bubbaz28

I have been doing a lot of searching here and it seems like I would be better off with 3", but dang hard to find the 3 intermediate pipe. 2.5 is much easier to get of course, and maybe easier to install. Do I need 3" if I'm not looking to get massive power gains?

As for what I would like to achieve- not looking for 400 H.P. or anything like that, but I would like to squeeze some more horses out of her... As the 305 is pretty anemic... so from what I've learned, open up the exhaust first, then a dual snorkel, then I'll see where to go from there.

1983 LG4 that is otherwise all stock. I have 2055's magna flow cat and Aerochamber muffler that will go on also...

Thanks and kind regards,
Bubba

PaulyC

I say go for 3”, you aren’t rpm capped by a TPI like a lot of fbodys are. Throw your 3” and the rest you have then maybe a cam down the road and you’ll be golden. You’re sporting a q-jet correct? Whuub-Whaaa! Respect the ‘jet.

Drew

iTrader: (58)

There are a few options in 3" intermediate pipes, but really most of the time you'll have to order a complete exhaust system. If you want individual parts, most of them are going to be manufactured as 2.5" into the muffler, because that's what GM used.

Stock LG4 exhaust is 2.25" same as a V6 car. The exhaust for most of the HO cars are 2.75" necking down to 2.5" when it enters the muffler. When you get right down to it, something like the Walker intermediate pipe for TPI cars, that measures 2.75" with a 2.5" outlet, and a flange to bolt up to a 3" cat, is going to give you the bulk of the benefit a full 3" pipe would give.

83 Crossfire TA

iTrader: (2)

Where are you looking? Back when I did my first 3rd gen (in '91) that was the case, so I eneded up picking up a later Iroc 2.75" intermediate pipe and cut off the end where it went in to the muffler (necked down to 2.5") and "sleaved" it with some 3" to use a 3" muffler.

now I'm not sure where you'd get a stock replacement 2.5" (well I'm sure Walker has a PN, but if you can find that Walker is also dynomax and they have a separate PN for their 3" pipe). There are at least a few other options in both stainless and aluminized that you can get easily if you look around.

For that matter, it's more common to find a used stainless piece than anything else, I know that I've grabbed them every time I've run across one and have a few in the garage just to have when I need them.

As far as do you need it? Depending on what the rest of your setup is you'll start seeing a real difference around 200hp, it's not hard to get that out of a V8 with very little work. You'll see a difference in MPG before that.

dmccain

iTrader: (2)

You can get the 3" pipe designed for a 4th gen. It fits the same only a few hangers may be different. I bought it in pieces off Amazon and had my muffler shop tie it in to my y-pipe.

naf

iTrader: (7)

the 3" two-piece I pipe for the fourth gen will fit by modifying the location of one of the hangers in back but

It has a slip fit connection to the cat, so the cat will have to match AND be 3"

It has a 3" input to the muffler. I used a magnaflow 3" in with two 2.5" outputs which used the third gen outlet pipes.

dmccain

iTrader: (2)

Had a flat tappet LG4 engine in a Formula back in the day. Used some Summit brand headers, edelbrock performer intake, 650 Holley DP, 3in exhaust, and ran a Summit K1102 or 1103 cam. It ran pretty strong. Think it would have turned mid 14s if it would have had better gearing and a lil stall. It turned 14.8s. Stock it only turned 15.8s.

paul_huryk

You do in fact need a 3" system - not just the cat back portion, but the cat, and y-pipe too.


Here is an ancient article of how changing these parts gave an LG4 f-body 30hp (or more):


https://thirdgenfbody.wordpress.com/...aft-july-1987/


https://thirdgenfbody.wordpress.com/...phr-june-1987/

dmccain

iTrader: (2)

Interesting read. Huge gains. As far as 3" vs 2.5".. With the shi% exhaust design we have you need every bit of help you can when you have 1 strangled snaky piece of exhaust running under these cars.

82tarecaro

iTrader: (4)

I think the headers and y pipe gave the most benefit there. The second test is running a stock TPI cat and catback.

83 Crossfire TA

iTrader: (2)

third gens used all sorts of different cat connections, even if you find a 3rd gen pipe at this point you'll be hard pressed to find one with the right cat connection, it's up to someone that knows what they're doing to make that work, of if you still have the original cat then you might be able to find it by year, but I think some of the early LG4's used the old pellet cats that you'd be better off swapping for a newer monolith cat. Point being unless you find the intermediate pipe that is correct for the cat you have in the car it doesn't really matter what intermediate pipe you use. I have a 4th gen Magnaflow one in my '87 TA.

