91 catback - what's unique about it?
Thread Starter
Burning Brakes
Joined: Nov 2001
Posts: 1,189
Likes: 2
From: Austin TX
91 catback - what's unique about it?
The '91 rear y-pipe and mufflers are different than the 86-90 and 92-96,
according to some of the direct fit manufacturers like Walker, for instance,
yet some of the aftermarket mfrs advertise both y-pipes by themselves
and catback systems for 86-91 (inclusive), and some specify they only
fit 86-90.
Does anyone know what is unique about the '91? I got the impression
somwhere that it was 2 1/2" in the back instead of the 2 1/4" for 86-90, but that
wouldn't make sense for the mfrs that are advertising that their y-pipe
is a direct replacement for 86-91. I also gather from a diagram, which
of course may not be accurate, that the inlet on the '91 muffler is
offset to one side rather than centered like the 86-90.
I'm curious to know the difference, but my primary goal is I'm looking for
a 2 1/2" rear y-pipe option other than the one Borla offers (which is stainless)
in case I need to weld it or modify it.
Thanks,
Dan
Le Mans Master
Joined: Jul 2002
Posts: 5,818
Likes: 2
From: Alive and well in Burlington NC
Re: 91 catback - what's unique about it? (danno85)
:lurk:
I know how you feel. The 91 seems to be a transition between the L98s (85 to 90) and the LT1 in 92. When I decided to go with Flowmasters, I found that there is only one set for the 91. For the years before there are a few choices and also for 92 and above.
I know how you feel. The 91 seems to be a transition between the L98s (85 to 90) and the LT1 in 92. When I decided to go with Flowmasters, I found that there is only one set for the 91. For the years before there are a few choices and also for 92 and above.
Thread Starter
Burning Brakes
Joined: Nov 2001
Posts: 1,189
Likes: 2
From: Austin TX
Re: 91 catback - what's unique about it? (Steel Blue 91)
I know how you feel. The 91 seems to be a transition between the L98s (85 to 90) and the LT1 in 92. When I decided to go with Flowmasters, I found that there is only one set for the 91. For the years before there are a few choices and also for 92 and above.
a different system for 91 only. After doing some digging I found out that the
Flowmaster y-pipe is available (the their y-pipe is unique to 91 also), but
I can't tell what's different about it. The Borla 2 1/2" y-pipe they say only
fits 86-90, even though you have to get their mufflers.
You don't happen to know what the y-pipe size is on your '91 Flowmaster
catback system is, do you?
Thanks,
Dan
Melting Slicks
Joined: May 2000
Posts: 2,029
Likes: 63
Re: 91 catback - what's unique about it? (danno85)
I don't know what is so special with '91 L98 cat back but one thing I do know: it is 2 1/4" like the older ones. I bought the Walker Y-pipe and Dynomax mufflers for mine - they fit just fine.
Le Mans Master
Joined: Jan 2004
Posts: 7,276
Likes: 3
From: Why are there squished peanut butter cups in my underware?
Re: 91 catback - what's unique about it? (TA)
Here is what I learned about the `91 mufflers last year when I bought a new set.
The 5hp difference during the `88 through `91 was because of two different mufflers for the L-98s. All convertibles and 2.59 axle coupes had the "restricted" mufflers (only one of the two nozzles are functional). Coupes with 3.07 auto and manuals had the "sport" muffler (both nozzles functional with the 5+hp).
I work at a Corvette shop, and have noticed that all `91 L-98s have the "restricted" mufflers! Including my `91 6-sp coupe when I bought it! Who knows, maybe because of the previous years having two different mufflers, most of the catalogs and part sources assume the `91s have a different muffler than previous years L-98s.
When buying a new set, just get what you want. If it will fit with a L-98 system, it will fit with a `91.
The 5hp difference during the `88 through `91 was because of two different mufflers for the L-98s. All convertibles and 2.59 axle coupes had the "restricted" mufflers (only one of the two nozzles are functional). Coupes with 3.07 auto and manuals had the "sport" muffler (both nozzles functional with the 5+hp).
I work at a Corvette shop, and have noticed that all `91 L-98s have the "restricted" mufflers! Including my `91 6-sp coupe when I bought it! Who knows, maybe because of the previous years having two different mufflers, most of the catalogs and part sources assume the `91s have a different muffler than previous years L-98s.
When buying a new set, just get what you want. If it will fit with a L-98 system, it will fit with a `91.
Drifting
Joined: Apr 2003
Posts: 1,379
Likes: 4
From: rome ny
Re: 91 catback - what's unique about it? (Z-07 freak)
i just went threw this with my 91. the rear y-pipe on the 91 has a little different angle on the pipes going to the mufflers. thats why if you buy borla mufflers you must buy the y-pipe to go with it. i tried to use 85-90 mufflers with my stock y-pipe and it wouldnt work. i think i may be to the new style rear end. also the stock y-pipe on a 91 is 2 1/4 inches not 2 1/2. if you are going to buy a complete borla system buy the stingers. thats what i put on mine, and its great.
[Modified by mos90, 11:45 PM 3/26/2004]
[Modified by mos90, 11:45 PM 3/26/2004]
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Thread Starter
Burning Brakes
Joined: Nov 2001
Posts: 1,189
Likes: 2
From: Austin TX
Re: 91 catback - what's unique about it? (mos90)
Thanks for everyone's input - it was all helpful.
Just to fill you in, I've got an '85 but with Hooker headers, 3"
front y-pipe and high flow 86-up cat. Right now the catback is
pretty much stock. I'm running a miniram and HP peaks at 6200rpm.
I know that the rear y-pipe and mufflers are a restriction, but even
with that I'm running 12.7s @ 114 and making 330 rwhp.
I also don't want a really loud exhaust note.
So I'm going to try the Dynomax Super Turbo mufflers for an LT1
which have 2 3/4 inlets and will settle for a 2 1/2 rear y-pipe. I was hoping
that the '91 might be 2 1/2, but it's not. So that leaves two more expensive
options. I'll get one of them, adapt the LT1 mufflers to it and see how
it goes.
In restrospect I should have gone with a LT1 system, but, you know what
they say about hindsight...
Thanks again,
Dan
Just to fill you in, I've got an '85 but with Hooker headers, 3"
front y-pipe and high flow 86-up cat. Right now the catback is
pretty much stock. I'm running a miniram and HP peaks at 6200rpm.
I know that the rear y-pipe and mufflers are a restriction, but even
with that I'm running 12.7s @ 114 and making 330 rwhp.
I also don't want a really loud exhaust note.
So I'm going to try the Dynomax Super Turbo mufflers for an LT1
which have 2 3/4 inlets and will settle for a 2 1/2 rear y-pipe. I was hoping
that the '91 might be 2 1/2, but it's not. So that leaves two more expensive
options. I'll get one of them, adapt the LT1 mufflers to it and see how
it goes.
In restrospect I should have gone with a LT1 system, but, you know what
they say about hindsight...
Thanks again,
Dan
Team Owner
Joined: Sep 2001
Posts: 62,146
Likes: 1,730
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Re: 91 catback - what's unique about it? (Z-07 freak)
When buying a new set, just get what you want. If it will fit with a L-98 system, it will fit with a `91.
Who knows why GM did these things with the L98 catback.
