Flowmaster Restricts more than stock?

[LIGHTNINGMCQUEEN]

Once and for all i want to know if the Flowmaster muffler restrics more than stock.

[96Firebirdformula]

Doubt it flows worse.

My dad wanted me to get flowmaster but i told him im geting magnaflow instead

[JoshieDoom]

I think their single chambers are almost as good as a cutout.

Dyno Proven

Ive got the american thunder and I love it..

[RandomOmen]

YES, assuming this poll is about the 80 series. I know from seat of the pants experience. Flowmaster 80 series muffler is the worst for performance.

[SAGGIN]

If they do take form horsepower over stock It can't be more than 2-5hp if that.

[Mr. Luos]

I think their single chambers are almost as good as a cutout.

Dyno Proven

Ive got the american thunder and I love it..
Damn near ANY other catback would gain you a few ponies.


Flowmaster outflows stock. But is the bottom of the barrel for aftermarket flow numbers.

[Speed Psychosis]

if it does it isn't noticeable. buy it for the sound. if performance is a concern, you should be looking at duals.

[JoshieDoom]

A guy right down the road from me has a straight pipe true dual(with x pipe) setup and with dual single chambers it only reduced output by 2 horsepower and no torque loss.

The 80s series sucka da wee wee tho

[LS1buckey]

I don't buy a muffler for power gains, thats why I did LT's and an engine tune flowmaster flows more freely but it's the sound you should be going for when buying an after market muffler IMO.

[blackbirdbrain89]

un less u have a 98 single pipe ls1 then your stock muffler flows better then the flowmaster 80 s, imp they sound like crap and they make ls1's soune like 3.8 v6s. if any one cares to look it up maganflow is the best flowing and imp best sounding. close 2nd is borla not as loud but deep tone and flows close to magnaflow slp is junk as well

[nhraformula]

un less u have a 98 single pipe ls1 then your stock muffler flows better then the flowmaster 80 s,

above is bullshit.
when speed inc swapped out my muffler back in 2000, they welded in a flowmaster 80 series into the stock piping.
on back to back dyno pulls, the flowmaster 80 made 7 rwhp over the stock set up.
while the flowmater 80 series isnt the best flowing muffler out there, its better than stock.

[LIGHTNINGMCQUEEN]

they make ls1's soune like 3.8 v6s.

???? ......no way.

[01ws6er]

I think their single chambers are almost as good as a cutout.

Dyno Proven

Ive got the american thunder and I love it..


I have td's with single chambers and they are 6 1/2" inlet to outlet. They sound really good, and my god are they loud! I was gonna go Magnaflow, but changed my mind at the last second.


above is bullshit.
when speed inc swapped out my muffler back in 2000, they welded in a flowmaster 80 series into the stock piping.
on back to back dyno pulls, the flowmaster 80 made 7 rwhp over the stock set up.
while the flowmater 80 series isnt the best flowing muffler out there, its better than stock.

Nice to see someone put up #'s before bashing them. My friend had a muffler shop gut his 80 series and it made the sound/seat of pants power so much better.

[Mastermindc3pro]

Flowmasters just dont flow baby

[01ws6er]

So you mean to tell me that a 6 1/2" long (4"case btw) muffler that is completely open except for a little v in the middle isn't gonna flow? :jerkit: I assume you are talking about the 80 series.... I will be putting my car on the dyno soon so I'm interested to see how freely they "do not flow"

[Ls1_385hp_T/A]

Flowmasters just dont flow baby

Alright austin powers....super 40/ super 44 seem to be pretty good

[4get gto]

As of right now the poll says Flowmaster 63 % other 33%........???????

Whats are thoughts on that guys ??????????????????



I have the Flowmaster and think it sounds like one of the best....
As far H.P. goes you could'nt prove otherwise.............

[Speed Psychosis]

^ flowmaster is proven do be worse with flow. not by dynos, but actually measuring air flow accurately. however, exhaust should always have sound as first priority. if you aren't looking at getting headers anytime soon, i'd suggest a loudmouth 1 or 2, or bassani if you like it deep. but its all preference.

[Mr. Luos]

^ flowmaster is proven do be worse with flow. not by dynos, but actually measuring air flow accurately. however, exhaust should always have sound as first priority. if you aren't looking at getting headers anytime soon, i'd suggest a loudmouth 1 or 2, or bassani if you like it deep. but its all preference.
Personally...I am performance minded.

I pick an exhaust with performance in mind.
Then pick according to sound.


Although...nothing but Magnaflow for me now.
I can't seem to find it, but there is a flow chart of popular mufflers. Flowmaster is always at the bottom.
Does that relate to lower dyno numbers and ET's??? Probably. I am sure it depends on the set-ups.

