Searching did me no good.
I need new headers. I have a great flowing intake, heads, and then my exhaust sucks. I ordered the SLP 1 3/4" kit and I am not happy with the performance. The designer at SLP should get his **** kicked. When I measured the pipe, they put a 2 1/4" y-pipe on these headers!!!!!!!!
Anyways, who has the best y-pipe setup? I need at least 2 1/2 inch to flow my air. This will be running into a Mufflex 4" setup soon.
I know several companies "say" they have a 2 1/2" (SLP did when I called), but who really does.
I can get by with 1 5/8" headers as long as the y-pipe flows a lot of air.
Any advice on this?

 

hedmans are 1 5/8" primaries into 3" collectors with a 2.5" mandrel Y pipe...

I think you measured your SLPs wrong.

 

I measured them with a caliper.....they are 2.25" O.D.
I called SLP to verify this, and the Tech guy said "Yeah, the 2 1/4" mandrel bent flows real well."
I asked him to verify this, but he has not called back yet......but I'm not holding my breath.
I thought something was funny at first, then I went back and looked at the 2 1/2" pipes coming out of my muffler, and sure enough, they were bigger!
I am positive.......SLP y-pipe is 2.25" pipe, coming together into a 3" at the cat.

 

I supposedly have the 2.5 slp y pipe. I just had it put on not really a big difference in performance. I will go out and check the O.D. for you later on tonight

 

I just called SLP again......they said that on the 4th Gen's, the y-pipes are 2.5", on the 3rd Gens, they are 2.25". The guy said that they were designed around a 500hp 383...........
Anyways.......they say that is all they make for the 3rd gens. Let me know how big your pipe actually is.
Mine is definitely two 2.25" going into one 3".
Anybody know if the SLP y-pipe for the stock manifolds is bigger which is confusing everyone?

 

I have the slp y-pipe that goes into the stock manifolds... Just measured seems that the o.d. is 2.5... Guess slp likes to screw the 3rd gens

 

My SLP Y-Pipe measures 2.5" outside diameter going into a 3" collector. They mount to the stock exhaust manifolds on my 91 LO3. I have part #31031

 

Here's the picture of the Y-Pipe that fits on the stock exhaust manifolds and it is two 2.5" diameter pipes going into a 3" collector like SLP advertises.

 

Here's what 2.25" looks like.

 

My dad is an exhaust specialist, he made up our own custom 2.5" y-pipe for our cars. Try that route.

 

So the y-pipe for manifolds is 2.5", and the y-pipe for 1 3/4 headers is 2.25"
SLP SUCKS!!!!!!!
I paid $600 for those headers!!!!!

 

Dragula,
Did you have Hedmanns on your set up before the SLP's?

 

Sure did....but not on this engine. When the 350 TPI was in my car, I had the Hedman setup. I sold them when I put the 383 in. Perhaps I will buy some more Hedmans.
I'm not too thrilled with the SLP's right now. I like the headers, but they just constrict too much after. Even the collectors on the headers go down to 2.25", so I can't really make a lager y-pipe to fit the headers.

 

I was dissapointed to find out my slp 1 3/4 headers go into a 2.25" y pipe but you have to figure bigblock cars used to come with dual 2.25" exhausts so it isn't that bad. can you fit the 2.5 y pipe to the headers? are the header outlets in t6he same location as the manifolds were.

 

Don't think they are, but they could be cut and rewelded perhaps. After some calculating......the single 3" catback is restricting more that the dual 2.25's!