Secondary bypass -- what do you like?
02-27-2004, 10:09 PM
#17
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Originally posted by Wachuko
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???
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???
When I combine the comments here, especially Joey's experiments, along with the posts I read from similar discussions when I did several searches, I think that, depending on what you want for noise, horsepower, and torque, leaving the primary and taking the secondary gives a bit more torque and a bit more rumble.
Leaving the secondary and taking the primary is a bit louder still, gives a little more horsepower (but not torque).
Removing both is obviously louder and seems to give poorer results than either bypass by itself. (Fabspeed seems to disagree with this on their website, perhaps because they want to sell bypass pipes.
)Removing the cat seems to be noisy enough it's probably only good for track, and the removal of the cat seems to intensify the effect downstream.
If I goofed any of this up, I hope someone will let me know.
I experienced a great setup a couple of weeks ago: a fellow in NH (no emissions testing) had B&B headers w/no cats and a Fabspeed dual exhaust. Loud for sure, but full of authority, and (combined with a chip) what a powerhouse! If I didn't live in Mass., that's what I'd want. J
02-27-2004, 11:51 PM
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I have done it both ways. I bought the car with a primary bypass and the secondary muffler with a sport (100 cell ???) cat. I then went to GHL and no secondary. Noise wise was comparable. Maybe a tad bit louder with primary bypass. Powerwise, very similar also and maybe a just a hair faster with primary and secondary bypass.
I changed out sport cat with cat by-pass without realizing I already had the sport cat. Didn't know this until they went to take it off. The car is louder now and has a great sound. The service manager at my dealer drove my car today and commented on how great it sounded. He is more of the conservative type that deals mainly with new cars and I don't think he would have liked it so much if it would have been too loud.
Unfortunately, I cannot really comment on performance gains by cat by-pass over sport cat because I had other engine work done at the same time. My shop said absolutely not a concern with too little back pressure with this set-up for what its worth.
My car is a torque monster right now. The torque is about the same as the hp which to me in preferrable for accelleration 0 - 60 purposes. If you are shooting for good low end grunt and quick accelleration, I would go ahead and do cat by-pass and secondary by-pass. HP is over rated in my opinion in that it seems what everyone focuses on. I would rather have a great torque curve with lots of low end torque. My torque comes on real early and hovers between 235 and 245 at the rear wheels from 3,800 RPMs and it stays virtually flat until around 5,400 or so. If I recall correctly, it was over 200 at the rear wheels around 3,000. No waiting for power, this things hits full accelleration at around 3,000 and pulls with a constant pull until about 6,200. I am hoping Lenz will cure the drop off I have at around 6,200.
I changed out sport cat with cat by-pass without realizing I already had the sport cat. Didn't know this until they went to take it off. The car is louder now and has a great sound. The service manager at my dealer drove my car today and commented on how great it sounded. He is more of the conservative type that deals mainly with new cars and I don't think he would have liked it so much if it would have been too loud.
Unfortunately, I cannot really comment on performance gains by cat by-pass over sport cat because I had other engine work done at the same time. My shop said absolutely not a concern with too little back pressure with this set-up for what its worth.
My car is a torque monster right now. The torque is about the same as the hp which to me in preferrable for accelleration 0 - 60 purposes. If you are shooting for good low end grunt and quick accelleration, I would go ahead and do cat by-pass and secondary by-pass. HP is over rated in my opinion in that it seems what everyone focuses on. I would rather have a great torque curve with lots of low end torque. My torque comes on real early and hovers between 235 and 245 at the rear wheels from 3,800 RPMs and it stays virtually flat until around 5,400 or so. If I recall correctly, it was over 200 at the rear wheels around 3,000. No waiting for power, this things hits full accelleration at around 3,000 and pulls with a constant pull until about 6,200. I am hoping Lenz will cure the drop off I have at around 6,200.
02-28-2004, 04:14 PM
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That sounds (oops 
) great for NA, Joey. Unfortunately, the cat bypass is not streetable in an emissions control state. Other than that, I'm planning a similar layout to what you have.
Doug, you do not deserve your car.
Send it to me. 
J
) great for NA, Joey. Unfortunately, the cat bypass is not streetable in an emissions control state. Other than that, I'm planning a similar layout to what you have.Doug, you do not deserve your car.
Send it to me. J
02-28-2004, 08:37 PM
#21
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FWIW, I use Fabspeed's Euro Pre-Muffler, kinda looks like a catalytic converter (kinda) and has the "bung" for the O2 sensor. 
For my muffler, I have a FACTORY primary muffler that Fabspeed took and welded their tip on, so it goes directly out the bumper slot for the tailpipe and there's no need for a secondary bypass.
I LOVE the sound...and others seem to as well, I get LOTS of compliments on the sound. I would have to say, coupled with the custom chip I have from Cyntex, it makes a nice combo.
No HP claims, just "butt-dyno" claims...it seems my 964 can out pull most on the straights...that's ALL I need to know.
For my muffler, I have a FACTORY primary muffler that Fabspeed took and welded their tip on, so it goes directly out the bumper slot for the tailpipe and there's no need for a secondary bypass.
I LOVE the sound...and others seem to as well, I get LOTS of compliments on the sound. I would have to say, coupled with the custom chip I have from Cyntex, it makes a nice combo.
No HP claims, just "butt-dyno" claims...it seems my 964 can out pull most on the straights...that's ALL I need to know.
02-28-2004, 08:52 PM
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Hi Jeff, I think this pipe is what Fabspeed calls a 'J' pipe, right? How do you think it would work for the street (i.e., with cats) -- do you get resonance? (I've read a discussion elsewhere that resonance was behind the design of the 'G' pipe design.) Any reaction to all that? J
02-28-2004, 09:42 PM
#23
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Joe, I have NO "bypasses" per say on MY 964, just a baffled design, what Fabspeed refers to as a "Euro" Pre-muffler (a catalytic bypass, for all intended purposes, but a bit quieter) and a FACTORY primary muffler (the one in the middle, furthest rear) with their tip welded on it, instead of the curved pipe that would normally lead over to the secondary muffler (which would then require one of the "J" or "G" pipes that several are referring to.
The simple idea of welding on a nice Fabspeed tip to a factory primary eliminates the need for all these "accessories".
...and I don't have that abrupt bend either.
FYI, I'm not trying to "plug" Fabspeed products, it just so happens that's what I have...they work great, and to date, have lasted over two years, 50+ track events, a few autocrosses and gets me to work and back on time.
The simple idea of welding on a nice Fabspeed tip to a factory primary eliminates the need for all these "accessories".
...and I don't have that abrupt bend either.
FYI, I'm not trying to "plug" Fabspeed products, it just so happens that's what I have...they work great, and to date, have lasted over two years, 50+ track events, a few autocrosses and gets me to work and back on time.
