Going to 2½” sizing on the exhaust can potentially reduce the backpressure to the point that the fuel mileage during cruising will take a dump.  2” pipes with a crossover or H pipe is what I would recommend for a daily driver and where fuel economy is a concern.

Lorena, Texas (South of Waco)

The outlet on the exhaust manifold looks to be about 2 inches. I slid a piece of 2.5 up to bottom of the manifold, looks like sewer pipe hangin off it.

I don't think it will affect performance significantly. If anything, I'd go 1/4" larger than the manifold and that's it. If anything, keeping it as small as possible will ease the installation. Think about instaling an H or X pipe while you are at it.


Lawrenceville, GA

OVERKILL, in my humble opinion...the duals on my mild-cammed 312 in the T-Bird MIGHT be 2", no bigger...ran just fine, thanks...

I have dual 2 1/4" exaust on my 500" cadillac in my '60 F-100...it also does just fine... 

Look at your collector size on the manifolds...anything much larger than that would seem to be a waste...and a waste of $$...the tip size will make wondrous changes in the note without effecting torque...

My 2 cents, and my experiences...

Todd in Central California...about half way between Fresno and Sacramento

1956 Thunderbird - 1960 F-100 - 1961 Starliner - 1961 Imperial

I have a '74 Galaxie with a 292, and dual exhaust. It was single exit from the factory, just like your car. I eliminated the Y connection, and ran dual 2.5 inch pipes all the way, with an H balance intersection just after the tranny, and one glasspack on each side. When I did the job, the car felt more "loose" with the dual exhaust. Nothing bad happened, so I think two 2.5 inch tubes is ok for your car.

One very interesting thing is that the exhaust sound got lower (I had one single tube, already with a glasspack). I was surprised, but is logical, since that with just one tube, all the engine gases will pass trough one glasspack. With the dual sistem, the gases will pass trough two glasspacks, and the sound will result a little lower.

Túlio Lazzaroni "FORD", Florianópolis SC Brasil.

'74 Ford Galaxie 500 292 V8

'82 Ford Galaxie Landau 302 V8

'98 Chevrolet S10 4.3 V6

'01 Ford Focus 1.8 Zetec

I have 1957 Custom, 272, auto, and I'm going to dual exhaust from the single thats on it. Is 2.5 inch overkill or would that work okay.