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Old 09-20-2000, 10:19 AM   #1
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Aftermarket exhaust....Does low back pressure = loss in low end torque?

Hello everyone,
I want to replace the stock exhaust system in my 91 GTA. I want to change everything and replace it all with aftermarket parts by SLP. I was hoping to go with SLP headers and a complete cat back muffler system. I also want to change my existing catalytic converter to one of the free flowing kind.

My question is, if I alter my exhaust system
to include the free flowing exhaust parts, will I end up with a large loss of low end torque? Basically, I don't want to feel a large loss of power at a low RPM in order to gain horsepower at a high RPM.

If anyone has done a lot of work to their exhaust, please let me know what you have found to be the benefits and negatives of the new parts.
Thanks
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Old 09-20-2000, 10:38 AM   #2
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No, if you keep your cat(s), you will experience no loss in low end torque. In fact, you'll gain it. The headers will help you in midrange and top end. I ran a gutted cat for a while then switched to a Catco high flow cat, and picked up noticeable low end with little top end loss.

------------------
91 Trans Am WS6
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

supposed 'peanut cammed' car (yeah, right)

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Old 09-20-2000, 10:52 AM   #3
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Thanks MrJ....

A friend of mine was trying to tell me that replacing the stock exhaust would take away too much back pressure, which would then eliminate all my low end power.....I thought he was wrong, but I just wanted someone who had done the exchange to tell me their experience.
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Old 09-20-2000, 12:31 PM   #4
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A free flowing exhaust will not hurt your low end power that much. You will gain big ponies in the upper rpms but I'd say the low rpm torque would not really be affected.
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Old 09-20-2000, 05:18 PM   #5
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When I put the Edelbrock TES and the Hooker Cat-back on my car, I did loose a little down low, its almost un-avoidable, but its nothing to loose sleep over. With just the headers on a stock engine, my ETs dropped by .4 in the 1/4 mile, and my 60' and 330' times were almost identical, only a few thousands slower.

------------------
1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission with 2.77:1 Rear End

Current Mods: Edelbrock TES 1 5/8" Headers, Hooker Aerochamber Cat-Back System, Performance Resource Chip with 160* Thermostat, Accel Ignition Components, K&N Filters, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET : 14.3 @ 97mph
(corrected for elevation)
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Old 09-26-2000, 03:00 PM   #6
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I have an 89 IROC-Z (L98) with stock exhaust manifolds, dual cats, 3'' mandral bent piping with no muffler. I don't think I lost any low end power, but it does seem to pull harder up top.

------------------
1989 IROC-Z
350c.i. TPI
rebuilt 700R4 with shift kit
3'' Monza Pacesetter cat back exhaust (minus the muffler)[SOUNDS OF THIS ON MY WEBPAGE]
new dual cats
3.23 Posi rear
hypertech chip
under drive pulleys
adjustable fuel pressure regulator
K&N Air Filters
Excalibur alarm, keyless entry and remote start
new:
struts, shocks, bearings, distributor, cap, rotor, alternator, battery, regulator
245 ZR16 50 Tires, Rotors and brake pads all the way around

Go to my webpage to find out more about it.
You can also see pictures, and hear sounds as well.
http://go.to/iroc-z

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Old 09-26-2000, 04:50 PM   #7
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Car: 1988 Trans Am GTA
Engine: 383
Transmission: 700R4

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When I had my stock exhaust removed and replaced with the aftermarket peices, I noticed a gain in both low and high rpm power. Acceleration was the most noticeable improvement, and when you really mash the gas, she burns rubber like never before!! Click the image to open in full size.

------------------
88 GTA
L98 350
700R4
3:27 axle
MODS,
Edelbrock TES headers, 3" straight pipe, Flowmaster 80 series, K&N filter, Accel 8.8mm wires, Bosch Platinum plugs, Wells cap and rotor button, Wells ignition module, MAF screens removed, Hypertech TB air foil, Thermomaster stage II chip, 180* Powerstat, Hypertech cool fan switch, B&M shift kit, B&M power clutch pack, B&M servo, GM fuel filter
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Old 09-26-2000, 04:53 PM   #8
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Car: 1988 Trans Am GTA
Engine: 383
Transmission: 700R4

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Send a message via ICQ to speed88
When I had my stock exhaust removed and replaced with the aftermarket peices, I noticed a gain in both low and high rpm power. Acceleration was the most noticeable improvement, and when you really mash the gas, she burns rubber like never before!! Click the image to open in full size.