[Speed Psychosis]

^ I believe there is a chart on ls1sounds.com

[SAGGIN]

Flowmasters just dont flow baby

they sound good thought

[nhraformula]

^ flowmaster is proven do be worse with flow. not by dynos, but actually measuring air flow accurately. however, exhaust should always have sound as first priority. if you aren't looking at getting headers anytime soon, i'd suggest a loudmouth 1 or 2, or bassani if you like it deep. but its all preference.

its proven to not be the best flowing, but its better than stock.
personally i think the flowmaster sounds great until you get headers and y pipe.

[brynnda]

flowmaster blows, magnaflow WTW!!!!

[TOMASINO]

flowmaster blows, magnaflow WTW!!!!

i think im goin with magnaflow since i put 80 series on, my car feels slow and louder then when i had it stock..

[RandomOmen]

I love my magnaflow catback.. especially with the Kooks LTs

[Speed Psychosis]

its proven to not be the best flowing, but its better than stock.
personally i think the flowmaster sounds great until you get headers and y pipe.

thats what i meant. not worse than storck but aftermarket. probably should have written that better.

right from ls1sounds.com

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



i wish they had catbacks and dual kit flows as well.

[9t8z28]

thats what i meant. not worse than storck but aftermarket. probably should have written that better.

right from ls1sounds.com

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



i wish they had catbacks and dual kit flows as well.

Were these flow tests done using the same equipment? I hope so or they don't mean shit.

Also, typically a straight path (straight through) design muffler will most of the time flow better than a chambered muff i.e. almost all Flowmaster. Most people would rather a better sounding muff over a better performing muff. This is true except for the typical F-Body enthusiast

[Mr. Luos]

Were these flow tests done using the same equipment? I hope so or they don't mean shit.
Of course they were. :yup:

This test was performed by 5.0 Mustang & Super Fords Magazine, December 2002 issue (page 55) on a '90 Mustang LX coupe with 370hp and 11 second potential. 66 pulls were made for this comparison:
I am too lazy to see if I can find the magazine link.

[9t8z28]

Of course they were. :yup:


I am too lazy to see if I can find the magazine link.

Thats alright. It is a good comparison

[shady milkman]

magnaflow sounds amazing on my bird...at 2k it sounds sooooooooooo good...i :stuck: a lil everytime

[Firebirdjones]

I would have thought this had been put to rest many years ago. Everyone has their own opinions on sound,,,thats just personal preference.

But as far as performance is concerned a friend of mine and myself have been down this road not too long ago using his Z28 as a test bed.

We have tried many single cat back systems on his car, about a dozen to be exact,,,,spending well over $2,000 in the process,,,(some systems were borrowed for the test to save some coin)

Bottom line was,,,,we tried borla, magnaflow, edelbrock, hooker, spintech, mufflex, flowmaster, loud mouth 1 and 2, etc.....

This car produced and performed nearly identical with every system with one exception,,,when the pipe size was changed!!! Thats it!!! Mufflers didn't do a damn thing for the car except change the sound.

When I say pipe size was changed,,,I am talking about the typical 3 inch cat back,,,,once the mufflex 4 inch single system was installed the car showed an instant improvement!!! Didn't matter whether it had the flowmaster or the spintech hanging on it.

In the end, when it comes to the muffler, don't worry about it!!! Pay more attention to the pipe design and system overall.

If you are looking for an all out single catback,,,go with the 4 inch mufflex hands down the best one out there as far as HP and performance producing.

The only thing I regret is not testing the Bassani true dual system. With a real dual system along with an X pipe it looks to be promissing, I would have loved to compare that to the single 4 inch mufflex system, which was the best performing out of all the single catbacks. Unfortunately time constraints and money ran out.

Would be hard to beat a real dual system though, and the Bassani looks like top notch quality. I'm willing to bet the 4 inch mufflex would come damn close.
All of the other 3 inch catbacks performed the same,,,,so don't worry so much about it. You guys are really beating a dead horse here.
Go with the sound you like and be happy.

[LS1buckey]

^^ Well put!

[punisherTA]

Some people around here call them Slowmasters. lol
I couldn't tell you if they are better or worse then stock. The general train of thought is that they are slightly better then stock and sound great but are not nearly as good as the straight through designs of some other mufflers.
It would stand to reason an open muffler would be better then a matrix of passages the Flowmasters use.

[OnEbAdReDSS]

80's flow better than stock and the 40's flow great i gained 2 hp lower than the magnaflow and i though the 40's sounds more muscley than the magnaflow

[Y2KArcticSS]

Flowmaster is always at the bottom.


Could also have to do with price. Flowmasters are CHEAP, so of course, they aren't going to be the best. I have a 40 series, it works and sounds fine, but if I had the money, I would have a GMMG....just to say I have GMMG...because it is THE most bad-a$$ exhaust I have ever heard...and the most expensive I've ever seen.

