alpine247

i thought i had 2 1/2 but today i notice it was a 3in while i was changing the differential gasket,just asking if it came stock on iroc-z cause my bro firebird exhaust is 2 1/2in...

4playta

No

alpine247

umm i wonder if someone had 3in put in then,but the thing is it still had the stock muffler on so who would put 3in pipe and leave the stock muffler on..but now it has a flowmaster

JamesC

iTrader: (5)

I believe the L69 and the L98 both had 2.75" intermediate pipes.

JamesC

irocz28boy

iTrader: (2)

My '88 IROC LB9 came with 3 inch.

five7kid

iTrader: (14)

2.75" was the largest factory pipe. If yours was 3", it was aftermarket.

89transam*pearl

iTrader: (1)

My T/A (305) HO came with stock 3" pipe....

L69HAWK

iTrader: (1)

this should be good.

JamesC

iTrader: (5)

Though they're sometimes called 3", 2.75 is the reality.

JamesC

sofakingdom

iTrader: (1)

I still have my stock L69 I-pipe. It's about ¼" smaller than the 3" I replaced it with.

None of these cars came with a 3" exhaust.

L69HAWK

iTrader: (1)

don't mean to jack this thread but,
i have an 84 L69 ws6. so what is the exhaust size of the Y and intermed pipe? just so i'm clear on this. it also has the 3.73 possi and what i'm guessing to be a 9" rear i haven't counted the bolts yet.

89RsPower!

it probably doesn't have a 9 inch rear unless someone swapped in a ford rear.

JamesC

iTrader: (5)

As members mention above, the intermediate pipe is 2.75. I'm unsure of the Y size but here's a comparison pic of the LG4 and L69 Y:

https://www.thirdgen.org/forums/atta...tion-ypipe.jpg

The rear is insignificant in the discussion.

JamesC

L69HAWK

iTrader: (1)

it isn't insignificant to me since i'm not sure of the rear other than i know its a stock rear.hence the appology for jacking the topic.but thanks anyway.

LAFireboyd

iTrader: (3)

I was gonna post this morning, but yeah, I knew it would get good, so I waited, lol.

Though the performance single cat system was commonly referred to as a "3 inch exhaust," the I-pipe on the L69, LB9 and L98 was 2.75" OD. However, the collector portion of the Y-pipe and the cat were actually 3".

But the single cat exhaust system on later LB9 engines('90-'92, I believe) was downsized to 2.5".

alpine247

well im pretty sure its a stock pipe ,probably gonna take out my cat since i dont need it for emissions laws thing.if i do i take a pic showing 3in from a tape line

irocz28boy

iTrader: (2)

Yeah, I'm sure it is just 2.75". I've just been misinformed is all.

89transam*pearl

iTrader: (1)

That's what the fabricator told me after welding in straight pipe when I had the seized cat's removed....which I am replacing with hi-flo cats due to the increased gas smell.

ezliving4ume

iTrader: (1)

NO 3rd gen came from the factory with a 3" exhuast. If anyone tells u any different thier full of

alpine247

i guess mine is aftermarket then

antman89iroc

Hmmm. Are we talking ID or OD here?

five7kid

iTrader: (14)

OD.

89importeater

is it possible the ID is 2.75 but the od is 3? i know thats thick walls but i dunno doesnt really affect me just curious.

Mr.84TransAmer

If the L69 and L98 exhaust were the same, then I should be fine swapping an L98 into an L69 thirdgen, right?

JamesC

iTrader: (5)

The L98 won't have a heat stove on the driver's side, and, IIRC, one or both of the air tube connections faces the opposite direction.

JamesC

billybird

so what did the 89 lb9's come with?

JamesC

iTrader: (5)

Check the following link:

https://www.thirdgen.org/forums/exha...-question.html

JamesC

IROCZTWENTYGR8

iTrader: (1)

Quoted for truth heheh!

Josh R

iTrader: (1)

speaking of exhaust sizes, what did an 86 LG4 come with. The y-pipe looks 2.25 and the I pipe looks like 2.25. Does anyone know exactly?

83Firebird420

ive owned 2 87 TA's. both had 3 inch from y pipe to muffler...my first TA i bought with dynomax muffler, so it could be possible that it was aftermarket.. second TA was bone stock and low mileage. i dont see why someone would go through the trouble to do 3 inch exhaust from y pipe but go back to 2.5 inch at the muffler...i think some may have come stock with the 3 inch.

samiam91RS

i always thought they didnt come stock with 3in exh. but in that quote above is that a full 3in all the way? not to sure about ta's. and ford 9in def didnt come stock lol.

aged 86 transam

i had the same question my 86 ta has 3 in all the way back, it is killing my power because there isn't enough power to support the 3 in!

