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I recently bought a manual, 305 TBI RS and am trying to figure out what has been done to my exhaust. It looks like the previous owner has added 2.5" cat-back pipes with a Magnaflow muffler, but I don't know if everything from engine to cat is stock. Can you take a look at my pics and let me know what ya think?
Gotta love GM's "T" pipe posing as a "Y" pipe! You have the stock 2.25" single cat LO3 exhaust from the muffler to the engine. You can see where they welded an adaptor into the muffler for the smaller exhaust pipe.
Thanks alot Vinny and Airwolfe. Looks like I'm heading to the muffler shop. I'm not gonna be registering the car in CA, so maybe I can eliminate cat or upgrade to a high-flow version.
Does it make sense to have 2.5 " or 3" pipe installed from the exhaust manifold back before I get new exhaust manifold, or should I do all of that at the same time?
You should do it all at the same time. IIRC there is no aftermarket "y" pipe that matches those LO3 manifolds, which are junk anyway (only a 2" outlet) so I would not spend the $$ on a custom made "y" pipe. I also would wait on the high flow cat until you replace the rest of the exhaust. I am not sure if there is such a thing with a 2.25" size pipe.
You want to find the L69 manifolds from the HO 305's and 350's, make sure they come with the spacer for the passenger side. From there you can use the Magnaflow 16450 "y" pipe. This has a 3" outlet that you can get a high flow cat to bolt to. You will need an 3" intermediate pipe from the cat to your muffler. You can also get headers and the matching "y" If you can't source L69 mannies. The LO3 exhaust is so restricted that if you don't change the whole thing anything you do will just be a waste of money IMHO. The upside is once the whole garbage system is where it belongs in the trash, you could gain 30hp. That exhaust is how they choked 25hp from the TPI engines.
Thanks for the thorough answer Vinny. I'll have to start looking for those L69 manifolds - are those something I could get from a junkyard and bring to a muffler shop to install?
Thanks for the thorough answer Vinny. I'll have to start looking for those L69 manifolds - are those something I could get from a junkyard and bring to a muffler shop to install?
You're welcome.
You can find these in a yard, hopefully where you live has some yards with 80's cars. Thes manifolds where used on a bunch of GM cars, but only the HO or performance package engines. You could also post on this site in the parts wanted section and maybe a member here has a set they will sell.
You're welcome.
You can find these in a yard, hopefully where you live has some yards with 80's cars. Thes manifolds where used on a bunch of GM cars, but only the HO or performance package engines. You could also post on this site in the parts wanted section and maybe a member here has a set they will sell.
These manifolds won't be found on any other GM cars, only 3rd gen Camaro/Firebird. Most junkyards no longer have these cars there anymore. They're just too old and no longer have much demand for used parts for the yards to keep them there. There are a couple of specialty boneyards for these cars (Hawks and ThirdgenRanch come to mind). Might find them on Ebay, or as vinny suggested, post in the wanted to buy section here on the forum. Lots of these manifolds were removed and replaced with headers and are probably sitting in a corner of a garage somewhere.
What to look for are manifolds from the following:
83-85 305HO (L69 Vin G)
85-89 305TPI (LB9 Vin F)
90-92 305TPI (LB9 Vin F) 5-speed w/performance rear gear ratio and dual converters.
87-92 350TPI (L98 Vin 8)
If the original 2.75" y-pipe is available with the manifolds, I would grab that too. 83-85 would be a 4-bolt flange converter style and 86-89 would be a slip fit style. Both are fine, just get the correct converter to fit. You can also do the Magnaflow y-pipe as suggested if the stock y-pipe isn't available with the manifolds (but often they are set aside together since all headers need their own y-pipe). The manifolds from the dual converter setups are the same, but I wouldn't use the dual converter y-pipe setup. By now the converters are probably shot and the whole thing is welded together, so cutting it apart and welding in new cats would be more of a PITA than just getting the Magnaflow y-pipe and a new cat.
Thanks for the very detailed answer Transam. I will need to spend some time researching them. Will the manifolds you listed above outperform Hooker 2055's or similar shorty headers?
Austin, have you considered how much you're willing to spend and do? Because by changing the manifolds and y-pipe, then you should replace the rest of the exhaust system too, which will be expensive.
If money's no object, then get headers and their specific y-pipe, a new 3" cat and cat-back and be done with it.
But if money IS an object, then, "for now," you can use a reducer to connect whatever y-pipe to your existing cat and cat-back, whether it's with new headers/y-pipe or used manifolds/y-pipe/Magnaflow y-pipe. That won't be ideal, but it's an option for doing this in stages, if necessary. Unfortunately, "for now," on these message boards often ends up being forever, which is why it's better to do everything all at once, if money permits.
