420hp 454 questions
 

I'm doing a quick refresh on a 420. I'd like to bump the compression a bit, so i thought I'd have the heads milled. The problem is that I'm not really sure how much to have taken off my 088's. I was planning on changing the cam as well, but after looking around, I'm not sure a roller cam is in budget. Ive also read many threads on these engines lately, and there's many opinions on cylinder heads and cams, but many threads are derailed and don't have part numbers. Help me out OSO...

I see you are in highland, indiana. There's a great cylinder head guy about 30 minutes from you. If your looking to freshen the heads, and gain a bit of power, you want to talk to him. He's a great guy, and knows his chit. No propaganda or pushing product down your throat. He's worth the phone call.


Mike at High Flow Heads
(708) 396-0505

If you mill the heads enough to gain any amount of HP to make it worth while, you may have to mill the intake, and possibly have to shim the distributor.

1 point of compression is like 4% increase in power. these are already close to 9;1 motors. i don't know if raising compression is the best way to go, not retaining the stock iron heads.

Milling the heads.030 will only raise compression to about 9.0 from the stock 8.75.

ok, i didnt think it would take that much to raise it one point, and i didnt even consider the intake possibly needed to be modified. I suppose i'll have the standard .010 to level them out and run the thinner gasket and call it a day..

this is my first hi performance build, so i'm pretty new.. thanks guys!

I did a refresh on my 420's with the only upgrade from stock being a conversion to mild roller cams from Bob Madara. The boat picked up 3 mph. This was in a Formula 311SR1. In hindsight I would have gone more aggressive with the cams but at the time thought I wanted more low end grunt. The stock cam is not a great match for the rest of the combination.

On a dart iron head, .005 flat milled =1cc. You can take that 121cc chamber to 110cc per dart. So if you had a 8.75 compression 454 with the dart heads, by flat milling to 110cc, you can effectively go to 9.5:1. The race series aluminum darts can be milled more than the pro 1's.

As far as the maximum on the gm iron head, I'm not sure of the spec on them.

Any chance the intake valve would be below the head surface if you mill .055 off. What would that do to the piston to valve clearance .

if you mill the head i recommend checking piston to valve clearance,i check it even if only doing a cam swap.

My dart race series aluminum heads have been flat milled a lot. The intake valve seat edges have been cut into, but not enough do damage the actual sealing of the valve. This is with a 2.25 intake valve. No PTV clearance issues with a 236/245 630 lift 114 hyd roller. With a flat top JE piston that is

I believe the reason dart gives those specs of maximum flat mill cc's, is for the reasons you mentioned. And why I said some heads can be milled more than others. Not all the same .

On afr's site, on the 325cc head , the chamber is 117 as cast, and 121 CNC ported. Their spec is .006 per cc . maximum flat mill to 108cc for as cast chamber , and 114 for CNC chamber. Angle mill, .009 per cc to 104cc for as cast or CNC chamber.

I'm not trying to start an argument, just wanted to point out one action causes a reaction, mill the heads all you want. At some point you have to cut the valve seats to recess the valves back to where they belong, which changes the installed height of the springs, and may cause the need for new push rods. Angle milling the head surface creates the need to mill the intake surface back to the proper mating angle. There is a point where the intake manifold has to be cut to match the heads.

Sound like more trouble than its worth.