[itsfess]

i wanna hear that mufflex system on a car with long tubes.

[Firebirdjones]

i wanna hear that mufflex system on a car with long tubes.

It's one of the best I have heard in a long time as far as single cat backs go. Pipe diameter has alot to do with that. Awsome to see sewer sized pipes under the car,,,lol.. Actually fits quite well and as I said, it performed the best out of all the single cat back systems, didn't matter what muffler we had on it.

The car we used for all this was a longtube header car with an offroad Y-pipe,,,,although when the mufflex system was used,,,they have their own Y-pipe that we used with this setup.

[Speed Psychosis]

Could also have to do with price. Flowmasters are CHEAP, so of course, they aren't going to be the best. I have a 40 series, it works and sounds fine, but if I had the money, I would have a GMMG....just to say I have GMMG...because it is THE most bad-a$$ exhaust I have ever heard...and the most expensive I've ever seen.

its $50 cheaper than hooker. thats not a big difference. the flowmaster catback is terrible, but the 40 series are good. but if you want more than a muffler there are better options.

[LIGHTNINGMCQUEEN]

Could also have to do with price. Flowmasters are CHEAP, so of course, they aren't going to be the best. I have a 40 series, it works and sounds fine, but if I had the money, I would have a GMMG....just to say I have GMMG...because it is THE most bad-a$$ exhaust I have ever heard...and the most expensive I've ever seen.

I like my flowmasters because it has a good sound and when i rev it, it doesnt make that popping backfire sound. Ive never heard the GMMG but i wonder does that one along with other better flowing mufflers make that popping noise im not to fond of.
And if someone has a clip of what the GMMG sounds like please post it...id like to hear it.

[Firebirdjones]

its $50 cheaper than hooker. thats not a big difference. the flowmaster catback is terrible, but the 40 series are good. but if you want more than a muffler there are better options.


As compared to what???? I have used most all of them on the same car including the flowmaster system,,,they all performed the same as I have already mentioned. They are all 3 inch cat backs,,,,not much more to be had here,,,,,It's not until you jump to the larger Mufflex system with 4 inch piping when you will see a difference in power. Been down this road and done that, spent alot of money and time doing it.
Nothing but internet hype.

[01ws6er]

TD's FTW!!!

[Midnight02]

I can't believe that 20 people actually think the Flowmaster mufflers flow WORSE than stock.....this is internet hype at its best!

I am curious to see if those 20 people can produce any relevant dyno or flow test results that would support that.

We've seen a bunch of info regarding flow tests as well as dyno results and every single one of them support the Flowmaster muffler being an improvement over the stock setup. That being said, we all recognize that the Flowmaster 80 series design is far from a top performer on the F-body, so at the end of the day go with a catback that meets your needs (whether they are sound OR performance related).

[Firebirdjones]

Yep Midnight,,,,thats exactly what I'm getting at. We did a bunch of dyno sessions when available but did more track testing than anything as I had mentioned in an earlier post.
It's nothing but internet hype. Somewhere this rumor got started and just expanded from there.
I have seen more threads pop up lately asking about flowmaster mufflers and it makes me chuckle.
If I had the ability to post all the dyno graphs with various cat backs along with all the ET slips and log book info we compiled on all this over a 3-4 month period,,,I would ask to make it a sticky and put this myth to rest.
In a nut shell,,,all the 3 inch catbacks will show very similar results give or take 2-3 HP, (hence not enough to affect ET or MPH really),,,jump to a 4 inch single mufflex and see a significant difference,,,then of course the real dual systems are in a league of there own.
This is really just beating a dead horse. Just pick a sound and go with it.

[Speed Psychosis]

eh, exhaust is the most opinionated mod there is, by far. some people will focus on power more than sound. imo this doesn't let you enjoy the car as much, but their choice.

yes it might not make a big difference, a few horsepower. but hell, most of our mods are just a few (maf, throttle body, pulley, filter, intake manifold). it all adds up. and it depends on your setup. im will make difference with heads and stock manifolds are the real bottle neck in the exhaust, there's no question there. if you replace them and remove cats and get a tune, flowmasters might have held you back (esp 3 chamber). look a the flow rates on the other page (2). yes its better than stock, but there are much, much better flowing options like the hooker max flow. it would probably take some engine internals to really make a noticeable difference though.

[Firebirdjones]

The car we tested them all on was a well built Lingenfelter LT1 that put about 430 HP to the rear wheels,,,no slouch,,,but the flowmaster didn't hold it back anymore than any of the other 3 inch catbacks. :dunno:
I don't have a problem with them like everyone else seems to.

Then again, there seems to be quite a few things the internet says is great for 4th gens and I find the opposite, and vice versa.