The rear bracket can be dealt with a few ways, I've used a 4th gen one with a large bolt welded to it to slip through the 3rd gen hanger, you can cut your 3rd gen one off of it and weld it on in the place of the 4th gen one, and on my current setup I took some 3/8" steel rod and bent it up to fit the 3rd gen hanger on the passenger side and I bent up some of that rod to make both the exhaust and the body side on the driver's side and used a honda style rubber donut hanger between them (you can get them for like $2.xx at an autoparts store).

the stock exhaust is actually a pretty good design, great for the era.

A single large pipe flows more than 2 pipes of the same cross-sectional area and is lighter. The intermediate pipe run is about as straight as can be. The stock manifolds are, well stock manifolds, and the only real problem with the y-pipe is how the 2 pipes come together. The factory dual cat cars had a very nice y-pipe and it wasn't worth the HP that most people think they were going to get from "fixing" the y-pipe.

The early performance models got a dual muffer rear setup that sounded freaking incredible for a factory exhaust, the later crossflow mufflers didn't sound as good but they had a large case and quite decent flow. I tested this on my 4th gen which at the time was running 11's with the stock muffler on it, and I had the intermediate pipe flanged so I could remove it by pulling 3 bolts and I wasn't able to document any difference at the track on the same day with or without the factory muffler. Almost none of you arguing how bad the stock exhaust is are running mid 11's.

Aftermarket crossflow mufflers sound better, but very few flow great. The flowmaster is one of the louder ones and it flows significantly less than the factory muffler. The easy solution is to run a single tailpipe with a good high flow 3" in/out muffler. My TA is running a dynomax ultraflow welded that flows way more than most of us need and is quieter than some stock mufflers I've heard. I like my tailpipe tucked up behind the bumper anyway.

The closer you get to the engine the more the exhaust design matters. Even on cars that see a significant improvement with say a 3" intermediate pipe will likely show no loss with a single 2.5" and maybe even a 2.25" tailpipe after the muffler, well it will be quieter.

There used to be a really cool test published online back in the day testing this with a 70's pontiac wagon (that would launch with the front wheels up in the air) trying to get it as quiet as possible without any horsepower loss and he ended up a dual exhaust with 3" pipes off the headers but by the time he got to the tailpipes he was down to 2.25"

dmccain

iTrader: (2)

I do not agree for one second our exhaust is a good design. Period. Imagine if we could run true dual exhaust like a G-body or even a Fox body Mustang. Have you heard one of those with a nice exhaust system? No way our exhaust with the mangled y-pipe and especially an Lg4 car with single 2.25in exhaust flows anywhere near that capacity. Its just a flaw in third gens just like the 7.5 10 bolt is. I will agree with you on two points, had an 82 with the two muffler setup once and it did sound freaking good. Also 1 pipe is lighter than two and a 145HP LG4 or 170HP L03 probably doesn't need true duals anyhow.

bubbaz28

Yea got a q-jet. Thanks for all the replies- helped a lot, and I will definitely go 3" made for a 4th genand get it in 2 pieces. Hopefully I can make that work.

sofakingdom

iTrader: (1)

Not sure what the problem is here? How is this hard to find?

https://www.summitracing.com/parts/hok-16820hkr

There's acoupla other part #s that are similar; main difference between them is the connection to the cat.

I put this on my car laying on the floor in my garage with it on jack stands. One afternoon. Bolts right up as if made for it. Piece o cake. Not only that, but it's for the car you actually have, and won't require any adaptation or anything else at all, unlike buying something for a 4th gen and trying to make it work.

You don't have to use those funky tips... you can put regular turn-downs on it, stainless ones are available even, and make it look totally stock.

bubbaz28

That is a great setup- thanks- I already have the muffler and would rather not buy another one. I will check with Summit to see if, by chance, I could get that set minus the muffler.

kaos420

https://www.summitracing.com/parts/wlk-89009

Drew

iTrader: (58)

That's the LG4/TBI version, note that it necks down below 3" to meet the tiny cat. 16823 is the full 3".
Never liked the tips or the Aero-Chamber muffler on those...

Or for $300 less, there's the Walker 2.75" pipe that necks down to 2.5" all the way back at the muffler...

https://www.summitracing.com/parts/wlk-46669

83 Crossfire TA

iTrader: (2)

Well, about the only thing you did get right is that the Mustang exhaust is well tuned to sound good, and ford has put a lot of effort in to maintain that sound with the Mustangs since.

It flowing better is simply not fact, and we could run a true dual exhaust.

Again, a single pipe of the same cross-section as dual pipes will flow more because there is less internal area that the flow is in contact with cutting down frictional losses. The biggest source of restriction in the pipes are bends which most dual exhausts like fox chassis mustangs have more of and are tighter. Finally the biggest restriction in the exhaust tends to be the chambers (mufflers and less so cats), which obviously the mustang has more of and the further upstream they are the more restriction they pose, and in a mustang, they are all further upstream than in an f-body.

