I find it interesting that aftermarket exhaust manifolds are widely available for our cars. Not speaking of headers, but manifolds. I can't imagine there is a big market for them..

 

While only 10s of thousands of 3rdgens had SBCs with the logs, millions of other SBCs used them too. At least the aftermarket reproduced the "best" version, those being the ones used on the LB9 and L98.

But I've read that the quality of the aftermarket manifolds is poor. The cast iron is inconsistent in thickness, weak and prone to cracking and crumbling. I suppose if someone doesn't have access to a sand blaster to clean up rusty old OE manifolds, or he doesn't want to sand and paint them, then the aftermarket manifolds, at least, are new and look nice. But turns out it's best for people to try to "restore" OE manifolds the best they can.

There used to be a company that modified 4thgen LT manifolds to use on SBCs with typical square port heads. He began using new aftermarket manifolds, but he had so much trouble with their quality that he eventually switched to modifying and refurbishing OE manifolds. Unfortunately, he just retired earlier this year.

 

It was Randy Brzezinski that did the 4th gen LT1 exhaust manifolds.

 

Were those the ones that came up over the engine ? Like the D port LT1 manifolds. Are there pictures ?

 

Yes the manifolds I'm talking about that Randy Brzezinski did were the ones used on the cars that came with the 4.3L/5.7L V8 L99/LT1/LT4 engines installed in GM cars aside from the Y-Body C4 Corvettes. The C4 Vette 1992 to 1996 LT1/LT4 manifolds also flow well for factory cast iron manifolds and flow a little bit better than the other L99/LT1/LT4 manifolds but absolutely CAN NOT be used in B-body, D-body, or F-body applications or other V8 engine swap applications like S10 trucks because the Vette manifolds are center dump design with the manifold outlet between cylinders 3 & 5 and cylinders 4 & 6 and the exhaust will run right into engine cradle/suspension on cars that can't run center dump style manifolds.

At one point in time Randy had 3 videos on his YouTube page about the LT1 manifolds. One was this technical video below that he has since put back online, one was a video about how the aftermarket passenger side manifold casting quality sucked and he only wants to modify factory GM manifolds from now on, and the other video was about him not keeping the modified manifolds in stock ready to go because he had other more important projects to focus his time on but he would still do them if you sourced the factory GM manifolds, removed the heat shields and other fittings, and made sure they weren't cracked on the passenger side manifold between cylinders 6 & 8.

He made the videos not available on his page about 4 or so years ago back when he quit fooling with them on a regular basis. He has since put the video below back up again with some of the other videos about other things he had removed so that the information will still be out there for people wanting to know. He said he was going to put some of his older videos back online before he sold the business and retired so the information would be there and not lost forever. The video below was one of them I was hoping he would put back online. I just today noticed it was back online when I went to look to see if I could find some pictures for you to see the modified LT1 manifolds.

You Tube

 

Those LT1 manifolds are a direct replacement for the L98 manifolds? LB9 manifolds.. or you need to modify the Y pipe. (down pipes)

 

It's not a 100% bolt in deal. If this was as easy as a just bolt it right in swap there wouldn't be a 4th gen LT1 manifold left on Earth to buy because they would all be on 3rd gens replacing those horrible log manifolds.

There will have to be some modifications done to the Y pipe. A 4th gen LT1 Y pipe will not work either in a 3rd gen without modifications. Both will require modifications so best to start with a 3rd gen Y pipe that is made to fit your 3rd gen's underbody and modify it to fit the LT1 exhaust manifolds.

3rd gen manifolds have a 2 bolt ball & socket flange while 93/94 50 state single cat and 95 49 state single cat 4th gen manifolds have a 3 bolt ball & socket flange. The manifolds will have to have the missing holes machined into them. All the additional holes can be machined into them for a 6, 7 or 8 bolt pattern head except for the passenger side rear of a 6 bolt pattern head. So if you have a 7 bolt pattern head like a L03, L05, LB9, L98 or an aftermarket 7 or 8 bolt pattern head you good to go on being able to machine all the holes required. If you are using Vette L98 D port heads or similar aftermarket L98 style 7 or 8 bolt pattern D port heads you should be good to go.

Your going to have to get the Y pipe spatially located in the car where it needs to be then modify the the down tubes on the Y pipe to position them where they spatially need to be to mate up with the outlets on the LT1 manifolds. Also going to need to use a 3 bolt flange on the down tubes to mate up with the 3 bolt flange on the exhaust manifolds.

 

Good question. I would think our manifolds were only designed for the Camaro and Firebirds, but that still is a lot of cars.