[Z28collection]

anything out there aftermarket has got to flow a little better than stock whether it be a couple of horsepower or 15 - 20 horses.:wtf:

[N20LT4]

People can keep arguing all day about which exhaust system is better, and there will never be a definite answer to the debate. Exhaust is all about preferance. Yes I have had flowmaster systems and they did prove to be restrictive, but it wasn't nothing a flip of a switch to my e-cutout couldn't handle. It's all about which one you like. I spent $715 on my B&B Tri-Flo system because I loved the sound of a buddies '96 LT4 Corvette, and I never regret buying it. But the main poll topic of this thread is very halarious to me: Is a Flowmaster more restrictive than stock muffler? Come on now, that's just a bizarre question.

[fast enough Z28]

Although I don't like the sound of my flowmaster my dyno numbers proved to me that it couldn't be that bad. I am switching to a magnaflow but only for sound not looking to gain much.

[Firebirdjones]

Although I don't like the sound of my flowmaster my dyno numbers proved to me that it couldn't be that bad. I am switching to a magnaflow but only for sound not looking to gain much.

There ya go, exactly. I think most of the flowmaster smack talk is heresay,,,,most of the naysayers have never compared them on an actual dyno or track testing to other like systems.

[Firebirdjones]

People can keep arguing all day about which exhaust system is better, and there will never be a definite answer to the debate. Exhaust is all about preferance. Yes I have had flowmaster systems and they did prove to be restrictive, but it wasn't nothing a flip of a switch to my e-cutout couldn't handle. It's all about which one you like. I spent $715 on my B&B Tri-Flo system because I loved the sound of a buddies '96 LT4 Corvette, and I never regret buying it. But the main poll topic of this thread is very halarious to me: Is a Flowmaster more restrictive than stock muffler? Come on now, that's just a bizarre question.

I agree,,,just the posts alone on flowmasters lately is all bizarre to me.

[TRANS-DAD]

Hey Fast,
Going From Flows To Magnaslow Is Guna Suck
Uha............ Unless You Like The Sound Of Stock Exahust!!!

[fast enough Z28]

Hey Fast,
Going From Flows To Magnaslow Is Guna Suck
Uha............ Unless You Like The Sound Of Stock Exahust!!!

I've got lt's and ory!

[TRANS-DAD]

Yhea,
Still Gona Be Quiet But If It's A Dd That's Cool!!
(my 02 Dodge Ram W/stock Exahust Sounded Better Than My 01 T/a W A
Magnaflow!! ) J M O

[nhraformula]

Yhea,
Still Gona Be Quiet But If It's A Dd That's Cool!!
(my 02 Dodge Ram W/stock Exahust Sounded Better Than My 01 T/a W A
Magnaflow!! ) J M O

magnaflow is not going to be quite with headers and catless y pipe.
ive had above and its nowhere near quite unless your deaf

[TRANS-DAD]

magnaflow is not going to be quite with headers and catless y pipe.
ive had above and its nowhere near quite unless your deaf

OK, YOUR RIGHT :) AT LEAST FROM 4000 RPMS AN UP!!!:ughlaugh:

[LIGHTNINGMCQUEEN]

No, i agree with Trans-Dad. Magnaflow doesnt have a noticable exhaust note. Same thing as Stock Muffler.

[98 Stang Killer]

how good does the loud mouths sound i heard it on ls1 sounds but want some opinions before buying

[Speed Psychosis]

^ i just ordered it an hour ago. but my car is running rich which destroyed all my cats and all oxygen sensors so i have to get a tune before i show any videos or drive it. afterwards, i can show u a vid of anything u want.

but in the meantime, these are the 3 vids that convinced me.

watch this guys 2 vids.
http://youtube.com/watch?v=RFiEkJxmcX8

and watch this one. boring until about 50 seconds into video.
http://www.youtube.com/watch?v=IZ7yXyK50Yk

there are a lot of complaints of drone, but also a lot of great compliments. also, most complaints were from either people with headers (if you plan on getting some you might want to reconsider, way too loud and raspy) or they have an a4. m6 people naturally have less drone since we cruise at 60 at like 1500 rpm.

[nhraformula]

No, i agree with Trans-Dad. Magnaflow doesnt have a noticable exhaust note. Same thing as Stock Muffler.

when you have headers and off road pipe, i dont see how anybody can say its like stock.

[nhraformula]

how good does the loud mouths sound i heard it on ls1 sounds but want some opinions before buying
reminds me of a garbage truck

[Y2KPewterSS]

reminds me of a garbage truck

Reminds me of a farm truck :shrug:

[Speed Psychosis]

reminds me of a garbage truck

an aftermarket catback for our cars makes our exhaust quiet and the sound of a large turbo?