For manifolds, shop for part numbers 14094063 and 14094064, not "L-whatever" manifolds, because people will often not know what they're selling, or they might tell you it's something that it's not. Those were on L98s and many LB9s. Ebay, used parts vendors, TGO Classifieds, etc. Dorman offers brand new replacement manifolds that cross-reference to those part numbers, and they're reasonably priced, but reviews aren't very inspiring on some Dorman manifolds.
The passenger side manifold will require a spacer between it and the y-pipe. Your car probably has one, and while it might not be ideal for the L98 manifolds, it will probably fit and work. But try to get the correct spacer for the L98 manifolds, if you can. It's likely to be needed with the Magnaflow y-pipe too, so that seemingly insignificant little part is an important piece of the factory puzzle. Not needed with headers/y-pipe.
The Magnaflow y-pipe is made specifically for those L98 manifolds, and it's MUCH better than the factory y-pipe. But it's expensive, probably about 1-1/2 to 2 times more than a used factory y-pipe, so if you can't find or don't want the factory L98 y-pipe, then the Magnaflow is your best (and only) single-cat aftermarket option. "They" have been saying for years that Magnaflow y-pipe is being discontinued, but it's still listed as available from Summit and Magnaflow.
There is another new aftermarket option for manifolds: a factory-style dual-cat y-pipe. It's for the "money is no object" project, but it includes the cats, which is a large part of that price, so it might be more reasonable than it appears to be at first glance.
If you choose used factory manifolds/y-pipe, and you want to make them look nice and new, a good ceramic paint is Cerakote Glacier series. It's a high-heat, AIR-CURE, very easy to use product that works well and looks great, available in several colors.
Speaking of making it look nice and on the cost of a complete system below is a picture of my system.
Those are the L69 manifolds, $50 form a member here and they already had the air tube plugs. Magnaflow Y-pipe, $200 at the time I bought it. 3" "test Tube" made by a shop (not pictured) $125. I don't run a Cat. Hooker Super Comp 3" Aero Chamber cat back system, it included the SS quad tips, $425 at the time. 4 cans of VHT Flameproof spray ceramic coat to coat the whole system, $75 at the time. Manifold gaskets $10. After I prepped the system I had a shop do the install. The Hooker system is mostly slip fit and I wanted it all welded. Cost from my shop for removal of the old system and install the new and weld it up was $550.
My Total came to $1435. From the research I did my approx. HP gain is 30. From the same research the estimated gain if I went with headers would have been 5-10 more. That's why I went with finding the manifolds. A good set of coated headers run around $500 (not including y-pipe) which ended up being 10X the cost. I didn't feel 10 HP max gain was worth the cost.
The seat of your pants feel and the sound of a 3" system made doing the whole thing worth every penny IMHO.
Last edited by vinny R; 10-12-2023 at 08:51 AM.
Reason: typo
LAFire, I am willing up to $1,500 for exhaust work I'd say. My impression is that manifolds couldn't compete with headers for performance, but if the difference is only 10% or 20%, it seems easier and cheaper to go with manifolds. I bought the car in CA, where I am working for a few months, but am going to title it in South Carolina, where I live. I've talked to people at muffler/exhaust shops here in CA and they don't want to touch header installs with a 10' pole - they are afraid of the SMOG ****'s locking them up apparently. I might be forced to bribe some guy with cold hard cash and several cases of Milwaukee's best.
Vinny, what was most responsible for your increased power? Manifold, cat-delete, or everything together?
LAFire, I am willing up to $1,500 for exhaust work I'd say. My impression is that manifolds couldn't compete with headers for performance, but if the difference is only 10% or 20%, it seems easier and cheaper to go with manifolds. I bought the car in CA, where I am working for a few months, but am going to title it in South Carolina, where I live. I've talked to people at muffler/exhaust shops here in CA and they don't want to touch header installs with a 10' pole - they are afraid of the SMOG ****'s locking them up apparently. I might be forced to bribe some guy with cold hard cash and several cases of Milwaukee's best.
Vinny, what was most responsible for your increased power? Manifold, cat-delete, or everything together?
There is definitely a hassle-factor with headers. Headers do sound nice and will make more power, but not that much more, especially on a stock-ish motor. If your budget is $1,500 for the whole exhaust system and you are paying a mechanic to do the install, I would stay with manifolds.
