A different kind of body cutout to header question

[Mountain-Metalworks]

There are SOOOO many well discussed questions on header alignment with body cutouts already(I've read almost all...). 99% discuss mis-alignment of the factory hole once the engine is installed and headers put on, or sidepipes not being parallel to the ground or body. In either case, the problems are dictated by relatively fixed large objects, i.e. engine block, mounts, headers, pipes, etc... and are fixed with small adjustments(wedges, mount spacers, smaller diameter bolts...) to get them as good as possible.

But I'm coming at it from a different direction, I'm making my own headers and need to place the sidepipes first to figure out how to build the headers. My thought is to put the body on, place the pipes evenly in the cutouts and aligned with the body, then build a jig that holds the pipes and/or the 4-port header to sidepipe flange in a static position. Remove the body and then build the headers.

To do this, I'm looking for suggestions to refine my plan. I'm curious what placement or dimensions people end up with for things like:

1) How far off the ground should the bottom of the pipes be? Level with the 4" frame tube? higher or lower? Would you change it if you could? I would think they shouldn't be any lower than the frame or else they'll hit first if you encounter anything at the 4" ride height.

2) How far away from the body should they be? Most people can't change this, but if you could, would you? i.e: closer to the body with less space? I wouldn't think you'd want them further away or else you'd get even more hot "snake bites" when exiting.

3) Should the pipes be parallel with the frame from front to back in both the vertical and horizontal plane? It may not be necessary but again, if you could change it, would you?

4) This won't be even close to final body fitment with doors, etc... but I'll at least pull the bottom in and attach it to the outer under-door square frame tube. Should I also install the front elephant ears to pull the body in or out near the header cutouts? I know that makes a huge difference when doing this the "normal" way.

I'd love to hear from people that have done multiple cars and are potentially hamstrung by things they can't control. If given the chance to do it from scratch, what would you do differently? Of all the crazy customizations I've done on this car, this is one I've put the most thought into and determined to get the outcome I want the first time. There's no second chances here like other trial and error mods I've done.

Thanks!
-TJ

[CraigS]

A few thoughts. Looking down on the pipe it should be parallel to the body/frame. W/ the slight exception of pulling the body out or in to better fit the doors the frame and body are parallel. Looking from the side I like them parallel to the ground. The pipe mostly hides the bottom of the body in side view, and most run the rear a little higher than the front so I wouldn't want it parallel to the frame in side view. As you realize distance from the body is fairly standardized. Closer gets the inside of the bend at the body exit hole too close so would require a larger cut out. Further away and you will start to see the bolts/nuts that attach the pipes to the header. Since you are obviously capable of welding pipe, consider cutting the tips and rotating them so they point toward the ground some. Also consider installing a spiral to take some of the bark out of the pipes. Don't worry too much about the elephant ears. W/ the MkIV body wrapping around under the frame, the body is pretty stiff from rear wheel well to front fender. As you move it to fit the doors, that will determine where it ends up at the exhaust cutout.
BTW, I am curious why you are making custom headers.

[Mountain-Metalworks]

Thanks Craig, great info! I've come to the conclusion that getting the body back on for the first time since delivery is going to be a key step. I can try visualizing in my head all I want but getting the physical body back on frame will be important. I'm getting help from two local FFR guys(ThickCobra and Makgecko) on Saturday to fetch my body out of storage and bring it back to my house.
I'm making my own headers since my engine choice dictates custom, there aren't any pre-made ones available. Plus it's something I've never tried before so I figured why not give 'er the old college try.... :D

Thanks again!

-TJ

[CraigS]

That will be key. One other thing to look at is front to rear position. The FFR headers have the cutout for the pipes going right to where the fender flares out and sometimes a little into the flare. If you could move them rearward just 3/8 inch (while keeping them away from the front of the foot box) I think that would be an improvement.

[bobl]

I would get some measurements of exactly where the SBF/FFR headers end, relative to the frame. Then try to replicate that with your headers. Of course the theory is the body and side pipes would fit as designed at that point. Ideally would be for you to measure a completed car and make up a template or jig that would position off of the frame. At least in my mind it seems like it would work.

Bob

[Mountain-Metalworks]

I would get some measurements of exactly where the SBF/FFR headers end, relative to the frame. Then try to replicate that with your headers. Of course the theory is the body and side pipes would fit as designed at that point. Ideally would be for you to measure a completed car and make up a template or jig that would position off of the frame. At least in my mind it seems like it would work.

Bob

That's what a started with, I took a ton of measurements off a local Roadster(ThickCobra) with a 351-based 427 engine and 4 into 4 headers. But he had to trim his header cutouts to get things to fit once everything was installed. I realized using those measurements wasn't really a benefit to me in the long run if I'd have to trim the body as well. The height off the ground and distance from body would work, but definitely not the front to back.
In the end, getting my own body on the car with be the safest way to do this in my mind. Tedious since it's hanging in a storage unit, but definitely not as tedious as drilling hundreds of #30 holes in aluminum panels... ;)

-TJ