offey help

[small ranger]

I have an offenhauser dual plane intake. Which end of the upper intake goes forward(closer to the radiator), the large open end, or the small long runners end? The front of the carb has the primaries and the back( closer to the fire wall) has the vac secondaries. I think I had the upper intake on backwards because the large open end had the primaries over them. Which does not make any sense, but if you look at all the pics of the intake they have the large open end in front. So what should I do?

 

[Big Jim M]

When running on the primarys I'd think the smaller longer runners would help with the velocity of the mixture. So I'd favor instaling it backward from the way you have described. But any oil or coolant passages would positively play into the instellation.
Big JIm

 

[Hotrodlincoln]

Is the upper water outlet on the intake? Put it on with the water outlet in front.

 

[JoshT]

From what I can tell from pictures, the way mine is set up, and the Steve Pruitt book you have it set up correctly.

 

[JoshT]

Is the upper water outlet on the intake? Put it on with the water outlet in front.

The upper water outlet in on the lower section of the Offy intake manifold.

 

[small ranger]

Thanks "JoshT" I will look into it. Do you have a build thread with pics?

 

[JoshT]

The "build" was done in the late 80s by my dad. He couldn't have made a build thread if he wanted to, and since I was only 2 or 3 at the time I didn't even know what a camera was.

I rebuilt the motor a couple years ago and was going to do a build thread, but I never stuck with getting pictures and updating it. Since I'm going to be starting a complete resto-mod here soon I may try again. That's restomod as in pick-up engine drive "new" truck under it, while taking the time to fix up the "new" truck.

 

[small ranger]

well here is my delema. Blow is a pic of an offey intake.

On the left is the front of the intake. The front oval port opens to a large open area type intake. The two round intake on the right (back of the intake) use long runners to each cylinder. I was under the impression the primaries of the carb (facing forward, to the left) should use the long runners first. When the vacuum is high enough to open the secondaries, they should just use the larger open intake for fuel delivery.
The upper intake does not turn around so the single larger intake is in the back and the two round intakes are in the front to match a 4 barrel carb. So am I wrong to think the primaries should run on long intake runners for good throttle response and the vacuum secondaries should use the large intake for good wide open throttle power?

 

[Big Jim M]

Nope! Nope! Nope!!

well here is my delema. Blow is a pic of an offey intake.

On the left is the front of the intake. The front oval port opens to a large open area type intake. The two round intake on the right (back of the intake) use long runners to each cylinder. I was under the impression the primaries of the carb (facing forward, to the left) should use the long runners first. When the vacuum is high enough to open the secondaries, they should just use the larger open intake for fuel delivery.
The upper intake does not turn around so the single larger intake is in the back and the two round intakes are in the front to match a 4 barrel carb. So am I wrong to think the primaries should run on long intake runners for good throttle response and the vacuum secondaries should use the large intake for good wide open throttle power?

I feel sure offy did lots of testing to get their intake to operate the best it could. It should be a rare occasion the back barrels are pulled open. The front is wide so it will accept a variety of carbs. Since all the known, by me anyway, carbs have two back barrels they built it thataway. I'm guessing that the long runners direct the secondaries to the individual cylinders. Once the back barrels are open the mixture is so rich that a pleminum area isn't needed.
I cannot imagine myself ever needing to get the back barrels open.. but to each his own I guess.
Big JIm

 

[small ranger]

well my bad I did some reading and figures it out. Offey does have it right with the single opening in the front and the long runners to the vac secondaries. "Big Jim" you would be suppriesed how often the secondaries open up on this set up. The primaries on a 390 cfm Holley are quite small and the 2.8l motor moves a decent amount of volume at 4-6k rpm.

 

[Big Jim M]

I don't see any way a 2.8 will be able to use 390cfm. A 6.0 can barely use 450cfm. I betcha that carb would be real good on a 4.0 or even a 5.0. I'd be putting a real strong spring on the secondaries. Doing that would keep the velocity up in the front side and make them work as designed. Not to mention the timing increase from the increased vaccum.
Big JIm

 

[small ranger]

When I tuned the carb I bought a spring kit for it. I tried the heaviest spring and the secondaries still opened a decent amount.

 

[F150hybred]

I don't see any way a 2.8 will be able to use 390cfm. A 6.0 can barely use 450cfm. I betcha that carb would be real good on a 4.0 or even a 5.0. I'd be putting a real strong spring on the secondaries. Doing that would keep the velocity up in the front side and make them work as designed. Not to mention the timing increase from the increased vaccum.
Big JIm

A Holley 350 cfm 2bbl is a direct replacement for the Motorcraft carburetor and the engine, when well worked over, will use every bit of it up to and including 7800 rpm. Just a little FYI... the "factory" 2.8 liter manifold works wonders when the center divider is hogged out some. Did it to mine when I had one.

 

[hucki78]

Hey guys, i have an principle question about the offy 6115DP and a holley 4160 390cfm.

some engine specs:

Cologne 2.8l V6
Mild cam Kent V6T2, Druation 280degr.
Ported intakes
janspeed header
Higher compression
flywheel lightened
Duraspark ignition
Holley 4160 390cfm
#51 main jets
#59 sec. metering plate


Problem: Engine has rough idle, unequal fuel distribution, spark plug 3+6+1 more or less black, the rest grey/dark grey

I had some testruns and tried a lot with adjustments.
Primary system seems to be fine. react well to idle screws. (2 turns out)

The problem is that the secondary idle system is flooding the upper section caused by closed throttle plates.

I tried to fix this with lower fuel level in secondary bowl and opened the secondary plates as far as possible

- but for me it can`t be right or?

Without secondary idle fuel its too lean, 2 turns out is minimum-otherwise engine dies
With secondary fuel the upper sec. flooded

Whats wrong?

Thank you in advance!

Denis