the truth about flowmasters.
Race Director
Joined: Dec 1999
Posts: 11,096
Likes: 990
From: Sierra Foothills CA
Many years ago I bought a system from Flowmaster (American Thunder if I remember right) for my 70 Z28 which was putting out about 425 HP at the time. It was complete from headers back & had a transverse single unit to fit where the original muffler went in front of the gas tank. It had each pipe entering & exiting in opposite directions, left to right through seperate chambers. I knew the similar stock system was restrictive (replaced shortly after I bought the car) but Flowmaster confidently claimed that theirs would flow very freely & would outperform the conventional true dual glasspack set up that I had been running. I bought it based upon their claims because I liked the fact that it tucked up out of the way, improving ground clearance.
In fairness to them I must say that the system was very nicely designed & constructed w/ clean bends in the pipes. However, once in place I found that I'd lost a significant amount of mid range & top end power. It felt like the motor was being strangled. I called them to discuss the problem & the tech told me that he'd call me right back after they had a chance to discuss it in a meeting.
He did call back on time & said they'd concluded that it was breathing so much better that it had thrown my tune-up off & I'd need to play w/ jetting & timing to find my increased power. I knew I had it properly set up before but I figured I'd give them a chance & work on it. After alot of time & effort on my part I simply couldn't get back my lost performance. Another call to Flowmaster got me the same response as I'd had before. I replaced it w/ the true dual system I currently have using Ultra Flo mufflers & guess what- all of my lost mid range & top end came back w/ a vengeance.
A few months later I was discussing this at a local speed shop & as it turned out one of the employees there had been w/ Flowmaster during the time I was having my problems- very nice guy. He felt bad & acknowledged that the system I'd bought had never performed the way it should have. He said that if I brought the muffler in as proof that it really was mine he'd give me 2 free new design Flowmaster mufflers (he still had friends at Flowmaster) to replace it. He was good for his word & I gave the mufflers to a buddy for his Camaro.
That guy saved me from feeling totally bitter towards Flowmaster but between my experience & the flow numbers I've seen I won't be buying anything except Ultra Flos from here on out.
There, I said it & I feel better now.
In fairness to them I must say that the system was very nicely designed & constructed w/ clean bends in the pipes. However, once in place I found that I'd lost a significant amount of mid range & top end power. It felt like the motor was being strangled. I called them to discuss the problem & the tech told me that he'd call me right back after they had a chance to discuss it in a meeting.
He did call back on time & said they'd concluded that it was breathing so much better that it had thrown my tune-up off & I'd need to play w/ jetting & timing to find my increased power. I knew I had it properly set up before but I figured I'd give them a chance & work on it. After alot of time & effort on my part I simply couldn't get back my lost performance. Another call to Flowmaster got me the same response as I'd had before. I replaced it w/ the true dual system I currently have using Ultra Flo mufflers & guess what- all of my lost mid range & top end came back w/ a vengeance.
A few months later I was discussing this at a local speed shop & as it turned out one of the employees there had been w/ Flowmaster during the time I was having my problems- very nice guy. He felt bad & acknowledged that the system I'd bought had never performed the way it should have. He said that if I brought the muffler in as proof that it really was mine he'd give me 2 free new design Flowmaster mufflers (he still had friends at Flowmaster) to replace it. He was good for his word & I gave the mufflers to a buddy for his Camaro.
That guy saved me from feeling totally bitter towards Flowmaster but between my experience & the flow numbers I've seen I won't be buying anything except Ultra Flos from here on out.
There, I said it & I feel better now.
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Originally Posted by AlwaysWave
OEM..................................... ........................................ ...225
Gibson SuperFlow 788200.................................. ............311
TTS Bullet Cat Converter............................... ..................324
Flowmaster 40 series 42540................................... .......352
Flowmaster 50 Series.................................. ...................362
Flowmaster 40 series 43040................................... .......392
Dynomax Super Turbo................................... .................410
Flowmaster 62631................................... .......................435
Carsound Cat Converter............................... ..................436
FLP Cat Converter............................... ............................440
Edelbrock Victor 5535.................................... ..................562
Flowmaster 40 series 435409.................................. ........576
Edelbrock RPM series 5511.................................... ..........579
Flowmaster Delta Force Racing 54040-10........................634
Edelbrock 304 series 5560.................................... ...........640
Edelbrock Gen App 5505.................................... ..............708
Dynomax Race Magnum Welded 17216...........................711
Borla XR-1 40600................................... ..........................836
Borla XR-1 40615................................... ..........................854
Dynomax UltraFlow SS 17263................................... .......1000
Dynomax Race Magnum Welded 17218...........................1000
Borla XR-1 40575................................... ..........................1100
Dynomax UltraFlow............................... ...........................1133
Edelbrock Victor 5537.................................... ..................1400
Borla XR-1 40450................................... ..........................1400
Borla XR-1 40741................................... ..........................1450
Dynomax UltraFlow SS 17296, 17268..............................2200
Dynomax Race Magnum Welded 17220, 17224...............2200
Dynomax Race Magnum Welded 17225...........................2600
The formula for required exhaust flow is: horsepower times 2.2. Pretty simple eh?
