Split manifold swap on a 300?? (exhaust discussion)
 

Dammit Clyde, why cant you stay fixed.....

For those who dont know, Clyde is my "daily driver" truck, a 1981 F150, 2wd, 300 six, C6, regular cab, longbox. While it's slowly shaping up to be a solid running truck after some early on carb issues, the exhaust was in dire need of repair. cobbled together mess with a blown out muffler... overall just a mess.

Being as i work at a shop that does exhaust work, mainly custom exhaust work, i couldnt have this. Thoughts of my customers hearing me roll up in a clunky rattly mess cant be good for business. So saturday afternoon i put Clyde up on the lift, removed everything except the first foot or so of pipe (recently replaced, it appeared) and went on my way with the tubing bender to build the rest. the tire guy decided to help me hold the pipe up as i was ready to weld it together, he gave that front foot of pipe a hard wiggle, and SNAP!

my exhaust manifold broke in half. literally, two separate parts. i rolled my eyes, packed everything up, and drove the truck 10 miles home, sounding like i was set up for a 10 second quarter mile.

Now, i am faced with a dilemma ... do i go search for a factory 1981 Manifold, or do i swap to the 87-up split manifolds?? keep in mind, every part of emissions equipment has been gone off this truck for years, so there are no AIR tubes, etc to have to fight. Has anyone done the split manifold swap before?? I do have one of the manifolds off my old 87 (the rearward one), so i would only need to find a front one that wasnt damaged.

As for the rest of the exhaust, if i go split manifolds, im going to run duals to a Y pipe, which will feed into a single in, single out 3" muffler and a mandrel bent 3" pipe designed for a 92-up powerstroke. Why the excessive tailpipe, you ask? because it was purchased a few years ago for a different project that is no longer around.

So, please, give any input, info, or comments on what you think i can, or should do.

Id say go for it. You have all but 1 piece. Why not?

On a side note. Isnt the open manifold sound awesome (for a little while)?

the open manifold sounds pretty sweet until i got it up to about 70... i dont have a tach in yet, but im sure that the non overdrive with 3.55 gears wind that old 300 pretty damn high.

idling around the yard, it sounds like a top fueler, i cant resist punching the throttle.

is the single 3" going to be too much pipe? on my 87 with a 300, i ran dual 2.5" with no cats and welded mufflers, and it sounded decent, a bit loud, but decent.

I did this on my 82 F100. I used the EFI manifolds to a factory front pipe that was cut off of a cat. The two 2" pipes are merged into a single 3" collector which goes into a 3" in 3" out Magnaflow cat. From there it goes through a 3" in 3" out Magnaflow muffler, then 3" mandrel bent to the rear bumper. It was a bit loud at cruise, so I went back and added a second small 3" in 3" out muffler behind the rear axle. I am very happy with it.

F100jim, did you have any issues with swapping on the manifolds themselves?

EDIT: i also saw your thoughts on shortboxes vs longboxes. I own several shortboxes, but they are all hot rodded versions of a truck, lowered or lifted. Clyde, the truck in this thread, is my very utilitarian longbox.

picked up the other manifold today, now to tear it apart and get a gasket.

For those who have been down this road, do i use an 81 gasket or an 87 gasket? do i need to do ANYTHING to the intake manifold?

The only issue that I had with the manifold swap was that I had to make new washers for the studs that hold the manifolds in place. However, iirc, this was due mainly to the ears on the Clifford intake, not the ears on the EFI manifolds. The washers had to be a bit larger OD to work with the intake. I made them from stainless steel. I also had to notch a few, but again this was issues with fit on the intake. I think you are in good shape as far as the exhaust manifolds go.