Athenian.

Has anyone installed a later model (1987 and up) complete exhaust including the catalyst to an earlier (1982 - 1984) car??

Assuming it's possible, will there be any horsepower gains with the bigger exhaust??? Why do the GT cars have dual pipes coming out of the catalyst??? My '83 has only a single tube....why are their tubes so much longer than the early cars??

Thanks for your thoughts

Tony

2V4V

Tony,

I am currently finishing just such an update.
The list of stuff is...

1.SS tubular headers from 86
2.(slightly modified)GT cats (87+ got 2 separate cats)
3. 86 mid muffler (2 pipes in, 2 out)
4. Rear muffler is, as of tonight, undecided

I have HEARD of 15-20 hp gains, but until my rubber hits the dyno wheel, I won't place any bets on how much.

I am doing a few other projects on the car, so it may be a few more days before I know for sure.

Why bigger pipes? So as to exhale better.

Keep in mind the exit point of your rear muffler is off to the left, whereas the exit point of all the 87+ rear mufflers is to the rear (unless somebody special ordered a "Bo und Luke Duke" sidepipe package that I haven't seen yet). So you may not want to go any later than early 86, unless you wish to hack up your bumper cover.

HTH

Joe R

My 78 5speed is set up just like yours. What I did is put in a CAT by pass pipe and a Borla. Headers are in the plan just as soon as I rework (hog out the heads). Right now it sounds cooler don't know if it makes more horsepower. Did you consider an RMB vs a muffler?

Athenian.

Hey Joe and HTH

Thanks for your responses...One of my concers about the 87+ exhaust setup is the way the rear pipes rwist and turn away from each other and meet back again at the rear muffler....Is there enough clerance on the underside to install the later exhaust???

Yes, I have considered the RMB replacement and I will probably go with that...I don't see the need for 3 mufflers + the cat....I won't bother with the headers at this point.
A little too much $$$ for me.

Let me know how you make out with the installation and if you notice any HP gains.

Regards

Tony

Randy V

Good question Tony - I'm in the middle of this mod myself on my '79 convertible.

As you know, the early models have but a single pipe from the manifold merge to the tail pipe. This setup is routed to a single chamber cat down the center of the car, then veers to the left (driver's side), through the resonator then onwards to the rear muffler.

The early 32 valve engines ('85 and early '86 - not 86.5) went to a two pipe setup that utilizes a dual chamber cat, following the same routing as the 16 valve cars.

The 86.5 and later models utilize two complete and separate systems that are routed down each side of the car.

So, the answer is to either buy a complete used exhaust system from an '85 or early '86 that easily swaps with the stock single pipe setup without any modifications at all, or have a custom exhaust built using a Borla or similar setup with the dual chamber cat. That's assuming you are in a State that requires catalytic converters.

I went with a complete used system (including the heat shields) from an early '86. The stock Porsche exhaust systems are fabricated completely from stainless steel, so they last forever, compared to some after market systems.

I'll let you know how my car performs after the switch next week - I may have the performance shop do dyno runs before and after to get some real world numbers.

Jim V

The '87+ systems don't look like they'd be
an easy fit, the spots for the front muffler
on both sides is much smaller on the early
cars than the S4 up.
Also where the R.S. must cross back over at
the front of the trans is quite a bit tighter.
If you do get a system like the to work,please let us know I've been thinking
along the same line.