Cat delete completed - WOW! Big difference!
10-22-2005, 01:43 AM
#16
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well supposed to take it to the dyno this weekend but last time I checked it was 13.5 max and dropping quickly at high rpms......but I also added an LBE so it feels much better now.
10-22-2005, 01:52 AM
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My boost was set to around 15 on my stock wastegate. I could only hold about 13-14 for a little bit in the higher RPMs, and could only get like 6psi in the first 2 gears. The Tial 38 completey fixed all of the problems, I now always have at least 15 and can achieve 18+. It's sooo worth it!
~Josh
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10-22-2005, 02:55 AM
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Originally Posted by Ahmet
I imagine your experience was an exception to the usual life span of a catalytic converter on a 944 turbo. I've seen very minimal gains myself from removing a cat on several 944 turbos, perhaps I had not come across a "bad" one yet. Anyway, you could always replace your cat with a high flow one if you're indeed sure that it is clogged, they're not that expensive.
Ahmet
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I was part of the "cat delete" crowd until I had first hand experience. On a track car, "cat delete" makes sense (you want top end gains from a free flowing exhaust), but on a street car, folks should get a "hi-flow" cat like Ahmet suggested, it's the better solution. I've been told that Porsche and Audi (probably VW too) actually tune (design) their turbo engines with an expectation of exhaust restriction.
I also own an Audi B5-S4 which is the twin turbo sports sedan. It comes with 2 main cats and 2 pre-cats. Most S4 guys eliminate the pre-cats (faster spool up - yes) and KEEP the main cats (for emission purposes, keeps ECU from tripping a CEL) because the restriction actually helps the turbos hold boost. No restriction - it's like a wind tunnel on the "hot side" of the turbo.
Sorry, but STREET CARS need the mid-range torque that the cats provide when your turbo is on boost.
Just my $.02.
jy951
10-22-2005, 03:54 AM
#20
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Just my $.02.
That was properly valued. Do a search. This has been beaten to death. The headers and crossover create all of the spool up characteristics. The opening of the exhaust a ton. If not why did the cup cars run a factory 4 inch exhaust on the same enguine? Too much restriction causes back pressure.
As for the TIal, if you have been using your stock, original wg, you will see a noticeable improvement. as your stock wg will almost certainly have a worn diaphram.
BTW Ahmet, a 20 year old cat, if on a car that has been running rich for any period of time, and/ or owned by someone who didn't take care of it, is by now on its last legs. I was hitting 1800 f before the cat and about 600 immediately aft. When we pulled it, and cut it off, you could barely see a ray of light from a flash light through it. Adding exhaust and new WG I increased hp and torgue by 43 and 48 over stock. I also picked up almost 600 rpm of earlier boost.
The three first mods on an otherwise solid engine should be Vitesse chips, 3' exhaust, and new wastgate.
That was properly valued. Do a search. This has been beaten to death. The headers and crossover create all of the spool up characteristics. The opening of the exhaust a ton. If not why did the cup cars run a factory 4 inch exhaust on the same enguine? Too much restriction causes back pressure.
As for the TIal, if you have been using your stock, original wg, you will see a noticeable improvement. as your stock wg will almost certainly have a worn diaphram.
BTW Ahmet, a 20 year old cat, if on a car that has been running rich for any period of time, and/ or owned by someone who didn't take care of it, is by now on its last legs. I was hitting 1800 f before the cat and about 600 immediately aft. When we pulled it, and cut it off, you could barely see a ray of light from a flash light through it. Adding exhaust and new WG I increased hp and torgue by 43 and 48 over stock. I also picked up almost 600 rpm of earlier boost.
The three first mods on an otherwise solid engine should be Vitesse chips, 3' exhaust, and new wastgate.
10-22-2005, 05:15 AM
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Cat Elimination On A STREET CAR - AGAIN - My $.02
Originally Posted by ehall
Just my $.02.
That was properly valued. Do a search. This has been beaten to death. The headers and crossover create all of the spool up characteristics. The opening of the exhaust a ton. If not why did the cup cars run a factory 4 inch exhaust on the same enguine? Too much restriction causes back pressure.
As for the TIal, if you have been using your stock, original wg, you will see a noticeable improvement. as your stock wg will almost certainly have a worn diaphram.
BTW Ahmet, a 20 year old cat, if on a car that has been running rich for any period of time, and/ or owned by someone who didn't take care of it, is by now on its last legs. I was hitting 1800 f before the cat and about 600 immediately aft. When we pulled it, and cut it off, you could barely see a ray of light from a flash light through it. Adding exhaust and new WG I increased hp and torgue by 43 and 48 over stock. I also picked up almost 600 rpm of earlier boost.
The three first mods on an otherwise solid engine should be Vitesse chips, 3' exhaust, and new wastgate.
