muffler flow comparison data

[red79]

Hey guys, there's always a lot of talk on the forum about the flow capabilities of different muffler types. Dynomax for performance and minimal restriction, flowmaster for when you want your tailpipe to sound like a trumpet, etc. This chart pops up a lot here and on other sites like moparts:



However, other than anecdotes about a swap making someone's ride quicker, is there any data to back up all of the claims? For instance, where did the data for the above chart come from? It makes strong statements about the performance of different designs, but at the end of the day it's just a bunch of numbers in a grid--who gathered the data? When? How?

[c00nhunterjoe]

I always love hearing the bashing towards flowmasters but it always seems like people compare the alternative choices to the 40 series. Well what do you expect from a basic 2 chamber muffler other then raw noise? Flowmaster has different mufflers for different wants and needs. As for all the flow numbers: if your muffler outflows the capability of your engine then what's the purpose? If my muffler flows 1000 cfm but my engine only puts out 700cfm then what do I have other then bragging rights about my muffler flow?

I have yet to see proof that a flowmaster muffer costs you horsepower and all of the flow charts show ultraflows as 50% more flow. If they flow so much better then where is all the unleashed power? Show me paper charts all day long. It means nothing until you put it on the dyno and drive it on the street.

If you don't want a loud, obnoxious, drony muffler then don't buy a 40 series flowmaster. But don't bash the whole product line based on 1 muffler's features.

Sorry for the rant but I'm tired of hearing the flowbastards, and exhaust trumpet comments. I stand by the flowmaster and any doubters that live local are welcome to stop by and check mine out.

[Mick70RR]

I love the sound of my exhaust, 3" system to the rear bumper with Flowmaster 40's and an H-pipe, I don't have any sort of drone with them either.
As for the flow numbers, I fitted electric cutouts before the mufflers and the car ran the same ET and mph with them open or closed so they flow enough for my engine.

[Budnicks]

I would put money on the test was done by or paid for by Dynomax to make them look better than the others I call BS on that flow chart, I have no proof to back it up, but that's my opinion anway... I guess the study & chart was supposedly done by University of Mich. I have no idea of what specifics or parameters

[Budnicks]

I always love hearing the bashing towards flowmasters but it always seems like people compare the alternative choices to the 40 series. Well what do you expect from a basic 2 chamber muffler other then raw noise? Flowmaster has different mufflers for different wants and needs. As for all the flow numbers: if your muffler outflows the capability of your engine then what's the purpose? If my muffler flows 1000 cfm but my engine only puts out 700cfm then what do I have other then bragging rights about my muffler flow?

I have yet to see proof that a flowmaster muffer costs you horsepower and all of the flow charts show ultraflows as 50% more flow. If they flow so much better then where is all the unleashed power? Show me paper charts all day long. It means nothing until you put it on the dyno and drive it on the street.

If you don't want a loud, obnoxious, drony muffler then don't buy a 40 series flowmaster. But don't bash the whole product line based on 1 muffler's features.

Sorry for the rant but I'm tired of hearing the flowbastards, and exhaust trumpet comments. I stand by the flowmaster and any doubters that live local are welcome to stop by and check mine out.

Me Too, well said...

[myk]

How do you perform better than 100%?  On that note, I wonder how the bad 'rep for Flowmasters came about?

[440]

I like moroso race mufflers but I put Super 44's on my pickup instead and am totally disappointed in the way they sound. First thing I want to do is flog them off and get something better. Not sure which to get so I'm interested in what this thread reveals.

[Nacho-RT74]

I got these:

http://flowmonster.com/i-6682692-fm1226s-flowmonster-stainless-performance-muffler-2-5-2-1-2-o-c.html

which I guess will be similar on numbers to the magnaflows

[Nacho-RT74]

I meant, dynomax ultraflow welded, being is the same design

Flowmonster


Dynomax

[c00nhunterjoe]

If you rate the flow measured for open header as 100% then use a muffler that promotes cylinder scavenging, then you could measure greater then 100%.