[nhraformula]

an aftermarket catback for our cars makes our exhaust quiet and the sound of a large turbo?
no, it sounds unrefined. its just loud

[shady milkman]

no, it sounds unrefined. its just loud


thats why i love my magnaflow..very refined but can be a loudmouth when i get on it.

[LIGHTNINGMCQUEEN]

when you have headers and off road pipe, i dont see how anybody can say its like stock.


Well thats different. I was commenting on the muffler its self with out any other add ons.

[JoshuaGrooms83]

2 cent time.
Mufflers primary job......
-control sound (thats why its called a muffler)
-Create some sort of back pressure
....... mission complete

[shady milkman]

2 cent time.
Mufflers primary job......
-control sound (thats why its called a muffler)
-Create some sort of back pressure
....... mission complete

backpressure is a myth..exhuast is all about scavaging..gmhtp and every major exhaust company said so.

[Speed Psychosis]

^ porsche and ferrari say otherwise. you need some pressure. open headers does make you loose power. but the piping itself does a good enough job. you don't need a restrictive cat or muffler. and although a variable exhaust would be better, we already have so much low end it doesn't matter. thats for the engines built for high rpms that don't have much power in the low.

[shady milkman]

well this is what gmhtp said and i have to agree...in a exhaust system ..you want the spent fumes to be exited from the system as fast as possible..so why would you want backpressure ? also on the open header part they say run the headers a little farther out ..the lost can be attributed to the exhaust fumes not smoothing out ..so they dont flow as well. i dont know though...i'm no exhaust expert..but if gmhtp and magnaflow ect tell me backpressure is a myth and not need then i shall believe them.

[N20LT4]

backpressure is a myth..exhuast is all about scavaging..gmhtp and every major exhaust company said so.

Whomever told you backpressure was a myth...lied to you! Different exhaust setups undoubtedly will alter low-speed grunt.

[shady milkman]

Whomever told you backpressure was a myth...lied to you! Different exhaust setups undoubtedly will alter low-speed grunt.

they said that has to do with the savaging..different exhausts have different scavaging points/levels..so some header/exhaust will have more low-end grunt compared to others.

[N20LT4]

they said that has to do with the savaging..different exhausts have different scavaging points/levels..so some header/exhaust will have more low-end grunt compared to others.

yes, I agree with that theory, but at the same time from experience you can and will alter the low-end power, atleast in the case of running open headers vs. a closed exhaust. Not to say you won't gain any...in most cases you actually gain more power up top, but you will lose some low-speed pull.

[shady milkman]

this is a writeup i found take it with a grain of salt. but it backs up gmhtp and the exhaust manufacturers' statments ..sorry for the long read


There is a common misconception that engines need backpressure in order to run properly, generate low end torque, etc. That is simply untrue. Backpressure is a bad thing. Always. Take a look at a top fuel dragster...how much backpressure do you think those zoomie headers make? Very little, and those engines produce 6500 hp.

So, what is backpressure? Any fluid flowing through a pipe experiences drag on the walls of the pipe. This depends on a number of factors, including the diameter of the pipe, the smoothness of the inside of the pipe, the viscosity of the fluid, and the velocity of the fluid. This drag results in a pressure drop through the pipe. In order for the fluid to flow at all, the pressure on one end of the pipe must be higher than at the other. In an exhaust system, that pressure drop is what we refer to as backpressure. It's pretty obvious that the engine has to produce this pressure differential, so the less power it has to spend making pressure to push the exhaust out, the more power it can send to the wheels.

Given that exhaust pipes are pretty smooth, and that we can't change the viscosity (thickness) of the waste gas being forced through the pipes, we are left with basically 2 parameters we can have any control over: The pipe diameter and the gas velocity.

Unfortunately, the pipe diameter controls the gas velocity since the volume of gas is prescribed by the engine. So, we really only have one thing we can change. So, bigger pipes allow less pressure drop for a given volume of gas because the velocity is lower. The pressure drop (backpressure increase) is proportional the gas velocity squared, so if I double the gas velocity (by reducing the cross sectional area of the exhaust pipe by half) then I quadruple the pressure drop.

Well, there's an easy solution for that: Just make the exhaust pipe bigger. Bigger pipe, lower gas velocity, less pressure drop, so less backpressure. Wow, that was easy. After all, this is the way it's done for basically any type of commercial plumbing system. Need less pressure drop on a chilled water pipe or a natural gas line? Just make the pipe bigger.

But wait, there's a problem....Having a huge exhaust pipe has killed my low end torque!!! What's different? Oh, there's no backpressure!! Therefore backpressure makes torque!

Wrong.

