Hi everyone. I've been thinking of swapping out the stock chambered muffler in my fiero to a newer aftermarket chambered muffler from Amazon. The one thing that I'm wondering is if I do swap the muffler, will it mess with the back pressure enough that it would decrease engine performance due to not enough back pressure? If anyone has swapped the muffler in their 4 cylinder fiero, please let me know if you had any problems. Thanks
To be completely honest, the stock Fiero L4 exhaust is actually really well suited for the performance of the Iron Duke. It's a 1-7/8" thick exhaust piping, and up until the point it gets to the muffler itself, the exhaust is identical to the V6 Fiero of the same year. So, you won't really gain any performance by replacing it.
The thing I would ask is... what catalytic converter are you currently using? The original factory catalytic converter (if it's the one I think it is) is ... HORRIBLE. You can get a 2" replacement catalytic converter from the Fiero Store that will slide over the 1-7/8" piping (when you cut out the old cat), and it will absolutely improve performance, fuel economy, AND the sound of your exhaust.
My daughter has a video where she goes into detail on some upgrades, and one of them is the catalytic converter (around the 1 minute 30 mark):
To be completely honest, the stock Fiero L4 exhaust is actually really well suited for the performance of the Iron Duke. It's a 1-7/8" thick exhaust piping, and up until the point it gets to the muffler itself, the exhaust is identical to the V6 Fiero of the same year. So, you won't really gain any performance by replacing it.
The thing I would ask is... what catalytic converter are you currently using? The original factory catalytic converter (if it's the one I think it is) is ... HORRIBLE. You can get a 2" replacement catalytic converter from the Fiero Store that will slide over the 1-7/8" piping (when you cut out the old cat), and it will absolutely improve performance, fuel economy, AND the sound of your exhaust.
My daughter has a video where she goes into detail on some upgrades, and one of them is the catalytic converter (around the 1 minute 30 mark):
It is still the stock catalytic converter that is welded into the exhaust manifold.
Originally posted by 87FieroEnthusiast: It is still the stock catalytic converter that is welded into the exhaust manifold.
The CAT is welded to the exhaust pipe not the exhaust manifold. Just cut the CAT off using a reciprocating saw. Takes no more than 5 minutes!. Then bolt the new CAT on in 10 minutes or less. The OEM CAT is very restrictive and clogs over time.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
The CAT is welded to the exhaust pipe not the exhaust manifold. Just cut the CAT off using a reciprocating saw. Takes no more than 5 minutes!. Then bolt the new CAT on in 10 minutes or less. The OEM CAT is very restrictive and clogs over time.
My bad, meant to say exhaust pipe. Is there a specific CAT that you would recommend to replace the stock one?
My bad, meant to say exhaust pipe. Is there a specific CAT that you would recommend to replace the stock one?
A CAT about the same length as the OEM unit and having female connectors 1 7/8" -2" at both ends should work. The easy safer far more cost effective solution would be a non-restriictive straight pipe for about $10 which can be legally purchased for "off road" use. .
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
The easy safer far more cost effective solution would be a non-restriictive straight pipe for about $10 which can be legally purchased for "off road" use.
You neglected to mention "irresponsible" and "illegal".
A new high flow cat is not expensive, not restrictive, and the difference it makes with the emissions coming out of the exhaust tips is immediately evident to anyone who's ever stood behind a running car.
I started to look into Magnaflow catalytic converters. I can get the Magnaflow 53004 catalytic converter from RockAuto for about $40. Does anyone have any opinions on Magnaflow converters? (I can't do a CAT delete because it wouldn't pass inspection. It's also illegal.)
[This message has been edited by 87FieroEnthusiast (edited 09-12-2025).]
I can get the Magnaflow 53004 catalytic converter from RockAuto for about $40.
If it's the right size, that appears to be an excellent price for a Magnaflow cat.
I should also mention, that besides a reduction in stench, a new high flow cat will even make your exhaust sound better. The original OEM cat muffled the sound more, and a straight pipe in place of the cat introduces a "rasp" which isn't pleasant at all.
So... installing a new high flow cat is a win/win endeavor!
[EDIT] I went to RockAuto's site. The price for that cat is actually less than $28! This particular cat is not CARB compliant, but that may or may not matter depending on where you live.
[This message has been edited by Patrick (edited 09-13-2025).]
I should also mention, that besides a reduction in stench, a new high flow cat will even make your exhaust sound better. The original OEM cat muffled the sound more, and a straight pipe in place of the cat introduces a "rasp" which isn't pleasant at all.
I just want to foot stomp this... the sound improvement from the original OEM catalytic converter, to the newer style one... I can't even begin to explain. It's night and day... it sounds so much better, and performs so much better too. It actually does a better job of emissions-work than the original one too, despite being more high performance.
If it's the right size, that appears to be an excellent price for a Magnaflow cat.
I should also mention, that besides a reduction in stench, a new high flow cat will even make your exhaust sound better. The original OEM cat muffled the sound more, and a straight pipe in place of the cat introduces a "rasp" which isn't pleasant at all.
So... installing a new high flow cat is a win/win endeavor!
[EDIT] I went to RockAuto's site. The price for that cat is actually less than $28! This particular cat is not CARB compliant, but that may or may not matter depending on where you live.
It is $40 after shipping, which is still a great price for it. I've been finding them around $100 everywhere else. It doesn't need to be CARB compliant where I live. (I live in PA)