That was properly valued. Do a search. This has been beaten to death. The headers and crossover create all of the spool up characteristics. The opening of the exhaust a ton. If not why did the cup cars run a factory 4 inch exhaust on the same enguine? Too much restriction causes back pressure.
As for the TIal, if you have been using your stock, original wg, you will see a noticeable improvement. as your stock wg will almost certainly have a worn diaphram.
BTW Ahmet, a 20 year old cat, if on a car that has been running rich for any period of time, and/ or owned by someone who didn't take care of it, is by now on its last legs. I was hitting 1800 f before the cat and about 600 immediately aft. When we pulled it, and cut it off, you could barely see a ray of light from a flash light through it. Adding exhaust and new WG I increased hp and torgue by 43 and 48 over stock. I also picked up almost 600 rpm of earlier boost.
The three first mods on an otherwise solid engine should be Vitesse chips, 3' exhaust, and new wastgate.
On a track car..it makes PERFECT sense to eliminate the CAT. On a STREET car eliminating the CAT SIGNIFICANTLY reduces MID RANGE TORQUE. This mid range torque is what you need when you try and merge on to a freeway @ 40-60 mph and the car doesn't grab a quickly.
BECAUSE many of these cars have 18 yr old CATS clogged full of Sh*t, when the owners remove them, they think they are getting this TREMENDOUS spool up and POWAH! They FAIL to REALIZE (or understand) it's because they just took an 18 yr old clogged up tube of Sh*t out of the exhaust flow!
As Ahmet clearly stated, any "high flow" cat will yield basically the same spool up and feeling of POWAH as a straight tube (an exhaust w/o cat) on a street car, and it will STILL produce some restriction in the exhaust flow, thus ALLOWING the turbos to MAINTAIN optimal boost (thru the assistance of back pressure) throughout the power range.
All you guys that rip off your cats (on a street car) and feel all this BUTT DYNO POWAH are FOOLING yourselves. Yes, this topic has been debated ad-naseum. This SAME topic has been (is) debated on AudWorldi in the B5-S4 forum too.
In fact, the B5-S4 should get even greater performance gains from cat elimination than a 951 since it's a bi-turbo. Elimination of a CAT on a STREET CAR is the MOST distorted topic to appear in both AudiWorld and Rennlist forums. Like I said, I've been there (got rid of my CAT a few yrs ago) and realized the performance loss (in the mid-range) and installed a "high flow" aftermkt CAT. I already had a Lindsey Racing DP Wastegate and KoKeln chips when I eliminated the CAT.
Oh, did anyone mention that it is illegal in all 50 states of the USA to operate a STREET car without a cat! That's why many race shops sell "HIGH FLOW" cats for STREET CARS!
The fact that you referenced the "Cup Car" told me right away that you have no concept of how street cars operate DIFFERENTLY than track cars (by DESIGN). NO CAT on a track car - makes sense - on a STREET CAR - illegal and you lose performance in the mid range for POWAH up top. Problem is - YOU DON'T race STREET CARS during normal every day driving (like most folks on this bd do) - so you very rarely get the most out of the benefits that an elimnated CAT gives you (more powah in the top end of the rpm range).
jy951
10-22-2005, 07:12 AM
#23
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On a turbocharged automobile engine, any restriction after the turbocharger is bad for efficiency, as well as power, period. I'm not arguing this. I've had quite a few 944/turbo and other Porsche cats apart, and I have yet to see a clogged one (the cat on my 86 turbo with 170k+ didn't net me more than 5hp, and looked practically new inside). If you have to have the extra bit of performance, and don't mind the increased noise, that's your choice, but it IS illegal for a street car, and there's really no good reason not to go with a high flow cat when the original cat is removed.
Ahmet
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10-22-2005, 10:30 AM
#24
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Wow this has created quite a stir!
Of course if I'm missing any mid-range torque I haven't noticed because I didn't have much when I bought the car. The PO didn't truely "drive" the car. Just stop and go stuff and probably ran cheap gas. My cat was severly clogged with only 77,000 miles.
Before I wasn't getting boost until about 3500 rpm and only achieving 7.5 psi. Now boost comes on at about 3100 rpm and peaks quickly at 11.5 falling off just a little before redline. So to me the cat delete was well worth it. We'll see what a new wg and chips will do.
As far as emmissions go we don't have any inspections in So. Dak. If you get pulled over for an illegal exhaust you get a "fix it ticket" and have 30 days to comply.
I don't quite understand the whole backpressure argument for mid range torque. In my book air+fuel=power. With less back pressure the trubo spins with less resistance doesn't it? So the sooner you get the turbo spinning the more boost pressure you create allowing more fuel to be delivered. Should this not make more power available through out the entire curve? If not why hasn't anyone increased exhaust resistance to optimize for mid-range power for street applications?
