Factory exhaust size 1988 Firebird formula
 

I have a 1988 Firebird Formula with the LB9 305 TPI. I need to know what the stock exhaust pipe size would have been on this engine. The cat has been removed long before I had it and will stay removed. If anybody has the GM parts manual or the diagram showing the exhaust sizes and layout, that would be helpful as well. I'm trying to put this car back stock as possible w/o the cat because it would be stopped up anyway, and make a good driving car out of it. Any help is appreciated.

Re: Factory exhaust size 1988 Firebird formula
 

Stock it could have been 2.25" or 2.5". Rock Auto sells exhaust pipes in OEM sizes that are reasonably priced.

Re: Factory exhaust size 1988 Firebird formula
 

The LB9 would have had 2.5 im pretty sure. The L03 had the choking 2.25. Do yourself a favor and go ahead 3in all the way you wont be sorry. With the way these cars are setup with one exhaust pipe it helps to go a lil bigger especially if you upgrade with a bigger stronger engine down the road.

Re: Factory exhaust size 1988 Firebird formula
 

Is there a bolt on kit that does not have a provision for a catalytic converter? Most bolt on systems I've found have the flange at the front of the pipe for it and I'm not going to put one back on. I guess if that were the case Id have to cut the flange off and put in a piece of pipe for that part.

Re: Factory exhaust size 1988 Firebird formula
 

That's what ive always had done