I'm currently in a debate about how a 3 inch exhaust makes sense on a 305 and will actually be beneficial. The other party says that it is too big and will not create the right back pressure or otherwise move my powerband.

Since I'm putting it all on today, please tell me something about how this will make a difference and not be a waste of my money and time.

 

Are we talking true duals or shorty in a y pipe and single exhaust back to the muffler.

 

I had a 3" flowmaster cat back with no cat behind the stock manifolds and y pie with no problem. Ran well till I started my Ramjet 350 swap.

 

3" single exhaust is definitely not too much for a 305. It is too LITTLE for a strong 350 or larger.

 

I've got a 3" sittin around waiting to go on mine. Should be fine.

 

Personally I thought it made a night and day difference on my car...of course maybee 2/3rds was imagination due to the throaty rumble it had compared to the stock crap exhaust....

 

i have 3" on my 305 with 5 inch tips out of the muffler LMAO its louder than hell but runs very very nicely with it so no your exhaust setup will work more than fine

 

The smaller the engine, the bigger the tips. LOL

 

Edelbrock TES (I know, not the best but better than stock) with 3" pipe all the way to the muffler with stock 2.5" turndowns out.

At this point I really am going for a better sound (my car will never be a screamer) but I am worried about it throwing codes related to different O2 readings or EGR problems.

We'll see tomorrow. Thanks for the feedback!

 

I tend to lean towards that 305s need a little back pressure. This is what we see with dyno sheets run before and after changes like this with Camaro-Mustang Challenge cars. The most lost torque came from removing mufflers altogether. Possibly you have enough restrictions with the cat and mufflers to keep your torque up.

It would be great if you had dyno figs before and after!

 

I do have a dyno run from a summer ago. Does that count? Really embarassed to show it: Transmission messed up and it had a crappy chip in the ECM but here you go:

 

Rats... attachment can be seen here:

Old TBI thread.

 

im thinkin about doing the same exhaust mods that you are. what are the specs of your TES headers. did you get the headers with or without the AIR hookups?

i dont know much about exhaust, but from what ive heard on the issue, a 3" exhaust is the minimum size to go when upgrading exhaust. i think you will be fine to do what you had planned.

 

3" catback was factory stock on 305 TPI and it will be ok on other 305's also.

 

hey now lol the car came with 5 inch tips but the thing sounds incredible and performance on the exhaust is amazing lol it looks good if you seen it , ill show ya a pic when i get a chance lol

 

No, it was not. 2.75" outside diameter was the largest cat-back exhaust GM put on a thirdgen f-body. You'll find them on all 87-92 TPI 350's and some 305 TPI's.

We put a stock 2.75" IROC exhaust on a 1992 TBI and gained 8 hp and 20 tq, with no other problems. You'll be fine with 3".

 

Orignal 1987 305 TPI IROC-Z owner and I had 3" catback stock from the factory, but that stock system is long gone from my car. your info is incorrect . Later years had the 2 1/4 & 2 3/4 size on 305 TBI & TPI and you have one on 91 model

 

Check my sig. very happy with the results, more power, better sound.

 

I think I've argued with you before on this, but you have your own car, and I have my dad's experience as an exhaust mechanic for the last 45+ years. He has changed well over a hundred stock exhausts on thirdgen Camaros and Firebirds since the 80's and not one came with anything larger than a 2 3/4" exhaust. I guess yours was a factory freak.

 

No 3rd gen came with a 3" exhaust stock, no matter what anyone seems to think their car came with. People had 2.75s and mistake them for 3". No factory freaks.

 

im pretty sure the L69 H.O's had 3" from factory...

 

To bring the thread back full circle from the bickering, the exhaust is on. I gotta say the sound is way different that what I expected. There is a distinct throatiness that wasn't there and a louder rumble from the back. The TES pipes bolted in with relative easy and threw no codes after install. I have to get high temp, 90* boots on my spark plugs but other than that, it's good to go.

I'll drive it like this for a while and see what else has changed with the car as a result. So far though:

 

I had L69 exhaust... its not 3". it 2.75.

 

Ditto. I've been under dozens upon dozens of third-gens over the past seventeen years and none of them ever came with three-inch exhaust pipes. Your friend with the factory three-inch pipes was most likely measuring with a grade school plastic ruler.

 

Good to hear you like it. I was happy with mine when I did it. Sounds good on a long cruise it didn't give me a headache and I could hear my stereo. I just did a cat back preparing for my motor swap and the trusty old butt dyno it felt like there was more pep in the step.


This thread sounds like the story of my life...always complaining about a lousy 1/4 inch

 

Thanks guys. I know I'm arrogant because I think I'm always right, but its nice when someone else proves I'm right.