The cat-bypass "X" crossover
08-24-2002, 11:16 PM
#1
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The cat-bypass "X" crossover
I spoke with a recommended muffler shop today about modifying my exhaust for some better sound and performance. He recommended keeping the existing stock center and rear mufflers but to take out the cats and install an "X" cross-over. He said he could fabricate the bypass and make it work with the O2 sensor....half day work for $350 total.
Questions:
1. Is the price sound right?
2. What change in sound can I expect? (remember, the stock mufflers will remain)
3. What change in performance can I expect (no idea if cats are clogged or not)
4. Will the engine need to be tuned after the "X" cross-over?
I know there is considerable debate about the effect of bypassing cats....I'm looking for input only from those that have done it.
Thanks in advance!
Questions:
1. Is the price sound right?
2. What change in sound can I expect? (remember, the stock mufflers will remain)
3. What change in performance can I expect (no idea if cats are clogged or not)
4. Will the engine need to be tuned after the "X" cross-over?
I know there is considerable debate about the effect of bypassing cats....I'm looking for input only from those that have done it.
Thanks in advance!
08-25-2002, 12:11 AM
#2
The price you mentioned is probably about right, but could probably vary a fair bit from one place to the next.
The car will be louder without the cats. The "X" pipe is more efficient at producing power than the "H' style of crossover, and it also smooths out the exhaust tone more. It won't have that raspy sound to it that you'd get with an "H" crossover.
You will get an increase in power without the cats. It won't be a huge amount, but you will gain some.
You won't have to tune the engine afterwards, but doing so should give you more of the benefit that the bypass provides. How much of an effect that tuning would do really depends on the particular car. You would still pick up power even if the car wasn't tuned afterwards though.
The car will be louder without the cats. The "X" pipe is more efficient at producing power than the "H' style of crossover, and it also smooths out the exhaust tone more. It won't have that raspy sound to it that you'd get with an "H" crossover.
You will get an increase in power without the cats. It won't be a huge amount, but you will gain some.
You won't have to tune the engine afterwards, but doing so should give you more of the benefit that the bypass provides. How much of an effect that tuning would do really depends on the particular car. You would still pick up power even if the car wasn't tuned afterwards though.
08-25-2002, 04:42 AM
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Louie Ott makes an X crossover i believe. Not sure for what MY's. Perhaps some one will chime in. Exhaust work is my next "project". Definitely the DEVEK Level 2 headers...but from there back their $$$'s get really hard to swallow!
They pretty much have the 928 exhaust sytem tuned to the nats a$$ though.
As far as catbypasses, i have the test pipes on my car as well as the RMB. It sounds ok, not the refined sound i want. Its a little too raw when you open it up and a little raspy at idle. Doesnt bother me though. I get MANY MANY MANY comments on how sweet it sounds at local "cone" events. The dyno numbers all went up going catless as did the dbs. First thing you will notice is how much freely the engine revs.
Every year i bolt up my cats for smog here in NV. (FYI it passes with out them, unless the guy looks) No biggy as i take the time to check my thrustbearing health and pinch collar situation.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
They pretty much have the 928 exhaust sytem tuned to the nats a$$ though.
As far as catbypasses, i have the test pipes on my car as well as the RMB. It sounds ok, not the refined sound i want. Its a little too raw when you open it up and a little raspy at idle. Doesnt bother me though. I get MANY MANY MANY comments on how sweet it sounds at local "cone" events. The dyno numbers all went up going catless as did the dbs. First thing you will notice is how much freely the engine revs.
Every year i bolt up my cats for smog here in NV. (FYI it passes with out them, unless the guy looks) No biggy as i take the time to check my thrustbearing health and pinch collar situation.
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
08-25-2002, 04:56 AM
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[Here we go again....]
-You will gain, at the most....perhaps 3 percent more power by pulling off your cats. Do you really think that you can feel an additional 3 percent when you probably have 300+ hp already?
Serious diminishing returns!
If you want great sound, why not leave the cats alone, and simply delete the center muffler and add a good aftermarket exhaust. I put the Borla system on my '85 and it sounds awesome! By the way, my cat-equipped 5 speed turns 13.8 second quarters at 106 mph~
[when it runs right-]
Normy!