------------------
88 GTA
L98 350
700R4
3:27 axle
MODS,
Edelbrock TES headers, 3" straight pipe, Flowmaster 80 series, K&N filter, Accel 8.8mm wires, Bosch Platinum plugs, Wells cap and rotor button, Wells ignition module, MAF screens removed, Hypertech TB air foil, Thermomaster stage II chip, 180* Powerstat, Hypertech cool fan switch, B&M shift kit, B&M power clutch pack, B&M servo, GM fuel filter
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Old 09-26-2000, 04:55 PM   #9
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Join Date: Sep 2000
Location: St. John's, NL, Canada
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Car: 1988 Trans Am GTA
Engine: 383
Transmission: 700R4

Classifieds Rating: (0)

Send a message via ICQ to speed88
When I had my stock exhaust removed and replaced with the aftermarket peices, I noticed a gain in both low and high rpm power. Acceleration was the most noticeable improvement, and when you really mash the gas, she burns rubber like never before!! Click the image to open in full size.

------------------
88 GTA
L98 350
700R4
3:27 axle
MODS,
Edelbrock TES headers, 3" straight pipe, Flowmaster 80 series, K&N filter, Accel 8.8mm wires, Bosch Platinum plugs, Wells cap and rotor button, Wells ignition module, MAF screens removed, Hypertech TB air foil, Thermomaster stage II chip, 180* Powerstat, Hypertech cool fan switch, B&M shift kit, B&M power clutch pack, B&M servo, GM fuel filter
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Old 09-26-2000, 07:11 PM   #10
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Yes and no. Depends on how much back pressure is lost, and that will subsequently affect low end throttle response. However, in the worst case scenario of totally "zero" backpressure, the low end throttle response would not be sufficently affected to really even care about.

In the situation you are describing, it will be a win-win situation all around. You will gain both low end grunt and top end breathing ability. You can't go wrong.

------------------
FORMULA 350 TK
Southern California 3rd Generation F-Body Organization©
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Old 09-27-2000, 10:22 AM   #11
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The way I look at it,is if you gained torque by adding a cat,then Warren Johnson would have cats on his Pro Stock car.Just my o2.

------------------
We need Perry Mason
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Old 09-27-2000, 11:03 AM   #12
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Warren Johnson doesn't drive a street car with EFI. I definately gained low end when I got a high flow cat, not to mention how much better it sounded over the gutted cat.

------------------
91 Trans Am WS6
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

supposed 'peanut cammed' car (yeah, right)

MoreMoodThatMod
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Old 09-27-2000, 08:49 PM   #13
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I think this is only true in the V8s. On my camaro, their is always enough backpressure, no matter what you do past the cats. I ran best straight 3" piped reduced to a 2 1/4 tip with two 90 degree turns so it exited on the driver side.(My engine is a custome built 305 TPI with mods) Now to contrast, on my 98 malibu with a 3.1 V6, it ran like CRAP when i freed up the exhuast, infact it barely started. Then i added some alumium baffles to give the exhuast some back pressure. That really made that POS fly. It was so sweet an edelbrock 304 with properly tuned intake and exhuast allowed me to really chirp the front tires and that thing flew.

BTW i got a hooker free flow aerochamber muffler hooked onto the standard G92 exhuast, and it runs noticibly weaker then when it was striaght piped but better then the stock.
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Old 09-28-2000, 09:00 PM   #14
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A gutted cat causes turbulence where it opens up from the pipe into the open porcelinless chamber and then back into the pipe. I was wondering how much the stock Y pipe is hurting the engine with that nice 90 deg. intersection where the exhaust pulses meet.
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Old 09-28-2000, 09:00 PM
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