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I recently ordered an APH-X5500 from Summit. It is 3” od. I think it is made for a 4th gen. I won’t get to fitting on the car until sometime this Fall after the new engine goes in but it has a significant crush where it goes over the rearend and above the pan hard bar.
Hey Chazman - Have you ever run across flow numbers for our iron manifolds? I'm wondering if they are really all that bad. Why would GM limit flow, seems like better flow = better gas mileage and an easy way to meet standards. I guess I sort of answered my own question concerning GM - they only needed enough flow for the HP of the day, but would still be interesting to see flow numbers.
Last edited by LiquidBlue; 07-14-2024 at 01:05 PM.
@LiquidBlue Does your 1990 Formula with 5.0L LB9 TPI engine and MD8 4L60 transmission have the factory installed exhaust manifolds and exhaust system on it now?
If the answer is yes.
Then you have the worst cast iron exhaust manifolds ever installed on a TPI engine and the worst exhaust system ever installed on a TPI engine. It's basically a 2.8L/3.1L V6 exhaust system. Your SLP Cold Air Induction system and Siamesed runners look pretty and that is all they do. 40+ HP has been left on the table.
@LiquidBlue Does your 1990 Formula with 5.0L LB9 TPI engine and MD8 4L60 transmission have the factory installed exhaust manifolds and exhaust system on it now?
If the answer is yes.
Then you have the worst cast iron exhaust manifolds ever installed on a TPI engine and the worst exhaust system ever installed on a TPI engine. It's basically a 2.8L/3.1L V6 exhaust system. Your SLP Cold Air Induction system and Siamesed runners look pretty and that is all they do. 40+ HP has been left on the table.
The part numbers are on the manifolds, I will grab them some day. Building a house at the moment, keeping me away from the Bird. I should add that a 1990 car is not about HP, its nostalgic. HP is fun, but so is history. So, where do we draw the line? I can grap another 200 HP for the Formula with no problem, or I can buy a Toyota that will keep up with that extra 200 HP easily. So, what is more important. At a car show, I want to see what Detroit produced back in the day, so the line is fine my friend.
Last edited by LiquidBlue; 07-14-2024 at 09:16 PM.
In 1990 to 1992 GM screwed the LB9 MD8 Camaro & Firebird owners. Your car has the 230 HP 300 FT-LB engine. It also had or has the LO3 TBI exhaust manifolds and the LO3 TBI exhaust system. This choked the life out of it down to 200 HP and 285 FT-LB. 5 HP was killed by the Firebird's more restrictive air induction system.
You car can have the power GM stole from you and reap the rewards of your SLP C.A.I. and runners while remaining stock appearing using factory stock TPI H.O. exhaust manifolds. Add a factory GM 2025 RPM stall torque convertor and 3.23 or 3.42 rear end gears and be mind blown by the seat of the pants feel of the before & after comparison between the two configurations.
I recently ordered an APH-X5500 from Summit. It is 3” od. I think it is made for a 4th gen. I won’t get to fitting on the car until sometime this Fall after the new engine goes in but it has a significant crush where it goes over the rearend and above the pan hard bar.
SLPs 3" over axle pipe is built the same way with the clearanced area. No performance loss
@Airwolfe - Thanks for the info, I'll have to look into that a bit closer. I was reading around here that the iron exhaust manifolds also could use a little porting, like top and side or something, forget the specifics.
In 1990 to 1992 GM screwed the LB9 MD8 Camaro & Firebird owners. Your car has the 230 HP 300 FT-LB engine. It also had or has the LO3 TBI exhaust manifolds and the LO3 TBI exhaust system. This choked the life out of it down to 200 HP and 285 FT-LB. 5 HP was killed by the Firebird's more restrictive air induction system.
You car can have the power GM stole from you and reap the rewards of your SLP C.A.I. and runners while remaining stock appearing using factory stock TPI H.O. exhaust manifolds. Add a factory GM 2025 RPM stall torque convertor and 3.23 or 3.42 rear end gears and be mind blown by the seat of the pants feel of the before & after comparison between the two configurations.
Yup, big cam, small exhaust on '90-'92 non G92 LB9.
The intermediate pipes I linked earlier in the thread are for the 1986 to 1989 LB9/L98 style 2 bolt flange ball & socket cat convertor and exhaust system.
