Milled 200/250ci cylinder head: Seeking information

C

cook11

Well-known member
Milled 200/250ci cylinder head:

Whose done it here on the board?
Was it worth it?
What proven horsepower/torque gains did you get?
Is it worth it to mill off both the intake/exhaust ports essentially having a flat face on the side of the cylinder head and then brazing/welding on a machined plate with ports so that a custom intake and header can be bolted on?
 
Howdy Cook:

Yes, I've milled a D7xx casting to use on my 250. I milled to- 1. obtain a level mating surface, 2. to reduce volume to compensate for a thicker, aftermarket head gasket, and 3. to attain a static compression ration of 9,6:1.

Milling improved torque and power. How Much? Can't say because I added a two barrel carb mod, performance cam and a header. IT was a thrill compared to before and after.

I can't comment on your last question because I haven't done it.

HOpe that helps you.

Adios, David
 
cook11":ley1hhqo said:
Milled 200/250ci cylinder head:

Whose done it here on the board?
Was it worth it?
What proven horsepower/torque gains did you get?
Is it worth it to mill off both the intake/exhaust ports essentially having a flat face on the side of the cylinder head and then brazing/welding on a machined plate with ports so that a custom intake and header can be bolted on?
Click to expand...

The first milled off log was likely done very soon after the first Falcon engine came out so sometime in 1959. Every so often you can find one of these early modded heads off a 144 or 170 being sold with a set of the early Hilborn Fuel injecters bolted to it. Is it worth it depends on how much you would have to spend to do the job but if you have access to some machine shop equipment or even just using a hack saw to cut off the log yourself then yes for sure. There is no real need or advantage in milling the exhaust port side much beyond truing it up. On the exhaust just add a carefully fitted center port divider and weld it in then true up the surface. Good luck :nod:
 
I'm in the process of an engine build right now so I can't give you any driving performance information. I can give you the flow numbers for
a milled head that has been ported.

Intake at .5 lift is 187cfm
Exhaust at .5 lift is 148cfm

Hope this helps. If you are going to mill off intake and exhaust, you'll have to custom build both (I could not find any support oem parts that
would work).
 
CZLN6":15y174o2 said:
Howdy Cook:

Yes, I've milled a D7xx casting to use on my 250. I milled to- 1. obtain a level mating surface, 2. to reduce volume to compensate for a thicker, aftermarket head gasket, and 3. to attain a static compression ration of 9,6:1.

Milling improved torque and power. How Much? Can't say because I added a two barrel carb mod, performance cam and a header. IT was a thrill compared to before and after.

I can't comment on your last question because I haven't done it.

HOpe that helps you.

Adios, David
Click to expand...

I'm very interested in your mods.... do you recall what cam and header you used?
 
Howdy Back Lathi:

Yes, but this was pre-CI. I used a Comp 260 cam and a Clifford header. I had the header HPC coated. It was a single exhaust system with a 2" pipe and DynoMax turbo type muffler. This has been a few years ago and I do not know if Clifford is still in the header business. The last number I had for them was 1-888-471-1161. Last web contact was cliffordperformance.net. Clifford went through the same process that Classic Inline is going through now, when the patriarch, Jack Clifford died and family sort of took over the business.

I selected the cam based on flow hence data and intended uses. With a OEM log head, even modified like mine lifts past about .425" are wasted efforts. FYI my head was ported and the exhaust ports and combustion chambers polished. I used stock 1.75 intake valves with a 30 degree back-cut and 144 intake valves for exhaust at 1.468". Note- I did not know about the SI 1.50" exhaust valve availability at that time. It was also modified for a direct mount 2 barrel carb. It was milled .070" to attain a 9.75:1 CR. (I'm at 5,000 Ft El).

FYI- in addition to compensating for the thicker, modern composite head gaskets and a performance/economy goal of 9:1 CR, milling the head also drops the valves slightly deeper into the chambers, lessening shrouding and improving flow. For example, if you were to mill a head .075", .025" would accommodate for the thicker head gasket. The other .050" would equate to .050" increase in valve lift. So, assuming a stock cam lift of .348", the effective lift would now be .050" greater. Note- this is not the same as lift, but the effect is the same, without the added stress on rockers, rocker shaft, valve springs and valve seats. In the end, milling not only effect CR but also flow.

Current thinking is that the Comp 260 is old school and that since then cam technology and design specifically for our Ford sixes has improved. However, I'm hearing of folks still using the Comp 260 for a moderate street cam with satisfaction. We do know that Mike (CI) did a lot of work with Clay Smith Cams to come up with the CI line of cams.

I hope this is helpful to you. Keep us posted on your process and keep the questions coming.

Adios, David
 
David,

What did you end up with for a combustion chamber volume when you did the 0.070" mill? I'm curious as this is what I've requested from my machine shop. This is on a C9 head with ~61cc chambers prior to milling.

Thanks!
 
I have a 200 in my 65, I found a 70 200 head at yard, I’m wanting too put the 1970 head on my 65. I’ve heard others say mill .070. What all else would be involved

Appreciate in thought thank you
 
The reason for milling the head on a later one is to drop the combustion chamber cc's. The 65 had 50cc head chambers while the later ones like my 73 have over 60 cc chambers. Both have .019 deck height (space above the top of the piston at TDC and the top of the block). Taking .040 to .050 off the head and .005 to .010 off the block will get you down to about 9 - 1 static and 8.5 - 1 dynamic on a newer head. Much depends on when the Intake Valve closes. The sooner it closes the higher the dynamic compression. DYNAMIC is what the chamber actually sees as the piston starts up the cylinder. With today's ethanol gas and 87 octane at some stations (even 86 octane at some) the 8.5 dynamic is safe...most of the time. I run 89 most of the time just to be safe.
 
Another reason to use the 73 head is the smaller valves, which are the same as the 1965. Way too many car guys jump on bigger valves for their street engine, not understanding VELOCITY also plays a part in street power. Smaller valves force the air movement to speed up, helping create a swirl in the chamber. A swirling fuel-air mix stays in a better "vapor" mix for better ignition. It is also more likely to ignite. The spark in the chamber lasts only so long, and a moving mix is more likely to hit that spark and go BOOM. Bigger valves are great at top end speeds where max fuel-air are needed. At street speeds that is really not wanted.
 
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