what head what offy 3x1?



I am ready to start collecting parts for a 3x1 upgrade. I figure I will start with a 77 or later 200/250 head so that I get the larger valves and hardened seats. Apparently there are flat log and hex log styles from 77 on up.

If I get the hex log version can I run my Offy manifold that says it works on 61-69 engines?

Clifford lists the two types as 61-69, and 1970 on. Can I assume that the 61-69 version will work on all hex logs including a 77 hex log?
nice question , because the 6 cyl is verry rare here i would like also to see the difference type,s of the log intake , someone got pic of the 2 difference setup,s ? flat log / hex log ??
sometime,s it is a little diffeculd for me to now what typ,es engine,s and parts there are , here in holland not much , so i,m learning a lot in here ! thx M8
Here is a flat topped log off of a '74 250

And not easy to see but this is a round log from a '66 200

The flat topped logs are the ones that people look for to do the direct 2v installations on. I have never seen a hex shaped log though, I guess I had better keep looking. Round logs have 1.5" carb opening, flat topped logs have 1.75".

I believe that hex and round are interchangeable terms- D. Schjeldahl calls them hex shaped
thx for explaine , so the hex and the round log are the same ! i do have a 66 head [ round log ] and a 78 head [ flat log ] already did thought there whas another head with a differend intake log [ hex ], ! thats why i never did see a HEX log , 8)
o.k. so we got the terminology straightened out. . . what about the question?
You cannot use a offy intake adaptor made for 61-68 on a 69+ head. As far as which is better, that is debatable. I used a 68 head because that is what I had available. I know the later heads have a larger intake log, but honestly with an offy, it doesn't really matter. the earlier heads I think have a smaller combustion chamber and that can help. You can always have the valves enlarged.

There are three different log shapes: Round logs (1960 to first 1/2 of 1969). Flat-topped logs (last 1/2 1969 to 1978-?) and Hex-shaped logs (1980 ? to 1983?) The jury is still out on the dates. BUT for certain, there are three log designs.

In answer to the original question -"Will the '60 to '68 3x1 adapter fit on a hex log?" IMHO, no. The '60's log is MUCH smaller in design and diameter than the '80's design.

Here are some pictures for this post.

The first is a flat-topped log. Look at the 1 1/2 inch wide flat surface between the carb and the front of the engine.

This is another flat-top in the area of the casting numbers. Again, notice the 1 1/2" flat surface.

This a "hex log" Look at the angles at the ends of the log and between the flanges. The top surface is approx 1/2" wide as are the "hex" faces. It has approx a 2" diameter compared to 1 1/4" for the sixty's log. It also shows what you can do with some exhaust tubing and a couple of flanges.


Good Luck
Quick question, but what exactly are people referring to when they say the M head?
I understand that the D8 heads and later are more favorable due to larger valve sizes, but the M just throws me for a loop. :unsure:

Be sure that you read my brother's Sticky message on Head Swapping. Also go to the "Hardcore Tech" section and read my two "Sticky"s on porting and three angle valve jobs.

In 1969 Ford used both the round log (I don't have a picture of it) and the flat top log.

In the first half of the year, there were C9DE-6090 C or F or J or K suffixes on 200 ci engines. These heads have the 1.5" intake bore and the small log manifold. As best as I can determine NO 250 ci engines used these heads.

Part way through 1969 Ford switched to the C9DE-6090 M head. There is the "M" you were asking about. It has a 1.75 intake bore and the larger volume flat-topped log. It is the same casting number as the '69 250's used.

Flat-topped logs have come to be called "M" heads even for later years. The '69 head is basically the same through D5 (1975). Combustion chamber volume may change.

If you put the 1.76 diameter valves and hardened seats into a '69 through '75 heads they would be basically the same as the D7 or D8 heads.

Good Luck
now when we are talking a 3x1 setup the log size doesn't matter as much so would the hp gains be real close between the two (say 9.5:1, 260* cam, header) with the only difference being top end HP and low end torque? the reason I ask is that I want to do a 3x1 setup but have a c6 head and was wondering if I should look for a m head instead (the c6 being rebuilt already) or if the cost would outweight the gains?


You are probably right about the size of the log being less important with the 3 x 1 intake.

I think you've got a well thought out plan. The C6 head wil have the 1.649 intakes and 1.38 exhaust. The cam will help get the charge into the cylinders. The headers will help get it out.

Give this combo a DuraSpark II to light your fire and you'll be super pleased with the results.

Good Luck