The intermediate pipes I linked earlier in the thread are for the 1986 to 1989 LB9/L98 style 2 bolt flange ball & socket cat convertor and exhaust system.
So much has been about your Formula lately, and you rarely talk about your other cars, that I forgot about the others.
Since any new I-pipe you get for the IROC will have to be modified anyway, and you've already had a shop make a new I-pipe for the Formula, if you liked their work, then why not just have them fab the new pipe for the IROC in the size you prefer? Seems like the simplest solution. You might end up there anyway.
There's a shop in Chicago called Fluid Motor Union with a lot of cool videos on YT, where they design, build and explain the reasons and theories behind everything they do. They do very high-end custom exhaust systems for exotics and such, so 3rdgens aren't quite on their radar lol. I contacted them about the possibility of discussing something for a 3rdgen, which they're happy to do, for $100/half hour. Price doesn't bother me because they clearly know their stuff, but it just seems like there isn't much different that can be done with an exhaust system for a 3rdgen, given clearances and lack of routing options. But it would be cool to see them design a maximized exhaust system for a 3rdgen. Take your Formula there (because I know you aren't going to modify your other 3rdgens), and maybe they'll do a video where they design, build and install a custom exhaust system for it. If I lived there, I would. It would, at least, be fun to visit and watch.
So much has been about your Formula lately, and you rarely talk about your other cars, that I forgot about the others.
Since any new I-pipe you get for the IROC will have to be modified anyway, and you've already had a shop make a new I-pipe for the Formula, if you liked their work, then why not just have them fab the new pipe for the IROC in the size you prefer? Seems like the simplest solution. You might end up there anyway.
There's a shop in Chicago called Fluid Motor Union with a lot of cool videos on YT, where they design, build and explain the reasons and theories behind everything they do. They do very high-end custom exhaust systems for exotics and such, so 3rdgens aren't quite on their radar lol. I contacted them about the possibility of discussing something for a 3rdgen, which they're happy to do, for $100/half hour. Price doesn't bother me because they clearly know their stuff, but it just seems like there isn't much different that can be done with an exhaust system for a 3rdgen, given clearances and lack of routing options. But it would be cool to see them design a maximized exhaust system for a 3rdgen. Take your Formula there (because I know you aren't going to modify your other 3rdgens), and maybe they'll do a video where they design, build and install a custom exhaust system for it. If I lived there, I would. It would, at least, be fun to visit and watch.
The only shop still bending pipe that I know of, only bends 2.25" pipe. I'm happy with the current exhaust on my LG4 Formula. It was a commercially available 2.5" which was modified to work on my car.
I have seen Fluid Motor Union on Youtube. I haven't reached out to them, but they appear to do first rate work.
I recently ordered an APH-X5500 from Summit. It is 3” od. I think it is made for a 4th gen. I won’t get to fitting on the car until sometime this Fall after the new engine goes in but it has a significant crush where it goes over the rearend and above the pan hard bar.
I think this is the one. I know it will need a front extension and flange. All of them will. I'd always want to go with Dyno Don, but that's more than double the price and will still need cutting and welding.
I was just about to ask you where you got that convertor and the part number because it looks so much like an OEM convertor and has a huge opening and ask you to lay a ruler across the flange both ways so I could get an idea of the opening size if you hadn't mounted it yet. I thought it would make a nice looking and flowing cat for my friend's 86 GN for when we install his 3" SS downpipe and 3" SS single shot passenger side exit cat back exhaust system. Stock GN has a 2.5" downpipe with 2.5" round inlet cat and 4 bolt flange exit that Y off to two 2.25 pipes to a transverse crossflow muffler with two 2.25 tailpipes. I think the 4 bolt flange pattern is the same on an IROC and a GN but the oval opening in the cat looks smaller on his factory cat because it's kind of a 2.5" size oval. The opening on your NOS GM cat looks much bigger and it closer to the bolts.
RJC Racing GN Flanges. Stock size is top right. They also make this style flange in a 3" opening size. NOS GM GN cat vs Highway Stars reproduction cat opening sizes.
What 3" inlet muffler and tailpipes did you end up with on your IROC-Z?