An exhaust system is different than just about any other plumbing situation. How? Because the flow is pulsed, and this turns out to be a big deal. Every time a pulse of exhaust gas runs through the pipe, a strange thing happens: it as it passes, it has a little area of vacuum behind it. Just like a NASCAR stocker running around the track, the pulse generates a little bit of a vacuum behind it. In NASCAR, a driver can take advantage of another driver's vacuum by getting right behind him and driving in it. The wind resistance is drastically reduced. This is called drafting.

Well, how big the vacuum behind each pules is depends on the gas velocity. The higher the velocity, the bigger the vacuum the pulse has behind it.

Now, this means that I can "draft" the next pulse, just like in NASCAR. In NASCAR, it's called drafting, in an exhaust system, it's called scavenging. You've probably seen this term used when talking about headers, but the same concept applies in the pipe.

I get the maximum scavenging effect if the gas velocity is high, so the pipe needs to be small. By maximizing the scavenging effect, I help to pull pulses out of the combustion chamber, which means the engine doesn't have to work as hard to do that.

This has the most effect when there's a bunch of time between pulses...in other words, at low rpm. As the revs rise, the pulsed flow becomes more and more like constant flow, and the scavenging effect is diminished.

So, at low rpm I need a small pipe to maximize scavenging, and at high rpm I need a big pipe to minimize pressure drop. My exhaust pipe can only be one size, so it's a compromise. For a given engine, one pipe diameter will make the most overall power (i.e., have the largest area under the curve on a dyno chart).

So, the loss of torque has nothing to do with backpressure, and everything to do with gas velocity. So you need exhaust components that are not restricive (manifolds/headers, mufflers) and that are sized correctly for your application.

To further dispel the "backpressure is necessary" theory, try this if you want. If you have access to a vehicle with open headers, make a block off plate that will bolt to the collector. This plate should have only a 1" hole in it for the exhaust to flow through. That will give you PLENTY of backpressure, and zero scavenging. Then you can report back on how much low end power it has.

The one exception to sizing an exhaust is for turbo cars. Since the turbo is in the exaust stream, the gas flow spinning the impeller tends to come out of the turbo with the pulses greatly diminished. In this case, you can get away with running a larger pipe than on an equivalent HP N/A engine because you can't take as much advantage of the scavenging effect.

[shady milkman]

let me make this clear tho..i have ALOT of respect for you N20LT4..i dont have really any hands on experience like you..so i am not calling you a lier or anything like that just trying to share some of the knowledge i have read about with people and even you.

[N20LT4]

let me make this clear tho..i have ALOT of respect for you N20LT4..i dont have really any hands on experience like you..so i am not calling you a lier or anything like that just trying to share some of the knowledge i have read about with people and even you.

That is a great write up! You know, the whole back pressure issue has always been a debate. I've always believed in it, but there has never been any solid proof - or any real way to prove that it does contribute to low-speed torque. Nonetheless, that right up speaks on several key points that forces me look at the issue in a different light. Thanks for sharing that!

[shady milkman]

That is a great write up! You know, the whole back pressure issue has always been a debate. I've always believed in it, but there has never been any solid proof - or any real way to prove that it does contribute to low-speed torque. Nonetheless, that right up speaks on several key points that forces me look at the issue in a different light. Thanks for sharing that!

anytime man.

[JoshuaGrooms83]

soooooo? was i right?

[shady milkman]

no on the backpressure ..but yes on sound.

[JoshuaGrooms83]

ok. :nana:

[nhraformula]

Whomever told you backpressure was a myth...lied to you! Different exhaust setups undoubtedly will alter low-speed grunt.

why is it that all drag cars run open headers if its a myth?
any amount of low end tq you may lose will quickly be made up.

[TRANS-DAD]

Yes,
I Do Agree With You On That!!
I Think You Could Cut The Muffler Completly Off And The Stock Small Pipe Into A Y Would Still Create Plenty Of Backpressure.

[N20LT4]

why is it that all drag cars run open headers if its a myth?
any amount of low end tq you may lose will quickly be made up.

Drag cars are built for the strip only. There builders could care less about how much low-speed grunt, throttle response, or low-speed passing power they have. Those cars are focused on top end, i.e. top half of the track.

[Speed Psychosis]

^ exactly. most fbodys aren't track cars. low end doesn't matter when you have a drag car that starts by launching at high rpm in the first place. low end does need back pressure. just because some exhaust company says something doesn't make it true. ferrari and other exotic companies have spent millions more on research on cars.

[N20LT4]

]^ exactly. most fbodys aren't track cars. low end doesn't matter when you have a drag car that starts by launching at high rpm in the first place.[/B] low end does need back pressure. just because some exhaust company says something doesn't make it true. ferrari and other exotic companies have spent millions more on research on cars.

