Hi all, I'm new to the site, and a new owner of a 97 Trans Am. My question is regarding exhaust sizing, and I guess how restrictive my current exhaust setup is.

The TA I bought already had quite a bit of engine work done to it:
- 355 CI
- 11.5:1 CR
- LE1 ported heads and intake manifold
- Comp Cams 306 cams, 1.6 roller rockers
- 58mm TB
- 36 lb injectors

It also has the Pacesetter Long Tube Race Headers, the matching Pacesetter 3" Y-pipe, and a 3" Flowmaster catback. The car has never been dyno'ed, but based on the mod list and butt dyno I'm guessing it makes somewhere around 400 HP. The exhaust piping is in good shape, but the cat was clogged and the previous owner decided to weld in a cutout rather than replacing it. I want to put something a little more neighbor and emissions test friendly, and obviously the easiest and cheapest route would be to stick with the 3" Y-pipe and catback and just replace the pieces in between. However, I'm worried I'm robbing myself of some horsepower by doing this.

Of all the online exhaust size calculators out there, some will say a single 3" pipe is good for "up to 400 HP", while others will say you need to go larger. Options I've seen out there are 3" true duals, or a 4" single like the Mufflex setup - any of these options look like they run about $1,000 or a little less, depending on the specifics.

I guess my question is, does anyone have experience with running a similar 3" single pipe setup on a similarly modded LT1, and if so how did it perform? It would be ideal if someone out there had before and after dyno's showing a 3" pipe versus going to a larger exhaust, but that's pretty specific information. I know bigger is better generically, and if I was starting from square one with no exhaust, I'd definitely upsize. But given my current options are to spend less than half the money on fixing the single 3" system vs. spending twice what I 'need to' on a whole new system, I'm trying to weigh what exactly the cons are to the smaller setup. Will I be sacrificing something noticeable, like 20+ WHP? Or are we talking like a 5 WHP loss over a larger system?

Please anyone with experience with this chime in - I've read so much generic information that goes both ways, I am really hoping to find some solid evidence from those with first hand knowledge. Thanks in advance for any replies!

 

Using 3" exhaust from primaries to rear muffler is just fine for what you're doing. Four inch is extreme. Another option would be dual exhaust with cats and muffler on each pipe, but not sure how your emissions station would like that one, and most likely it would still be loud AF.
As far as a catalytic converter is concerned you can install a high flow. I don't know how much of a restriction it would be, however.

 

I have think inch exhaust on mine, makes like 600hp

 

Glad to see you back posting in the community dishing out rock solid advice.

 

Your over thinking it. The pacestters and y pipe are more than adequate. Ditch the flowmasters and choose a different muffler. Depending on whether emissions are a factor use a cat or not. If you wanna step up a little from what you have run a x pipe and true duals and your exhaust will not be the restriction

 

Thanks for the reply! I have considered duals but it's kind of the high end as far as cost from where I'm at now. I'd have to ditch the whole Y-pipe setup and start fresh from the headers, and buy 2 cats and 2 mufflers on top of that. If money was no object this would be ideal, but it's definitely more than I'd prefer to spend.

 

Did you mean to say 3"? What's your setup? I'm not very familiar with these cars yet but it must be forced induction to make that kind of power?

 

Thanks! I'm probably over thinking it, but a lot of websites show 3" as a preferred size for the mid-300 hp type numbers. I'm sure there's at least some truth to that, but I'd also like to know what kind of power I'm leaving on the table with the 3" single.

Do you have any recommendations on a muffler? I'm new to these cars and coming from imports. I'd like something loud enough that it sounds tough and good when I get on it, but not so loud that it rattles windows when I leave at 6 AM.

 

If I were you I would ditch the pacesetter y pipe. It has a nasty merge and hinders flow.

 

I had a flowmaster and replaced it with a magnaflow and sounds much better and sounds like it can actually breath. If your concerned with neighbors I would just get a nice muffler and since you already have a cut out you can open it up when you want some more noise. I have the same setup as you except no cats.

 

If it were my car I would go with true duals or a 3.5” catback setup with a better merge collector so the exhaust would not be a restriction. Now since you want to keep things on a budget, I think your best bet is to weld on a Flowmaster merge to your existing y-pipe and ditch the Flowmaster muffler for a less restrictive muffler. The merge which will gain power and reduce rasp. I hate y-pipes and think most y-pipe cars sound shitty but the merge makes them a lot better so I think they are a must. The Flowmaster merge is dual 3” in and single 3.5” out so you would have to put a 3.5” to 3.0” reducer on after the merge. It’s really popular with the LS f-body guys and I’ve seen some heads/cam cars pick up 10+hp from just the merge alone. Next I would ditch the Flowmaster muffler for something else. Depends what you like sound wise, Magnaflow may be a decent option since it won’t be obnoxious and flows well.

