I'm not looking for opinions as much as facts. I just bought a bone stock 2000 Trans Am that I'm going to slowly mod. This will be my 5th LS1 project. The TA is a 6 speed model. The only non-stock part on it is a Flowmaster cross-flow muffler piped into the stock tips. I've head some people say that they flow no better than stock. Some say they make as much power as other aftermarket mufflers of similar pipe diameter. It sounds freaking bad-*** and I hate to change it, but I will if it's really that much of a horsepower detriment. Believe me, I've done nearly ALL the mods before. I'm not afraid of making changes...it's just I'd hate to get rid of a great sounding exhaust, spend $700 on the latest and greatest, only to gain 2 rwhp.

My eventual goal is to go with long tubes, but I always want the exhaust to exit out the rear. Too old for a loud exhaust dumping under the car. For now, I'd just like to find out if I'm wasting effort keeping the Flowmaster. Remember, I prefer facts to opinions or hearsay.

 

I'm with the people who say "FLOWMASTER SUCKS!!!" I went from a B&B to a Blowmaster 80 series (wanted more sound.....B&B was too quiet) and the car actually lost 5 HP (felt even more on the Butt-O-Meter).

Then I went and did a Loudmouth (MEGA FLOW) and the car went crazy

 

If you just have the muffler ONLY, then you should probably upgrade to a full cat-back system anyway (especially if you are going with LT headers and other modifications so that the car can breathe efficiently).

But to answer your question, yes, Flowmaster cross-flow mufflers do not flow as well as other aftermarket mufflers/systems. Is this relevant on an otherwise stock or mildly modified car like yours, NO! The difference in power from the Flowmaster muffler/cat-back to another aftermarket muffler/cat-back will never be anything you'll feel on a car already making over 300rwhp. Probably like a 2-3rwhp difference (maybe 5 or so). Now on cars that aren't exactly stock, the Flowmaster has dyno-proven (I've seen it) to become a pretty big restriction, especially compared to most other aftermarket mufflers/systems or against cutouts.

But here's the thing: If you really love the sound of it that much (I actually think Flowmaster sounds GREAT too), then don't worry about this lack of flow stuff and just keep it and stick a cutout on the I-pipe. This way, you'll have the cutout (which will outperform just about every other muffler too) for when you need the max flow at the track and the Flowmaster exhaust for that great sound when you're just running around on the streets.

So it sounds like you should just keep that Flowmaster (or at least upgrade to the Flowmaster cat-back depending upon how much you want to modify the car) and just stick a cheap $35 cutout on it rather than spring more $$$ for another system you probably won't like the sound of as much...

Just my .02,

Mike

 

Interesting review of about 15 mufflers

This was posted on www.fullsizechevy.com which is a truck forum. Supposedly this review was performed by Martel Brothers...

*******************
All tests via an independent lab
All tests @ 15” wc

2 “ Straight Pipe 283 CFM
2 ¼ “ Straight Pipe 365 CFM
2 ½ “ Straight Pipe 521 CFM

2 ¼” Typical Bent tailpipe 268 CFM
2 ½” Typical Bent Tailpipe 417 CFM

2 ¼” Inlet/Outlet_ Glass Pack Tips- No Louvers- Smooth 274 CFM
2 ¼” Inlet/Outlet- Glass Pack Tips-Louvered 133 CFM
Same as above set for reverse flow 141 CFM
2 ¼” Cherry Bomb 239 CFM
2 ½” Cherry Bomb 294 CFM

2 ½” Inlet/Outlet Dynomax Super Turbo 278 CFM
2 ½” Inlet/Outlet Ultraflow Bullet 512 CFM
2 ½” Inlet/Outlet Gibson Superflow 267 CFM
2 ½” Inlet/Outlet Flowmaster ( 2 Chamber) 249 CFM
2 ½” Inlet Outlet Flowmaster ( 3 Chamber) 229 CFM
2 ¼” Inlet/Outlet Thrush CVX 260 CFM
2 ½” Inlet/Outlet Maremount Cherry Bomb 298 CFM
2 ½” Inlet/Outlet Hooker Aero Chamber 324 CFM
2 ½” Inlet/Outlet Hooker Max Flow 521 CFM
2 ½” Inlet/Outlet Borla Turbo 373 CFM
2 1/2" Inlet/Outlet Magnaflow 284 CFM


Standard OEM 2 ¼” Inlet/Outlet 138-152 CFM
Standard OEM 2 ½” Inlet/Outlet 161-197 CFM

The madrel bending of the pipes done by aftermarket exhaust companies is good for 2-4 h.p. depending on the severity of the stock bends. Most local exhaust places dont have a mandrel bender so changing the pipes out doesnt do anything if pipe size it not increased.

My opinion, if its more noise and a little more power just add the best flowing stainless muffler to the current system and never do it again. If you increase pipe sizes, then a local shop and only stainless. Dont care about money but want ease and better gains than most local shops can offer with no pipe size increase, and aftermarket exhaust.

NOISE does not mean power, some think it does is why Flowmasters are sold in the numbers they are!!!

