I have been spending all night researching options to choose for my exhaust manifolds and matching y-pipe and wanted to get someone with more experience (this is my first ever project car) to help me decide what makes the most sense for my situation. I have an 88 trans am 305 tbi with full stock everything. The current old manifold on the driver's side is leaking like crazy, so it needs to be changed anyway. I am currently between upgrading to the bigger stock manifolds from the TPIs or finding a header set that would be in a reasonably close price range to that. I know my car won't make crazy power numbers, so I am not concerned with increasing HP a ton. Mainly looking at something that will be fairly straight forward to install and not cost an arm and a leg.
- For a header option the hooker 2460s seemed reasonably easy to install but the y-pipes I have found that go with it seem a little expensive for my price range currently.
- For a more stock option, the Dorman OEM manifolds and walker y-pipe on rockauto seem decent enough just don't know if they will fit or be too restrictive.

The main sound output I am looking for will come from a great deal on a Magna flow muffler with tailpipes I picked up. The guy I bought it from cut off the inlet flange so I can weld on either a 2.5in or 3in connector to fix that. This will depend on what you guys suggest I shoot for for overall exhaust system diameters. Any help would be greatly appreciated let me know if you need more details on my situation. Also, I'd like to remove the smog AIR stuff eventually if that determines anything.

 

Can you post us up a couple of pictures of the Magnaflow muffler and tailpipes you got so we have an idea what you are working with? Mainly so we can see where and what was cut off.

 

Since cost is an issue and you're not concerned with HP, the OEM's seem the way to go. The piping from the headers can get expensive and thorny with some state laws. I did the LS swap with Hedman long tubes on my trans am, and I had an exhaust shop fabricate the rest. Take a look at this old thread, though:

https://www.thirdgen.org/forums/exha...rs-2460-y.html

HED-68470 and HED-17478 seemed to work well, and Summit still sells them.

Also, are TBI and TPI manifolds interchangeable? This old ZZ3 article has good images of the upgrades for a TPI dual cat system:
https://www.camarotech.com/engine-ZZ3.html

And this old comment describes the Y piping differences:
https://www.thirdgen.org/forums/exha...ml#post1084669

 

If using Dorman, make sure you locate the correct cast iron spacer that does not come with their right side manifold. I found one on EBAY (lucky) and it fits the Dorman manifold perfectly. They need to reproduce this! Are you listening Dorman?

 

Here are a few images of what I am working with. It looks like a big enough space to work with welding on a new flange.

 

What is this spacers part number/look like? Also how crucial is it to have?

 

Thank you for all this great info. I think I am going to go with the oem ones off of rockauto and hope installation is fairly straight forward. I am glad to see the TPI manifolds should just bolt right up to the block. Hopefully the provided walker y-pipe on rockauto also connects with little to no extra fab work.(I assume it should since they are oem)

 

Mine does not have a part number. I've heard they have HO cast in them. There probably is a spacer for the smaller manifolds so be aware, I would expect them to be smaller. Here is a photo of one. You can barely see the "HO" cast in it. Mine is probably corroded but it fits like a glove.

 

you can re-use your existing spacer, it will likely just be a bit narrower

 

Headers and reasonably easy install don't really go together. There always seem to be fitment challenges with them. Definitely not as straightforward as swapping exhaust manifolds.

For a 305TBI motor, going with the HO exhaust manifolds and full 3" exhaust system does make a noticeable difference. But, headers won't do much more than the HO manifolds on a stock TBI motor. Not worth it in my opinion.

The HO manifolds bolt right up to the motor no problem. You'll need the cast iron spacer on the passenger side. Your existing spacer might bolt up (it's been a long time, I don't recall), but the ID will be narrower, kind of defeating the purpose of the larger manifolds. Use the 3" Y-pipe and 3" intermediate pipe and connect to your Magnaflow muffler/tailpipe setup.

Some other things to do on that 305TBI to wake it up a bit

-Get a higher flow air cleaner setup. The stock single snorkel is pretty restrictive. The dual snorkel from the 305HO motors is the ideal option, but those are very hard to come by (and expensive) these days. Even a round open element air cleaner assembly will be better than the stock setup, but not as good as the dual snorkel since it will be pulling in hot underhood air. I have also seen other setups with an intake tube and filter with an adapter to the throttle body. There are options out there.
-Bump the base ignition timing up to 6BTDC (should be 0BTDC stock) and run 93 octane

Somewhat costly, but will make a big seat of the pants difference:
-Swap the rear end gears and add a posi. 3.23 or 3.42 for an auto, 3.42 or 3.73 for a manual

 

I appreciate all of this information. I will be going with the HO manifolds and Y-pipe. Unfortunately my muffler is only 2.5 inches i will just go with the walker HO I-pipe that is 2.75 inch with 2.5 inlet and outlets. I just need to find some kind of way to connect the 3 inch out Y-pipe to a cat that fits with the I-pipe. This is still bigger than the choking stock one thats on there and the leaks need to be fixed anyway so as long as it sounds good I'm happy. If someone has personally used the Walker 40439 Y-pipe and know how to get to the I-pipe (Walker 46669) with a cat that would be a lot of help.

The open air element was actually going to be my first "mod" I just cant get the air tube in the valve cover out and dont want to break the dry-rotted grommet out into the cover so that will have to wait until i remove the covers again.