'85 S2 5 Speed
-You will gain, at the most....perhaps 3 percent more power by pulling off your cats. Do you really think that you can feel an additional 3 percent when you probably have 300+ hp already?
Serious diminishing returns!
If you want great sound, why not leave the cats alone, and simply delete the center muffler and add a good aftermarket exhaust. I put the Borla system on my '85 and it sounds awesome! By the way, my cat-equipped 5 speed turns 13.8 second quarters at 106 mph~
[when it runs right-]
Normy!
'85 S2 5 Speed
08-26-2002, 01:57 AM
#5
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Normy:
I'd eat my shoes if my shark was already producing 300+ HP. Seems I'm surprised each week with something new that is sapping my engine's power (this week's award goes to Greggg for pointing out the vacuum leak).
I wish I could jump in a time machine to feel with the seat of my pants what kind of power my car had 17 years ago.
When you're talking about 3% increase in HP from removing the cats....are you talking about clogged or unclogged cats?
Few things can increase HP by any substantial amount. I'm trying to figure out what combination of changes will get me a decent increase cheaply. <img src="graemlins/icon107.gif" border="0" alt="[icon107]" />
I'd eat my shoes if my shark was already producing 300+ HP. Seems I'm surprised each week with something new that is sapping my engine's power (this week's award goes to Greggg for pointing out the vacuum leak).
I wish I could jump in a time machine to feel with the seat of my pants what kind of power my car had 17 years ago.
When you're talking about 3% increase in HP from removing the cats....are you talking about clogged or unclogged cats?
Few things can increase HP by any substantial amount. I'm trying to figure out what combination of changes will get me a decent increase cheaply. <img src="graemlins/icon107.gif" border="0" alt="[icon107]" />
08-26-2002, 02:26 AM
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Dave-
I'd eat my ASICS too if I made 300 hp right now..supposedly my S2 makes 310, and adding 10 for the Bola pipes that makes 320. Feels like more than that when it is running right...
That's the trick; reference the "Rough Running" posts I've made. As of late, I've changed the MAF sensor gaskets to no avail- the car still misses like crazy. ::sigh::
3% more horsepower is what I've heard you can gain from removing a properly functioning catalytic converter from your car. Removing a plugged cat will obviously result in a greater benefit...
My point is that at our level, we are getting into dimishing returns. Add 100 hp to a 115 hp VW Golf and you'll think that the laws of physics have changed. Add 100 to our cars...and it just seems like the beast is running good for a change.
Add 3%- I bet you won't even feel it.
Removing the cat adds a small amount of sound, but it is illegal and really...I suspect that those tests that some people are forced to endure in their states or countries are not accurate at all in predicting pollution capability of the cars that wander in. They show a car with low emmsions at the test...when in fact that car probably pollutes considerably under real-world conditions.
I just know I can tell when some kid has pulled the cat from his Honda- it smells like an old school bus!
Normy!
'85 S2 5 Speed
I'd eat my ASICS too if I made 300 hp right now..supposedly my S2 makes 310, and adding 10 for the Bola pipes that makes 320. Feels like more than that when it is running right...
That's the trick; reference the "Rough Running" posts I've made. As of late, I've changed the MAF sensor gaskets to no avail- the car still misses like crazy. ::sigh::
3% more horsepower is what I've heard you can gain from removing a properly functioning catalytic converter from your car. Removing a plugged cat will obviously result in a greater benefit...
My point is that at our level, we are getting into dimishing returns. Add 100 hp to a 115 hp VW Golf and you'll think that the laws of physics have changed. Add 100 to our cars...and it just seems like the beast is running good for a change.
Add 3%- I bet you won't even feel it.
Removing the cat adds a small amount of sound, but it is illegal and really...I suspect that those tests that some people are forced to endure in their states or countries are not accurate at all in predicting pollution capability of the cars that wander in. They show a car with low emmsions at the test...when in fact that car probably pollutes considerably under real-world conditions.
I just know I can tell when some kid has pulled the cat from his Honda- it smells like an old school bus!
Normy!
'85 S2 5 Speed
08-26-2002, 03:18 AM
#7
An extensive amount of dyno testing on different exhaust configurations has been done by Louis Ott and Tom Cloutier on a 1990 GT. The results showed that removing the stock cats increased rear wheel power by 8 hp and 9 ft/lbs. That was from replacing the cats with straight sections of 2.25" pipe, but still using the stock "H" crossover located at the front of the cats. Replacing that stock "H" crossover with a 4" "X" crossover resulted in an additional 11 hp and 14 ft/lb increase in power. Replacing the stock cats with an "X" crossover cat bypass pipe would result in a 19 hp and 23 ft/lb increase at the rear wheels according to their results.
