Under Car Rear Exhaust on MK4 Roadster?

[Hoschton Hotrod Haus]

Has anyone done undercar rear exit exhaust on a MK4 Roadster?

[frd2]

Love mine. Coyote with Irs. Helps with noise and smell. No snake bite either.

[Lancaster Lad]

Am still under construction but also with new IRS. Following other builds in the past I drilled holes in rear
cross member than lined with 3 IN tubing. I had a muffler shop run exhaust between engine and 4 IN rails,
through the rear cross member angle to center to go under center section than angle out to go around the
fuel tank. He put small Flowmaster mufflers on the side of fuel tank then on to the rear similar to the
original street Cobras.
One problem is with these being cars lower than the originals is flatbeding. When we loaded the car the
tailpipes just touched the ground and unloading was even more fun.
I plan to wrap the muffler and the pipes next to the trans with heat blanket.

[Hoschton Hotrod Haus]

Do you have any under car photos showing the arrangement?

[mlewis]

Check out Dukes build thread

http://https://thefactoryfiveforum.com/showthread.php?19953-8793-MK4-Build-(-15-IRS-16-Coyote-15-quot-wheels)

Don’t know it I pasted the link, so you can search for this:

https://thefactoryfiveforum.com/showthread.php?19953-8793-MK4-Build-(-15-IRS-16-Coyote-15-quot-wheels)

[Joecobr]

Do a Google search...lots of leads to good information.

[Lancaster Lad]

HOTROD
Here are some photos of someone else and I don't know who that I used for an example.
The difference is that it is a solid axle, with IRS no room for muffler in that location.

https://thefactoryfiveforum.com/attachment.php?attachmentid=141337&d=1611514459
https://thefactoryfiveforum.com/attachment.php?attachmentid=141337&d=1611514459
https://thefactoryfiveforum.com/attachment.php?attachmentid=141335&d=1611514268
https://thefactoryfiveforum.com/attachment.php?attachmentid=141339&d=1611514500

The next is where my muffler is.

https://thefactoryfiveforum.com/attachment.php?attachmentid=141348&d=1611517256
https://thefactoryfiveforum.com/attachment.php?attachmentid=141349&d=1611517275

I hope this works, first time trying to post pictures.
Need to edit previous post the hole drilled is 3 1/4IN.

If pictures do not work then you can look in my just loaded gallery.

[65 Cobra Dude]

Spintech makes ovalized tubing and thin mufflers that work well. It’s not cheap but you get what you pay for. I’ll look for under car pics when I get home. 141352
Coyote with Tremec and 3 link. Pipes coming out in front of the wheels.

Thx,

Henry

[Jim1855]

I like it. Put similar but smaller holes through my frame, not for exhaust though, then added some diagonal bracing between the cross and side tubes.

Just an FYI. A number of years ago I had a chance to drive another Superformance car with rear exhaust, he also had a 427W but with stacked injection. That owner drove my carb'd, side exhaust Superformance. Pretty much the same cars except for induction and exhaust. Huge difference, quiet, smooth power compared to my loud and snarly. I liked his, don't think he liked mine.

I hope the rear exhaust does everything you're looking for, lots of work. Now you just need to tame the wind noise.

Jim

[John4337]

I did it, Mk4 with IRS. Not too difficult. 2 1/4 inch pipe with Spintech cruiser mufflers, also 2 1/4 inch thick. Ford shorty headers flipped to dump at the front. I have about 20000 miles on this, no issues.

From header. Blue tape was for mock up

https://thefactoryfiveforum.com/attachment.php?attachmentid=141360&d=1611530470

Muffler
https://thefactoryfiveforum.com/attachment.php?attachmentid=141361&d=1611530554

Home made hanger
https://thefactoryfiveforum.com/attachment.php?attachmentid=141362&d=1611530601

DS out for paint, you can see the swing in at the back to clear the LCA.
https://thefactoryfiveforum.com/attachment.php?attachmentid=141363&d=1611530666

Here’s a side shot, exhaust exits just behind rear wheels.
https://thefactoryfiveforum.com/attachment.php?attachmentid=141365&d=1611531680

[CobraboyDR]

I did it, Mk4 with IRS. Not too difficult. 2 1/4 inch pipe with Spintech cruiser mufflers, also 2 1/4 inch thick. Ford shorty headers flipped to dump at the front. I have about 20000 miles on this, no issues.

From header. Blue tape was for mock up

Very clean. What is your ground clearance?

[John4337]

3 1/4 at the mufflers

[Hoschton Hotrod Haus]

Thanks John4337!
That is EXACTLY what I was looking for!

[John4337]

Very welcome, if you need anything else, I’ll be happy to help. If you’re running a a SBF, remember to order the 90 degree oil filter adaptor. You can see mine in the first photo.

[Hoschton Hotrod Haus]

Do you have any photos of the tailpipe install (ie. over the rear axle and the exit out the back)

[John4337]

I’ll try to get some. My car is IRS, so I just used 45’s to turn in toward the center of the car under the lower control arms. I built the system with the car on jack stands with the suspension at full droop to avoid any clearance issues.

