Underbody Exhaust Help...ERA 427 Street

[427 Street]

Hi All...my first post. In fact, I have not even picked up my car yet. I think it will be ready on Tuesday, and hopefully the weather will cooperate.

I will post the details about my new car when I do a formal introduction, but I had a quick question about underbody exhaust. I really prefer the smooth yet tough look of the street cars, and ERA makes a beautiful example. With that said, the underbody exhaust goes along with this version, either rear exiting or side exiting. Mine are side exiting in front of the rear tires.

So the only thing I do not like is the sound note of the exhaust system.

Does anybody know what my muffler limitations are on an ERA car? I am really intrigued with the Classic Chambered exhaust system, but I am not sure if his mufflers will fit?

My car has a period correct vintage 500hp+ 427 side oiler. Even though I love the sound of side pipes, I knew I would not enjoy it after time, and I know my wife would not like it. I would like to it to have a deep rumble at idle and while cruising but still have it roar when I jump on it.

Any thoughts? Thank you. I am looking to contributing here in the future.

BTW: Until I take better pics, here are some quick cell phone pics when I first saw the car.

[lippy]

Hi,

I'm building an ERA too and considering a similar option. I believe they use a 2" Dynamax system and 2" pipes. Check out this post: Undercar exhaust exiting ahead of rear wheel

I also sent you a PM.

[blykins]

I would definitely look into another pipe/muffler option. A 2" diameter pipe is going to choke the poo-poo out of an engine. On a 500-600hp engine, I usually recommend around 3" exhaust.

With that being said, most sidepipes are killer restrictive as well and you usually can't even roll a golf ball through one.

I would have your builder or ERA look into some different options. There are oval pipe and muffler designs out now that will fit into small areas and increase flow area.

[DanEC]

I'm fitting a full 2-1/2 inch exhaust system - out the rear - to my ERA. The mufflers and headers are out being ceramic coated right now but I hope to have them back and hung within 30 days or so. Do you have the standard ERA Jag rear suspension or the ERA suspension? ERA says you can't run tailpipes with the ERA suspension, although I suspect if it was custom fabricated to run up real high up and over the rear half shafts - it might fit. But - I can't be sure. It's possible that run up that high the tires may start to hit the pipes even if the suspension clears them. So, if you don't have the Jag suspension you may be stuck with the exhaust turning out in front of the rear wheels. I'm managing to fit 2-1/2 inch tail pipes by virtue of using the Jag rear suspension and only running a 255/60-15 inch tire in the rear. Even then it is tight.

If the quality of the exhaust sound is the main issue, I don't know how much difference tailpipes will make in the car's sound. I'm using Spintech mufflers which I understand are pretty loud. The usual means of mellowing out a car's full length exhaust system sound (besides muffler selection) is to run an "H" or "X" pipe connecting both sides (and increase power slightly also). It probably wouldn't be impossible to do so on a Cobra - but it would be a real challenge.

[mdross1]

When building our car knowing we were going go with undercar exhaust used 1/8" plate welded flush with floor making for solid feel and never feel any heat from the mufflers.We used Stainless Specialties custom made stainless chambered mufflers 2 1/2" out the back.They sound just right.

[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.

[DanEC]

I thought that might be Chuck Brandt's car but his has rollbars. Here is a link to his build site. He went through some issues in fitting an undercar exhaust system and you might pick up some useful information from it. Nice looking car.

Chuck Brandt

[ollykiwi3]

gidday all
I am also building a project with underfloor mufflers.same reasons as most i guess,asthetics and noise. I have found some edelbrock mufflers which fit mine, between main rails and outriggers. using 2 1/4
" pipes all the way to back. I have a jag rear end and have manages to fit mine under the centre of the diff and then 90 deg out to rear end. all very tight, but I have built all myself, so was able to fit how i needed it. My biggest problem was,and still is with the floor to muffler clearance. I have a fibreglass floor, and only about 1/2" gap. I have just put on a heat shield by ACL Australia, but havent run it for long enough to see if it has improved.I see there are a few of us crazy buggers trying to do this, but has anyone got similar clearance issues and heat problems with the floor pan, and if so, do you have a remedey??
i am more than happy to spill the beans on what ive discovered to save someone else the grief.
I have to cut my outriggers(4"-3" c section) with a slot on the bottom web, then install a piece of half round(not quite half round) to go around the pipe for clearance. I too tried to keep it all above the bottom of the rails, but its not possible. centerline of 4" muffler is2", and if main rails are 4", that leaves no gap above muffler. the whole system has to be moved down a bit, or run those spintech mufflers to allow a gap. I didnt know they existed ubtil today, and they are too expensive for me here in NZ.
Anyway, what a ramble, but was really hoping someone could advise on heat shield issue, and I can help with you not making the same mistake as me.
cheers

[DanEC]

ERAs have aluminum floor pans so it's not quite as difficult for us. I coated mine with several coats of ceramic based Lizard Skin on the underside. And then on the top side I used a thin mastic damper-proofing and a double sided insulation layer by EZ Cool. With fiberglass floors I think I would apply something like the Lizard Skin material but also use a metal or aluminum heat shield between the muffler and floor. I'm also ceramic coating my head pipes and mufflers which I hope will knock a few degrees off of their external temperature when the car is running.

[427 Street]

Originally Posted by DanEC

ERAs have aluminum floor pans so it's not quite as difficult for us. I coated mine with several coats of ceramic based Lizard Skin on the underside. And then on the top side I used a thin mastic damper-proofing and a double sided insulation layer by EZ Cool. With fiberglass floors I think I would apply something like the Lizard Skin material but also use a metal or aluminum heat shield between the muffler and floor. I'm also ceramic coating my head pipes and mufflers which I hope will knock a few degrees off of their external temperature when the car is running.

Good tips.

Doug at ERA is the tech guru and he said that the stock mufflers are resonators from a '79 Trans-Am....when he said that, a bit of my breakfast came up . He said that they are a 14" body in length (not including the inlet/outlet), and that they are 3.75" thick. They are an offset inlet and a center outlet...2" in and 2" out.

He also said that most tubular glass-packs are 4" in diameter, so 1/4" should not make a huge difference. He also said that he is "pretty sure" I could fit a 24" muffler under the car.

I am really tempted to try try the Chambered Classic muffler after speaking with Eric. It seems like it is the best of both worlds for tone and volume. Eric is an engineer who worked at Dynomax for over 12 years, and I think he developed five of their current mufflers. He said that SIDE pipes are very restricting to flow, too loud for the street, and real HP suckers, but he started his company to change all of that.

So my underbody exhaust questions to all of you: What mufflers have people tried? What works? And what have you been happy with and sounds amazing?

[DanEC]

A 24 inch muffler would have to hang entirely below the chassis outriggers. My mufflers suck up between the outriggers in the pocket they form. Only the 2-1/2 inch pipes have to clear the outriggers. (See Bob's note above about the pocket measuring 19.25 inch). So I'm not sure I understand what Doug is saying about a 24 inch muffler fitting. That would put the mufflers about 1-1/4 inches lower than my mufflers at least. That is going to be hanging down pretty low.

[Green Hornet]

I have been through several exhaust systems on ERA 669. What I have found that works the best are the Mega Oval Mufflers from Stainless Specialities. They were very helpful and agreed to make me a set with an offset 2.5" inlet and a center 2.5"outlet. The mufflers measure 6.5" X 2.5" X 18" which fits between the rails perfectly with no modifications. I have fabricated headers and 2.5" over the axel pipes. All of it is ceramic coated in black which looks great and semi original. The mufflers sound great! Not too quiet, not too loud, Just a deep healthy tone.