I'm wondering what's the easiest and cheapest way to raise compression on a 428? Mill the heads down? If so, how much do I have them milled down? How much could I expect to pay for this? What kind of HP increases could I expect?
Milling the heads is one of the easiest ways of raising compression, but you have to know what compression you have now. To do that you need to know the volume of the heads, the actual bore size, actual deck clearance, actual stroke, and actual dish or dome volume. I can email you an excel spread sheet to do the calculations. Or look in back of the Ford Motorsport catalog. My 2000 catalog had all the formulas.
You may also need to recheck your valve to piston clearance once you have milled the heads if you are running an aftermarket cam.
Thinner head gasket or change to heads with smaller combustion chambers. There are no other easy ways to increase your compression ratio.
Milling the heads would increase the compression ration, but not by a lot unless you milled quite a bit, which leads to a whole host of problems. Besides the valve-to-piston clearance problems that could result, milling the heads would in turn require milling the intake in order to get everything to fit. You're also changing the geometry of the pushrods, which may well require different a different length.
A thinner gasket (say, one that is .020" compressed instead of .041" compressed) would increase your CR by approximately one half of a point.
If you have heads with relatively large combustion chambers, say 74-76 cc, you can change to heads with chambers as small as 67-69 cc. That change would be good for approximately eight tenths of a point of compression gain (for example, if your CR with 74-76 cc heads is 10.0:1, your CR with 67-69 cc heads would be approximately 10.8:1.
If you really want higher compression, do it right. Use heads with smaller chambers, or change to higher compression (taller, less dish, etc.) pistons.
I forgot about the heads - brain wasn't all the way on this morning. Where can you get a thinner head gasket? I keep coming up empty handed when I search for these. Found one copper gasket, but it is the same compressed thickness.
Milling the heads will get the compression down - but you can't go hog wild with it, and it only reduces chamber volume by 1 cc for every .005" for an increase of a tenth of a point of compression.
To get that half point, the head would need to be milled about .020-.025.
Smaller combustion chambers are easier. Besides, you can get the heads ported at the same time.
John, how much compression do you want ? Most 428s have almost 10 to 1 or more already, and raising it will only cause you to need more exspensive gasoline. I like 9 1/2 to 1 engines, 'cause they run on the cheap stuff. My 10 1/2 to 1 stroker motor is parked because it runs only on premium and that does not fit the budget right now. Anyways....what head gaskets are you running ? Most of us run the fel-pros, which are .041 thick when torqued down. Lots of FEs came from the factory with .015 thick steel shim gaskets. Sometimes you can find them for sale on Ebay. Fel-Pro also offers the 8554 SP, a copper shim that is .020 thick. Milling the heads will help as well. You can safely cut .050 off the decks without any fear. If you mill the heads, you must also mill the intake face of the heads. NEVER EVER mill the sides of an intake manifold. On an FE, the intake face of the head and the deck are at right angles to each other, so the amount to mill is the same on both surfaces. Throw away your end gaskets for your intake and use a fat bead of RTV. The shop I work in will mill both surfaces of both heads for around 80$, we will take off as much as you want. But before you have anything milled, what kind of intake are you running ? Might be easier to find some extra power with a better intake and leave compression alone.............DF