I like moroso race mufflers but I put Super 44's on my pickup instead and am totally disappointed in the way they sound. First thing I want to do is flog them off and get something better. Not sure which to get so I'm interested in what this thread reveals.

What don't you like about them. Its hard to give advice without more info? What exactly are you looking to get out of your muffler?

[red79]

...I guess the study & chart was supposedly done by University of Mich. I have no idea of what specifics or parameters...

Cool, where did you hear that? I haven't been able to find references to any source whatsoever.

[Budnicks]

...I guess the study & chart was supposedly done by University of Mich. I have no idea of what specifics or parameters...

Cool, where did you hear that? I haven't been able to find references to any source whatsoever.

Someone on, www.forBbodiesonly.com , forum quoted that, there is a thread there in the general discussion section {I think it was} "new pipes on the Roadrunner" thread, with the flow chart too... I have no facts to support that it was actually done by them, oneway or another, just hearsay...

[c00nhunterjoe]

I've seen multiple charts all over the net on different forums. ALL of the charts shared only 1 thing in common- whichever muffler was being discussed had the highest numbers and everyone else's were far below.  Flowmaster is the only muffler company that I have NOT seen argue flow charts to sell their product.

[Budnicks]

I've seen multiple charts all over the net on different forums. ALL of the charts shared only 1 thing in common- whichever muffler was being discussed had the highest numbers and everyone else's were far below.  Flowmaster is the only muffler company that I have NOT seen argue flow charts to sell their product.

[firefighter3931]

Several years ago there was a member here trying to make his car go faster. He had a 493 with E-heads, 2in TTI headers using 4ft of straight 3in pipe into a set of Flowmasters....pretty much the most unrestrictive extension pipe arrangement possible. I remember sending him a message to try dropping the exhaust on his next track day.

Low and behold, he drops the pipes/mufflers and picks up 7 tenths and 6 mph....the car went from high 11.60's (11.68) to low 11's (11.04) and picked up a bunch of speed at the big end.  In case you were wondering....the ex pipes were 3in to 3in Flowmasters with dumps at the rear axle. No compression bends, tailpipes or anything that would hinder exhaust gases. It was all in the mufflers. 

Flowmaster is the only muffler company that I have NOT seen argue flow charts to sell their product.

There's a reason for that....if you had a poorly flowing design, the last thing you would want to do is compare it with something superior.  Flowmasters are marketed on their sound which is unique and mostly annoying to some. Granted, on some builds that aren't making enough power the use of a restrictive muffler won't hurt performance but on high HP stuff those mufflers will slow your car down....that is a given. 


Ron

[c00nhunterjoe]

In my opinion a long stroke 500 inch engine probably needs more then a 3 inch hole to breathe through. You had 2 inch tubes per cylinder dropping into what? A 3.5 inch collector? Then you drop that down to 3 inch pipe? You can't blame the mufflers for the wrong choice of exhaust. Same reason a stock 440 through manifolds and 2 inch duals is a dog.

[firefighter3931]

In my opinion a long stroke 500 inch engine probably needs more then a 3 inch hole to breathe through. You had 2 inch tubes per cylinder dropping into what? A 3.5 inch collector? Then you drop that down to 3 inch pipe? You can't blame the mufflers for the wrong choice of exhaust. Same reason a stock 440 through manifolds and 2 inch duals is a dog.

That is incorrect. I know lots of guys running 500in builds into 3in full exhaust....tailpipes and all and they don't slow down uncapped. None of those guys run Flowmasters though   

My 572 runs a full exhaust system as well and i have 2in TTI headers going into a Dr Gas 3.5 x 3 X-pipe into 3in Ultraflows and 3in TTI tailpipes exiting at the bumper. I also have cutouts just behind the collector and have uncapped it on back to back passes. Guess what....no difference in ET  A 3in Ultraflow works fine on my 700+ HP pump gas 572 with full exhaust. That alone tells me that this is a quality high flowing muffler that doesn't sound like a tinny coffee can full of rocks. 

