From a price stand point, is a cat back system worth the money for my car? I have a set of Edlebrock headers and y pipe pipe flowing into an empty cat and a factory back exaust with a 2 3/4" pipe. Would the price of a catback really be worth the power increase if there is any?

 

depends on your budget mostly. Everything sounds good except the cat back part. I'd either keep the 2 3/4 or go up to 3 inch. Probably 2 3/4 cuz a 3 inch could cause vacuum problems on a 305. Go with a new muffler like a flowmaster or something affordable, sounds good, and flows well.

 

 

Last time I checked my car, I haven't been able to see where an exhaust would affect the vacuum system, unless its channeled directly out of the EGR, which is now non-existent. Hmm.....

 

plumbing that "empty cat" would be worthwhile too while you're down there.

A hollow converter just creates turbulence, stick a pipe in it!

 

ok, ok hold on, I read a book that discussed exhaust builds and (if im correct) it stated that there may be some connection between vacuum and pipe size. I know it sounds corny but ill have to go find that book. hold your horses.....

 

You're thinking scavenging, which too large a diameter exhaust can harm. However, 3" is not too much diameter for a 305, its about right, and it will support better scavenging at higher rpms, which is where a smaller motor is going to want to run. I think you're on the right track, but not quite straight on things. You want good exhaust velocity, to large a pipe, and you can't get scavenging at low rpms. Too small a pipe will create excellent scavenging at lower rpms, but will choke and hold the engine back at higher rpms.

Discuss....

 

Is that a fact? hmmm.... Reason I emptied the cat was because my exaust guy told me that it would keep the car quiet by acting as an "expansion chamber" as he put it. Never thought it about the turbulance issue. Makes sence though.

As for replacing the factory 2 3/4" pipe to a 3", would it really help out a small 305 enough to increase any power? That's what I'm really after. I'm not concerned about the sound of an aftermarket muffler as I would like to keep the car as quiet as possible. Don't want the attention from the local authorities What do you guys suggest I do from a performance standpoint?

 

no sense in installing larger piping only to bottle neck the system once again by a factory muffler that will not compliment the higher flowing capabilities of the larger piping.

 

Sorry, I wrote that a little misleading. What I meant to say was that I'm willing to change the muffler and pipe if it will give me a performance increase. If it will just sound better with no performance increase, then I think it is just a waste of money and time in my opinion. So again what do you guys think? Will it indeed make a difference on my 305, or is there nothing to be gained by going to an aftermarket cat back system?

 

i thought the stock exhaust size was 2 1/4 not 2 3/4 ??? just checking things to make sure, i know there were 2 1/2 inch stock exhausts and 2 1/4 stock exhausts but 2 3/4?

 

No, it's a 2 3/4" factory pipe that hooks up to a factory muffler with 2 1/2" tail pipes. That was part of the LB9 option in 1985. Don't know about other years, but I know for a fact that it's the original exhaust on my '85.

 

A good 3" catback is a mandatory piece of equipment for anyone interested in V8 performance. You will notice a difference, especially if you already have headers.

Yes piping the cat will give you - slightly - more power over an empty cat due to reduction in turbulence.

Stock exhaust sizes ranged from 2 1/4" to 2 1/2". 2 3/4" stock exhaust didn't come into play with F-Bodies until the '93 LT1s.

Go get a catback and some 3" piping

 

Alright, I just went underneath to double check. It is infact a 2 3/4" pipe from the converter to the muffler. I checked it with a circumferance tape so I know for sure that's what it is. I'm also the original owner so I can say for sure that it's the factory exhaust cat back system. If I had a 2 1/2" pipe I could see the advantage in going to a 3", but do you guys really think the extra 1/4" upgrade from what I have will make a difference?

 

I believe the L69's had the 2 3/4 as well as some of the TPI cars. I put a stock L69 exhaust on my LG4, to include the intermediate pipe, and the stock L69 was larger than the aftermarket catback I'd previous swapped on.

