21 Stud hop up... Milling the head?

mustangbrandon

mustangbrandon

Member
Hey All,

So I've got the 35 Tudor project and it has a 37 21 stud. I'm pretty much restoring the car and adding a little Hot Rod to the engine, but trying to be pretty correct for the era. I've got some Miller pump block off plates and air cleaners. Obviously for looks...

So, to get a little more compression out of this, I want to mill the heads. I've heard flat mill and angle mill.

Where my brain starts to cook is that if I angle mill the heads, do you then have to angle mill all of the stud holes (on top?). It seems to me that if it's angle milled, it will never line up again. Maybe I am overthinking this. If I do angle mill it, does anyone know what the proper angle towards the valves would be? Trying to end of with the right clearance at the valve. (Stock Cam). Oh and these are cast iron heads, not AL U Mineeum.

Thanks for any help!

Brandon
 
I had a 221 that I used a straight thru muffler, 1 7/8ths tail pipe, model 48 stromberg carb and backed the vacuum brake full out and it would run 89 mph. Engine stock.
 
I am not an expert but, it seems logical that if the surface of the heads are angled milled, the stud holes will no longer be perpendicular to the deck of the block.

This question has been posed before; Read on:
https://www.fordbarn.com/forum/showthread.php?t=228269

Here's lots more info:
https://www.google.com/search?q=wha...kgEDMC40mAEAoAEByAEDwAEB&sclient=gws-wiz-serp

In fact, there are those who say milling is not always a good idea.
https://www.speed-talk.com/forum/viewtopic.php?t=30703
 
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Straight milling the heads enough to increase the CR very much would require re-doming the head as well. By angle milling the heads aprox .070" will allow you to clearance the head with a Dremel for piston clearance. The rule here is valve clearance. With a stock cam this isn't an issue. However, on the 37 block I built I used the L-100 with .260" net lift. This will raise the CR about 1 point. Doesn't sound like much, but the original head is just about 5:1 Takes allot of measuring to get all this done, for more CR you have to fill the ex side if the head with brass for another point. this is expensive and should be done by someone with experience and a good wood stove!!
Take care Gramps
PS Don't worry about the studs/bolts
 
Hi Ron, Your input is always "solid gold" and much appreciated..

Please give us your thinking as to what you mean when you say:
"Don't worry about the studs/bolts".
Thanks, JIM
 
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Jack: That is good news. There have been horror stories about studs or bolts seizing to heads causing removal problems. A friend of mine is dealing with that issue right now where a stud broke off below the head surface. Heads were not angle milled.
 
Ol' Ron said:
Straight milling the heads enough to increase the CR very much would require re-doming the head as well. By angle milling the heads aprox .070" will allow you to clearance the head with a Dremel for piston clearance. The rule here is valve clearance. With a stock cam this isn't an issue. However, on the 37 block I built I used the L-100 with .260" net lift. This will raise the CR about 1 point. Doesn't sound like much, but the original head is just about 5:1 Takes allot of measuring to get all this done, for more CR you have to fill the ex side if the head with brass for another point. this is expensive and should be done by someone with experience and a good wood stove!!
Take care Gramps
PS Don't worry about the studs/bolts
Click to expand...
Thanks Gramps!!!! Sincerely appreciate the expert help. Also been reading my '51 Edition How to Hop Up F&M V8 Engines...
 
There's no need to over torque the heads. The trick is to get all the thermal movement from the block (Cast iron) and the heads, ( aluminum ) I do this by torquing to 45ft lba for three heat cycles/ Most of you guys start the engined on a run stand, so not a problem,
 
Since your 21 stud, is a 37 block, you haven't said where it has flat top or domed pistons. My same block has domed pistons, with head mounted WP's.

Compression in a 21 stud is very hard to come by. Angle milling will ad a little but, the best way to get it, is with pistons. They set .043 below the block and my Victor head gaskets are .060, compressed so, you have .103 space (or quench). That's at least .060 to much. That is 7.38cc. Ross pistons CH is 1.561 and that will bring the piston up to the deck and gain 4.9cc and if you can find a head gasket of .040, compressed thickness, that should gain you close to 10cc.

Then add your angle mill to that. The pistons, although expensive, would be worth it.

I'm a aircraft machinist and it would be best the spot face bolt hole after angle milling. It doesn't take long to do. The counter bore tool would be piloted and you just touch the bolt boss, until it cleans up. It would take 2-3 seconds per bolt hole.
 
frnkeore said:
Since your 21 stud, is a 37 block, you haven't said where it has flat top or domed pistons. My same block has domed pistons, with head mounted WP's.
Click to expand...

Hey Frank, it's got domed pistons and the proper domed heads. But the heads are cast iron, not aluminum so it's my understanding that they are truck heads. Reading the chart on Vanpelt it looks like the truck heads had slightly higher compression but who knows.

I'll take a look at the Ross pistons, but this engine was rebuilt then barely run so the .030 pistons in it are basically brand new. I don't mind spending the money on them but I hate changing somehting "new". I'm not going for anything crazy on the engine, just a little kick. I've got a friend that does all my machine work so expense wise, milling the heads is basically free to me... Thanks for your input on this!
 
In my opinion, why not just mill and clearance the heads to provide a consistent .050" gap over the piston top? This will increase the compression and optimize the quench over the piston, leading to optimum combustion efficiency. Most stock heads have enough piston to head clearance that doing this significantly increases the compression ratio. There should be no clearance problems with valve to head clearance with a stock cam. I have done this to a couple of engines and it was the step that yielded the most performance increase. (It increases fuel economy, as well.)

I have followed "ol' Ron"'s posts on angle milling, and while I don't fully understand all of the details, it probably does provide the optimum increase. It does seems to require a significant amount of extra work. I believe a "straight" milling and clearancing will get you 95% of the way there.
 
Truck heads tend to have lower compression to reduce the chance of detonation under load (larger clearance volume). They usually always have a T in the prefix. A person can raise the compression on a 21 stud but the limited cylinder to outer side wall dimension on the exhaust sides can create sealing problems. There isn't much sealing area on a stock 21-stud and that was the reason Ford developed the 24-stud design. When they are bored out to limits, the sealing area is even less.
 
I have to admit the 37 block was a 239 with an 8ba crank assy. With all the trouble I had putting the 8ba crank in I should have used a Merc crank. Nit wasn't sure it would work.
G
 
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