I agree. I don't know why we are comparing street cars to all out dragsters? :think:

[Firebirdjones]

None of mine are strictly track cars,,,yet I have 3 of them that I occasionally open the headers on via a pair of cutouts when I'm in the mood. The cars always pickup 2-3 tenths and about 3 mph give or take depending on weather....and these are dual exhaust cars with 3 inch piping,,,x-pipes etc....it's not like the motors are choked down....

Generally speaking if you open headers on a car and it slows down,,,,it's more than likely due to a lean condition. The car needs to be tuned accordingly.

[N20LT4]

None of mine are strictly track cars,,,yet I have 3 of them that I occasionally open the headers on via a pair of cutouts when I'm in the mood. The cars always pickup 2-3 tenths and about 3 mph give or take depending on weather....and these are dual exhaust cars with 3 inch piping,,,x-pipes etc....it's not like the motors are choked down....

Generally speaking if you open headers on a car and it slows down,,,,it's more than likely due to a lean condition. The car needs to be tuned accordingly.

First of all, I can only speak from personal experience. Second, once again I am refering to torque lost down low, not quarter-mile performance. The 1320 gives plenty of room to ring every bit of power out of the band - the street can be a different story. Again, I never said open headers takes away horsepower - infact, it actually gains power over closed exhaust in the upper-midrange/top side. But from my experience it deducts low-end power. When my cap is open, I notice a decrease in fuel mileage due to the fact that I have to give more throttle everytime I come off a stop light. It takes my car more effort just to get up to the speed limit under normal driving when my exhaust is open, versus when my exhaust is closed it is the complete opposite: has more throttle response, i.e. more down low, but doesn't breath as good in the upper rpm's versus my cut-out. This is just my car.

[Firebirdjones]

First of all, I can only speak from personal experience. Second, once again I am refering to torque lost down low, not quarter-mile performance. The 1320 gives plenty of room to ring every bit of power out of the band - the street can be a different story. Again, I never said open headers takes away horsepower - infact, it actually gains power over closed exhaust in the upper-midrange/top side. But from my experience it deducts low-end power. When my cap is open, I notice a decrease in fuel mileage due to the fact that I have to give more throttle everytime I come off a stop light. It takes my car more effort just to get up to the speed limit under normal driving when my exhaust is open, versus when my exhaust is closed it is the complete opposite: has more throttle response, i.e. more down low, but doesn't breath as good in the upper rpm's versus my cut-out. This is just my car.

Sounds like a classic lean condition...:D

I still run same 60 foot times in the 1.52 range carrying the left front wheel with or without the headers open,,,,so I'm not loosing any torque down low :shrug:

[N20LT4]

Sounds like a classic lean condition...:D

I still run same 60 foot times in the 1.52 range carrying the left front wheel with or without the headers open,,,,so I'm not loosing any torque down low :shrug:

Nope. Had the car on the dyno 10 days ago. Runs like a gem ;) Remember though, we have two different cars. :yup:

[Speed Psychosis]

None of mine are strictly track cars,,,yet I have 3 of them that I occasionally open the headers on via a pair of cutouts when I'm in the mood. The cars always pickup 2-3 tenths and about 3 mph give or take depending on weather....and these are dual exhaust cars with 3 inch piping,,,x-pipes etc....it's not like the motors are choked down....

Generally speaking if you open headers on a car and it slows down,,,,it's more than likely due to a lean condition. The car needs to be tuned accordingly.

um, your missing the point. it ruins drivability. on the road at low rpm u need some backpressure. not at wot on the dragstrip.

[shady milkman]

so we are back to square one huh? so we choose not to believe savaging.. how is drag ever good on the functionality of a engine???? do you want drag in the induction???? nope...how bought spent fumes evacuating the cylinder ?? nope doesnt make sense. so why would the exhaust be any different..that article backs up what exhaust manufacturers say..it even explains why you feel a "lose in low end grunt" ...so under the backpressure theory..we want as little drag as possible of air into the engine..and out..but only to the exhaust ]..the "Y" then we want drag to make torque??? that makes NO sense what so ever....also the dragster thing about no low end torque b.s needs to be thought about...do you think those dragsters have no torque? ...You can not get hp without torque.

[shady milkman]

um, your missing the point. it ruins drivability. on the road at low rpm u need some backpressure. not at wot on the dragstrip.

????? your kidding right??? do you think the more torque you have...the better drivability is??? hp doesnt kill drivability..its the torque.

[shady milkman]

why would you want a freer flowing /aka bigger pipes and straighter path....since it reduces drag..there for it reduces backpressure..under that thought we should keep the stock manis on because they create more bp therefore more torque..but that makes no since since you see power&torque gains through out the powerband.

[nhraformula]

just because some exhaust company says something doesn't make it true. ferrari and other exotic companies have spent millions more on research on cars.

so just because ferrari says so its true then.

