Remove cat=power gain? [Archive] - SaabCentral Forums

: Remove cat=power gain?


elementforlife
21st April 2004, 10:17 PM
Do our C900's have restrictive cats? I'd like to remove mine, possibly add Abbott's silencer, or maybe just make it a straight pipe. What other options do I have? Will I see a performance gain?

O and I don't have to pass emissions, I'm a FL resident, and I live VA, and my car is registered in FL, so I don't have to pass emissions tests, thats not a concern.

I'm thinking silencer and BOV would sound pretty nice too, but I don't know, maybe a straight pipe would sound nicer.

Will
1987 Saab 900 Turbo T16

RallySaab=68=
21st April 2004, 11:02 PM
I took the entire exhaust system off from the cat back one day and it was loud! But very cool. I drove down the main street in my town and people thought they heard a hopped up v8 and they turn around and see my little saab chugging along... Very fun to see the surprised look on their faces.

Doing that made the engine reach the higher rpms quicker, but it was deafning and illegal. :nono; If you don't need the cat get rid of it. You could do a straight pipe all the way back with a free flowing muffler somewhere in there. That should free up the motor a bit. My NA 900 definitely seemed to rev higher and accelerate better.

stevehayes01
22nd April 2004, 01:13 AM
If you look on Ebay you can find pre made test pipes for sale that bolt right in.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&category=33633&item=2473304907&sspagename=STRK%3AMEBWA%3AIT

This ones already gone but if you watch this seller you can catch the for around $40 US. It will give you quicker spool up with less resitance and around 5 or 6 HP gain.

Jezzadee
22nd April 2004, 08:30 AM
I removed the cat and had a straight through pipe fitted. It sounds great, not loud at all but a much deeper burble - I've been told at idle it sounds like a fishing boat. There is a small performance gain, but not much. Its hard to notice, but is probably around 5 BHP.

Johann F
22nd April 2004, 09:31 AM
Removing the cat lowers the exhaust gas temperature near the turbo which reduced exhaust speed and your low down peformance and spoolup will suffer. You will gain some power at the top end where the cat starts to impede the flow of a the larger volume of gasses. Wrapping the downpipe ( not header or turbo) with some glassfiber insulation tape will keep temperatures up and solve the problem.

SteveS
22nd April 2004, 12:18 PM
i removed the cat from my ex-lpt and the dyno results proved what johann says. increase in bhp was 5bhp as jezza and steve suggest and the sound was fantastic. i actually lost about 10lbs in torque tho.

great for the sound but the lost torque is something you will miss. If you are really performance minded do a few other mods first to compensate for the loss in torque then put the de-cat in.

if you don't mind the loss in torque then i would highly recommend it as it will bring a smile to your face while doing 30mph in traffic! really is a great sound.

actually i might put my de-cat back in this weekend now you have mentioned it 8)

elementforlife
22nd April 2004, 12:27 PM
That kick I get after I floor it is why I love my Saab. I do want the sound though. What mods can I go about doing to keep my from losing those 10 lbs of torque?

Removing the cat lowers the exhaust gas temperature near the turbo which reduced exhaust speed and your low down peformance and spoolup will suffer. You will gain some power at the top end where the cat starts to impede the flow of a the larger volume of gasses. Wrapping the downpipe ( not header or turbo) with some glassfiber insulation tape will keep temperatures up and solve the problem.

Would that solve the torque problem completely?

Will

Johann F
22nd April 2004, 01:08 PM
Yes

GearHead
22nd April 2004, 02:17 PM
what about having High-flow cat and a glasspack.aswell as insultating downpipe... 8)

johniemi
22nd April 2004, 02:37 PM
Johann, will thermo-tec insulation tape do the same thing? I have a downpipe that is covered with thermo-tec and I plan to install it soon.

-John

Johann F
23rd April 2004, 05:21 AM
It should work - as long as it's rated for exhaust applications. I used simple glassfiber tape but the better stuff has some sort of ceramic coating to stop all the fibers blowing around - very messy. One big tip is to put it on the pipe before you put it in the car. Also make sure you use stainless steel compression straps to hold it in place at both ends.

