200 CI Head Swap Question

mustang652

Well-known member
:?: Trying to take the next step in my Offy 3x1 conversion. I have already purchased the log adapter for my 65 with a 66 engine. As I want to do most of the head work prior to taking down my car and have read quite a bit on this forum that a later model head with larger valves is a good idea. Does anyone know if the adapter for the older 200 will work on one of the later models that already have the larger valves. Got one opinion that stated big vacumme problem, and increassed cc of head would be a problem. The plan is to complete the head work, milling porting, rockers and valves done or ready, then have 264 cam, new double chain timing gear done when head is ready.
 
The later heads had a "flat" top surface to the log. I'm not sure if there was a large valve, round log head with valves the same size as a 250 head. Offy also made a tri-power adapter for the "flat" log heads. I have a '69 round log head for my buildup(IIRC) & the valves are much larger than the 144 valves. Gotta be an improvement..... I'm saving my quarters for the 'lumium head. YUM!
Darryl
 
Howdy Mustang652:

No, the log adaptor you have will not fit the later big valve heads. That's not a big problem though. When you do your head specify a three angle valve job, mill to compensate for the thicker composite gasket that will replace your steel shim stock one and to attain your goal CR, install an exhaust port divider, have the intake valves back cut and clean up the chambers.

With the tri carb set up you will not notice the small difference in intake valve size, 1.69" to 1.75", or the difference in intake tract volume. The extra two carbs will more than make up the difference on the top end where it would matter.

Enjoy the journey.

Adios, David
 
Thanks for the information. Based upon what I had already read, I picked up the port divider when I got the adapter and planned on milling the headby .60. I want to start looking for the "new" head this next week and did't want to end up with the wrong one. Am I right in that 65 to 68 is the year span that will fit the earlier 200's. Can larger valves be put in the earlier heads and would it help with the low end.
 
Howdy back:

'65 to '68 and most '69s will have the 52 cc small chamber heads. Castings Casting with a C5, C6, C7, C8 and C9s- other that the "M" suffix casting. These heads will have 1.69" intakes and 1.38" exhasut valves.

You can fit 1.75" intakes and 1.50" exhaust valves, but they will be of little value because of shrouding in the smaller chambers. The larger valves would be a bigger help at higher rpms. If I were you, I'd opt to stick with the stock size valves and have hardened seats installed. The biggest gain in valves takes place within an inch of the seat. That's why I suggested a three angle seat and back-cutting the intakes. That along with a little port and bowl clean up and polishing the chambers will get you a long way to better flow.

If you do opt for the larger valves, spend some time unshrouding the chambers to take full advantage. The plus of the smaller chamber heads is a higher quench to bore ratio, for better turbulence and combustion efficiency.

Again, your tri-carb set up will take care of many of the single carb issues on the top end.

Adios, David
 
Thanks again.
That's why I suggested a three angle seat and back-cutting the intakes. That along with a little port and bowl clean up and polishing the chambers will get you a long way to better flow.
I will follow the above suggestion. Sounds like the cost factor will be a lot easier on the wallet. Found the articles on some of the work, the bowl clean up and the Offy adapter installation on earlier postings. Just a side note, I did order and receive The Falcon Performance Book, just haven't had a chance to go through it cover to cover. I have no doubt, I'll be back for more advice before this project is done.

Thanks

Stan
 
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