Y-Pipe
06-14-2017, 02:49 PM
#3
Supreme Member
iTrader: (4)
Join Date: Dec 2001
Location: Chicagoland
Posts: 9,666
Received 546 Likes
on
376 Posts
Car: 1989 IROC-Z. Original owner
Engine: LB9. Dual Cats. Big Cam
Transmission: World Class T-5
Axle/Gears: BW 3.45
Re: Y-Pipe
The definitive post on 3rd gen exhaust by TransAmGTA350:
Originally Posted by TransAmGTA350
There were only 2 different manifolds for the V8's throughout the years, but they were different depending on what motor and gearing package they came on. Here is the breakdown.
2" outlet manifolds with single 2 1/4" y-pipe
82-87 305 LG4 (VIN H)
88-92 305 L03 (VIN E)
82-83 305 Crossfire
90-92 305 LB9 w/o G92 axle (VIN F)
2 1/4" outlet manifolds with single 3" y-pipe
83-86 305 L69 (VIN G)
85-89 305 LB9 (VIN F)
88 350 L98 (VIN 8)
89 350 L98 w/o G92 axle (VIN 8)
2 1/4" outlet manifolds with dual 2 1/4" cats
89 350 L98 w/G92 axle (VIN 8)
90-92 350 L98 (VIN 8)
89 305 LB9 w/G92 Axle (VIN F)
90-92 305 LB9 w/G92 (Vin F)
The manifolds from the single 3" cat and the dual 2.25" cats are interchangeable. On the passenger side manifold, some will have the heat riser butterfly valve, some will have a spacer, and some will just have a donut gasket. You most likely have the wrong manifold for your application. If you have the larger manifolds, then it may be worth it to get the larger y-pipe for some more performance.
2" outlet manifolds with single 2 1/4" y-pipe
82-87 305 LG4 (VIN H)
88-92 305 L03 (VIN E)
82-83 305 Crossfire
90-92 305 LB9 w/o G92 axle (VIN F)
2 1/4" outlet manifolds with single 3" y-pipe
83-86 305 L69 (VIN G)
85-89 305 LB9 (VIN F)
88 350 L98 (VIN 8)
89 350 L98 w/o G92 axle (VIN 8)
2 1/4" outlet manifolds with dual 2 1/4" cats
89 350 L98 w/G92 axle (VIN 8)
90-92 350 L98 (VIN 8)
89 305 LB9 w/G92 Axle (VIN F)
90-92 305 LB9 w/G92 (Vin F)
The manifolds from the single 3" cat and the dual 2.25" cats are interchangeable. On the passenger side manifold, some will have the heat riser butterfly valve, some will have a spacer, and some will just have a donut gasket. You most likely have the wrong manifold for your application. If you have the larger manifolds, then it may be worth it to get the larger y-pipe for some more performance.
06-14-2017, 02:53 PM
#4
Junior Member
Join Date: Nov 2016
Posts: 10
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1991 Pontiac Firebird
Engine: 305 TBI
Transmission: Auto
Axle/Gears: 7.5 and 3.42:1
Re: Y-Pipe
That Y-pipe is meant to be used with a matching set of headers - do you have headers or the factory cast-iron exhaust manifolds? If you have the cast iron manifolds then you will not be able to use that Y-pipe. I went through something similar with my own Firebird with the low output 305. I brought the car to a shop and they ended up exchanging the passenger side exhaust manifold with the one that was used on the 350 cu in V-8 - it sounds strange, but it has a different outlet configuration that allowed them to bolt up a Magnaflow Y-pipe. I see that you are in the Netherlands and I don't know if it is cost-effective but I want to mention that the passenger-side manifold and Y-pipe are still available. Here is the information:
Dorman exhaust manifold, part number 674519
Magnaflow Y-pipe, part number 16450
Hope that helps.
-Mike
Dorman exhaust manifold, part number 674519
Magnaflow Y-pipe, part number 16450
Hope that helps.
-Mike
06-14-2017, 03:13 PM
#5
Re: Y-Pipe
I have these headers:
https://cimg1.ibsrv.net/gimg/www.thi...9d3fa43972.jpg
I need an Y-pipe for them, and I do have the single cat, and the #8 in my VIN...
https://cimg1.ibsrv.net/gimg/www.thi...9d3fa43972.jpg
I need an Y-pipe for them, and I do have the single cat, and the #8 in my VIN...
06-14-2017, 03:36 PM
#6
Junior Member
Join Date: Nov 2016
Posts: 10
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1991 Pontiac Firebird
Engine: 305 TBI
Transmission: Auto
Axle/Gears: 7.5 and 3.42:1
Re: Y-Pipe
I don't want to mislead you and hopefully someone with more knowledge of those headers will chime in, but...Those look like the Flotech headers, and there is a Y-pipe available, it is part number 1102YFLT. Note though that the Y-pipe looks like the GM factory Y-pipe which is not considered to be a good design (the diameter of the pipes coming from the flanges and the "merge" pipe are all the same; no true merge collector - the one pipe just "tees" into the other).
In the picture it shows 2 flanges; if it were me, then I would take it to a shop and have them build a "proper" Y-pipe (for example, something that looks like that Magnaflow one I posted earlier).
-Mike
In the picture it shows 2 flanges; if it were me, then I would take it to a shop and have them build a "proper" Y-pipe (for example, something that looks like that Magnaflow one I posted earlier).
-Mike
Trending Topics
06-14-2017, 04:24 PM
#8
Junior Member
Join Date: Nov 2016
Posts: 10
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1991 Pontiac Firebird
Engine: 305 TBI
Transmission: Auto
Axle/Gears: 7.5 and 3.42:1
Re: Y-Pipe
No, the Magnaflow Y-pipe will not fit those shorty headers that you mentioned in post #5.
06-15-2017, 02:13 PM
#10
Re: Y-Pipe
You either need the specific y-pipe for your brand/model headers or you need to make your own. There's loads of similar headers (headman and hooker shorties are nearly identical but the collectors are at different angles) and none of the y-pipes interchange.