To answer your question about the increased power, the 3" cat-back and cat delete will give a small increase in power (but mostly just louder, so you'll think it's faster but not really). The HO manifold/3" y-pipe along with the 3" cat or cat delete and 3" catback is going to give you the most noticeable difference. I did this on a 92' with the 305TBI and it made a big difference. Along with that, bumped the base ignition timing up from 0BTDC to 6BTDC and ran 93 octane, swapped the restrictive air cleaner assembly for an open element style (Dual snorkel from a 305HO is better if you can find one). All of this together woke the car up a lot. Then swapped the rear end gears from 2.73 open to 3.73 posi and that also made a big difference. I wouldn't say the car was fast after all of that, but it was much more responsive, sounded great and a lot of fun to drive.
It is the complete system all together. The LO3 system is so restrictive at every turn that if you only change one thing at a time you probably won't notice much of a difference. I did do a cat delete in my original LO3 system and it proved to do nothing really. After that waste of $ is when I said it all has to go! I decided to keep the cat-delete in my new system as the shop made a cate-delete pipe cheaper than a 3" high flow cat, although these new high-flow cats really don't have a restriction to them.
Thanks again for the input guys, I got a lot to chew on now. I am planning on paying a mechanic to do the work Transam. I'll keep ya posted...and I will probably come up with more questions
Thanks again for the input guys, I got a lot to chew on now. I am planning on paying a mechanic to do the work Transam. I'll keep ya posted...and I will probably come up with more questions
Hi Austin, how is your progress? I am planning the same modifications on my 1984 T/A so I am curious to know how it is going? I would like to replace it from headers to mufflers. I prefer cast iron headers but actually didnt find anything for reasonable price. Like this Hooker headers
I did something very similar to what Austin sounds like he is planning on my '92 T/A w/TPI 305. Replaced everything from the manifolds back. Installed the HO/350 manifolds that LAfireboyd detailed (got them from a member here on TGO for $50), and mated that up to a Magnaflow 16450 y-pipe and magnaflow 3" high flow cat (also sourced from TGO in a trade / about $300 trade value for both pieces IIRC). I had to source the stupid spacer though. For the intermediate pipe, I bought a Walker exhaust pipe from Summit for around $50 or so. The muffler and tail pipes was left over Edelbrock parts that came off my '91 GTA when I replaced them with a GMMG chambered exhaust. I removed all the parts myself, and installed the manifolds after blasting and painting them. Then I took it to the exhaust shop and had them finish the job. My shop charged me $430 for the install. Would have been a little cheaper, but the studs on the manifolds weren't long enough to accomodate the spacer with the flange Magnaflow puts on the y-pipe, so the shop had to remove the stud and install a new one. Still, $430 for the work they did was a pretty good price. All together I came in at around $1000 for a complete exhaust replacement.
AustinF, where in CA are you located? If you're in SoCal, I highly recommend Kenz Muffler in Oxnard. They do absolutely great work.
BTW; if anyone wants a Borla muffler with tail pipes, I have the one that came off the T/A when I replaced everything.
Guys, I tried to investigate which new cast headers can I get for my LG4 engine. Talked to Speedway, Summitracing and Holleys, different sellers, different answers. From Summit I get a recommendation for Hooker - 8525HKR Hooker
But Holleys told me that it won't fit. I also checked other sellers - SLP, Hedman ... But there is nothing. So, there is really no option to get new cast headers for this generation of SBC? ....
Those 8525 HKR should work. Below is a link to a page about these. If you scroll down you will see the different part numbers, 1HKR-4HKR there is also a 8527 HKR and they all look the same. Maybe you just need one of the other PN's.
Michi, those Hooker manifolds are very nice, and they'd be a huge improvement. But it's not the engine that they won't fit, it's the car. The passenger side flange is likely to hit the firewall, rather than pass under it, or it will be extremely close, making it difficult to connect a y-pipe.
Also, it will require fabricating the ends of your y-pipe to make the connections to the manifolds. By design, they won't simply bolt together. And because of the angles, they won't even meet up to each other. The dimensions of the manifolds are in some of their pictures, so do the measuring and calculating first.
A y-pipe larger than your LG4's would be better too, at least, eventually.
And the manifolds don't have provisions for air tubes or O2, because they were designed with 1stgens in mind, so Holley can't legally say they'll work in a 3rdgen.
As long as all of those potential issues won't be problems for you, an installer, and your local laws, then those manifolds can probably be made to work successfully in a 3rdgen. Otherwise, it would be much simpler and more beneficial to get actual headers with their own specific y-pipe.