JamesC

 

I went with headers, Y-pipe, and a 3" performance pipe, to a flowmaster muffler, then to duel stainless steel tips that are 18" long and 3" in diam. I LOVE it. It was the 1st thing I did to my car and it improved its performance alot. And it sounds awsome. I didnt think it could sound any better until I installed my new cam.

 

Regardless of the size of the factory system, an aftermarket mandrel-bent 3" system will be a nice improvement in flow.

- Justin

 

That's news to me. I've personally seen several L98 exhaust systems and they were 2.5". Maybe it just depended on what they had laying around

L69s were interesting cars, I wouldnt be surprised if they had larger pipes.
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Yep. Even if you have a 2 3/4" going with a 3" will support more power.

 

1985 Lb9's and L69's got the larger 2 3/4" exhaust with the corvette 3" oval cat (4 bolt)-which by the way is a horrible restriction (the stock cat). The piping necks from a 3" oval at the cat to a 2 3/4" round I pipe which then necks down into a 2 1/2" inlet for the muffler (also a good restriction) with dual 2 1/2" outlets. If you are replacing the exhaust you will need a newer style converter (3" round slip fit: cto-9118) to complement the 3" I pipe. You will also need a muffler shop to make an adapter to the factory oval four bolt y pipe. OR you can order the exhaust for the L69 and buy a high flow 4 bolt cat.

So to sum it up:
if your car was a 1985 L69/LB9 (or any 4 bolt cat car) either convert it to 1986+ with headers exhaust cat etc. OR order L69 exhaust and a new high flow 4 bolt cat. Also edelbrock just came out with a TES set made just for the 4 bolt L69 an Lb9 cars with a 4 bolt y pipe. I wonder if the 4 bolt 3" oval is more restrictive compared to the 3" round on a 305?

 

The guys on Horsepower swapped the stock exhaust in a 4th gen with an LSx motor for a 3" flowmaster system. Got a gain of about 8 hp over their baseline.

The 3rd gen Flowmaster system is not all that differrent, I imagine you would get similiar numbers.

 

I swapped on the L69 exhaust, and the first cat I purchased was for a Corvette--it was of the four-bolt variety and looked close but was restrictive (CTO-9143). I later learned I had the wrong cat. I was much impressed with the "correct" high-flow converter, Summit CTO-4116.

JamesC

 

Monsterous is the adjective. Check the LG4 Y compared to the L69:

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

By the way, I was under the impression that the L69 and the L98 were equipped with the same exhaust. As general info, the following was posted by TransamGTA350:

There were only 2 different manifolds for the V8's throughout the years, but they were different depending on what motor and gearing package they came on. Here is the breakdown.

2" outlet manifolds with single 2 1/4" y-pipe
82-87 305 LG4 (VIN H)
88-92 305 L03 (VIN E)
82-83 305 Crossfire
90-92 305 LB9 w/o G92 axle (VIN F)

2 1/4" outlet manifolds with single 3" y-pipe
83-86 305 L69 (VIN G)
85-89 305 LB9 (VIN F)
88 350 L98 (VIN 8)
89 350 L98 w/o G92 axle (VIN 8)

2 1/4" outlet manifolds with dual 2 1/4" cats
89 350 L98 w/G92 axle (VIN 8)
90-92 350 L98 (VIN 8)
89 305 LB9 w/G92 Axle (VIN F)
90-92 305 LB9 w/G92 (Vin F)

Crap

JamesC

 

I think you'd see a gain expecially on that shot of nitrous you're running with a high flow muffler... not a flowmaster.

 

Cool info, I've added it to my collection

 

Thanks guys!! From what I gather, I'll get a 3" cat back as it seems that I have something to gain from it. I'll probably weld a pipe in the converter as well to reduce turbulance as stated above. The cat is in fact the 4bolt design. Now to decide on which system to get