As soon as I bought my 1965 F100 with 300 I-6, I swapped out the intake for an Offy Intake and put on a Holley 390 4bbl carb. The truck ran like crap when I got it and I figured it was because the 1bbl carb that was on there was missing linkage and didn't have a choke etc. Anyways after putting the Offy intake on, it's still running rough at idle and gets horrible gas mileage. I've been chasing intake / exhuast leaks and I thought I had it fixed, but it still runs rough at idle.

I noticed that the Offy intake flange and exhaust flange are not the same thickness and as a result the intake bolt "washer" then has to be angled as it pushed on the exhaust flange and the adjoining intake flange. This doesn't seem to be an ideal bolted joint. I didn't measure the Offy intake flange thickness compared to the stock intake flange (and the stock intake is away in storage now). Has anyone else noticed this difference in flange thicknesses when using an Offy intake and is there a difference in flange thicknesses between the stock intake and stock exhaust manifold.?

 

just curious, what are you using for a gasket?

 

I'm using a Fel-Pro intake and exhaust gasket kit. I didn't use any tube sealant etc.

 

did you get a used intake? it sounds like its been milled and had alot of metal taken off.

 

Yes, the Offy Intake was a used one. I wasn't aware that it had been machined. So are you suggesting the Offy intake flange should be the same thickness as the exhaust manifold flange?

 

Not same, but very close. You can...

1º Machine exhaust to proper thickness or

2º Add gaskets as requiered and use plenty sealant...