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08-26-2002, 08:19 AM
#8
Burning Brakes
Wow, those are great numbers.
But let's not forget some simple facts. 1: Our cars are getting really old. A 20-year old cat, is NOT running like new. 2: Our engines produce ALOT of heat. Removing the cats will help lower your engine temps by a good bit.
I would leave the stock mufflers alone for a street car. This is a personal opinion. It makes the car sound really loud, very much like an old Chevy! Yes, you will get many comments...but from who?? 928s without stock mufflers, seam to have lost all those things that make a 928 so special in the first place. That is: Smooth Euro Power.
This is just an opinion from someone who has had many 928s, with and without exhaust.
But let's not forget some simple facts. 1: Our cars are getting really old. A 20-year old cat, is NOT running like new. 2: Our engines produce ALOT of heat. Removing the cats will help lower your engine temps by a good bit.
I would leave the stock mufflers alone for a street car. This is a personal opinion. It makes the car sound really loud, very much like an old Chevy! Yes, you will get many comments...but from who?? 928s without stock mufflers, seam to have lost all those things that make a 928 so special in the first place. That is: Smooth Euro Power.
This is just an opinion from someone who has had many 928s, with and without exhaust.
08-26-2002, 12:03 PM
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I'm afraid the only input I can give is from my 79 shark. Remember, I don't have any sensors and such to worry about in my 928.
I had my cat removed, but also installed a custom exhaust. While doing the exhaust work, my mechanic and I tried some things. The catalytic convertor was too good. After removing the rest of the exhaust, the convertor still acted like a muffler! The exhaust wasn't loud at all! Heck, you would have thought the complete exhaust was still there!
The catalytic convertor was robbing, or restricting the exhaust enough that my 79 was losing 3-4% power. Now, that isn't much. But what about power at speed?
0-100 MPH times, gained maybe 1/2 sec, maybe not.
60-140 MPH times, gained...yes! Only rarely could I coax the old shark over 140 MPH (no jokes about tail winds or going over a cliff). It would run over 130 easily. Now, 140-145 MPH easily! That's letting the old 4.5 liter engine breath more easily and that seemed to be the problem. The cat on the exhaust!
I added a custom racing resonator where the middle muffler was and a custome 3-chamber resonator where the rear muffler was placed.
I'm not saying my way was the best, but the cat-convertor adds back pressure, very slightly restricts and heat. My cat wasn't plugged, but it was the muffler also. That's how well made or packed it was.
<a href="http://clik.to/PORSCHE928DRIVER" target="_blank">Personal Shark Website</a>
I had my cat removed, but also installed a custom exhaust. While doing the exhaust work, my mechanic and I tried some things. The catalytic convertor was too good. After removing the rest of the exhaust, the convertor still acted like a muffler! The exhaust wasn't loud at all! Heck, you would have thought the complete exhaust was still there!
The catalytic convertor was robbing, or restricting the exhaust enough that my 79 was losing 3-4% power. Now, that isn't much. But what about power at speed?
0-100 MPH times, gained maybe 1/2 sec, maybe not.
60-140 MPH times, gained...yes! Only rarely could I coax the old shark over 140 MPH (no jokes about tail winds or going over a cliff). It would run over 130 easily. Now, 140-145 MPH easily! That's letting the old 4.5 liter engine breath more easily and that seemed to be the problem. The cat on the exhaust!
I added a custom racing resonator where the middle muffler was and a custome 3-chamber resonator where the rear muffler was placed.
I'm not saying my way was the best, but the cat-convertor adds back pressure, very slightly restricts and heat. My cat wasn't plugged, but it was the muffler also. That's how well made or packed it was.
<a href="http://clik.to/PORSCHE928DRIVER" target="_blank">Personal Shark Website</a>
08-26-2002, 01:27 PM
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I've been running an O2 equipped bypass with stock mufflers for about a year. It definitely is louder and making a bit more power. Revs a little more crisply. The sound is kinda raspy at low revs, very gnarly on the gas toward red-line. I paid $100 second hand for a standard Y-pipe. Bolted it up myself in about an hour. I didn't do anything to engine tune, the FI doesn't seem to care.