 

I have a 2000 Camaro SS that had one non stock part and that was a Flowmaster catback w/chrome tips. Now I have a set of Macs w/2 1/2" ORY into the Flowmaster catback and I'm kinda old too maybe thats why I love the sound it makes when its bellering to the tune of 4500 RPM and nice and throaty in the lower RPM range. The car has a SLP lid and KnN filter with no other mods just a tune and Running 12.80 at 109 1.80 60ft on Nitto 555r Drag Radials. I have a set of SLP LTs laying on the bench that I dont want to put on because I dont want to mess up the sound.
I LOVE MY FLOWMASTER SOUND
Tom

 

Flowmaster sounds great, but the fact is that the flow is horrible. Other cat-backs sound just as good or even better. There are better options out there.

 

Damn, even the $9 cherry bombs outflowed the Flowmasters.

 

Other cat-backs sounding just as good or even better is totally a matter of personal opinion...

I for one think that Borlas, SLP Loudmouths, SLP dual/duals, and a few other systems either sound like crap or just don't compare to the Flowmaster tone.

And while I do like the sound of my GMMG cat-back system, I would have just bought a Flowmaster cat-back for a 1/3 of the price if I could do it all over again because I happen to think it sounds bada$$ in its own way...

 

Personally, i would think that if you aren't going to do any major mods and aren't a track *****, whats the point in if you can gain 3-5 extra rwhp out of another catback?

But I have to say the one thing i dislike about flowmasters sound is, it comes across fake. There is a major difference from sounding mean and being mean. Flowmasters are all dick no *****. Not much performance wise you can do with that. So it really depends on what you want to do with your car.

Id suggest if you are gonna stick with flows, get the full catback. The cutout idea isn't a bad idea either. But if you like the sound that much, why would you change it? and this is coming from a guy who is on his 8th exhaust set up since october '03.

Another idea, I have to throw this one out cause sound wise it was the most successful with respect to my tastes...the Hooker Catback. its quiet at idle but has a nice rumble. at WOT it sounds absolutely amazing. plus its under 300 bucks. can't beat that and it outflows many other catbacks.

 

damn dude.....I thought I was bad.....I only had 4 cat backs before I did my x-pipe dual....

 

https://ls1tech.com/forums/showthrea...ter+borla+dyno

The dyno chart is gone from this thread, but it showed the Flowmaster crossflow costing 30 hp by 6000 RPM vs a Borla (or basically 30 HP down from ANY decent catback/muffler)....if you
would interpolate, you can figure the Flowmaster probably costs 15 hp vs
a stock muffler...

This muffler is right up there with selecting cams based on how hard they
lope

 

for your reference i had stock manifolds/cats/y pipe going into the flowmaster crossflow. i did a dyno run with my cutout open and closed. with it open i gained 9rwhp. i know thats not really a "fair" comparison but i have heard of people dynoing with a good catback and cutout and have gained next to nothing with the cutout open so that flowmasters gotta be holding something back..just my opinion.
matt

 

Exactly why I said to just keep the Flowmaster exhaust and get a cutout. You can drive around town with that great Flowmaster sound and open the cutout when you need max power during a race.

And besides, what difference is there between 338rwhp & 350rwhp on the streets (or even a little more than that) if you're not in an all out race???

If you can, I'd spring for the Flowmaster cat-back along with that cutout which will give your current set-up a little better flow when not running the exhaust through the dump...

 

I've got the catback and it sounds pretty good. I know it is restrictive because I have rode in cars with similar mods as mine with different exhausts and they do perform a little better. IMO a person doesn't buy exhaust for performance unless they race competitively. The reason it is bought is for sound. I am switching to true duals though when I get my headers, staying with flowmaster though, this time 10 series.

 

IMO, the things that perform good ARE the things that look good/sound good.

 

Pretty much like I thought. The Flowmaster sounds great, yes. But since I'm a hard-core power junkie and have been for years, I'll most likely swap it out with some thing that sounds badass (but not too loud) and flows like a **** as I build the motor. Lots of you like the GMMG. The sound clips are awesome, but it might be a little too intense without cats. I don't have to run cats where I'm moving to. I plan on taking this motor well into the 400-500+ rwhp level (as I have with past LS1 cars), but I want to do this one right. No downsides. No low hanging exhaust. No Frankenpipe setups. No tinny sounds coming from under the hood. I'm talking about 1st class all the way, from headers (if needed) all the way out the back to the duals coming out the rear of the car.

 

Just had to throw my .02 in on this one. I went from a cheap Flowpro single 3" exhaust on my truck to dual 3" flowmaster BB muflers and lost .6 in the 1/8!!!! I went home and cut the flows off and went back to the track and ran .8 faster than i had an hour earlier with the flows. Screw RWHP, look at the track time difference.

If i could go back and do my car exhaust over i would get rid of the cats, get the ORY, and keep the stock cat back. For races i'd get a 3" ele cutout. To late now though. lol

Hind sight, what a bitch!

 

FWIW I lose 15HP and 15TQ throughout the entire power band going from an open cutout to full exaust with my Flowmaster. The previous owner put it on and I have yet to remove it. I will be getting some T. Duals fabbed up after I complete my bolt on's.

Do yourself a favor and save up your money and get a reputable shop to do it for you. You wont be dissapointed. You should be able to get a set done for what it would cost you for a GMMG cat back. Good Luck.

 

A friend dyno'ed his with a flowmaster and cutout. He gained 41 rwhp through the cutouts. Course he dyno'ed 609 rwhp so maybe that had something to do with the huge power difference.

 

Screw Flowmaster and let the gasses loose. With LS1s less back pressure=more power.