If your car doesn't slow down at the track with a set of Flowmasters you aren't making a lot of power.   


Ron

[440]

Firstly I liked the Moroso race mufflers because they were supposed to increase exhaust scavaging. They are a bullet style muffler with a combination straight through design and also have spiral baffles to quiet them down slightly.

To me an exhaust should have a refined tuned note and perform well. The problem is mufflers always sound different between brands and different engines within brands, so you never really know what it's going to sound like. Unless you have a late model chevy or ford, they all sound like the next one.

The Super 44's really missed the mark in the sound department to me. I wanted something deep and loud but slightly quieter then the bullets. They are no way deep enough, and almost have a growl similar to an Infinity G35. The funny thing is I didn't want flows in the first place but the exhaust guy talked me into them. It's on mildly worked 400c.i. Ford, 2.5" tubes, H pipe, super 44's with side exits. I had the wrong size Moroso bullets on it before and it didn't sound right, so I'm leary to try them again in the correct size this time.

I can't say much on their performance as they havn't been on the truck long enough to tell and too many other variables have changed as well. A new carb being one of them. I expected to pick up a little bit of bottom end torque due to the slight increased backpressure, so far the bullets have my vote.

[404NOTFOUND]

Just today, I changed out my Flowmaster 40 series mufflers for Dynomax Ultraflow 20" mufflers, part #17513 on my Charger 440 which has all the popular mods done to it. Flowmasters were always my favourite and I've had them on many cars but on this car, they were a bit too loud. Even though I enjoyed them, I was actually starting to lose my hearing. Neighbour troubles also started. It was the usual scene. Man next door says rev it up, cut the hood and run open pipes straight up with a blower in the middle. Woman on the other side goes door to door trying to start a war against me. Cop car pulls up beside me at the lights, you can see the ticket or no ticket look on his face. It was time for a change. I would never have caved in except that I keep hearing how the Ultraflow is quieter yet sounds better while making more power. Type in "Ultraflow" on You Tube and you will see videos of a hot, red, 1970 big block Chevelle where he made a video of his car with Flowmaster 40s and immediately afterwards, another video of his car with Ultraflows. These are good videos with accurate sound. You be the judge. The manager at my local speed shop told me he also considering switching for all the same reasons. I took my car there today to let him hear the Ultraflows and he wants to switch too. These mufflers are much quieter unless you get on it. Actually, they are a bit too quiet for my tastes but, that is because today is day one. In a week or two, they should be just perfect. The butt dyno tells me I've gained a fair amount of horsepower too. Scary fast for the first time ever. One of my Flowmasters was cracked at the neck. I have read about others having that problem as well. I still love Flowmasters. Just not the best choice for my situation.

[c00nhunterjoe]

1st off, my car doesn't sound like a hollow tin can full of rocks. As I stated before, you are steriotyping all flowmasters to the 40 series sound....... I've posted clips of my car before and it sounds nothing like the "origonal flowmaster sound" I had 40 series and got tired of the tin cans and drone.

2nd, your right, compared to your 700+hp, my cute little 383 ain't shit. But behind a slipping 727 turning 2.76's I have video of it running 13.21@104. So I would guesstimate a solid 400 hp 383 on stock iron heads with an outdated racer brown cam and an outdated torker intake. it runs the same ET's open header or through full 3 inch exhaust through tailpipes.

Your high hp builds are run better with the ultraflow because its a glasspack. You can look right through it. The majority of us don't run monster hp engines in our street cars and right out of your post confirms it. Average engines won't see a difference.

I'm not here to bash the ultraflow- to each his own. To me it still drones, and I didn't like the tone or overall sound of it. I chose my specific muffler for its performance, lack of drone, sound, and noise characteristics.

