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H-Pipe size opinions

68stang289

68stang289

Member
I'm finally at the point to start considering exhausts for my 70 428. The car is a 4 speed car so space is TIGHT up on the driver's side manifold. What I'm debating is between going with a 2 1/4 or 2 1/2 exhaust. The 428 is pretty built - TRW .060 with big valve cuts, Crower solid cam, ported intake, Lemans rods polished with ARP bolts, windage tray, Ford power Parts rockers, stands, spacers and pushrods, shell lifters, steel roller timing with all machine work. The car had full length hedman headers on it, but I have switched back to stock aftermarket exhaust manifolds. I'm concerned that there will be too much back pressure going with the 2 1/4 with the manifolds and that the 2 1/2 will not fit properly due to the added 1/4". Thoughts?
 
I would use 2 1/2". If you can't get a good seal on the stock exhaust collector you could always us a converted tube that went from 2 1/4 to 2 1/2. I can't see why you could not get 2 1/2" to work with stock manifolds though.
 
My concern is that the extra 1/4" means it won't be able to clear the z-bar and fit up in on the driver's side. It looks super tight up there right now to begin with, and I just don't want to run into an issue with the drivers side pipe not clearing. That being said, because the motor is pretty built, I think it would be beneficial to go 2 1/2".
 
You have to think that moving the 1/4" difference is only 1/8" on both sides. You could also dimple that spot if the clearnace is too tight. No sense in building and engine just to choke it off.
 
My freind's 67 GT500 clone with 4 speed toploader and stock linkage has stock manifolds and am 99% sure that he has a custom 2-1/2" exhaust. I don't recall any clearance issues with it.
If you have a custom exhaust shop build the exhaust for you, then try to go with one that can do mandrel bends as the corners won't be choked down like a traditional exhaust. FYI, A Diet Coke can measure 2.6" diameter, you could use an empty as a quick gauge to see if there is enough room to run the 2-1/2" pipe.
 
I completely agree about not choking off the engine. Unfortunately the one "decent" exhaust shop we have here did a total crap job on the exhaust system on my 66 289, so I'm really looking for something that is bolt up right now. Plus no one in the area does mandrel bending and that would be ideal. Anyone know of any places that carry 2.5" pipes for a 70 428?

I will definitely check it out with a coke can to see what I would be looking at clearance wise.
 
If you've got a mig welder, you could put together your own mandrel bent system. Summit sells mandrel "U" and "J" bends... I did my own exhaust and it was one of the most rewarding projects that I did on the car.
 
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