[jhealey1967]

I've been looking for a suitable way to increase compression without resorting to dome-top pistons (which I understand can disturb flame propagation during combustion), and have recently been reading about "angle milling." Prior to this, I hadn't known there was an alternative to the standard fare, straight across milling of the heads. It is my understanding that the maximum amount of material that can safely be removed from Pontiac heads is around .060", when regular milling is employed. However, does anyone know how much a Pontiac head can be "angle milled"? I am curious as to whether or not a significantly greater amount of reduction in combustion chamber volume can be achieved with this process compared with standard milling alone.

[Mr. P-Body]

j,

Angle-milling is typically restricted to small block Chevy engines. The primary purpose is to improve the valve angle to allow a better "shot" at the cylinder from the intake port. Another "benefit" was the chamber was lopped at a faster pace, to increase compression, due to the majority of material being removed from the spark plug "side".

I'm sure somebody out there has done this to a Pontiac, as most things that make a small block better are tried on others whether they need it or not.

What WE have done, is just the opposite. We've angle-milled them to "roll" the exhaust port exit back a bit, improving exhaust flow through the header. That would have the opposite effect on the chamber from what you're after. We also lay the flange (exhaust) itself, back about .060" and make it a bit less of an angle. Header fit is affected by that, so be careful.

What heads are you using?

Jim

[PITTSBURGH 64]

Is your block 0 decked?

[jhealey1967]

My block hasn't been decked yet, though I am considering it. I have to wonder if decking the block would require valve notches in the pistons, however. The stock pistons in my engine are flat tops with no notches.

And my heads are actually early 287 heads. I suppose I should have posted in the pre-61 forum, but I figured that there might be more experience with this type of machine work in the later forums, since a lot of guys with early cars more often than not just recommend using later engines, or at the very least, later heads. However, my goal is to simply get the best I can out of an early engine. I have no desire to swap blocks or heads.

[tom s]

a proper built dome will not hurt you that much.Tech has improved much over the years.Virtually all 14-15 to 1 CR race pontiac engines have somekind of dome.What exactly are you trying to do with what combo?Angle milling will just open up more things that wont fit right.JMHO,Tom

[jhealey1967]

Initially, I had actually intended to go with dome tops. I placed an order with Ross through Butler Performance, albeit after getting the run around from them for over a month (they never even submitted my order to Ross, I got the feeling they weren't too excited to get involved with an early engine), I sort of gave up on the idea.

And I'm actually somewhat glad that I did, because as of late, I've been hearing from numerous authorities (or at least self-proclaimed authorities) on Pontiac engines that dome tops are a poor way to raise compression, as they will destroy the flame front during combustion. Even Jim Hand advises against the in his book on building performance Pontiac V8's. So I must admit, I am a bit weary of dome tops, though they WOULD be the easiest way to raise the compression.

What I'm trying to do is make as much power as I can out of the first year (287) block and heads, which I'm currently rebuilding for my '55 Chieftain. Unfortunately, however, it seems that the most common advice I get is "dump the 287 and stick a 389 in there." That defeats what I am trying to accomplish here though...

[tom s]

how much CR do you want?What are the CCs of the chambers in the head?Tom

[jhealey1967]

I'm looking to make between 11:1 to 12:1 compression, suppressing detonation with an old (new old stock) water/methanol injection system that I have, similar to the old "Turbo Rocket Fluid" injection systems that Oldsmobile used on their early 60's 215 V8 turbo engines.

The combustion chambers on the heads I'm using (stock 287) are 73cc's.

[Jack Gifford]

As Tom S said, angle-milling a Pontiac head would leave you with all sorts of problems.

Are '55 chambers really that large? I'm used to seeing sixty-something cc's with '57/58 heads.

There are plenty of examples of guys cutting more than .060" off Pontiac heads. I cut about .100" off the heads of the '58 engine I've got ready for my truck. You just need to cut the same amount off the intake faces, and deal with valley pan fitment- trim some spots to clear the manifold, and double-gasket against the heads.

If you didn't care about being authentic down to the part-number level, I'd suggest other early heads. '57-60 are quite a step up from the '55 heads and valves.