[c00nhunterjoe]

Just today, I changed out my Flowmaster 40 series mufflers for Dynomax Ultraflow 20" mufflers, part #17513 on my Charger 440 which has all the popular mods done to it. Flowmasters were always my favourite and I've had them on many cars but on this car, they were a bit too loud. Even though I enjoyed them, I was actually starting to lose my hearing. Neighbour troubles also started. It was the usual scene. Man next door says rev it up, cut the hood and run open pipes straight up with a blower in the middle. Woman on the other side goes door to door trying to start a war against me. Cop car pulls up beside me at the lights, you can see the ticket or no ticket look on his face. It was time for a change. I would never have caved in except that I keep hearing how the Ultraflow is quieter yet sounds better while making more power. Type in "Ultraflow" on You Tube and you will see videos of a hot, red, 1970 big block Chevelle where he made a video of his car with Flowmaster 40s and immediately afterwards, another video of his car with Ultraflows. These are good videos with accurate sound. You be the judge. The manager at my local speed shop told me he also considering switching for all the same reasons. I took my car there today to let him hear the Ultraflows and he wants to switch too. These mufflers are much quieter unless you get on it. Actually, they are a bit too quiet for my tastes but, that is because today is day one. In a week or two, they should be just perfect. The butt dyno tells me I've gained a fair amount of horsepower too. Scary fast for the first time ever. One of my Flowmasters was cracked at the neck. I have read about others having that problem as well. I still love Flowmasters. Just not the best choice for my situation.

I'm glad your happy with their sound. Like I said, I had the 40 series and ditched them for the same reason, got tired of the headaches and too much attention. I still run flowmasters but a different series. I searched for months hitting car shows listening to people's engines because, as you said, youtube's sounds can be deceiving. I wanted to hear them in person. The ultraflows just didn't work for me. The sound was just wrong to my ears.

[Ronnman]

The person who has knowledge of the test is Tom Hand.  He is a regular on Moparts.  I am not sure he is on this board.  See thread below.
Ron

http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Board=QuestionAnswer&Number=6604983&Searchpage=2&Main=6602790&Words=Ronnman&topic=&Search=true#Post6604983

[red79]

The person who has knowledge of the test is Tom Hand.  He is a regular on Moparts.  I am not sure he is on this board.  See thread below.
Ron

http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Board=QuestionAnswer&Number=6604983&Searchpage=2&Main=6602790&Words=Ronnman&topic=&Search=true#Post6604983

Thanks a lot, that was one of my main reasons for starting this thread! Looking back though his posts on moparts I found plenty of references to his testing and methods.

[Budnicks]

Several years ago there was a member here trying to make his car go faster. He had a 493 with E-heads, 2in TTI headers using 4ft of straight 3in pipe into a set of Flowmasters....pretty much the most unrestrictive extension pipe arrangement possible. I remember sending him a message to try dropping the exhaust on his next track day.

Low and behold, he drops the pipes/mufflers and picks up 7 tenths and 6 mph....the car went from high 11.60's (11.68) to low 11's (11.04) and picked up a bunch of speed at the big end.   In case you were wondering....the ex pipes were 3in to 3in Flowmasters with dumps at the rear axle. No compression bends, tailpipes or anything that would hinder exhaust gases. It was all in the mufflers.  

Flowmaster is the only muffler company that I have NOT seen argue flow charts to sell their product.

There's a reason for that....if you had a poorly flowing design, the last thing you would want to do is compare it with something superior.   Flowmasters are marketed on their sound which is unique and mostly annoying to some. Granted, on some builds that aren't making enough power the use of a restrictive muffler won't hurt performance but on high HP stuff those mufflers will slow your car down....that is a given.  