So if your car makes 400 hp, you will need a total of 880 cfm muffler capacity for an unrestrictive exhaust system. So for dual exhaust, you would need mufflers that flow 440 cfm.
For reference, a 2.5 inch diameter pipe flows ~500 cfm. Adding non-mandrel bends will lessen that amount.
Gibson SuperFlow 788200.................................. ............311
TTS Bullet Cat Converter............................... ..................324
Flowmaster 40 series 42540................................... .......352
Flowmaster 50 Series.................................. ...................362
Flowmaster 40 series 43040................................... .......392
Dynomax Super Turbo................................... .................410
Flowmaster 62631................................... .......................435
Carsound Cat Converter............................... ..................436
FLP Cat Converter............................... ............................440
Edelbrock Victor 5535.................................... ..................562
Flowmaster 40 series 435409.................................. ........576
Edelbrock RPM series 5511.................................... ..........579
Flowmaster Delta Force Racing 54040-10........................634
Edelbrock 304 series 5560.................................... ...........640
Edelbrock Gen App 5505.................................... ..............708
Dynomax Race Magnum Welded 17216...........................711
Borla XR-1 40600................................... ..........................836
Borla XR-1 40615................................... ..........................854
Dynomax UltraFlow SS 17263................................... .......1000
Dynomax Race Magnum Welded 17218...........................1000
Borla XR-1 40575................................... ..........................1100
Dynomax UltraFlow............................... ...........................1133
Edelbrock Victor 5537.................................... ..................1400
Borla XR-1 40450................................... ..........................1400
Borla XR-1 40741................................... ..........................1450
Dynomax UltraFlow SS 17296, 17268..............................2200
Dynomax Race Magnum Welded 17220, 17224...............2200
Dynomax Race Magnum Welded 17225...........................2600
The formula for required exhaust flow is: horsepower times 2.2. Pretty simple eh?
So if your car makes 400 hp, you will need a total of 880 cfm muffler capacity for an unrestrictive exhaust system. So for dual exhaust, you would need mufflers that flow 440 cfm.
For reference, a 2.5 inch diameter pipe flows ~500 cfm. Adding non-mandrel bends will lessen that amount.
Thread Starter
Melting Slicks
Joined: Aug 2004
Posts: 2,165
Likes: 950
From: Keizer Oregon
Originally Posted by Fevre
Think there is a key bit of info missing here, what are the inlet and outlet sizes? There is mention of 2.5" exh pipe flow so how can mufflers flow more (more than 4x for some) than straight pipe assuming all are 2.5" in/out?
Racer
Joined: Jul 2003
Posts: 460
Likes: 18
From: Conroe, TX
Here's my own "flow test": If I look into a muffler inlet and can't see daylight, its a "no-go". And the fewer "louvers" and obstructions, the better. So, that eliminates Flowmasters. . . I probably couldn't pass a fart through 'em. . . 
The ORIGINAL and bestest
Joined: Oct 2000
Posts: 10,009
Likes: 240
From: Toronto Ontario
Toronto Events Coordinator
Just got off the phone with the Flowmaster tech, and he told me that cfm ratings for mufflers are BS. According to him those numbers don't mean squat, and that Flowmaster is a technology based company, and they are the only producers in the world of mufflers that use scavaging to draw the exhaust gases out. He also stated that blowing room temperature air through a muffler to determine cfm is not that same as hot gases passing through it. His analogy was comparing it to siphoning gas from a tank, creating a low pressure area that draws it out. If you go to the track, most of the fast serious cars are using Flows, so what do you believe............