By the late 3rd gen models the performance optioned f-bodies got exhausts that were essentially not a restriction for the stock performance level (most aftermarket exhausts were within a few hp of the factory exhaust with the notable exception being a few crossflow setups primarily Flowmaster which was something like 20hp down from the factory setup), which didn't happen with the mustangs till about 15years later. Like I mentioned before, I tested this on my 4th gen ('97WS6) that I had setup so that I could drop the exhaust with 3 bolts at the track, and wasn't able to document any ET/MPH changes either running NA (at the time high 12's) or on N20 (mid/low 11's).

If you want to compare aftermarket exhausts then you have to compare apples to apples, if you want to compare a 3" fox dual exhaust to an F-body one then you have to compare it to a 4" single (and they both fit about as well). The only thing the dual exhaust wins on is its easier to make it sound good (alternatively, it's harder to make a big single not sound like a UPS truck :P )

If there was a power advantage there would be more dual exhausts available for 3rd and 4th gens, it's not hard at all to run 2 moderately sized pipes down the path that the factory exhaust runs, there just isn't a point unless you just want to be able to say "I have dual exhaust on my car." It's not that much harder to run the driver's side dual down the driver's side, but again, you don't see it often because there is no advantage.

mmadden55

Headers to glass packs out the side in front of the wheels . Our cars sit close to the ground and there is really no room under there. The only way to get a decent exhaust system is to have one built. I ran glass packs tucked up tight 2.5 pipe 3.5 inch glass packs and dumped in front of the rear wheels. I smog laws don't come into it that is the way to go, may sub in some not to thick turbo muffs for the packs but either way it will be tight. Or you can run Vette Viper style side pipes.

Fast355

iTrader: (2)

Some of the factory 80s vans had tubular manifolds, dual 2.25" stainless exhaust from the factory and were built without cats. That was actually one of the first exhaust setups I had on my 1983 G20. Compared to the factory exhaust with its 2" manifolds and 2.5" Y-pipe it made a world of difference on the little 305. The engine also ran cooler not being choked by the pellet cat. Power and MPG were both far better. I changed the cam to a 204/214 and added a performer rpm spreadbore intake under the Q-Jet. Between the 3 major changes I felt like the engine gained close to 100 hp at 5,000 rpm. Back in the early 2000s when I first put together that combination I had a Vortec 350 Tahoe trying to keep me from passing him on the highway in the red brick but with the 3.08s and the top end power I drove around him and kept going. He hit his 98 mph speed limiter and I kept going.

Factory truck tubular manifold

DynoDave43

iTrader: (11)

Wow, I've never seen a set of those Fast.


There were stainless "headers" or tubular exhaust manifolds we had at the dealer in the late '80s for 454s in motorhomes that kept warping exhaust manifolds. And a couple of the old pushrod 4s of that era had tubular exhaust. But that's the first SBC piece I've seen. Thanks for sharing that.

Drew

iTrader: (58)

Looks kinda like the Corvette manifolds with the outlet moved to the back.

DynoDave43

iTrader: (11)

It does have a similar look Drew. Except for the brazed A.I.R. tubes, Vs. threaded on the truck.


Is that cylinder 1 tube smaller in diameter like the truck piece?

83 Crossfire TA

iTrader: (2)

The Corvette manifolds are literally 4, 1.5" stainless tubes under the heat shields, they're like the simple blockhugger hot rod headers you used to see all the time but with smaller tubes.

I've never seen the van manifolds, I'd like to get my hands on a set...

robertfrank

iTrader: (27)

You can build a catback CHEAP if you play your cards right. Go to the junkyard and get as much 3 inch tubing from newer Chevy trucks. It's all 3 inch mandrel bent. Get some slip connectors from vatozone with a decent cat and a $50 dollar race bullet from summit. You can build it all for damn near $100 if not cheaper. That's what I did with my 92 305 car.

robertfrank

iTrader: (27)

I see these manifolds all the time in the bone yards, I've though about picking up a few sets for giggles

QwkTrip

iTrader: (22)

I just don't think an engine that makes less than 200 Hp needs a large exhaust and muffler. I think 83 Crossfire TA is correct, the exhaust upgrades should be focused on the forward portion to promote cylinder scavenging and torque production at low and mid-range rpm.

1MeanZ

iTrader: (9)

I'll throw in my $.02. 83 Crossfire TA and I are on the same page for the most part. I don't feel there is a ton of power hiding in the stock muffler. If you have a stock 2.75" intermediate pipe, you're just fine up to at least 350hp, probably more. I don't really like the LG4/LO3 log manifolds with 2" outlets, but I've owned cars that ran in the 14s that had them. I think the stock single cat Y pipe is terrible however, and it's not the cat that's the problem, its the "T" shaped merge that's the problem. If I had a stock LG4/LO3 car, first thing I'd do is ditch the Y-pipe, and ditch the manifolds as a close second.