Ron

Don't take this wrong please... I'm not going to say there aren't better mufflers than Flowmasters, there probably are... I don't doubt your ability at all either, You seem to give great advice to many people, have you ever flow tested any of the exhaust systems or mufflers on an actual flow bench ??, but Were the guys muffler installed backwards or something ??, was the carb way too fat with the exhaust on it ??, was it properly tuned ??, did uncapping it just make it run LEAN & mean ??, was that the only change from the exhaust to uncapping in the tune ??, also there is a weight difference between the exhaust & no exhaust, but it wouldn't make anywere near that big of a difference... That seems like "way too much difference too me" on a properly tuned combo, even with Flowmasters & full exhaust... I have run 9.77et @ 135mph w/479-w/6bbl & 8.81et @ 152mph same car & bottom end & exhaust system, bigger roller camshaft, better {lighter} Ported Aluminum heads {50+ lbs weight savings off the front end}, 500rpm higher stall speed converter 4300rpm, 1050cfm trick Dominator, capped up full exhaust out the rear & when running threw 3" Flowmaster's old 50 Delta Flow Race series w/mandrel tubing on a prepped track, fully prepped 3520lb plus the 250lbs for me, in my old 68 RR about 3-1/2 or so years ago now, uncapped exhaust removed & installed 20"x 3.5" header extensions same 479ci w/1050cfm Dominator combo 8.58et @ 156mph Sacramento Raceway 95*-100*+ day on 315 Drag Radials, CalTracs, 3.73:1 gears, corrected altitude of 1200-1500ft depending on the day, all runs were made on all the above 8.81et & 8.58et combos with a Top Gun System 300hp total N20 activated at the 60' mark 100hp, then 200hp at 330ft then progressing to the full 300hp at 660ft, only difference was the 90-100+lbs removed exhaust weight & header extensions... Is that enough HP, N20 or not, that isn't a real HP killer too me 8.81 capped to 8.58 open & only the loss of 0.23 sec.s & 4mph... Explain that one....  I know others that have had similar results... Results may vary... That is the "long winded point" I'm trying to make... Sorry for such a long post

[red79]

...have you ever flow tested any of the exhaust systems or mufflers on an actual flow bench ??

After reading the posts on moparts, that's exactly how the chart in the first post was compiled. This guy Tom Hand took a whole bunch of different exhausts and blew air through them flowbench style, comparing them to straight pipe. The sound measurements are from attaching them to his wagon.

[Budnicks]

...have you ever flow tested any of the exhaust systems or mufflers on an actual flow bench ??

After reading the posts on moparts, that's exactly how the chart in the first post was compiled. This guy Tom Hand took a whole bunch of different exhausts and blew air through them flowbench style, comparing them to straight pipe. The sound measurements are from attaching them to his wagon.

I'm not saying that the Dynomax isn't the best muffler or not, I personally don't know for a fact... I guess I'm just in denial...LOL... It sounds like a decent comparison, I don't know that guy from anywere though, I too read the posts at the other forum, I don't care for that forum much either... I just see some stuff I personally don't 100% agree with, not that it isn't true either... That isn't what I'm saying at all... I was around a bunch of the guys first using/testing the Flowamsters many years ago late 70's at Sacramento, Fremont & Sears Point raceways {were they originated from} along with many in the winged sprint car series, out in Calif., when nobody was making performance mufflers except Super Traps & they were highly suspect, the loudness & droning effect of the mufflers {Santa Rosa Based company Flowmasters} was the biggest complaint that most people had, but the increase in performance was "hands down, much better" than anything that was available at the time... I have never experienced the supposed big power losses or droning in my personal use, except on big tube headers, big inch motors & large pipes, dumping at the axles, which I completely expected... I also have seen "in person" non-biased comparisons, side by side on many of the mufflers vs open headers on a friends flow bench at his shop in Sacramento, the Flowmasters outflowed all of them at the time, maybe the past few years there has been BIG improvement in a couple of brands, for sure 1 being Dynomax... But also some are making some kind of unrealistic claims, that I never saw in our private tests, with several different size & lengths of pipes 2.5"-3.5" with the bench at a constant 28" of flow {if I remember correctly} threw a 9" tube {I think it was} going to the head to simulate an intake, both  fully professionally ported & Non-ported Brand X BBC Brodix head bolted to a custom set of my headers from one of my personal Brand X race car, stepped 2" & 2-1/4" 34" custom tuned headers 3.5" 4-2-1 collectors, we/he used a air flow meter from an EFI set-up & a computer to measure flow differences "after the mufflers" & after the H-pipe, {a bunch of stuff I knew nothing about & can't completely explane}, but we actually saw a scavenging effect with the 3" Flowmasters Delta Flow Racing Mufflers, that we didn't see with any of the others, straight threw or not, {but any type of straight threw exhaust can logically flow better to a certain point}... We also saw a drop in flow the farther back the mufflers were mounted away fromthe collectors after like 20"'s or so {I think it was}, I was doing this for a reason, I was was going to Super Chevy Race in Phoenix were we wanted to be the fastest street car, with license plate, street tires & mufflers, 8.98et @ 156 mph, 2790lb full Chassis 67 Camaro 468ci BBC Brodix Head, full roller, PG, 4.56:1 9" Ford rear etc. & crappy MT 18"x33" Pro-sportmans {no Drag Radials allowed at the time}, we left with the trophy & a pretty messed up race car too {that's a different story for a different time}... I don't think anyone is lying or anything like that at all, but I have seen some different results, grant you they are old & antiquated by now... Opinions may vary & I'm sure they will... Especially you guy knowing I also have raced the Brand X stuff, in my past...LOL... SORRY FOR WRITING A BOOK