89RsPower!

NO THIRD GENS CAME WITH 3 IN. STOCK.

Guro 305

I've never seen a thirdgen with a 3" stock either. I've seen them 2 1/4" and 2 1/2" but never three. Not sure about the 1LE packages, but that's the only sizes I've seen.

Is it possible that people are mistakenly measuring the OD of the flange instead of the ID of the pipe?

jdhogg86

iTrader: (1)

The stock pipe is 2.75, but most muffler shops- midas, car-x, etc, will put a 3in one in it's place. That's where mine came from.

88 350 tpi formula

iTrader: (9)

this was covered years ago too anyway like it was said it's an odd size close to 2.75 or so. if you ever had a chance to look at the stock I pipe it has the 3" flanges and then goes smaller then 3" again befor the bend and even gets crushed by the axle and gets just about to 3" again just to go down again in size.

cam86104

iTrader: (1)

does anyone have the part number for the 2.75 or the 3" I pipe "what ever the size is" from walker or any other exhaust manufacture? I need the pipe that goes from the cat to the muffler , just the pipe not an entire cat back

Guro 305

Like I said, I've never seen a 2.75" or 3" pipe for the F-body. I can give you the part number for the Maremont 2.5" pipe. It's 369733. You can order it from Autozone and they'll ship it right to your door.

I checked Maremont's website just for giggles and they don't show anything stock replacement bigger then 2.5".

ws6transam

Hi Guro 305.
I've owned the same L69 third-gen for eighteen years now and got it with 39,000 miles on the clock. THe second mod I ever did was a replacement flowmaster muffler "just because".

The L69 305 H.O. was equipped with mandrel bent exhaust tubing from the exhaust manifolds to the 4-bolt flanged, oval single catylitic converter that was sourced from the Corvette program. After that, the aluminuzed exhaust pipe that went back and over the axle had an outside diameter that was nearly three-inches. Not quite, but close. I believe the dimension from my calipers was 2 7/8. The pipe was dimpled to clear the upper panhard rod, then turned to enter the single crossflow muffler. I ran that exhaust (stock pipes with Flowmaster muffler) from 1990 through the end of 2000. That very intermediate pipe, the one GM installed at the factory in June of 1984, lasted 125,000 miles and sixteen years. It was definitely a 2 7/8 O.D. mandrel bent pipe.

Guro 305

I can only tell you what I've seen and what's available. Maybe you can order the 2.75" pipe from GM direct but everything else I have seen or found is 2.5" unless it's aftermarket from someone like Flowtech or Flowmaster, etc.

Fast355

iTrader: (2)

Just because the aftermarket only makes 2.5" doesn't mean the factory setup didn't come with a 2.75". The larger size DOES exist and no its not quite 3".

JamesC

iTrader: (5)

The L69 Y in the following pic doesn't appear to be mandrel bent:

https://www.thirdgen.org/forums/atta...tion-ypipe.jpg

JamesC

firebird896

My '89 GTA has 3" exhaust. My dad has had the car since day 1. It is completely stock

IROCZTWENTYGR8

iTrader: (1)

It might look like 3", but it's not. As said before, no Third Gen EVER came with it. If you hold a true aftermarket 3" I pipe next to a stock one you can see the difference. I had stock exhaust on my L98 IROC-Z before I replaced it. Once again:

That goes for the I pipe on dual converter cars too.

Guro 305

Didn't I say that? I could've sworn I mentioned something about trying to order it directly form GM but................

cam86104

iTrader: (1)

I did find the part number for a walker pipe it is 2.75 o.d the number is 46669 it came on 87 to 89 5.7 tpi also in 84 they had the same size pipe but the front flange is different it is a bolt in flange with no donut . Most of the pipe is 2.75 but the front part that bolts on to the cat is a 3" in flange, and at the other end of the pipe is 2.50 to bolt on to the muffler.the price is $100, I hope this clears up some of the confusion. I depends on where you measure the pipe. I do not belive gm made a 3rd gen with a complete 3" pipe .

Guro 305

For that price, you can order it from Summit, Mandrel bent and 3" all around.

83Firebird420

alright so i changed teh trans fluid, and wile i was wating for the rtv to dry i measured the exhaust with a digital caliper. and i found that at the cat its just about 3 inches, y pipe is like 2.5 ish, beside the drive shaft is about 2.75, over the rear axle its about 2.8 or 2.9 ish. so yeah it looks like 3 inches...but u dont know what it really is till u measure it.