joey bagadonuts

Back in June, I swapped out my stock primary muffler for a Ruf bypass pipe, aka cup pipe. I liked the new growl and supposedly it gave me some extra top-end umph (technical term), so in general, I was pleased with the change.

That is until my last autocross. After coming out of some slow turns in 2nd gear, my car sounded like it was gasping for air and managed a cough or two before getting back into the torque band. What's that all about? I'd also gotten tired of those extra sputters and that faint cough as I backed off the throttle between gear changes. Sometimes, I must admit, these coughs actually sounded like backfires but Porsches don't do that, right?

I had previously drilled my airbox and thought, "What the hell, this couldn't make it any worse." So I got out my trusty jigsaw and cut off the entire side in Cup fashion. I'd say it looks just like the Fabspeed item, but that would be a bit of an exaggeration.

I then installed the new "cup" box and bam! ... no more sputter or backfire!

AND, to my amazement, shifting became much smoother. Only after I made the change did I realize that lifting between gears resulted in a rapid decline in revs. This sudden drop made for some pretty jerky upshifting. With my new "cup" box, the revs now drop at a more moderate rate which allows for a much smoother gear change.

Finally, throttle blips are once again instantaneous and my baby idles a helluva' lot smoother than before. There was no increase in interior sound and I'm sure I gained at least 50 hp, but who's got time for a dyno?

Your experience may vary and this certainly could have been a fluke. I know the relationship between induction and exhaust is a relatively complex issue, so I won't offer any conclusions. All I'll say is that I'm very pleased with the outcome and hope others might find some value in this information.

peter_964rs

I have both the Cup airbox and a Cup bypass pipe. The pipe gave a big midrange increase on my car, very satisfying, as well as the pleasing extra "gruffness" of the engine!

The Cup airbox was installed much later and made relatively little difference, apart from the sound. The engine pulls very slightly better over 5000rpm, but slightly worse just before. It is as though the "coming on song" part of the power delivery is accentuated. There is a louder "scream" once it has come on song, as well.

I'd recommend the Cup bypass pipe to anybody, but the Cup airbox is a bit more of a mixed bag to me. I never had your hesitancy problems with just the pipe installed.

Bob Haase

Do most folks on this list install their own cup bypass pipe, or have their mechanic handle the project. It is a difficult DIY project for the average person?

PS... moderators, might I suggest an "instant graemlin" that has a grimacing head holding a hammer that is busting up his project-du-jour. Just a thought

J-McDonald

I've heard from some that the cup bypass pipe may reduce low-end torque but increase higher-rpm performance. Could anyone who put on a cup bypass pipe comment on this?

joey bagadonuts

Here's Joel Reiser's take on this from the PCA website:

[quote] As I've reported elsewhere, the Cup cars used bypass pipes for each muffler. Bypassing the first one was said to add 10 hp at the top end of the range. Bypassing the second one was said to add 10 foot pounds of torque in the lower and middle part of the range. Bypassing both was said to lose the tuning, make lots of noise, and cancel out both power gains entirely. For a track car this is OK if your goal is to make it sound like a race is happening, even in the infield anytime you start the car. I recommend to replace the entire exhaust system if you really want 25 hp, but if you want to "take what the defense will give you", and keep the budget under control, replace only the final muffler with the U-shaped bypass pipe. This will make a louder deeper sound, but not outrageously so. I have friends who drove their 964s around perfectly civilized areas of Toronto for years without offending anyone. This change also saves close to 20 pounds, so the car will definitely be faster just for that reason.

Usually when we say we want more horsepower, we really mean we want more torque. Horsepower is what we need lot of to get another 10 mph at the END (not the beginning) of the straightaway or our top speed on the Autobahn. Torque is what you need to accelerate the car. I like both, but since I can't use top speed much in my cars, I go for torque if there's a choice. In this case there is, its the choice of which muffler to bypass. <hr></blockquote>

joey bagadonuts

Bob,

Here's the Tom Sharpes DIY from the Pelican Parts Tech section:

<a href="http://www.pelicanparts.com/techarticles/964_muffler_bypass/964_muffler_bypass.htm" target="_blank">Cup Pipe Installation</a>

Of course, I had my guy do it since he had it on the rack already, but it looks like a straightforward job.

Bob Haase

Thanks, Joey... I guess I'm afraid to hurt my baby. Ever started a project that ended up making things worse? Here's the graemlin/gremlin that I made on my computer this morning (moderators, feel free to take and use!)

jonfkaminsky

Bob-
its an easy job provided you can jack the back of the car up. I've had mine in and out on numerous occasions when I was doing the performance enhancements study last fall. I can give you a hand if you want to do it.

jon

scupper

Joey - who manufactured your final muffler cup bypass pipe? GLH, Dansk, FabSpeed? Where did you purchase it? Are you running a tip extension with it, or just the pipe coming out thru the rear valance?

Chuck

joey bagadonuts

I got a very nice deal from a fellow Rennlister, David K, when I asked the board which one to go with. It was a used Ruf item which I guess is a good make, but I've heard the Dansk and Fabspeed pipes are good-quality as well. Shop around because some of these guys want $350 for this thing but, jeez, it looks like something you could pick up at the plumbing department of your local hardware store.

As for the installation, a couple posts above I've included a link to Tom Sharpes cup pipe hack which includes pictures. This pipe replaces the primary muffler, the one that sits below the bumper, and then reconnects to the final muffler/tailpipe assembly which remain unchanged.

Bob Haase

Jon, thanks for the offer! I'll take you up on it. I caught a sale at Sears and purchased a 3.5 ton floor jack and stands. I'll hook up with you when I'm ready.

To Everyone: Which cup pipe will give the most deep rumble sound? I've always been amazed at these kids with their "tuned" exhaust systems... they get a deep throat sound out of a small 4-cylinder engine. Any ideas?

scupper

Joey -
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Help me clear my fogged brain.
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Primary muffler = long muffler below the rear valance - as depticted in Tom Sharp's tech session. Sits between the Cat and the Secondary Muffler.
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Secondary muffler = box type muffler located in the right fender - input from the primary muffler above and output goes to the exhaust tip in the valance.
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Now - you said you changed your "Final" muffler for increased torque. Are you calling the primary muffler or the secondary muffler the "final" muffler?
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Thanks, Joey!

Cheers

joey bagadonuts

Yes, lot's of info to sort through.

I replaced the primary muffler on my car with a cup pipe. That's the muffler located under the bumper/valance which when replaced supposedly yields extra top-end hp.

Replacement of the final/secondary/box-type muffler with a bypass pipe will suppposedly provide better low-end torque. This is the u-shaped pipe which connects the primary directly to the tailpipe. Here are the items featured in <a href="http://www.fvd-usa.com/catalog/sound_964/index.html" target="_blank">FVD's online catalog.</a>

Hope that helps.

GP964

Hello folks,

After reading this topic, Im wondering if im losing hp or torque or both.

I have a 90C2 with

Intake: Autothority MAF

Exhaust: No Cat "straight pipe" leading to a dual Tezet muffler then leading to the secondary muffler (right rear square muffler).
I have the U joint that bypasses the secondary muffler but haven't placed it yet.


Question 1-With the current setup (no cat, tezet dual outlet, but the right outlet connect to the secondary muffler. am i losing torque? or hp?

Question 2- if i installed the U-joint from the Tezet muffler basically bypassing the secondary muffler will i gain or lose anything?

Any help would be great.

Thanks
GP