[c00nhunterjoe]

Freeflow of the muffler IS important. I cannot argue that. But there is much, much more to exhaust then slapping a set of mufflers on your car when it comes to horsepower. There are tons of articles available online that you can read about properly setting up your exhaust. Tuning the resonance, harnessing the exhaust pulses. Style, type and placement of mufflers with pipe and header combos all has to be taken into account.

Buying and installing exhaust on your car is exactly like buying and tuning a carb for your engine- out of the box may run. But change the jets, accelerator pump, squirters, cams.etc...etc. and th same carb will make lots more power.

[Dave Cleveland]

Several years ago there was a member here trying to make his car go faster. He had a 493 with E-heads, 2in TTI headers using 4ft of straight 3in pipe into a set of Flowmasters....pretty much the most unrestrictive extension pipe arrangement possible. I remember sending him a message to try dropping the exhaust on his next track day.

Low and behold, he drops the pipes/mufflers and picks up 7 tenths and 6 mph....the car went from high 11.60's (11.68) to low 11's (11.04) and picked up a bunch of speed at the big end.   In case you were wondering....the ex pipes were 3in to 3in Flowmasters with dumps at the rear axle. No compression bends, tailpipes or anything that would hinder exhaust gases. It was all in the mufflers.  

Flowmaster is the only muffler company that I have NOT seen argue flow charts to sell their product.

There's a reason for that....if you had a poorly flowing design, the last thing you would want to do is compare it with something superior.   Flowmasters are marketed on their sound which is unique and mostly annoying to some. Granted, on some builds that aren't making enough power the use of a restrictive muffler won't hurt performance but on high HP stuff those mufflers will slow your car down....that is a given.  


