a bench grinder. I ground the lifter (definitely NOT the rocker) end of the pushrod to a reasonably accurate spherical shape. They actually worked great. You obviously have to be careful in doing this, but it wasn't too difficult. I don't remember if adjustable pushrods were legal at the time (adustable rockers definitely weren't). It didn't make any difference if they were or not as I felt confident that I could do this. You have to roll the pushrods in your fingers and be careful not to grind a flat spot anywhere.
Ken B.:)

6 packin
02-08-2003, 01:00 AM
Hey b-1ken
Thats pretty slick! I thought about doing that once..no joke! That improvising at its best!

cuda66273
02-08-2003, 11:19 AM
Pass....

DartGT66
02-10-2003, 06:39 AM
B1-ken, that's what I have done too. The stock pushrods are solid and pretty hard stuff throughout. Instead of shims I have done just like you did and it has worked great. Have even made proper length pushrods to a SB out of old 440 pushrods :)

The exhasut ports of the 516 heads are pretty restricted especially in the middle of the valvestem and the center of the cylinder. I tried to port them to the newer style & size and hit the water. I don't remember the port CC's of the stock heads, but there is no significant difference between the 516 and the newer heads intakeports. The later heads are nowhere near 235cc's; even aluminum Stage VI's are only about 200 unported.

440barracuda
02-10-2003, 10:29 PM
Ive got 906's and plan to raise my compression ratio, the engine is in the car, and hasnt been run yet, but after building the motor , we realized, we put mopar performance 9:1 pistons, not the 10:1. What can i do to get that that extra oooomph out of the motor, becuase the overall comp. ratio will be low? I have 906 heads btw

DartGT66
02-11-2003, 04:08 AM
I have heard that the MP 9:1 cast pistons are actually the late model pistons that sit about .180" in the hole at TDC. Don't know about the current situation, but that's what they used to be. so even the 9:1 rating is total BS. You should have measured the CR in the first place. If you really do have those low compression pistons, about hte only sensible thing to do is to change them in to ones with a bigger compression height.

b-1ken
02-11-2003, 12:43 PM
Originally posted by DartGT66
B1-ken, that's what I have done too. The stock pushrods are solid and pretty hard stuff throughout. Instead of shims I have done just like you did and it has worked great. Have even made proper length pushrods to a SB out of old 440 pushrods :)

The exhasut ports of the 516 heads are pretty restricted especially in the middle of the valvestem and the center of the cylinder. I tried to port them to the newer style & size and hit the water. I don't remember the port CC's of the stock heads, but there is no significant difference between the 516 and the newer heads intakeports. The later heads are nowhere near 235cc's; even aluminum Stage VI's are only about 200 unported.

I hate to tell you how many of those heads went in the dumpster while I was cleaning out my garage. At one time I had over 60 BB Chrys. heads in there. I will say this about them though. The intake is identical to the 346 or 452 castings that I prefer to use. The exhaust is not too cool, but if you install the 1.74" valve and don't try to get crazy in the port, they actually work O.K. You cannot port them heavily where the wall protrudes into the port (on the intake side of the port) without seeing daylight) so don't try. I'm sure you're (Dart66) painfully aware of this, but I thought I'd mention it to others. Anyway, I wouldn't hesitate to use them on a street/strip car.
Ken B.
P.S. 906 heads that I have ported (lots of cast iron on bench) had MAYBE 198 cc's. I think the 235 number is for max wedge heads.

jelsr
02-11-2003, 05:00 PM
Have to agree on the 235cc being too large, thats a 50cc difference. Typing without having the brain in gear I suppose. Pretty sure on the 185 number though. Had a chart on the heads that was really a good one, had all the #,s including the trucks, and had cc's for chambers and ports. Lost it when the confuser took a dump. Looked in the Moparts tech archive thinking thats where I found it originally but no soap. Was an article on the 516 vs the 906 vs the 346 that was interesting, but no cc figures. We have used pocketed 516's with the exhaust hogged out to close to 906 dimensions in our Hobby cars. The three of us all thought they come out of the corners better than the 906's but thought it was due to compression. Could have been the smaller intake port I suppose. Using 346's on the Super Stock, work great.

6 packin
02-11-2003, 09:31 PM
Originally posted by 440barracuda
Ive got 906's and plan to raise my compression ratio, the engine is in the car, and hasnt been run yet, but after building the motor , we realized, we put mopar performance 9:1 pistons, not the 10:1. What can i do to get that that extra oooomph out of the motor, becuase the overall comp. ratio will be low? I have 906 heads btw

Hey the steel head gaskets have a comp thickness of around .020. The felpro have .045 thickness. That should help maybe 1/4 point.