Underbody Exhaust Help...ERA 427 Street

[strictlypersonl]

There are outriggers from the main chassis rail with 19.25" longitudinal distance between them.

4" from the floor surface to the bottom of the chassis rail.

The box containing the brake master cylinders (in front of the muffler cavity) extends out from the main rails 5", so that the muffler "In" must be offset to the outside. The muffler "Out" must be centered or in-line with the "In" pipe. It cannot be on the opposite side.

[lippy]

Originally Posted by strictlypersonl

There are outriggers from the main chassis rail with 19.25" longitudinal distance between them.

4" from the floor surface to the bottom of the chassis rail.

The box containing the brake master cylinders (in front of the muffler cavity) extends out from the main rails 5", so that the muffler "In" must be offset to the outside. The muffler "Out" must be centered or in-line with the "In" pipe. It cannot be on the opposite side.

So does this preclude using a 2.5" or 3" system?

[DanEC]

Originally Posted by lippy

So does this preclude using a 2.5" or 3" system?

It depends on what you are using for headers and for an outlet. ERA's undercar fabricated header collectors are 2-1/2 inch with neck down just before the mufflers to 2 inch. So there is no problem cutting the neck down off, welding a short piece of 2-1/2 inch pipe to fill the gap to the muffler and then fit a 2-1/2 inch muffler that fits within the two outriggers and between the main chassis rail and the rocker panel - such as the low profile Spintech muffler I'm using. If you want to go to a 3 inch collector and head pipe, you will have to have them fabricated to fit to the individual header pipes off the engine that ERA has bent up and welded. If there is a 3 inch in/out muffler that will fit in the allotted space I don't know. But, I'm pretty certain there is no way to run a 3 inch tail pipe to the rear - requiring a side exit in front of the rear tire.

A side problem however, is that the undercar exhaust hangs pretty low. I'm sucking mine up just about as close to the floor pan as I can, but it will still be hanging a little below the main chassis rail and most of the muffler and head pipes are going to be clearly visible from the side of the car. My Spintech mufflers are only 3 inches thick which helps considerably as most are 4 inches thick. The additional dimension of a 1/2 inch larger pipe and 1 inch thicker muffler is all going to be hanging down lower from where I'm at - and that is not going to be practical or attractive looking. At that point you need to be looking at oval pipe and 3 inch Spintech or Dr. Gas mufflers to maintain ground clearance.

My 2 cents are that 2-1/2 inch is probably the largest practical size for undercar use - unless you go to oval.

[427 Street]

Thanks for the replies.

I spoke with Doug today. Pete said he could answer all of my exhaust tech questions. When I have a chance later, I will get my notes together and post what he said.

Thanks,
Nick

[lippy]

Originally Posted by strictlypersonl

There are outriggers from the main chassis rail with 19.25" longitudinal distance between them.

4" from the floor surface to the bottom of the chassis rail.

The box containing the brake master cylinders (in front of the muffler cavity) extends out from the main rails 5", so that the muffler "In" must be offset to the outside. The muffler "Out" must be centered or in-line with the "In" pipe. It cannot be on the opposite side.

Bob - what about the MagnaFlow 11376 (http://www.magnaflow.com/02product/s...ain&id=10390)? It is 11" long, with a 4" x 9" oval cross section and 2.5" circular inlet/outlet. This model has both inlet and outlet offset/aligned, but it can be configured several ways.

[DanEC]

Originally Posted by lippy

Bob - what about the MagnaFlow 11376 (http://www.magnaflow.com/02product/s...ain&id=10390)? It is 11" long, with a 4" x 9" oval cross section and 2.5" circular inlet/outlet. This model has both inlet and outlet offset/aligned, but it can be configured several ways.

You really need a center outlet if running a tailpipe. You might be able to use an "S" shaped adaptor on the outlet to adjust the tailpipe. If exiting in front of the rear wheels it might work. At 4 inches depth it will hang down more than my Spintechs - but no more than most.

Here are a few pictures from my mock up. No - my tailpipes will not be PVC.

[strictlypersonl]

I found some Magnaflow mufflers that look close. Note that they are 4" tall, so they will hang below the chassis a bit. Also note (in case there are some lurkers with other than our late 427 model), that early (pre-731) 427s, FIAs and Slabsides only have room for a 14" long muffler.

Universal design
XL Series

I don't know the performance difference between those designs, but the second one is available in a longer case. I'm also assuming that the oval XL series can have the flow in either direction.

[RodKnock]

Originally Posted by DanEC

No - my tailpipes will not be PVC.

Well, you never know. I think Patrick used PVC for his roll bars, though it's hard to tell with the PVC insulation wrap around them.

BTW, Dan, really nice work.

[DanEC]

Originally Posted by RodKnock

Well, you never know. I think Patrick used PVC for his roll bars, though it's hard to tell with the PVC insulation wrap around them.

BTW, Dan, really nice work.

Thanks - I hope to have some pictures of the complete system in a few weeks.