Ron

Don't take this wrong please... I'm not going to say there aren't better mufflers than Flowmasters, there probably are... I don't doubt your ability at all either, You seem to give great advice to many people, have you ever flow tested any of the exhaust systems or mufflers on an actual flow bench ??, but Were the guys muffler installed backwards or something ??, was the carb way too fat with the exhaust on it ??, was it properly tuned ??, did uncapping it just make it run LEAN & mean ??, was that the only change from the exhaust to uncapping in the tune ??, also there is a weight difference between the exhaust & no exhaust, but it wouldn't make anywere near that big of a difference... That seems like "way too much difference too me" on a properly tuned combo, even with Flowmasters & full exhaust... I have run 9.77et @ 135mph w/479-w/6bbl & 8.81et @ 152mph same car & bottom end & exhaust system, bigger roller camshaft, better {lighter} Ported Aluminum heads {50+ lbs weight savings off the front end}, 500rpm higher stall speed converter 4300rpm, 1050cfm trick Dominator, capped up full exhaust out the rear & when running threw 3" Flowmaster's old 50 Delta Flow Race series w/mandrel tubing on a prepped track, fully prepped 3520lb plus the 250lbs for me, in my old 68 RR about 3-1/2 or so years ago now, uncapped exhaust removed & installed 20"x 3.5" header extensions same 479ci w/1050cfm Dominator combo 8.58et @ 156mph Sacramento Raceway 95*-100*+ day on 315 Drag Radials, CalTracs, 3.73:1 gears, corrected altitude of 1200-1500ft depending on the day, all runs were made on all the above 8.81et & 8.58et combos with a Top Gun System 300hp total N20 activated at the 60' mark 100hp, then 200hp at 330ft then progressing to the full 300hp at 660ft, only difference was the 90-100+lbs removed exhaust weight & header extensions... Is that enough HP, N20 or not, that isn't a real HP killer too me 8.81 capped to 8.58 open & only the loss of 0.23 sec.s & 4mph... Explain that one....  I know others that have had similar results... Results may vary... That is the "long winded point" I'm trying to make... Sorry for such a long post

It's resurection day. Lets clear something up for those who do searches for this kind of info and hope they read this far. After taking off the full length ehaust he did not mention re-tuning carb.  With headder extensions only it's going to change the a/f ratio at different RPM's. Did he have an a/f gauge and wide band he was looking at for differences on the 2 runs? I have one. And changing exhaust that dramatically WILL harm performance if it is designed to max performance WITH the exhaust.  Dial that a/f ratio back in through out the range and see what happens. And do the tests on a dyno where conditions are 100% the same each run. 
To answer his questions, yes the mufflers have been flow tested.  Flow testing don't account for scavenging. But you can make the pipes scavenge just as much as the muffler. A proper X pipe can have great scavenging effects. Why have a giant flow muffler? Because you want the muffler to be invisible to the motor. All the flow should be governed by the headder extention and X pipe, after that the exhaust needs to flow as much or more then the prior. So making it big, or extra big ensures that. Bends need to be made with pipe at least 1/4 inch larger then the straight pipe size to maintain the same CFM, even mandrel bends too. 2.5 inch pipe flows 521 cfm.  most mufflers even flow masters flow less the 400cfm with there 2.5 inch mufflers, while some get to 400 cfm, only a couple straight through, no s curve, mufflers actually flow over 500 cfm with there 2.5 inch muffler. Hooker max flow, and thrush glass pack.  CHerry bombs, glass packs with louvers suck, borls fairs ok high 300"s flow, magna flow 385 sux I had those.  If you want a muffler that flows the same as the pipe that feeds it your options are very limited. So if you go 1-2 sized bigger you can get more choices that meet your flow needs. just buy 3 or 3.5" mufflers for your 2.5" system.  All the info I have stated can be searched and found...

[BSB67]

Several years ago there was a member here trying to make his car go faster. He had a 493 with E-heads, 2in TTI headers using 4ft of straight 3in pipe into a set of Flowmasters....pretty much the most unrestrictive extension pipe arrangement possible. I remember sending him a message to try dropping the exhaust on his next track day.

Low and behold, he drops the pipes/mufflers and picks up 7 tenths and 6 mph....the car went from high 11.60's (11.68) to low 11's (11.04) and picked up a bunch of speed at the big end.   In case you were wondering....the ex pipes were 3in to 3in Flowmasters with dumps at the rear axle. No compression bends, tailpipes or anything that would hinder exhaust gases. It was all in the mufflers.  

Flowmaster is the only muffler company that I have NOT seen argue flow charts to sell their product.

There's a reason for that....if you had a poorly flowing design, the last thing you would want to do is compare it with something superior.   Flowmasters are marketed on their sound which is unique and mostly annoying to some. Granted, on some builds that aren't making enough power the use of a restrictive muffler won't hurt performance but on high HP stuff those mufflers will slow your car down....that is a given.  