I could "bend your ear" about things I've done to "modernize" the interior of this '58 engine, but not having run it yet, that info isn't especially valuable [yet!].

(I agree that this thread really should be in the "61 & Older Tech" forum. Maybe a moderator can move it for us?)

[Hillard]

Originally Posted by jhealey1967

My block hasn't been decked yet, though I am considering it. I have to wonder if decking the block would require valve notches in the pistons, however. The stock pistons in my engine are flat tops with no notches.
.

Usually it takes milling the deck .015"-.020" to achieve a zero-deck although you need to measure yours to know exactly how much needs removed. As fas as valve notches it would be no different than taking .015"-.020" off the heads. Either way the valves are that much closer to the pistons. With zero-decking you achieve more compression and better combustion by maximizing quench. It's a win-win situation. You will just need to check your piston to valve clearance when you assemble it.

[tom s]

with that small of motor you will need a dome to get too the CR you want.I saw 10 to 1 with a 90 over and a 3.56 stroke with 65 CC heads.I would not be afraid of a proper made dome.JMO,Tom

[jhealey1967]

I wouldn't be so much against using '57 heads if I hadn't already had my '55 heads completely rebuilt. I have over $650 invested into them, including hardened valve seats, a performance valve job, and screw in rocker studs. I also put a lot of hours into them myself doing a mild port and polish job. So unless someone out there has a set of '57 heads that they are willing to part with for free, or someone wants to buy my '55 heads, I can't really justify not using them.

As for the combustion chamber volume of the '55 heads, I got the 73cc specification from Rick Gonser, but in calculating the compression ratio with all the other known parameters (deck clearance, bore/stroke, head gasket thickness), I've been able to confirm that this number is indeed correct (stock '55 Pontiacs had a compression ratio of 8.0:1, and flat top [no valve reliefs] pistons). In '56, the volume was reduced to 70cc's.

I don't know what the chamber size on the '57 heads is, but going just on the information that they came stock with 10:1 compression, with a bore of 3.93" and a stroke of 3.56", I calculate that they must be around 60cc's. Now that WOULD be ideal; but again, I've already completely rebuilt my '55 heads, and I'd hate to lay them to waste.

Now, if I were to zero deck the block, it may very well result in valve/piston interference, which would require notches in the pistons. If I were to use notched pistons, which would probably have a depth/volume of 5 to 6cc's, it would negate any gains achieved by decking the block (zero decking the block would get the compression ratio up to about 8.3:1, notched pistons would, depending on how deep the notches were, would drop the compression back down to about 7.8:1).

It looks like the only way I'll get the compression I want to achieve out of this motor with the stock heads would be to zero deck the block AND mill the heads .100 (and I'm still not sure this is possible with these heads). The only other option would be dome top pistons I suppose, but I'm still not convinced they wouldn't negatively affect combustion, as they would require a pretty hefty dome.

Does anyone have a set of rebuilt '57 heads they'd like to part with for cheap?

[Jack Gifford]

Originally Posted by jhealey1967

1) ... I also put a lot of hours into them myself doing a mild port and polish job...
2) ... I got the 73cc specification...
3) ... if I were to zero deck the block, it may very well result in valve/piston interference...
4) ... mill the heads .100 (and I'm still not sure this is possible with these heads)...
5) ... rebuilt '57 heads they'd like to part with for cheap?

1) Only a flowbench can validate that work. I thought I did some "good things" with my latest '58 heads, but the cold, hard flow numbers told a disappointing story. Maybe you're better with fluid dynamics than I am (or luckier?).
2) Stop guessing- spend a couple of bucks for a 100cc burette and measure them.
3) I suspect that you're overly concerned about valve/piston clearance. This latest '58 has .540" valve lift, and I've got good clearance, even with my heads milled .100". I think you ought to start mocking things up and see where you stand.
4) There's absolutely no question that your heads can be milled that much.
5) You'll probably have a much better chance of a response if you ask about '57-'60 heads. Other than a casting number, they aren't going to look any different from your heads.

Hey, mods- thanks for moving this thread!