This is what I’m talking about, found pic on google:

 

Have I offended you in the past or something?

OP, yes my car is turbo, and yes the point still remains, 3 inch exhaust is more than sufficient for what you have in mind. Get a quality high flow muffler and enjoy life.

Chase HP elsewhere.

 

When I was first getting into modding my car I came across a post on camaroz28 that stuck with me. From none other than Injuneer: "Pressure loss (or backpressure in the case of an exhaust system) is caused by frictional losses as the gasses pass through the pipe. Frictional losses are approx. related to gas velocity. In an exhaust system, as the gasses cool down the density of the gasses increases and the velocity drops. The farther you are away from the engine, the less volume of gas you have to handle, and the less affect a smaller diameter pipe will have. A 3" pipe at the muffler will have less restriction than a 3" pipe at the "y"."

Since you say the pipes are in good shape and you don't want to spend a ton, I would focus on obvious restrictions. Get a good merge like stealth said. If you need a cat, go with Random Technology. They make a great high flowing cat, I believe over 500 cfm. I think I remember seeing in one of those muffler comparisons that Hooker Aerochamber and Magnaflow had good flow numbers. That Flowmaster is a giant brick wall in your pipes.

Anywho bigger is not always better. Restriction of a muffler, or catalytic can be overcome in a smaller system and be more efficient than a bigger pipe...as long as the flow is adequate.

https://www.thirdgen.org/forums/exha...-you-ever.html

 

Thanks for the info on the Y-pipe guys. I'll definitely look into that Flowmaster merge as it seems like a cheap and easy way to pick up some power. Might also be a good excuse to go to a 3.5" catback.

I'm also a little surprised the Flowmaster muffler is so restrictive, but since I likely need a new one anyway I'll be sure to get something better-flowing.

Again I'm a little surprised the Flowmaster is so poor - a guy I work with just put a Flowmaster (series 20 I think) on his Firebird and I thought it sounded quite decent. Although he is very much stock and just wanted a small amount more rumble. I'll look elsewhere for the muffler.

Also the cutout that's in the car right now isn't especially useful - you literally need to get under the car and bolt the block off plate over the opening to close it. So I wasn't really planning on using it. But I suppose I could at least rig up a manual pull door and keep it 'just in case'.

Thanks for all of this info - I've done a lot of reading about exhaust sizing, and even done some exhaust work on old imports I had, but there is just a lot of misinformation and conflicting opinions out there. The info in that link does make sense, and has more logic behind it than "bigger is always better" or other blanket statements.

Based on the info from the previous owner it sounds like a cat and muffler are a must if I want to get the full exhaust in working order, so I'll at least be doing that, and if I'm getting a new cat it wouldn't be much effort at all to get a better merge installed at the same time.

I'm still not completely sure if the 3" single is a good bet to stick with, or if I should just go 3.5" to the back, but by the time I replace the merge and put in a cat, there's really only the over-axle bend portion left, so it's not a big length to replace.

 

You can always get an electric cutout if you want that option. As far as exhaust size I would say a very high percentage of people on this site probably have a 3 inch exhaust.

 

He pulls his head out of his *** every now and again to see what's going on over here. I think this time it was only partially pulled out to get a quick breath of fresh air.
Your pink screen name offends me.

 

yeah I'm aware I'm a long time lurker and become used to his trolling smart *** remarks that don't help. It's just a shame because he's knowledgeable and has a well put together car but cant take the time to write a few sentences and help somebody especially new 4th gen owners just hunting simple answers. Frustration to see over and over .....

 

The boy is just left overs from the other silly ****** who used to post here not offering up a thing other than using this place as their own personal blog.

 

Hi Andy, sure the above quality "tech" is reported.

I would like to see you MEASURE the Exhaust Pressure first, before you spend the money for a new exhaust.
The "tap" could be there, just an extra EGO Bung not used at this time.
The Plug could be drilled, a pressure passage way, then connected to a gauge.

That Gauge is common on Amazon, a gauge used to measure static pressure OR low pressure as used by HVAC installers.
The one I found has TWO inputs both with Min/Max/Average memory storage AND a price of $58.00, a Manometer # AR1890P2.

This tool would measure the crankcase pressure, an item not observed often
with great effect fuel used.

Lance

 

as others have said, 3" is more than adequate for your power level and then some. really no need to step up to 4" unless you are 600+ and boosted.

figure out if you need cats or not for emissions and get a magnaflow or borla cat back to replace the chokemaster and you should be set