Hello all
I have an 1985 Trans Am 5.0 5 Spd with the 4BBL(code H LG4 I think).I have had the carbs rejetted and the cam for the HO installed and a 3" SLP catback system.This car has been stored for the last 10 yrs but i start it and drive it every 2-3 mnths to keep everything moving and had it coated in oil to try and keep the rust at bay.the other day while i was tending to it I noticed that when I started it it was running kind of rough so i proceded to put some carb cleaner and rev it up a little.Then i noticed smoke coming from the back of the motor WT>>>.Any way my catylic converter was cooking itself bright orange so i shut the car off and let it cool down.So Long story short it looks like I need a new cat..what I need to know is the diameter of the pipe from the Y to the cat..I have 3" after the cat but needed to use an adapter pipe to make it fit..if i get a 3"in-3" out hiflow cat will it work..any advice would be greatly appreciated.

 

https://www.thirdgen.org/forums/exha...-question.html

JamesC

 

that link shows.....

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)

so what your saying here is the y-pipe to the cat is 2 1/4 "
on my vin-H car
is that right??
can the vin-G manifolds fit on the vin-H motor just by bolt on or do the heads need to be changed
this would give me a 3" y-pipe to a 3" exhaust im guessing

 

The LG4 and L69 heads are exactly the same thing.