08-27-2002, 02:16 AM
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So what about fitting aftermarket "high flow" cats? Does anyone have any experience with them?
I would like to replace my cats (they are clogged) and at the same time achieve a slightly more agressive tone.
Scott
I would like to replace my cats (they are clogged) and at the same time achieve a slightly more agressive tone.
Scott
08-27-2002, 03:13 AM
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<a href="http://www.randomtechnology.com/" target="_blank">http://www.randomtechnology.com/</a>
theres the answer for your high flow cats.
Good info there Mike! Proof is with those that have done the research on the Dyno! With all due respect to our "seat of the pants" and the assometer
True, Normy, dropping the cats may get you only 3% as you say but when you start tweeking the motor as far as stroking and Supercharging, the exhaust WILL become one of the bottle necks.
Im just looking down the road a bit for the future
Good set of headers..merge colector..single 3" pipe.. single high flow cat(keep the smog boys happy on the visual) and dual inline Borlas is the plan. (may be one)
This, IMHO, is the ticket...
<a href="http://www.928developments.com/powerbroker.htm" target="_blank">http://www.928developments.com/powerbroker.htm</a>
and...
a 8100 series at ..http://www.randomtechnology.com/universal.html
and a couple of XR-1's, one inline, one offset at <a href="http://www.borla.com/xr1.sportsman.oval.mufflers/" target="_blank">http://www.borla.com/xr1.sportsman.oval.mufflers/</a>
Eh, maybe i should bolt up a couple of THRUSHES!
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
theres the answer for your high flow cats.
Good info there Mike! Proof is with those that have done the research on the Dyno! With all due respect to our "seat of the pants" and the assometer
True, Normy, dropping the cats may get you only 3% as you say but when you start tweeking the motor as far as stroking and Supercharging, the exhaust WILL become one of the bottle necks.
Im just looking down the road a bit for the future
Good set of headers..merge colector..single 3" pipe.. single high flow cat(keep the smog boys happy on the visual) and dual inline Borlas is the plan. (may be one)
This, IMHO, is the ticket...
<a href="http://www.928developments.com/powerbroker.htm" target="_blank">http://www.928developments.com/powerbroker.htm</a>
and...
a 8100 series at ..http://www.randomtechnology.com/universal.html
and a couple of XR-1's, one inline, one offset at <a href="http://www.borla.com/xr1.sportsman.oval.mufflers/" target="_blank">http://www.borla.com/xr1.sportsman.oval.mufflers/</a>
Eh, maybe i should bolt up a couple of THRUSHES!
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
08-27-2002, 04:31 AM
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Tony you've brought up part of my point...
If you ONLY pull the cats, your gain will be so tiny that it isn't worth doing.
Sure, a catalyzed exhaust along with no X pipes will always produce less, But funny thing: my cat-equipped S2 5 speed is nothing less than a hooligan when it runs right. For example, it has hung with a C5 corvette in a short, impromptu race, and killed a Buick GN another time. A '98 vette basically followed me through traffic one night, and cornered me at a Chevron station. Some kid in his dads car, wanted to run me BAD. Again, an impromptu race resulted...and to make it short he LOST.
I have the timing slips to prove my catalyzed two-valve 4.7 will turn a 13.8 second quarter. Tell me, what was your before/after times at the strip when you removed your cats? I'd be interested to know just how much improvement 6% actually is...
Time wise-
N~
If you ONLY pull the cats, your gain will be so tiny that it isn't worth doing.
Sure, a catalyzed exhaust along with no X pipes will always produce less, But funny thing: my cat-equipped S2 5 speed is nothing less than a hooligan when it runs right. For example, it has hung with a C5 corvette in a short, impromptu race, and killed a Buick GN another time. A '98 vette basically followed me through traffic one night, and cornered me at a Chevron station. Some kid in his dads car, wanted to run me BAD. Again, an impromptu race resulted...and to make it short he LOST.
I have the timing slips to prove my catalyzed two-valve 4.7 will turn a 13.8 second quarter. Tell me, what was your before/after times at the strip when you removed your cats? I'd be interested to know just how much improvement 6% actually is...
Time wise-
N~