Of course if I'm missing any mid-range torque I haven't noticed because I didn't have much when I bought the car. The PO didn't truely "drive" the car. Just stop and go stuff and probably ran cheap gas. My cat was severly clogged with only 77,000 miles.
Before I wasn't getting boost until about 3500 rpm and only achieving 7.5 psi. Now boost comes on at about 3100 rpm and peaks quickly at 11.5 falling off just a little before redline. So to me the cat delete was well worth it. We'll see what a new wg and chips will do.
As far as emmissions go we don't have any inspections in So. Dak. If you get pulled over for an illegal exhaust you get a "fix it ticket" and have 30 days to comply.
I don't quite understand the whole backpressure argument for mid range torque. In my book air+fuel=power. With less back pressure the trubo spins with less resistance doesn't it? So the sooner you get the turbo spinning the more boost pressure you create allowing more fuel to be delivered. Should this not make more power available through out the entire curve? If not why hasn't anyone increased exhaust resistance to optimize for mid-range power for street applications?
10-22-2005, 11:56 AM
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Originally Posted by Ryan in SD
So what are you going to do to pass emissions???
I've been thinking of going with the fabspeed 3" system with test pipe when I actually buy the car [this week]. Its pretty sweet looking too (not that anyones sees the under side of the car). http://www.fabspeed.com/944t.html
I've been thinking of going with the fabspeed 3" system with test pipe when I actually buy the car [this week]. Its pretty sweet looking too (not that anyones sees the under side of the car). http://www.fabspeed.com/944t.html
10-22-2005, 12:36 PM
#26
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Take a look at the difference a 3" upgraded to 4" makes on Wes's car. Peak torque comes in much sooner. I felt a difference when I went from a cat cutout to a cat bypass pipe as well. http://www.lindseyracing.com/Merchan...gory_Code=DYNO
10-22-2005, 01:48 PM
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The only reason that I could see that a cat could help power on a street car is if is restrictive in the sense that it acts a second wastegate (the back pressure takes stress off the "weak" wastegate allowing it to stay closed longer helping boost. But that is a stretch for me.
Engines are big air pumps the easier in and out the better.
If you "have" to pass emissions a high flow seems to be the only performance option.
Coincidentaly (sp?) I cut mine off yesterday and if feels a little more "free" but I am still bascially stock.
Engines are big air pumps the easier in and out the better.
If you "have" to pass emissions a high flow seems to be the only performance option.
Coincidentaly (sp?) I cut mine off yesterday and if feels a little more "free" but I am still bascially stock.
10-22-2005, 03:01 PM
#28
Burning Brakes
Here's an idea that I've considered, so request input and insight from others more knowledgeable:
Rather than gutting the cat outright or replacing it with a straight through pipe (as others have done, with various consequences such as noise or emmissions issues), why not bore a hole through the old cat. This could be done with the sort of saw used for cutting doorknob holes, and an extension inserted from the back side of the cat. This leaves the peripheral portions of the cat guts intact. Then, line the bore hole with perforated tubing of the correct diameter. Such stainless steel is available from SS suppliers found on Google.
This way, much of the advantage of straight-through exhaust can be had. The stock cat has no change in appearance, and of course fits perfectly back on the car. Some of the noise and polution advantages of the stock cat are retained, since the perforated tube allows some of the exhaust gas to bleed off laterally witihin the cat housing. Cost is minimal.
Now, why is this not an inexpensive, efficient, and simple aternative to a gutted cat or straight-throgh "test" pipe.
Rather than gutting the cat outright or replacing it with a straight through pipe (as others have done, with various consequences such as noise or emmissions issues), why not bore a hole through the old cat. This could be done with the sort of saw used for cutting doorknob holes, and an extension inserted from the back side of the cat. This leaves the peripheral portions of the cat guts intact. Then, line the bore hole with perforated tubing of the correct diameter. Such stainless steel is available from SS suppliers found on Google.
This way, much of the advantage of straight-through exhaust can be had. The stock cat has no change in appearance, and of course fits perfectly back on the car. Some of the noise and polution advantages of the stock cat are retained, since the perforated tube allows some of the exhaust gas to bleed off laterally witihin the cat housing. Cost is minimal.
Now, why is this not an inexpensive, efficient, and simple aternative to a gutted cat or straight-throgh "test" pipe.
10-22-2005, 04:03 PM
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I dyno'd my car on our mustang AWD dyno it put down a shade over 200 to the wheels consistantly. I removed the cat, and put it back up there, and it dyno'd 252 to the wheels consistently. It was so clogged you could not even begin to see through it. On the street it performs by far better, and i have the dyno numbers to prove "That seat of your pants feel."