BDD
23rd April 2004, 11:00 AM
By putting in a non-cat downpipe, will that not remove the torque loss but increase flow over the CAT application? I de-catted but used the non cat downpipe, nice improvement in sound, though don't know what degree (if any) of loss in torque resulted.

ejenner
24th April 2004, 10:42 AM
The Carlsson brochure quotes 175bhp with cat and 185 without.

SteveS
25th April 2004, 09:57 AM
The Carlsson brochure quotes 175bhp with cat and 185 without.

Yes but the catted engine/management system is set up for the back pressure/heat that the cat generates. As the lambda sensor is before the cat it can't see that it isn't there. as i mentioned earlier with my decat i only exceprienced a 5bhp increase. Maybe a de-cat and ecu upgrade would provide the 10bhp as quoted in the brochure, possibly more :-??

ejenner
25th April 2004, 10:06 AM
I guess maybe the ECU wouldn't know the difference.

Don't know if it's able to re-calculate anything or if it is setup just to maintain a continuous performance level.

Looking to get something else in place of my OEM ECU. Don't really like all this "work-around" business. Think that's the first mod I'm going to make.

ejenner
25th April 2004, 10:08 AM
Suspect the readings would be different without the cat in place. If there is additional heat from the CAT and extra pressure. The Lambda reading would be different.

SteveS
25th April 2004, 10:23 AM
I think that the lambda sensor readings wouldn't change that much as it is only measureing Co2 content not pressure or exhaust velosity? correct me if im wrong!

would like to see the difference in torque/bhp with a non cat ecu installed!

Johann F
25th April 2004, 10:54 AM
You can get 185bhp with a CAT car by using 98RON fuel and adjusting the APC for more boost.

ejenner
25th April 2004, 10:59 AM
Think it measures the O2 volume. Not the C02. And I guess differences in heat and pressure would make a difference.

Johann F
25th April 2004, 11:14 AM
Also remember that a non cat downpipe does not flow as well as a straight pipe cat replacement. The perforated section interferes with gasflow.

ejenner
25th April 2004, 11:26 AM
So is you sayin that removing the CAT and replacing with a straight pipe is even better than a standard, non-cat system?

I guess if you didn't have the central silencer...

Johann F
25th April 2004, 11:39 AM
In terms of total hp it is better but you loose torque and suffer lag unless you keep the gases hot in the downpipe by wrapping it. Non cat downpipes are very expensive as well.

ejenner
25th April 2004, 11:56 AM
Don't you just increase the size of the bore - So gasses can excape quicker. Rather than trying to keep them hot so they are of a lower density. or would you wrap a large exhaust as well.

Johann F
25th April 2004, 12:10 PM
No idea - PFS are doing 3" complete systems for only a bit more than you can buy a genuine Saab downpipe for!

ejenner
25th April 2004, 12:16 PM
yeah - until I can afford I new system I would probably be heading down the same road.

I have the problem with the broken mounting stud, so my exhaust saggs slightly in the middle. Would be great to remove the central silencer - would get better ground clearance.

Car is off the road for a while tho. Should be pulling the engine so I will have a chance to get the exhaust problem fixed.

SteveS
25th April 2004, 02:09 PM
You can get 185bhp with a CAT car by using 98RON fuel and adjusting the APC for more boost.

Im running a modyfied LPT so no easy bhp through APC tweaks for me :cry:


for the moment anyway

hansiu
25th April 2004, 03:36 PM
Will the torque loss happen with a non turbo 900 as well?

NLspiked02
26th April 2004, 12:41 PM
i had removed the cat off my 90 turbo. i know what you mean by bottom end loss. however i feel that the top end that i gained more than made up for it. however my results may not be as well documented as the cat on it was clogged. you could hear a very loud hiss out the exhaust from it being clogged. the garggle that the car gives now makes me happy. :lol: many ppl mistaken it for a V6. very astonished when i open the hood to find that it is a small turboed 4.

later
dave

hansiu
26th April 2004, 05:26 PM
So the bottom end torque loss only happen with the turbo models?

ageybaby
26th April 2004, 06:04 PM
i've removed cat n i had no probs even passed the mot today vvv easily :cheesy: with no cat :nono; :nono; :cheesy:

Saabian
26th April 2004, 07:08 PM
What about leaving the cat and replacing the stock muffler with a glass pack? Any loss or gain there?

-Ian