ofenhouser manifold your experiences

The engine can use a carburetor up to about 400 CFM with out any problem, I have used the Carter (or today's version the Edelbrock Performer) AFB successfully a couple of times in engines that size and am currently building a '3 vintage 232 using that carburetor. I happen to have a Offenhauser manifold I am using too, a dual port design. The theory behind a dual port design is there is two passages per runner, one is for the primaries and the other for the secondaries and the primary is smaller thus keeping the air velocity up which helps keep the fuel in suspension as it moves through the manifold making driving on the primaries more efficient. A "Wet" manifold such as this one is and important when using a carburetor or even a "throttle body" fuel injection system vs a port injection system, keeping the fuel in suspension makes for better mixture into the cylinder, so the theory goes. The other side of the story is simply higher rpm is some what limited because the total runner size is smaller than one that simply is a single big runner back to the Carburetor.
Now how much merit is there to the theory is open for question and I would not worry about it as the manifold works well on small I-6 engines. It happens to be the one I came across used at a swap meet and it lets me put a 4bbl carburetor on the engine so I am going to use it.
As to cam shafts? I personally am a fan of Iskenderian cams and have used the following: The 256 supercam with .450 lift and 256 degrees of duration and the Z50E4 Super cam with Lift and also 256 degrees of duration with engines that size and were quite satisfied with the overall performance. Although for this engine I am going to order the HL/HYD   with Lift and   degree duration, a grind I have used with V8 engines and have been quite happy with the results. When I order the cam I generally will order a set of lifters to e shipped with the cam so I have components from the same vendor. The important thing to keep in mind unless you are willing to go through the agravation (if that is the proper term) of dealing with changing valve train components and makeing sure you get things working correctly, keeping the lift at the valve under .500 inches will let these cams and others work with the OEM valve train components with out any problems.And work reliably. Comp cams I have heard require the use of heavier duty valve springs,and that starts to get into cam shaft wear problems. Or could. But even they should not be a problem if the lift is under .500 inches.
As to your costs? They can run as high as you have indicated, but with careful shopping it can also be considerably less. How well do they run?
The make the I-6 run as if it was a small v8, they tune well with what ever carburetor I have chosen to use with the 256 Super cam and other modifications and using the OEM BBD 2bbl I could tune the car to pass local smog tests. But that was a feature that satisfied me. I have used the 256 Super cam with a MULTI-Port fuel injection system on a 258 and have driven it almost 50,000 miles at the present.
Good luck and have fun and one thing for sure,an in line 6 dressed up for a night on the town always draws a lot of attention at local cruise nights.

i am looking at the duel port . stock engine except for the hei dissy .  3.31 diff gears . with the 390 holley what jets & power valve did you use . 

Edited by Rambling On - Jan/27/2015 at 7:55am

I don't think the 465 will open...a 390 will be iffy with stock.

R O , that is a beautiful engine compartment!!!

The smaller venturii of the 390 will give better throttle response with any intake, the DP is even better. I've run a 390 on a 258 and it could have used a bit bigger carb. I don't think the 465 is too big, especially with a better cam (I ran stock).

As far as a "lumpy" cam goes, you won't like it. Those are short duration cams really made for high rpm performance. They don't drive well or get good gas mileage in a normally driven street engine. All you get is sound and poor low speed performance. That's why you really need a 2500-3000 stall converter to run one on the street.

Turn the idle down to about 500-600 rpm and the six will stumble along, giving you a lumpy idle -- after it warms up anyway. It will probably stall when cold, but that's just for the first 10-15 minutes after starting. A manual choke will fix that in warmer weather. I don't think you can adjust an auto choke enough to work well in cold and warm weather, not without adjusting it a bit for seasons anyway. Leave it adjusted for cold weather and it will likely stay closed too long in warm weather (with the low idle).

The Isky 256 Supercam is a great street performance cam. I wouldn't go more than the HL. Comp makes a cam similar to the 256 Supercam (I think it's a 260 duration instead of 256). I wouldn't use any of the Xtreme Comp cams -- lift is too high for stock springs and the Comp springs are way to stiff for today's oil.