Race Director
Joined: Nov 1999
Posts: 10,643
Likes: 8
From: Foxfield CO 1970 Convertible
FYI - There's a complete article on exhaust systems in this month's Popular Hot Rodding...
http://www.popularhotrodding.com/toc/phr_toc/
Has anyone run a 3" system under their Vette?
http://www.popularhotrodding.com/toc/phr_toc/
Has anyone run a 3" system under their Vette?
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Race Director
Joined: Jul 2004
Posts: 12,705
Likes: 329
From: Scottsdale Arizona
Originally Posted by Z-man
FYI -
Has anyone run a 3" system under their Vette?
Has anyone run a 3" system under their Vette?
There have been a couple of postings this year from people that do have 3 inch systems. As I recall they are oval tube so that they don't drag on the ground.
Pretty custon and very impresive setups.
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 38
From: Fremont CA
I run a 2.5" diameter system on my 12.28@117MPH 72 LT-1 Vette (that time is "through the mufflers" in case your interested.) My system is a Allen's Exhaust LT-1 304SS pipe set with a custom fabricated set of 2.5" Dyno Max Ultra Flow mufflers in the back and it has been on my car since 1996 or so. I will tell you right here and now that a Flowmaster system would have rusted out or broken an internal baffle off and plugged up by now where my system is still going well. Flowmaster has never offered a 304Stainless Steel muffler because they want their mufflers to fail and keep you comming back for more! I would never run their type of muffler (or the "Spin-traps") and know of several unhappy customers. I guess if you like the resonance of their mufflers, you go with them, I like the quiet steady state sound of my Dyno Max system but, they will make noise when under acceleration.
Last edited by Solid LT1; Mar 18, 2005 at 04:06 PM.
C6 the C5 of tomorrow
Joined: Nov 2000
Posts: 6,665
Likes: 2
From: Twin Cities Minnesota
Originally Posted by 7t2vette
Just got off the phone with the Flowmaster tech, and he told me that cfm ratings for mufflers are BS. According to him those numbers don't mean squat, and that Flowmaster is a technology based company, and they are the only producers in the world of mufflers that use scavaging to draw the exhaust gases out. He also stated that blowing room temperature air through a muffler to determine cfm is not that same as hot gases passing through it. His analogy was comparing it to siphoning gas from a tank, creating a low pressure area that draws it out. If you go to the track, most of the fast serious cars are using Flows, so what do you believe............
Race Director
Joined: Feb 2005
Posts: 16,100
Likes: 17
Originally Posted by Les
Many years ago I bought a system from Flowmaster (American Thunder if I remember right) for my 70 Z28 which was putting out about 425 HP at the time. It was complete from headers back & had a transverse single unit to fit where the original muffler went in front of the gas tank. It had each pipe entering & exiting in opposite directions, left to right through seperate chambers. I knew the similar stock system was restrictive (replaced shortly after I bought the car) but Flowmaster confidently claimed that theirs would flow very freely & would outperform the conventional true dual glasspack set up that I had been running. I bought it based upon their claims because I liked the fact that it tucked up out of the way, improving ground clearance.
In fairness to them I must say that the system was very nicely designed & constructed w/ clean bends in the pipes. However, once in place I found that I'd lost a significant amount of mid range & top end power. It felt like the motor was being strangled. I called them to discuss the problem & the tech told me that he'd call me right back after they had a chance to discuss it in a meeting.
He did call back on time & said they'd concluded that it was breathing so much better that it had thrown my tune-up off & I'd need to play w/ jetting & timing to find my increased power. I knew I had it properly set up before but I figured I'd give them a chance & work on it. After alot of time & effort on my part I simply couldn't get back my lost performance. Another call to Flowmaster got me the same response as I'd had before. I replaced it w/ the true dual system I currently have using Ultra Flo mufflers & guess what- all of my lost mid range & top end came back w/ a vengeance.
A few months later I was discussing this at a local speed shop & as it turned out one of the employees there had been w/ Flowmaster during the time I was having my problems- very nice guy. He felt bad & acknowledged that the system I'd bought had never performed the way it should have. He said that if I brought the muffler in as proof that it really was mine he'd give me 2 free new design Flowmaster mufflers (he still had friends at Flowmaster) to replace it. He was good for his word & I gave the mufflers to a buddy for his Camaro.
That guy saved me from feeling totally bitter towards Flowmaster but between my experience & the flow numbers I've seen I won't be buying anything except Ultra Flos from here on out.
There, I said it & I feel better now.
