Hi guys, is there any difference between 305 and 350 TPI exhaust manifolds, or are they the same part #s?

How fast have you guys gone with TPI exhaust manifolds (with the 350 ones, if they are better than the 305)?

I have a 327 that is a solid high 13 sec motor in my heavy 2nd gen, that I am going to swap into my 3rd gen. I hate headers leaking and being noisy. Will exhaust manifolds and my 3" 3rd gen single cat exhaust support my 327 running high 13s?

 

the manifold on a stock f-body are probably the worst manifolds ever in the whole history of manifolds

 

Hehehehe. You should see some of the Ford exhaust manifolds.

 

The 305 TPI and 350 TPI exhaust maniflolds should be the same. The 305 TBI manifolds I know were different.

 

Well I have all stock components (except for the free mods) and I've ran a 14.57 in the quarter, 93mph. However this was clocked by a laptop sitting in my passenger seat. Not an elaborate timing mechanism on a 1/4mile track. There are no 1/4 mile tracks near where I live.

 

The 305 TPI's with G92 got the better 350 exhaust manifolds. The 305 TPI's without G92 got the smaller LG4/TBI exhaust manifolds. The easiest way to tell is to look at the i-pipe. If its 2.75" you have the good exhaust. If its 2.25" you have the bad exhaust. If your cat-back pipe has been changed, then you'll have to guess. Search the exhaust board, I am sure the manifold part numbers have been posted.
Attached you can see the difference. The left outlet is the LG4/TBI manifold and the right outlet is the better TPI manifold. I have more pics if you need them.

 

Thanks, I can see the diff in outlet size, I will have to see if I can find the casting #s for the better manifolds. I have the 2.75" I pipe but it is not from the same car as the engine so I have no idea what the manifolds are. I am pretty sure they did not neck down inside and are the better ones.

 

The outlets on the larger TPI manifolds are also at a slightly different angle than those of the smaller/low output motors on the pass. side. You can barely see the difference with your eye, but believe me, it's different.

Although I've never tried it, I doubt a larger diameter TPI-style y-pipe (2-1/4" down pipes, 2-3/4" main pipe) would seal up against the pass. side manifold outlet if it was a lo-po manifold.

I don't think any TPI motor got the small diameter lo-po exhaust manifolds, whether it was single cat TPI or a dual cat system, regardless of horsepower rating, year or engine displacement. TBI engines did (all years) and the earlier carbureted LG-4 low output engines did (all years). But I don't think any TPI engine did, nor did any of the earlier carbureted L-69 HO motors.

 

Sorry, but I have proof. My dad's 1990 Trans Am with the 305 TPI and automatic (lo-po) had the smaller TBI exhaust manifolds. My 1991 Camaro Z28 with the 305 TPI and 5-speed (hi-po G92) had the larger 350 TPI manifolds. I also know of another 1992 Z28 with a 305 5-speed (lo-po single cat) that has the smaller TBI manifolds.

 

My friend's 91 Z28 with a 305 TPI and automatic had the smaller TBI manifolds and Y-pipe. My '87 IROC that had a 305 TPI and automatic had the larger manifolds and Y-pipe, which we swapped onto my friend's car after I installed headers on my car.

 

My 86 LG4 Trans Am ran a best of 14.94@92mph with the stock manifolds.
My 88 TPI Formula has only ran a best of 15.2 @ 93 mph with manifolds.

 

Thanks for the photo of the two manifolds. I guess my car has the bigger ones, since my stock Y pipe is pretty big, and the I pipe is 2.75.

 

So you're saying there are 3rd gen 305 TPI motors that came from the factory with the little manifolds, smaller 2" down-pipes, 2-1/4" y-pipe, 2-1/4" cat and, I guess, 2-1/4" cat-back, like the TBI engines got?

Well, I guess you learn something new every day. I've never run into one of them.

 

Damon's right on the money. I tried bolting the larger factory y-pipe to the TBI manifolds, and they won't seal up due to the difference in size. He's also right that the passenger side manifold is slightly different in length too. The passenger side collector on the larger manifold is about 1-2" lower than the small manifold. I was just going to bolt up the larger y-pipe, but I ended up having to change the manifolds as well to get everything to work together. Woohoo, my 1000th post!

 

Went a 13.50 with stock manifolds. they should be fine for what you want to do.

 

Super, sounds like i have the hi po manifolds and they will do what I need. GTA your car looks familiar, here's mine. Mine is actually a 1983 base model Firebird that I added all the 85-80 TA parts to and painted it myself. I converted it to 305/auto but will be putting my 327 in it soon.