Ron

Don't take this wrong please... I'm not going to say there aren't better mufflers than Flowmasters, there probably are... I don't doubt your ability at all either, You seem to give great advice to many people, have you ever flow tested any of the exhaust systems or mufflers on an actual flow bench ??, but Were the guys muffler installed backwards or something ??, was the carb way too fat with the exhaust on it ??, was it properly tuned ??, did uncapping it just make it run LEAN & mean ??, was that the only change from the exhaust to uncapping in the tune ??, also there is a weight difference between the exhaust & no exhaust, but it wouldn't make anywere near that big of a difference... That seems like "way too much difference too me" on a properly tuned combo, even with Flowmasters & full exhaust... I have run 9.77et @ 135mph w/479-w/6bbl & 8.81et @ 152mph same car & bottom end & exhaust system, bigger roller camshaft, better {lighter} Ported Aluminum heads {50+ lbs weight savings off the front end}, 500rpm higher stall speed converter 4300rpm, 1050cfm trick Dominator, capped up full exhaust out the rear & when running threw 3" Flowmaster's old 50 Delta Flow Race series w/mandrel tubing on a prepped track, fully prepped 3520lb plus the 250lbs for me, in my old 68 RR about 3-1/2 or so years ago now, uncapped exhaust removed & installed 20"x 3.5" header extensions same 479ci w/1050cfm Dominator combo 8.58et @ 156mph Sacramento Raceway 95*-100*+ day on 315 Drag Radials, CalTracs, 3.73:1 gears, corrected altitude of 1200-1500ft depending on the day, all runs were made on all the above 8.81et & 8.58et combos with a Top Gun System 300hp total N20 activated at the 60' mark 100hp, then 200hp at 330ft then progressing to the full 300hp at 660ft, only difference was the 90-100+lbs removed exhaust weight & header extensions... Is that enough HP, N20 or not, that isn't a real HP killer too me 8.81 capped to 8.58 open & only the loss of 0.23 sec.s & 4mph... Explain that one....  I know others that have had similar results... Results may vary... That is the "long winded point" I'm trying to make... Sorry for such a long post

It's resurection day. Lets clear something up for those who do searches for this kind of info and hope they read this far. After taking off the full length ehaust he did not mention re-tuning carb.  With headder extensions only it's going to change the a/f ratio at different RPM's. Did he have an a/f gauge and wide band he was looking at for differences on the 2 runs? I have one. And changing exhaust that dramatically WILL harm performance if it is designed to max performance WITH the exhaust.  Dial that a/f ratio back in through out the range and see what happens. And do the tests on a dyno where conditions are 100% the same each run. 
To answer his questions, yes the mufflers have been flow tested.  Flow testing don't account for scavenging. But you can make the pipes scavenge just as much as the muffler. A proper X pipe can have great scavenging effects. Why have a giant flow muffler? Because you want the muffler to be invisible to the motor. All the flow should be governed by the headder extention and X pipe, after that the exhaust needs to flow as much or more then the prior. So making it big, or extra big ensures that. Bends need to be made with pipe at least 1/4 inch larger then the straight pipe size to maintain the same CFM, even mandrel bends too. 2.5 inch pipe flows 521 cfm.  most mufflers even flow masters flow less the 400cfm with there 2.5 inch mufflers, while some get to 400 cfm, only a couple straight through, no s curve, mufflers actually flow over 500 cfm with there 2.5 inch muffler. Hooker max flow, and thrush glass pack.  CHerry bombs, glass packs with louvers suck, borls fairs ok high 300"s flow, magna flow 385 sux I had those.  If you want a muffler that flows the same as the pipe that feeds it your options are very limited. So if you go 1-2 sized bigger you can get more choices that meet your flow needs. just buy 3 or 3.5" mufflers for your 2.5" system.  All the info I have stated can be searched and found...

Do you have any personal test data, or just stuff you have read?  Please share you personal experiance and track results.  To suggest that flow is the the only measure to determine what is best or appropriate is a bit of an over simplification.