I was just about to ask you where you got that convertor and the part number because it looks so much like an OEM convertor and has a huge opening and ask you to lay a ruler across the flange both ways so I could get an idea of the opening size if you hadn't mounted it yet. I thought it would make a nice looking and flowing cat for my friend's 86 GN for when we install his 3" SS downpipe and 3" SS single shot passenger side exit cat back exhaust system. Stock GN has a 2.5" downpipe with 2.5" round inlet cat and 4 bolt flange exit that Y off to two 2.25 pipes to a transverse crossflow muffler with two 2.25 tailpipes. I think the 4 bolt flange pattern is the same on an IROC and a GN but the oval opening in the cat looks smaller on his factory cat because it's kind of a 2.5" size oval. The opening on your NOS GM cat looks much bigger and it closer to the bolts.
RJC Racing GN Flanges. Stock size is top right. They also make this style flange in a 3" opening size. NOS GM GN cat vs Highway Stars reproduction cat opening sizes.
What 3" inlet muffler and tailpipes did you end up with on your IROC-Z?
Probably the last NOS one left in the world. LOL! My friend found it in someone's parts stash, long story .....he had no idea what it was for, but when I saw it I recognized it and he gave it to me. I did take measurements of it in an old thread. I still have the banged up, original if you need any measurements.
I still have the banged up, original if you need any measurements.
Yeah that would be great if you would. But no hurry though. We took his GN to my exhaust guy July 3rd and had him replicate the 3" single shot exhaust in 2.5" smooth compression bent tubing from the downpipe eliminating the catalytic convertor and it sounds and runs so much better than the clapped out factory exhaust that was on it. The factory muffler with the insides rotted out and rattling around inside it must have really been killing exhaust flow. I got a feeling how nice this "temporary" exhaust system is has pushed back the 3" upgrade until we do the T/A Performance headers and bigger turbo upgrade.
3" 304SS GN1 Single Shot Exhaust
Originally Posted by chazman
Muffler/tailpipe assembly is OEM.
So you had it necked down to fit the factory muffler?
Yeah that would be great if you would. But no hurry though. We took his GN to my exhaust guy July 3rd and had him replicate the 3" single shot exhaust in 2.5" smooth compression bent tubing from the downpipe eliminating the catalytic convertor and it sounds and runs so much better than the clapped out factory exhaust that was on it. The factory muffler with the insides rotted out and rattling around inside it must have really been killing exhaust flow. I got a feeling how nice this "temporary" exhaust system is has pushed back the 3" upgrade until we do the T/A Performance headers and bigger turbo upgrade.
3" 304SS GN1 Single Shot Exhaust
So you had it necked down to fit the factory muffler?
Actually necked it up to slip over the muffler inlet.
it sounds and runs so much better than the clapped out factory exhaust that was on it.
To each his own, but I absolutely love the way the factory exhaust sounds. GM did an excellent job in making the car purr out of the box. That is something I've always been worried about if I was to install headers, etc.
Oh I love the way the factory exhaust sounds on our 3rd gen Camaros & Firebirds and the Buick Grand Nationals like my friend has.
When we had it up on the lift installing the Bilstein shocks we used almost an entire roll of exhaust system tape wrapping up all the holes. That was a vast improvement because it moved the nasty sound from under us and from the side of us all the way to the back of the car.
When I was referring to the clapped out factory exhaust system on my friend's Grand National sounding horrible it was due to the fact that from the Y after the cat there were pinholes and holes you could stick the tip of your pinky finger into on both intermediate pipes, small holes where the intermediate pipes enter the dual inlet/dual outlet transverse crossflow muffler and the same on the exit from the muffler and also in the tailpipes. When we took off the factory muffler I picked it up and shook it and all the guts inside had rusted out and it sounded rocks rattling around in a metal Folger's coffee can.
Here you go Airwolfe. Looks like 2.5" by about 3.5".
I fully expected this cat to be hollow. It was hit before I got the car and had a hole in the case. I patched it with high temp JB Weld. It rattled sometimes.One day about 8 or 9 years ago I gave it heavy throttle and nothing happened. A second later the car took off and I heard a bunch of stuff coming out of the exhaust. My friend who was behind me said it was a huge brown cloud. I assumed that was all of the cat's substrate coming out. The shrapnel took out the back part of my intermediate pipe. I had that repaired back then. But I was fully expecting this cat to be hollow and obviously it's not.