[nhraformula]

First of all, I can only speak from personal experience. Second, once again I am refering to torque lost down low, not quarter-mile performance. The 1320 gives plenty of room to ring every bit of power out of the band - the street can be a different story. Again, I never said open headers takes away horsepower - infact, it actually gains power over closed exhaust in the upper-midrange/top side. But from my experience it deducts low-end power. When my cap is open, I notice a decrease in fuel mileage due to the fact that I have to give more throttle everytime I come off a stop light. It takes my car more effort just to get up to the speed limit under normal driving when my exhaust is open, versus when my exhaust is closed it is the complete opposite: has more throttle response, i.e. more down low, but doesn't breath as good in the upper rpm's versus my cut-out. This is just my car.
so what are you racing, winner at 100 feet?
at 50 feet even a stock car is going to be in the 3000 rpm band atleast.

[nhraformula]

None of mine are strictly track cars,,,yet I have 3 of them that I occasionally open the headers on via a pair of cutouts when I'm in the mood. The cars always pickup 2-3 tenths and about 3 mph give or take depending on weather....and these are dual exhaust cars with 3 inch piping,,,x-pipes etc....it's not like the motors are choked down....

Generally speaking if you open headers on a car and it slows down,,,,it's more than likely due to a lean condition. The car needs to be tuned accordingly.

funny, my 81 Z/28 did the same as your cars, it ran faster in the 1/8 and 1/4 when i uncapped the headers. it was no drag car either.

[shady milkman]

so just because ferrari says so its true then.

ohhh of course ..because it is ferrari..see magnaflow and other EXHAUST COMPANIES ..you know..the ones that make their living on EXHAUST SYSTEMS dont know shit..i mean come on..its ferrari..they make their living on selling cars..what sells sports cars quite a bit? sound/style..people buy ferraris mostly for the status symbol..the beautiful design ..the "ferrari sound" there are cars that are faster ..but people dont buy the ferrari solely on power..nor do most ferrari buyers care about a loss of 20lb.ft of torque or less ect..now f-body and corvette owners...hell yes we do.

[Speed Psychosis]

so we are back to square one huh? so we choose not to believe savaging.. how is drag ever good on the functionality of a engine???? do you want drag in the induction???? nope...how bought spent fumes evacuating the cylinder ?? nope doesnt make sense. so why would the exhaust be any different..that article backs up what exhaust manufacturers say..it even explains why you feel a "lose in low end grunt" ...so under the backpressure theory..we want as little drag as possible of air into the engine..and out..but only to the exhaust ]..the "Y" then we want drag to make torque??? that makes NO sense what so ever....also the dragster thing about no low end torque b.s needs to be thought about...do you think those dragsters have no torque? ...You can not get hp without torque.

yes you want drag in induction. my old car had vris, similar to vtech. basically 2 doors in the intake manifold. when both are open, path is straight. when closed, it had to go through longer paths. one opens at 3000 rpms, the other at 5. i drove a car with the doors taken out. it had MUCH less power down low. and everyone online said the same as well. whats an exhaust shop know? what technology do they use? they make a different sounding muffler and sell it. wow that takes a lot of smarts and degrees behind that. more backpressure isn't necessarily better, but you need some in the low end.

[nhraformula]

ohhh of course ..because it is ferrari..see magnaflow and other EXHAUST COMPANIES ..you know..the ones that make their living on EXHAUST SYSTEMS dont know shit..i mean come on..its ferrari..they make their living on selling cars..what sells sports cars quite a bit? sound/style..people buy ferraris mostly for the status symbol..the beautiful design ..the "ferrari sound" there are cars that are faster ..but people dont buy the ferrari solely on power..nor do most ferrari buyers care about a loss of 20lb.ft of torque or less ect..now f-body and corvette owners...hell yes we do.

hay you should call ferrari. i think you just gave them a new slogan, buy our car not because of the exotic styling, but because of the sound.
you might even get a buck or two for the suggestion.
maybe they will even give you a tip on how to make an exhaust for a f-body

[nhraformula]

yes you want drag in induction. my old car had vris, similar to vtech. basically 2 doors in the intake manifold. when both are open, path is straight. when closed, it had to go through longer paths. one opens at 3000 rpms, the other at 5. i drove a car with the doors taken out. it had MUCH less power down low. and everyone online said the same as well. whats an exhaust shop know? what technology do they use? they make a different sounding muffler and sell it. wow that takes a lot of smarts and degrees behind that. more backpressure isn't necessarily better, but you need some in the low end.

companies like hooker or magnaflow that make headers and such for race teams dont know shit, that sounds right.

i would expect to hear that from a vtech owner.

[JoshuaGrooms83]

back pressure? myth? i didnt study that in mythology. but.....