144-250 head swap FAQ

[CZLN6]

Can I use a late model 200/250 head on my 65 200? Yes, But.....

All 144,170, 200, & 250 heads are interchangeable. But, dimension of valve size, chamber and intake tract volume changed over the years, but all will physically bolt on and function. If you were to put a head from a 1960 144ci engine (casting number, located on the intake log just behind the carb pad, CODE 6090- A) on a 250ci block it would suffer from too much compression and lack of ability to breathe, due to the smallest log and port volume, and valves.

Conversely, putting a late 200/250 head on a 144 would kill the CR, about 6.3:1, and the extra valve and port volume could not make up for that loss.

When putting a late model 200/250 head on a 66 200 block there are two dimensional factors that must be addressed to take advantage of the larger valves and port volume.

1st- All (that we've seen) OEM FoMoCo 144, 170, 200 & 250 engines came from the factory with steel shim head gaskets with a compressed thickness of approximately .025". These gaskets are no longer available and scarce as NOS (New Old Stock). What is available is a composite type head gasket from Victor, Fel-Pro and others at about .040" to .055" compress thickness. While the thicker, composite aftermarket gaskets cause a lose of compression, they do seal better and last longer than the OEM shim gaskets. The only down side is that, in a head swap, you must mill the head enough to compensate for the difference. To do that compare the thickness of the OEM gasket that you removed to the composite gaskets manufacturer's advertised compressed thickness and plan to mill the head that amount. For example, if your old shim gasket mics out to .025", and the Fel-Pro gasket has an manufacturer's compressed thickness of .050", you must mill .025" off the head to maintain the same CR.

2nd- Stock 200 heads from 1963 (Fairlanes) to somewhere in 1968 had a combustion chamber volume of about 52ccs. From 1969 to the end of production of the 200/250 engines, factory head chamber volume was increase to about 62cc. Please note the "about" compromise, because casting accuracy was not very accurate. Actual volumes must be carefully measures and recorded. Also note that this is a reference to a factory stock head. Dealing with 20 to 40 year old parts give no guarantee of OEM. More than likely these heads have already been rebuilt and milling to true the mating surface is typical when doing a valve job. The key here is to measure carefully, then mill cut to your compression goal. We use the formula of .010" mill cut equals approximately 2ccs reduction in volume. So to reduce a stock 62cc late model head to use on a 66 200, we mill .050" to reduce the chamber volumes by 10ccs, to achieve a new volume of 52ccs.

So, to use a late model 200/250 head on a 65 or 66 200, with a composite head gasket, plan to mill a typical 62cc chamber head a total of about .075" to maintain the stock 65 compression ratio of 9.2:1. That's .025" for the difference in gaskets and .050" for the chamber reduction.

Be sure to measure and record volumes after every change to the head.

CAUTION: Be sure to use hardened washers under the head bolts to take up for the reduced thickness due to machining. Also be sure to thoroughly clean the head bolt holes of dirt, grease and oil. IF YOU DON’T YOU COULD BOTTOM OUT THE HEAD BOLTS IN THEIR HOLES AND NEVER TIGHTEN THE HEAD!

FYI:
These heads can be safely milled to .090". If you need to go more than that you should do some sonic testing to determine the thickness of the deck. You should maintain at least .100" thickness to have a good, true, solid mating surface. If you have to go more than that to achieve your CR goal, you really should consider decking the block, using different pistons- flat-topped or taller pin height, or off set grinding the crank.

Milling the head also helps to increase flow slightly because it drops the open valves into the chamber a little deeper.

In determining your goal compression ratio, we suggest a comparison to the octane of the gas you intend to use. For example, if you plan to use 89 octane, unleaded regular, plan for a CR of 8.9:1. If you can stand the extra expense of 92 octane gas go with a 9.2:1 CR. Remember that regular leaded gas in 1965 was 92 octane.

Many factors limit compression ratio. The following are a few; elevation, ambient temperature, humidity, quench, cam and ignition timing, load, piston design, chamber quality and head material.

On the typical wedge shaped combustion chamber engine 1 point of compression, all else being equal, is worth a 4% increase or decrease in power.

BTW, the 200 and the 250 use the same head after about 1977.....

Adios, David

 

[Anonymous]

When all this head shaving is done at what point does it affect the length of the push rods? To change to longer or shorter push rods. Not withstanding the adjustable rockers.

 

[CZLN6]

Howdy '82cruiser:

Good question. And folks have addressed it various ways. Some have shimmed up the rocker towers an amount equal to the milling. We have always relied on the hydrauilic lifters to absord to tighter dimensions. So far it has worked. Dennis milled his D8 head and decked his 200 block past zero. And still the lifters have absorbed the tighter deminsions.

My 250 block was decked .070" and the head milled .030", and the hydraulic lifters did their thing. We both run vintage rocker arms, but I would not hesitate to use non-adjustible rockers. We both run a 260-ish Hyd cam- His is a Clifford, Mine a Comp.

Someone had reported noisy lifters prior to milling .050" off the head on a '78 Fairmont. He put it back together with a FelPro .050" composite head gasket, stock, non-adjustible rockers and reported that lifter noise was gone. Best we could figure was that he had some extra clearances due to wear, that the milling tightened up.

At some point you could exceed the roughly .125" of lifter collapse travel, but milling .075" is not close to that limit, and the composite gasket gives back .025", so the real difference in this case is only .050", which is easily covered by the hydraulic lifter.

Adios, David

 

[Anonymous]

One other thing I've run across: my local NAPA store carries a .060" shorter pushrod for the 3.3L / 200CID. It's the same price as the stock ones. They had both in stock when I did my rebuild: apparently it's the same as pushrods from some other popular car.

 

[Anonymous]

Thanks CZLN6. MARKP, I think you are right. The same think happen to me on the shorter push rods.

 

[Anonymous]

hi, i know that a 250 head fits perfectly on a 200 block. whats the major beny? Increased compression Ratio right? please excuse my lack of information

 

[Mike]

CZ,

In your performance handbook, you mention using 144 intake valves as exhaust valves on the 200 and 250. I been told that due to differences in the materials on intake and exhaust valves (unless stainless) that it would not be advisable to do this. Have you had any problems with this?

Thanks,

Mike

 

[Hot 6t Falcon]

Mike,

Both CZ and I have used the 144 intake valves as exhaust valves. CZ has a 250 and I have a 200. We have had no trouble with the valves and they been in our mules for three years (and run hard).

I asked three local engine builders. They all said that on stock low performance (that a good description of a 144) there is no difference in the material the valves are made from. My favorite machinist called Manley and they said the same thing.

Higher performance and Heavy duty engines use get into all kinds of special materials and construction differences - like sodium filled exhaust valves.

Good Luck

 

[addo]

Do you need bronze valve guides with these SS valves??

Bronze guides are good in any unleaded or high wear application. The spiral groove thin liners like K-lines are worth installing on any head. Being a sacrificial part, no more reaming and valve upsizing; just press out and replace much, much later on.

If you worry about the wear characteristics, consider how many frictional applications use bronze against a ferrous metal. Auto trannies are a great example. On a head, the spiral groove in K-lines keeps just enough oil for lube and cooling (heat transfer).

I am making use of the lessened valve stem side loads on my head project (roller rockers used), to further reduce the length of the guide's boss in the valve bowl. More flow!

Regards, Adam.