Oh I love the way the factory exhaust sounds on our 3rd gen Camaros & Firebirds and the Buick Grand Nationals like my friend has.
When we had it up on the lift installing the Bilstein shocks we used almost an entire roll of exhaust system tape wrapping up all the holes. That was a vast improvement because it moved the nasty sound from under us and from the side of us all the way to the back of the car.
When I was referring to the clapped out factory exhaust system on my friend's Grand National sounding horrible it was due to the fact that from the Y after the cat there were pinholes and holes you could stick the tip of your pinky finger into on both intermediate pipes, small holes where the intermediate pipes enter the dual inlet/dual outlet transverse crossflow muffler and the same on the exit from the muffler and also in the tailpipes. When we took off the factory muffler I picked it up and shook it and all the guts inside had rusted out and it sounded rocks rattling around in a metal Folger's coffee can.
Anything is a vast improvement over that.
Yeah, I tried everything to save the factory pipe. From the aforementioned shrapnel repair to plugging a couple dozen pinholes with JB Weld. When this happened I gave up.
Here you go Airwolfe. Looks like 2.5" by about 3.5".
I fully expected this cat to be hollow. It was hit before I got the car and had a hole in the case. I patched it with high temp JB Weld. It rattled sometimes.One day about 8 or 9 years ago I gave it heavy throttle and nothing happened. A second later the car took off and I heard a bunch of stuff coming out of the exhaust. My friend who was behind me said it was a huge brown cloud. I assumed that was all of the cat's substrate coming out. The shrapnel took out the back part of my intermediate pipe. I had that repaired back then. But I was fully expecting this cat to be hollow and obviously it's not.
Anyone have any idea what blew out of my exhaust and filled the curve over the axle part of my intermediate pipe with shrapnel holes if it wasn't substrate from the cat?
I have no idea what could have blown out the back part of your intermediate pipe but I bet it wasn't this.
This isn't a socket head. This is just a smooth round recess in the head of whatever this is.
When we were doing the exhaust on my friend's 86 Grand National this fell out of the end of the downpipe or the entrance of the cat. One owner car 100% bone stock and original. My friend that owns the GN and I have known the family that bought the GN new our entire life.
We had already chopped off the factory exhaust and only thing left was to remove the convertor. My guy had cut off the clamp and was using a torch to warm up the downpipe so it would expand while I was wiggling and twisting on the cat to pull it free. Finally it gave up its grip on the cat and this thing fell out. I was in disbelief thinking my lying eyes had deceived me and I didn't just see this fall out of the cat entrance. I looked on the ground and there was the intact clamp. I thought maybe something on the bottom of the car had fell off. I looked over at my guy holding the torch and he looked at me and said "Did that just fall out of the cat?". Then it hit me that my lying eyes weren't deceiving me and yes it did just fall out of the cat. I said "Yeah!!!". I had gloves on so I reached down to pick it up and look at it and it was hotter then a well digger's azz. Yep it was for sure inside there.
So the owner, my exhaust guy, and me walked outside into the bright sunlight to look at this thing and ponder WTF is this thing. At first we thought it might be something off the turbo or wastegate that was about to fall off anyways and the wiggling and shaking trying to get the convertor off knocked it loose. But it didn't look like something that would come off the exhaust side of a turbo or wastegate. Then we though maybe a worker on the assembly line dropped it in there when the car was built or maybe the car got serviced at the dealer they had to replace the turbo and they dropped it in there. The car still had its OEM GM AC cat and the cat back exhaust was the assembly line original because it was all one piece welded together where dealer replacement GM exhaust was slip fit multiple pieces with clamps.
I called the original owner later on and asked him about it and him and his wife said it never had the turbo or exhaust system worked on since they had it. This GN was a dealer demonstrator for Frank Davis Buick for the 1986 model year and had 5,000 miles on it when they bought it. It was a dealer ordered car and the centerpiece for their showroom ordered with all options except for engine block heater, security system, and limited slip differential.
To this day we still don't know what this thing is. I looked at exploded parts diagrams and actual turbo and wastegate parts and can't find anything like it. The GN runs like a champ too so if a turbo or wastegate part had fallen off it wouldn't do that.
Just one of life's unsolved mysteries I guess unless someone here see it and can tell me what it is.
07-13-2024, 04:04 PM
