I bought a Magnaflow 16450 Y-Pipe and it did not fit my '90 IROC 305 TPI stock exhaust manifolds. My perception was that there was just something wrong with the pipe as it was close but just off a bit in alignment.

Last weekend I ran across a guy selling parts and we were talking about this. He told me that he has some 350 exhaust manifolds that would fit this as there is a difference in 350 and 305 exhaust manifolds.

I always thought all the TPI setup exhaust manifolds were the same when it came to Y-Pipes?

 

ID changed slightly from 305 to 350, but the external dimensions are identical

Where are you having fitment issues?

 

I have a '90 IROC 305 TPI setup.

When I try to get the Magnaflow 16450 Y-Pipe to line up, from the bottom, I put the driver side up first, both nuts on loose. Then bring the passenger side up with the spacer in place and the top of the pipe going up to the exhaust manifold is off about an inch or so (too close to the block) plus it is still about 1/2" short even with the spacer in place. Also the driver side pipr coming over to connect up with the passenger side hits the oil pan.

I tried to get the dealer who I bought the pipe from to agree that there was something wrong with the pie and exchange, but he would not go for it.

I was just on the phone with Ted (TED Gerkach on this board) and he has some 350 exhaust manifolds, says there is definitely a difference in the way they line up.

I'll et you know later as I am going down to pick up some other stuff from him and will look at these 350 exhaust manifolds.

 

Sounds like a bent Y-pipe either from the welding process or damaged when shipping

Changing manifolds wont change that

If the seller wont make the Y-pipe deal correct, then post up in the vendor review forum and cut/weld it to work

 

Well here's the update.

Went over to see Ted and he had two sets of exhaust manifolds, one from a 305 and the other from a 350. The drivers sides are the same except for the size output, 305 was 2" and the 350 was 2.25". The passenger side was definitely different, angle that the flange was at was slightly different and a little longer, looks like exactly the right part to work with the Magnaflow 16450 Y-Pipe. Too bad I sent the Y-Pipe back!

I picked the 350 passenger side up from him and somewhere in the future I'll try it again. Needs some light cleanup, going to glass bead it, paint with high temp paint and put new studs in (as usual they are broken off!).

The GM part number on this one is 14084064.

Anyone have an idea what this exhaust manifold is off of from that part number?

 

So anyone know what the 14084064 is from?

 

Uhhh... It's not a 305 vs 350 issue... It's an HO vs low output issue. Below is a picture of 92 Z28 L98 manifolds (top & bottom) and TBI/Low output manifolds (center).



The low output manifolds have smaller outlets (by about 1/4"), the passenger's side HO manifold dumps at a different angle, so the Y-pipes aren't even close to interchangeable.

So which cars got the HO manifolds? Obviously 305 HO's, and 350s. Some 305 TPI cars got the smaller manifolds. The 2.73 gears and the fact it's in a convertible are the key red flags that your 305 is a lower output LB9.

PS: You read the casting number wrong... 14094064. The matching drivers side HO manifold is a 14094063.

 

i don't understand why gm used different manifolds on the 350s and 305s unless it was to give the 305 more torque.

 

More likely it had more to do with GM not wanting to spend the time and money casting high flow manifolds for more cars than they needed to. The low output manifolds were used in other GM cars, like the Caprice, Monte Carlo, Malibu, etc. The HO manifolds are specific to the thirdgen.