MK5 Under car exhaust

[cfriedman67]

I know it’s early but has anyone tried to do the exhaust under the car?

[Jeff Kleiner]

I know it’s early but has anyone tried to do the exhaust under the car?

Not possible with the flat bottom chassis.

Jeff

[cfriedman67]

Thanks

[Grubester]

Not sure on a Mk5, but on my Mk4 289-style w/BP347 and IRS, I'm doing out-the-rear exhaust.
Still designing it but I like the fit-up of an oval section created from a 3" dia. tube (0.062" wall).
When formed into an oval-section 1.5" thick, it is still 6% greater area than a 2.5" dia. round pipe, which would be normally used for a 347.
A common 2x4 works to "model" the exhaust pipe down the length of the chassis. There is clearance for custom hangers and does not hang lower than the bottom of the 4" chassis frame tubes.
Closest point is where it crosses under the IRS toe link.
However, muffler choices are still elusive. SpinTech, Flowmaster, MagnaFlo -- talked w/them all... still considering options.
Vibrant only supplies S.S. tubing in ovals, so I'm going to form my own with a hydraulic press and an "extensible internal mandrel" (still working on details)
***Pic of concept piece section, laid up against a 2x4.
218327

[michael everson]

Not a chance on the Mark 5
Mike

[Kbl7td]

Someone did it with the coupe.

[Grubester]

You and Jeff seem to make that clear. Too bad Factory 5 has foreclosed that option.

[Busydoingnothing]

Ok. I was hoping that under the car and out the back was possible. If anyone has any additional thoughts on this topic, please say so before I order a kit. Sounds like if I do not want the side pipes, it’s going to be a 289 or MK4 427 kit.

[J R Jones]

BDN, I am not a fan of side exhaust, the proximity to my ears, the tone or the hot surface.
My recently acquired AC project had an undercar exhaust but it was not pleasant to my ear. It had four glass pack mufflers plus two resonator tips (more glass packs).
Reviewing muffler performance I was impressed with the diversity of applications from Flowmaster. Lots of development in their product line. As you would guess the more sophisticated the muffler the more sound management. An independent evaluator has done comparisons on YouTube. Limited by tight packaging I picked the Delta Flow 50 with three chambers.
I have a 2.25 diameter crossover pipe near the front, I retained two of the glass packs and I added two Delta 50s. Flowmaster recommends 12 inches of tailpipe behind the mufflers but aesthetics limit me to seven inches. The tailpipes do make a difference.
I find the idle menacing and loud enough to get attention. At cruise there is little or no exhaust noise in the cockpit. WOT sound is linear with RPM and the four barrel sets it off.
I feel the two banks plumbed with tailpipes close together accentuates V8 sound, not like two four cylinders. That plumbing format works better with my IRS.
BTW the engine is a 302 with Edelbrock heads and intake, likely 335hp with long tube primaries.
jim
https://drive.google.com/file/d/1cYlt2fJwG7lHIY6nzDgbS6THabGBO8zW/view?usp=drive_link

[CraigS]

Jeff and Michael if not under the car how about through the car like a C7 Corvette? It would be a real project getting all the bends correct but maybe?

[Jeff Kleiner]

Jeff and Michael if not under the car how about through the car like a C7 Corvette? It would be a real project getting all the bends correct but maybe?

Not enough space in the tunnel so it would have to go through the passenger compartment. On the plus side that would eliminate the need for a heater :p

Jeff

[ggunter]

There was one guy here on the forum who made a very elaborate muffler system that was in the area between the rad and the engine with pipes coming out in the same area as the side pipes but only one pipe each side. Listening to the YouTube video of the sound it was quite remarkable how it came out. A lot of work but if you're not liking the sound maybe another way to go.

[Jeff Kleiner]

There was one guy here on the forum who made a very elaborate muffler system that was in the area between the rad and the engine with pipes coming out in the same area as the side pipes but only one pipe each side. Listening to the YouTube video of the sound it was quite remarkable how it came out. A lot of work but if you're not liking the sound maybe another way to go.

OR>>>build a Mk4. Just sayin' ;)

Jeff

[ggunter]

Now here's a wild idea... just think if you could use the 4" tubes of a MKIV frame as the exhaust. Slide a chambered glass pack up inside, cut in an exhaust flange in the front with a flexible connection to the J pipe. Cut in a tail pipe in the rear and presto under car exhaust. Might have to wrap the frame tube to keep the heat off your butt.

[ggunter]

Of course that won't work with a MKV. Sorry I'll be quiet now.....

[egchewy79]

Now here's a wild idea... just think if you could use the 4" tubes of a MKIV frame as the exhaust. Slide a chambered glass pack up inside, cut in an exhaust flange in the front with a flexible connection to the J pipe. Cut in a tail pipe in the rear and presto under car exhaust. Might have to wrap the frame tube to keep the heat off your butt.

I feel like it'd be too much heat in the cockpit/floor.

[Jeff Kleiner]

Condensation and resulting rust inside the 4” tubes.

Jeff

[JJK]

To Jeff's point, each gallon of gasoline releases approximately a gallon of water vapor in the exhaust. Definitely need to ensure the metal in your exhaust system is appropriately treated to accommodate the moisture.

[ggunter]

Wasn't a real idea, just being facetious.

[CraigS]

Not enough space in the tunnel so it would have to go through the passenger compartment.

On the plus side that would eliminate the need for a heater :p

Jeff
Good one Jeff :D

[CW_MI]

I just saw a post on FB where the builder did a full under the car exhaust, with tailpipes (four) that exited under the center of the body at the rear. I asked for details, and if they had a build thread on here and haven't heard anything back. Unable to find the post now.

Found the one I was looking for, and some others. All look like they are MIV builds. Some awesome examples of fabrications skills though.

Forte
https://www.facebook.com/share/r/1EBFr7K1UU/

Some others.
https://www.facebook.com/share/p/173xsH1NwE/

https://www.facebook.com/share/p/19VUbhEJ15/

https://www.facebook.com/share/p/14JtLRt1Hqh/

[PG_Cobra]

Twin exit on my Mk1. Exhaust is inboard of the frame rails, transverse 2 chamber muffler, all in 2.5".219073

[JTG]

There was one guy here on the forum who made a very elaborate muffler system that was in the area between the rad and the engine with pipes coming out in the same area as the side pipes but only one pipe each side. Listening to the YouTube video of the sound it was quite remarkable how it came out. A lot of work but if you're not liking the sound maybe another way to go.

Are you talking about this guy up in Maine? I'm impressed by his work, and clearly he's aiming to please no one but himself. I can respect that!

Random Werks (https://www.youtube.com/watch?v=DgC1ER1ev9U)

[ProfessorB]

Now here's a wild idea... just think if you could use the 4" tubes of a MKIV frame as the exhaust. Slide a chambered glass pack up inside, cut in an exhaust flange in the front with a flexible connection to the J pipe. Cut in a tail pipe in the rear and presto under car exhaust. Might have to wrap the frame tube to keep the heat off your butt.

It IS a wild idea, but from such ideas come some great ideas. Back in the Seventies, at some point, Triumph and BSA motorcycles eliminated the oil tank and oil "storage" was in the motorcycle frame itself.