In fairness to them I must say that the system was very nicely designed & constructed w/ clean bends in the pipes. However, once in place I found that I'd lost a significant amount of mid range & top end power. It felt like the motor was being strangled. I called them to discuss the problem & the tech told me that he'd call me right back after they had a chance to discuss it in a meeting.
He did call back on time & said they'd concluded that it was breathing so much better that it had thrown my tune-up off & I'd need to play w/ jetting & timing to find my increased power. I knew I had it properly set up before but I figured I'd give them a chance & work on it. After alot of time & effort on my part I simply couldn't get back my lost performance. Another call to Flowmaster got me the same response as I'd had before. I replaced it w/ the true dual system I currently have using Ultra Flo mufflers & guess what- all of my lost mid range & top end came back w/ a vengeance.
A few months later I was discussing this at a local speed shop & as it turned out one of the employees there had been w/ Flowmaster during the time I was having my problems- very nice guy. He felt bad & acknowledged that the system I'd bought had never performed the way it should have. He said that if I brought the muffler in as proof that it really was mine he'd give me 2 free new design Flowmaster mufflers (he still had friends at Flowmaster) to replace it. He was good for his word & I gave the mufflers to a buddy for his Camaro.
That guy saved me from feeling totally bitter towards Flowmaster but between my experience & the flow numbers I've seen I won't be buying anything except Ultra Flos from here on out.
There, I said it & I feel better now.
As far as muffler choices,I never really considered Flowmasters or Magnaflow after hearing them.To each his own,I say.
The ORIGINAL and bestest
Joined: Oct 2000
Posts: 10,009
Likes: 240
From: Toronto Ontario
Toronto Events Coordinator
It seems everyone has a different opinion on this matter,talk to 10 diffferent people and you will get 10 answers, and since I am not an engineer in this field, it is hard to figure out the truth. How does the average guy wade through all the BS numbers and claims to get to the truth? I personally like the sound of Flows, and they have a new muffler out now called the Super 40 that they saw outflows and makes more power than any other one they have made before........with less interior resonance. All of you guys who claim that they are no good, what scientific proof do you have to back this up? I have a "doubting Thomas" personality type, I don't believe much of anything unless I see it with my own eyes, and it can be backed up with hard evidence. I think this can apply to just about every type of aftermarket performance part made, so much hype and BS numbers everywhere!!!
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Originally Posted by Ex_F-Body_Enthusiast
Here's my own "flow test": If I look into a muffler inlet and can't see daylight, its a "no-go". And the fewer "louvers" and obstructions, the better. So, that eliminates Flowmasters. . . I probably couldn't pass a fart through 'em. . .
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Originally Posted by Ex_F-Body_Enthusiast
Here's my own "flow test": If I look into a muffler inlet and can't see daylight, its a "no-go". And the fewer "louvers" and obstructions, the better. So, that eliminates Flowmasters. . . I probably couldn't pass a fart through 'em. . .
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Run what you want, it's your car. FM 40's where on my vette when I bought it and I really like the sound, does drone but with the top down it ain't bad. I do not think I would buy them since they are a little pricey.
Race Director
Joined: Feb 2005
Posts: 16,100
Likes: 17
Originally Posted by 7t2vette
Just got off the phone with the Flowmaster tech, and he told me that cfm ratings for mufflers are BS. According to him those numbers don't mean squat, and that Flowmaster is a technology based company, and they are the only producers in the world of mufflers that use scavaging to draw the exhaust gases out. He also stated that blowing room temperature air through a muffler to determine cfm is not that same as hot gases passing through it. His analogy was comparing it to siphoning gas from a tank, creating a low pressure area that draws it out. If you go to the track, most of the fast serious cars are using Flows, so what do you believe............
The ORIGINAL and bestest
Joined: Oct 2000
Posts: 10,009
Likes: 240
From: Toronto Ontario
Toronto Events Coordinator
I agree, you would think that the least restrictive, clear shot through, would be the best muffler. The guy from Flowmaster seemed irritated I was questioning his statements, and got a little terse with me. He raised his voice to me saying "Flowmaster is a technology exhaust company, we do not cfm test our mufflers, those numbers are BS." I wish I had the money to put all these performance parts to the test in real world conditions!
Race Director
Joined: Dec 2000
Posts: 10,896
Likes: 2
From: CO
Originally Posted by 7t2vette
He raised his voice to me saying "Flowmaster is a technology exhaust company, we do not cfm test our mufflers, those numbers are BS."
How then can you say they are the masters of flow?
thats almost as good as the accounting company here that said "we have spend countless hours on this project"