JoeW

I've been reading about the secondary bypass pipes folk have been using for streetable (cat) versions of the stock exhaust. I wonder which ones you've liked? Any reviews or places for a good price? J

Doug H

My GHL simply came with its own pipe that angled right out the slot. No need for a G-Pipe or anything except the primary muffler itself. Its very clean.

Eric Kessel

My 90 C2 came with a B&B primary with the secondary bypass built in. I found it kinda loud (the sound wasn't bad, just loud........ or maybe i'm getting old.......), and have replaced it with a factory primary that I found used with a no name J pipe, which sounds good, and definitely not quiet, but no where near as loud as the B&B.

Joe, if you'd like to try the B&B, it's still sitting out in my shed....... let me know.
-Eric

Darrell E

I am currently running a Dansk primary bypass with stock secondary muffler and like it very much. Nice and throaty but no resonance. My RSA originally came with the stock primary muffler and a Ruf secondary bypass. I found this setup to have more resonance. The car sounded more like a motorboat. Additionally, a friend of mine tested his RSA with both configurations on a deserted road with a borrowed police radar gun (don't ask ) and found the primary bypass with secondary muffler to have the best top speed.

JoeW

The primary bypass gives a bit more hp, or so it seems is the consensus of comments I've picked up here. The secondary bypass adds a bit of midrange and low end torque ... what I'm after here, though I do hope the resonance isn't an issue with all of them.

Thanks, Eric, I'll keep it in mind. We need to get a drive together of all the locals this spring/summer, don't you think? J

Eric Kessel

Joe,
Sounds like a good plan to me. Are you (Or anyone else from the area) going on the NER/PCA Ramble this spring?
-Eric

Bob Krantz

I have the GHL 2ndry bypass. Part of my motivation was getting rid of the stock 2ndry muffler, which caught a lot of snow and crud on top (a bigger problem when I lived in Alaska, not an issue in Houston). The sound is louder but not unpleasant, and honestly I don't think I can feel any acceleration change. What I don't like about the GHL unit is that it is made from 2 pipe sections welded together at a fairly sharp angle--not a smooth radius bend like some (for example, the Dansk unit). I don't know how this affects air flow, but my instincts say smoother is better.
Bob K
1989 C4

Doug H

I may be wrong, but the GHL primary seemed to have a much smoother looking secondary bypass with a bend that seemed not tight as the one present on the G-Pipe. Here is a pic.

joey bagadonuts

Good point, Doug.



However, I have one of these on my car and even with the 180 degree bend, the thing seems to work all right. I ran some G-Tech tests and, off the line, the g-pipe seems to be quicker. Top-end hp may be a different story but that doesn't sound like what you're after. I also prefer the sound of the secondary--the cup pipe sounds a little sloppy, IMHO.

Here are the G-Tech numbers:

Stock chip, stock exhaust and airbox w/ holes
Avg 0-60: 5.4

Stock chip, primary bypass and airbox w/ holes
Avg 0-60: 5.8

GIAC chip, primary bypass and airbox w/ holes
Avg 0-60: 5.8

GIAC chip, secondary bypass and airbox w/ holes
Avg 0-60: 5.5

GIAC chip, secondary bypass and cone filter
Avg 0-60: 5.2

Doug H

I may be losing a little too much back pressure.

JoeW

Hi Joey,

So it's .3 due to the secondary bypass and .3 for the cone filter. Very interesting.

Which bypass is that a picture of? J

JoeW

Eric, you have a PM. J

joey bagadonuts

That's the g-pipe offered by Type-911 in the UK. I went that route because it cost about $130 w/ shipping about a year ago--now the exchange rate isn't as favorable. The good news is that Performance Products now offers one for $155 + shipping in their latest catalog.

As for the 0-60 improvements, while I was pretty careful and consistent with my test methodology, I'd stop short of saying everyone should expect similar results. I also have an aftermarket chip which was programmed with this intake/exhaust combination in mind, so I'd say it's the whole system which is producing the good results.

Subsequently, I removed the catalytic converter and feel I'm closing in on 5 seconds flat. Unfortunately, I broke my G-Tech while lugging it around in my track bag and have not been able to confirm the extra grunt. For the two exhaust pieces, filter and chip, the tab is approaching $1K but I'm very pleased with the car's performance. Again, YMMV.

Doug H

Removal of the cat or a cat by-pass is a good move for more torque and/or improvement of performance.

Wachuko

Soooo, what is the overall recommendation here?? My car came with the stock cat, stock primary, and a secondary homemade by-pass that I have been meaning to replace with one of those G-pipes (not the same diameter as the rest of the muffler... so it is like blowing thru a straw if you know what I mean...) so not like I can swap primary for a by-pass and use the secondary muffler (unless I find a second-hand stock secondary).

I am also concern with keeping enough back pressure...

So... put a cat by pass and G-pipe and keep the stock primary (seems to be the less expensive route but what about back pressure... will this setup provide enough??) or cat by pass, primary by-pass, and stock secondary???