You can see the exhaust exit a bit better here. I originally had the exit at the back, but I wasn’t happy the the hangers I made, actually had one break on a trip. Re doing it out the back is on my to do list.

https://thefactoryfiveforum.com/attachment.php?attachmentid=141495&d=1611709702

[Duke]

Has anyone done undercar rear exit exhaust on a MK4 Roadster?

yup, see my build thread. Spintech mufflers, had a local exhaust shop bend and hang the pipes.

[John4337]

yup, see my build thread. Spintech mufflers, had a local exhaust shop bend and hang the pipes.

Your car looks sweet. I tried the local shop approach, went to 3 so called custom muffler/exhaust shops in WPB, none would even look at it. Ended up doing it myself.

[John4337]

Do you have any photos of the tailpipe install (ie. over the rear axle and the exit out the back)

This is from under the bumper. Not sure why the gallery rotated it, or how to fix it.
https://thefactoryfiveforum.com/attachment.php?attachmentid=141526&d=1611765355

[Vspeeds]

I did it, Mk4 with IRS. Not too difficult. 2 1/4 inch pipe with Spintech cruiser mufflers, also 2 1/4 inch thick. Ford shorty headers flipped to dump at the front. I have about 20000 miles on this, no issues.

From header. Blue tape was for mock up

https://thefactoryfiveforum.com/attachment.php?attachmentid=141360&d=1611530470

Muffler
https://thefactoryfiveforum.com/attachment.php?attachmentid=141361&d=1611530554

Home made hanger
https://thefactoryfiveforum.com/attachment.php?attachmentid=141362&d=1611530601

DS out for paint, you can see the swing in at the back to clear the LCA.
https://thefactoryfiveforum.com/attachment.php?attachmentid=141363&d=1611530666

Here’s a side shot, exhaust exits just behind rear wheels.
https://thefactoryfiveforum.com/attachment.php?attachmentid=141365&d=1611531680

Wow! Great job. I have the 289 kit and this would have worked well if I did IRS

[JohnK]

HOTROD
Here are some photos of someone else and I don't know who that I used for an example.
The difference is that it is a solid axle, with IRS no room for muffler in that location.

https://thefactoryfiveforum.com/attachment.php?attachmentid=141337&d=1611514459




I've gotta say, it takes a LOT of stones to drill holes that large in the 4" crossmember. I have no idea how much structural integrity the welded-in sleeves add back, but kudos to you for blazing that trail. :D

If FFR ever comes out with a MkV, I'd love to see a frame design that's more conducive to an undercar exhaust, as it really opens up a whole new look for the car without the side pipes.

[Hoschton Hotrod Haus]

Thank John,
That looks very doable in my own shop!

[CobraboyDR]

I've gotta say, it takes a LOT of stones to drill holes that large in the 4" crossmember. I have no idea how much structural integrity the welded-in sleeves add back, but kudos to you for blazing that trail. :D
I recall the C2 & C3 'Vettes had large holes in round crossmembers for exhaust pass-through. I have not heard of any frame failures from them. The Mk4 is even lighter than the 'Vette so I doubt any problems will crop up.

I may be wrong, but from what I can tell it's the gas tank that prevents a full out-the-back exhaust. One wonders the possibility of a reconfigured gas tank that allows UCE.


If FFR ever comes out with a MkV, I'd love to see a frame design that's more conducive to an undercar exhaust, as it really opens up a whole new look for the car without the side pipes.Ditto! And add to the Mk5 wish list: a 15" pin-drive option for IRS. I do believe "traditional" Cobra replica enthusiasts would find that option hard to resist.

What I would give for a FFR MkV street roadster, clean with no hood scoop, sidepipes or roll bar, and an IRS suspension with 15" pin-drive wheels. Or even a configuration engineered for a bolt-in Jag IRS suspension/brakes.

A guy can dream, can't he? :D

[John4337]

I may be wrong, but from what I can tell it's the gas tank that prevents a full out-the-back exhaust. One wonders the possibility of a reconfigured gas tank that allows UCE.

This was my first setup. There’s room, I just couldn’t get a good hanger set up. I still want to make another run at it.

https://thefactoryfiveforum.com/attachment.php?attachmentid=141564&d=1611838968

[CobraboyDR]

This was my first setup. There’s room, I just couldn’t get a good hanger set up. I still want to make another run at it.

https://thefactoryfiveforum.com/attachment.php?attachmentid=141564&d=1611838968I love the look, but 3.25" of ground clearance is concerning. 4.5" is less daunting.

Clearance aside, you did an excellent, clean job. :)

[D Stand]

I love the look, but 3.25" of ground clearance is concerning. 4.5" is less daunting.

Clearance aside, you did an excellent, clean job. :)

Nice work on the exhaust but this is really an awesome photo!

[JMA0517]

I know this is a bit old, but really helpful in planning my build. I have been off and on the forum with various handles (would forget which login with which email acct, etc) since just before the MK 3 was introduced, and it looks like the problem of undercar exhaust for IRS is finally getting worked out. That is a relief for me, since I want a classic “street” look.

[JMA0517]

Was the MA RMV and MAC info ever posted?