I was thinking about going with a cat-back system on my 86 305 TPI.

I wanted to know if this is simply a bolt-on affair, or will it be more complicated?

Also, how much should I expect to gain from this mod? Any recommendations for a brand?

thanks,

Joe


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86 IROC TPI 305
700-R4
K&N Air filters
Next mod = trans-go shift kit (level 1)

 

Hey, I just got my Dynomax cat-back last week and the hard part was getting the old one off. Once I got that restrictive piece of junk off, it only took 1 hour to bolt the new one on and have it down and running. Dynomax IS a quiet system, but it is 3" and with dual outlets and a true bolt on. Looks like stock. But a side-by-side comaparison to the stock unit will tell you otherwise. It sounds nice and mellow. Not tinny. I love my new system. $154 from Summit.




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1987 GTA 350,rebuilt in 1998. new heads, Heddman headers w/y-pipe, Dynomax cat-back system, 45,000 coil, accel plug wires and cap&rotor, k&n, b&m shift kit and trans cooler, modified mass airflow sensor, manual fans switch. MSD 6A yet to be installed. No time slip.

1993 Bonneville SSE ALL STOCK. 98,xxx miles and stil counting...plan to install K&N and Flowmaster 80 series

 

I've had a Dynomax Super Turbo cat-back on my '87 IROC for nearly 5 years and I love the sound. Just wait until you get some miles on it and it "breaks in." When I had it installed, I wasn't into working on my IROC much, so I had my local shop install it for $50. I've had others compliment me on how it sounds, both with and w/out a cat...

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Greg Westphal
'87 IROC 305TPI/A4

 

After doing a few cat-backs (my '86 twice, and a friend's '91 Formula once), I've found the easiest way is to drop the rear axle down. This way the old system pulls straight out the back of the car, and the new system slides in easily.

The hardest part is swinging the intermediate pipe over the axle. If your cat-back has a two-piece I-pipe (cat-to-muffler), this is an easy job. If it's one piece, then you'd need the car on a lift to swing it over easily. By dropping the axle down, you eliminate having to swing the pipe over the axle.

Dropping the axle down is easy. You lift the car so the jackstands are directly "in front of" the rear lower control arms. You keep a hydraulic jack under the center of the axle. Then you:

1. Remove rear wheels
2. Remove lower shock-to-axle nuts
3. Lower axle until lower shock bolts are "unstressed" and push out of the axle easily
4. Lower the axle more until the springs are unstressed, reach up & remove them
5. Remove the panhard rod (track bar) going from left-to-right at a diagonal
6. Remove bolt holding the hard steel brake line to the body of the car
7. Lower the axle as far as you want, taking care not to stretch the body-to-axle brake hose, and not to kink the hard brake line

After that, the rest is easy! Good luck.

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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

You don't need to drop the axel down or anything that drastic. Just set the rear of the car on jacks and cut off your stock set up with a cutting torch or hack saw. Then bolt your new one on. I have installed an American Thunder cat-back system and 2 Hooker set-ups, none of them took me more than 2 hours to do. I would recomend the Hooker cat-back, its far superior to the Dynomax and only about $60 more. I got mine from Jegs for $260!

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission
Borg Warner 7.75" 9 Bolt Rear End

Current Mods: LT4 Hot Cam, Comp Cams 1.52:1 Roller Rocker Arms, Edelbrock TES 1 5/8" Headers, Hooker 3" Aerochamber Cat-Back System, Performance Resource Chip, Accel Ignition Coil, Cap, Rotor, 8.8mm Wires, K&N Filters, JET TPI Air Foil, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET (w/o LT4 cam): 14.32 @ 97.7mph
(corrected for elevation)

7.5" 10 Bolt with 3.42s soon to come!

 

Yet, nobody has mentioned any power gains!

Has anyone noticed a difference in power?
If its not noticeable, i wouldnt want to bother.

Joe


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86 IROC TPI 305
700-R4
K&N Air filters
Next mod = trans-go shift kit (level 1)

 

Joe,
I just added a 3in American Thunder cat back (has dual-out and nice looking chrome tips) and a 3in catco converter.It has a nice loud rumble.I did notice better throtle response,and above 3000 rpm it really seems to pull harder.Also added a dual snorkel and k&n filter at the same time.If i had to guess I'd say 20-25 hp from those mods combined.
By the way since I don't have a garage and didn't want to wait for warmer weather I took my converter and cat back to an exhaust shop and they charged me $100 to weld it all in.

 

Dan87IROC,-Z, you just not have had a one-piece i-pipe with any of those cat-backs. With a one-piece I-pipe (the pipe between the catalytic convertor and muffler), either the axle must be dropped, or you'll be raising the car pret-ty damn high in the air.

The reason is, the I-pipe is shaped like a ? mark. A two piece i-pipe is split into the "curve" of the ? and the "straight part" of the ?. So, you loop the curve over the axle, hook the straight part in, and you're done.

With a one-piece, the curve & straight pipe are one. You would need to have the car on a lift to hook the "curve" over the axle- that's because when you spin the curve two inches, the other end of the pipe will move 12 inches! The GM book figures you have the car on a lift, and then yeah, just hook the I-pipe over the axle. On a lift this swap would take maybe a half hour, max.

Before I had to replace my in-tank fuel pump, I did two cat-backs, both with a one-piece I-pipe. In both cases, I had to raise the Firebirds dangerously high in the air, using jacks & wood & etc. When I had to replace my fuel pump (requiring dropping of the rear axle), I noticed my cat-back could slide out easily. So, when I went to replace my 1st cat-back (it rusted out) with another, I dropped the rear axle. I pulled the old one straight out, and pushed the new one straight in. Nice & easy- and safe.

[edit] Oh yeah- when I went from a stock system to a cat-back, I noticed one heck of an increase! I didn't expect one either; it was my first mod, and I figured "why not?" Glad I did.

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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

[This message has been edited by TomP (edited March 15, 2001).]

 

Right on, Tom. When I did my Dynomax with the 1-piece I-pipe I had the back of the car on ramps, then I had to get the jack out of my ZR2 Blazer and put blocks under it to jack the passenger rear of the body enough off of the axle to get that damned I-pipe in. It can be a real pain in the a@@ to do it with a 1-piecer like the Dynomax systems, and unsafe as hell too without a lift or without dropping the rear like was mentioned. It took me longer than it should have because of my shade-tree mode of operation, and if I had to do it over again I would go with one of the 2-piece I-pipe systems like I'm assuming Dan did.

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1990 IROC 350
Mods: Too busy trying to make it run right to mod it.
Airfoil, Dynomax cat-back, Accel coil, 180 t-stat, Bald Eagle tires, Hypertech fan switch,
Ruger P95DC, hot wife, new oil filter, thick rubber floormats, towels in the seats.
18.0 @ 85MPH since I'm one big-a$$ MF
"It's better to have and not need than to need and not have."