So I bought this '74 F-100. She's got a nice 6" lift...sitting on 36's. But the Stock engine struggled to turn the tires.

So for a bit more performance...I got a 390 CFM 4 BBL Holley. And put it on a sweet Dual Plane Offenhauser Intake.

So, the stock Exhaust manifold, and intake manifolds coupled together, to re-burn exhaust fumes back through the intake.

Offenhauser doesn't do that.

When I put on the new intake manifold, I added a healthy amount of liquid gasket to the top of the exhaust manifold. Thinking....Errr...perhaps the new manifold would just seal against it.

So now...the engine is loud as SHI...Stuff, and there's exhaust everywhere.

So while the noise isn't a big deal, and the exhaust isn't a huge issue. I would like to know what the PROPER fix is, and whether my low cost option will work.

So I figure I could have....Milled out the bottom of my new intake. (which I don't want to do) to open the port to couple to the exhaust manifold.

OR

Weld the port on top of the exhaust manifold shut. (which I think is my low cost option)

OR

When buying a new intake, it's a given that in the same purchase I should have bought a sealed exhaust manifold or headers.

Last but not least, I can't help but think about the recirculating of the exhaust gas...if I don't do this with my new intake, is it going to completely obliterate my gas mileage? Or is it not that big of deal, and can properly tuning my carb compensate for that?

Any input is welcome.

 

"So, the stock Exhaust manifold, and intake manifolds coupled together, to re-burn exhaust fumes back through the intake."

No. The EGR system meters exhaust gases back into the intake system. The spot where the manifolds join together is to provide heat from the exhaust manifold to the floor of the intake manifold. Go through this Topic to get an explanation: https://www.ford-trucks.com/forums/1...ires-heat.html

The Offy intakes were made to bolt the stock exhaust manifold to the intake to provide heat to the intake. If you have exhaust leaks at the joint then you might be missing a gasket that goes between them.

 

What Harte said is right, it is to heat the intake and new and old should bolt together. There is a gasket between the two.

What you should do is run EFI exhaust manifolds to improve flow.There is also a heat plate you can buy that bolts to the intake that let's you run heater hose to it for heating intake.
I am on my phone right now but I have a post in the 80-88 bull nose area look for EFI manifold question.
Dave - - - -

 

Link to my EFI manifold swap.
The pictures start on page 2 and has a picture of the heating plate.
https://www.ford-trucks.com/forums/1...questions.html
Dave ----

 

I appreciate the help.