Last edited by LAFireboyd; 03-12-2024 at 10:46 AM.
Reason: Grammar... more better lol.
If you are looking to stay with cast iron manifolds, your only options will be stock thirdgen manifolds. Either the low output LG4/L03, or the high output L69/LB9/L98 with the associated matching y-pipe. Nothing else is going to fit the thirdgen F-body chassis.
If you want to go with a tubular header, then there are some other options. But still, it need to be specifically made for a thirdgen F-body.
Michi, those Hooker manifolds are very nice, and they'd be a huge improvement. But it's not the engine that they won't fit, it's the car. The passenger side flange is likely to hit the firewall, rather than pass under it, or it will be extremely close, making it difficult to connect a y-pipe.
Also, it will require fabricating the ends of your y-pipe to make the connections to the manifolds. By design, they won't simply bolt together. And because of the angles, they won't even meet up to each other. The dimensions of the manifolds are in some of their pictures, so do the measuring and calculating first.
A y-pipe larger than your LG4's would be better too, at least, eventually.
And the manifolds don't have provisions for air tubes or O2, because they were designed with 1stgens in mind, so Holley can't legally say they'll work in a 3rdgen.
As long as all of those potential issues won't be problems for you, an installer, and your local laws, then those manifolds can probably be made to work successfully in a 3rdgen. Otherwise, it would be much simpler and more beneficial to get actual headers with their own specific y-pipe.
Thank you LAFireboyd for explaining. The story is that I planned to replace everything from the engine to the tail. I was discussing the possibilities for new headers but my installer did not recommend the stainless steel headers (because of heat expansion and noise from under the hood). He recommends cast iron, so maybe the most realistic possibility seems to get one used from L69/LB9/L98 as TransamGTA350 proposed... They are all interchangeable? Meaning L69 is ok - I understand, but LB9/L98...? The whole exhaust system will be replaced, cat will be deleted.
If you go with manifolds like I did, make sure you follow his advice and verify the part number, not the reported engine it came off of. And if you can, try to get the passenger side spacer with it.
Originally Posted by LAFireboyd
For manifolds, shop for part numbers 14094063 and 14094064, not "L-whatever" manifolds, because people will often not know what they're selling, or they might tell you it's something that it's not
Thank you LAFireboyd for explaining. The story is that I planned to replace everything from the engine to the tail. I was discussing the possibilities for new headers but my installer did not recommend the stainless steel headers (because of heat expansion and noise from under the hood). He recommends cast iron, so maybe the most realistic possibility seems to get one used from L69/LB9/L98 as TransamGTA350 proposed... They are all interchangeable? Meaning L69 is ok - I understand, but LB9/L98...? The whole exhaust system will be replaced, cat will be deleted.
All L69's, All L98's, All 85-89 LB9's and some 90-92 LB9's will have the manifolds you are looking for, but as was also stated, check the part numbers of the manifolds to be sure. You will also need the y-pipe from the car the manifolds come from.
All L69's, All L98's, All 85-89 LB9's and some 90-92 LB9's will have the manifolds you are looking for
The reason I say to verify, aside from the obvious, is that my '92 T/A has the LB9 in it. Unfortunately, one of the previous owners replaced the exhaust manifolds with some that I believe came out of an '85-ish TBI car. So even if the engine is an LB9, L69, or L98, that doesn't mean they are correct.
The reason I say to verify, aside from the obvious, is that my '92 T/A has the LB9 in it. Unfortunately, one of the previous owners replaced the exhaust manifolds with some that I believe came out of an '85-ish TBI car. So even if the engine is an LB9, L69, or L98, that doesn't mean they are correct.
If your 92' T/A LB9 is a 5-speed w/o the performance rear gear or an automatic, it would have the smaller manifolds/y-pipe from the LG4/L03. This is the case for 90-92 LB9's. In 90-92, only LB9's with 5-speeds with performance rear gear (3.42's) came with the larger outlet exhaust manifolds. 85-89 LB9's all had the large outlet exhaust manifolds, regardless of transmission or rear gear.
Did not know that. Mine is an auto, but I know the manifolds weren't original. I don't remember what the p/n was when I pulled them, but when I looked them up they were for mid-80's TBI cars. Either way, they have the L98 ones on there now.
Did not know that. Mine is an auto, but I know the manifolds weren't original. I don't remember what the p/n was when I pulled them, but when I looked them up they were for mid-80's TBI cars. Either way, they have the L98 ones on there now.
It would have been the same part number as the TBI manifolds.
10-05-2023, 11:47 PM
