Drivetrain Exhaust Back Pressure Q
Thread Starter
|
5th Gear
Joined: Nov 2004
Posts: 890
Likes: 0
From: Rutherfordton, NC
Exhaust Back Pressure Q
I am a bit confused and would like to be enlightened on the subject of back pressure on a supercharged engine.
Ok I have heard that you want as little back pressure as possible because of the forced induction.
I have also heard just the opposite of this.
What is the deal hear?
Ok I have heard that you want as little back pressure as possible because of the forced induction.
I have also heard just the opposite of this.
What is the deal hear?
Originally Posted by spillman
I am a bit confused and would like to be enlightened on the subject of back pressure on a supercharged engine.
Ok I have heard that you want as little back pressure as possible because of the forced induction.
I have also heard just the opposite of this.
What is the deal hear?
Ok I have heard that you want as little back pressure as possible because of the forced induction.
I have also heard just the opposite of this.
What is the deal hear?
to put it simply, at low rpm, back pressure gives torque... at high rpm, back pressure holds hp... striking the balance is the key to a good exhaust system
now... on turbo cars that's a bit different, where backpressure ultimately slows the turbine speed and which lowers hp gains, that's why turbo exhaust tend to be very free flowing....
supercharger is similar to NA... in that back pressure gives low end torque... no back pressure means no low end torque... when one of the muffler joints on my exhaust came loose... i lost tons of low end torque, but there is a small gain in the top end that i can feel
6th Gear
Joined: Oct 2002
Posts: 3,652
Likes: 6
From: Lansdale, PA
With a supercharged engine, it's pretty complicated compared to a normally aspirated or turbo engine. With a N/A engine, you can use accepted guidelines to tune the header length and sizes to keep velocity up for good low rpm power. With a turbo engine, you just run as big a pipe as your ears can stand. 
With a supercharged engine, it's true that you have pressurized air on the intake side helping to evacuate the exhaust gasses during valve overlap, but you still want to reach that nice compromise of velocity and flow. Promini sells an exhaust backpressure gauge, but I can't recall seeing anyone use it.
I'd say with a supercharged engine, as with a n/a engine, testing, testing, and more testing is the only way to find an exhaust that adds power yet is pleasing to the ears. I found that the Magnaflow exhaust, for example, added some power but only at very high RPM. Below that, performance was almost identical to stock, yet sound levels were MUCH higher, even at low rpm and low load situations where stock would have performed just as well.
With a supercharged engine, it's true that you have pressurized air on the intake side helping to evacuate the exhaust gasses during valve overlap, but you still want to reach that nice compromise of velocity and flow. Promini sells an exhaust backpressure gauge, but I can't recall seeing anyone use it. I'd say with a supercharged engine, as with a n/a engine, testing, testing, and more testing is the only way to find an exhaust that adds power yet is pleasing to the ears. I found that the Magnaflow exhaust, for example, added some power but only at very high RPM. Below that, performance was almost identical to stock, yet sound levels were MUCH higher, even at low rpm and low load situations where stock would have performed just as well.
Thread Starter
|
5th Gear
Joined: Nov 2004
Posts: 890
Likes: 0
From: Rutherfordton, NC
Well the noise level doesn't bother me (I have earplugs for long journeys). I have the megan racing header which has no cat and the nrp exhaust minus one resonator.
I'm not exactly a chug-a-lug guy and like to let my MINI scream... so I'm not worried with the loss of low end torque. I am only seeking to improve my quarter mile times.
If I was to re-install the resonator how much of an increase would there be in backpressure? Is it as restrictive as the cat, or just a slight increase versus a straight pipe? Yes I know I just said above that the decibel level of the exhaust didn't matter, but I'm just tryin to get it to not sound so raspy.
I'm not exactly a chug-a-lug guy and like to let my MINI scream... so I'm not worried with the loss of low end torque. I am only seeking to improve my quarter mile times.
If I was to re-install the resonator how much of an increase would there be in backpressure? Is it as restrictive as the cat, or just a slight increase versus a straight pipe? Yes I know I just said above that the decibel level of the exhaust didn't matter, but I'm just tryin to get it to not sound so raspy.
Manufacturer
Joined: Dec 2002
Posts: 995
Likes: 0
From: Oregon
I would agree with Andy in that lots of testing needs to be done on an NA engine to fine the best size tubing for power/torque. Turbo, easy, 3" or bigger, done. SC a different story. The one thing a SC engine has is low end power. Whos to say a 3" would loose any lowend power. It surely will give you topend power. The back pressure at low RPM isn't important because the SC builds boost the second your foot is in it.
Many exhaust use a 2.25" tube, this is the same size tube an NA aftermarket honda exhaust uses. With the SC mini, and the HP it pushes, a the 2.5" has been proven, to give a few extra ponies. I belive a 3" system would do the same, just may be a little loud.
Esspecially with the twincharge cars, a 3" is the way to go. Maybe Andy if you would be insterested in this for testing we can work something out! I think 3" maybe the way to go! There is plenty of room to build it, and it wouldn't take much effort to build one. What do you think?
spillman,
your original question of BP. BP isn't worth much unless you can compare it to other things like HP and before and after a part is installed. It wouldn't be a gauge you would look at everyday. On a turbo car, the BP(before the turbo) can be 2x the boost pressure. But different turbos, will produce similar HP with different BP. On the mini, If someone were to drive back to back 5 different exhaust systems(on the same car), using BP they can determine which produces the most HP at redline. The less pressure the more HP. This is a good way to measure things without paying for dyno time. It will at least give you an idea which is the best, just not by how much.
Many exhaust use a 2.25" tube, this is the same size tube an NA aftermarket honda exhaust uses. With the SC mini, and the HP it pushes, a the 2.5" has been proven, to give a few extra ponies. I belive a 3" system would do the same, just may be a little loud.
Esspecially with the twincharge cars, a 3" is the way to go. Maybe Andy if you would be insterested in this for testing we can work something out! I think 3" maybe the way to go! There is plenty of room to build it, and it wouldn't take much effort to build one. What do you think?
spillman,
your original question of BP. BP isn't worth much unless you can compare it to other things like HP and before and after a part is installed. It wouldn't be a gauge you would look at everyday. On a turbo car, the BP(before the turbo) can be 2x the boost pressure. But different turbos, will produce similar HP with different BP. On the mini, If someone were to drive back to back 5 different exhaust systems(on the same car), using BP they can determine which produces the most HP at redline. The less pressure the more HP. This is a good way to measure things without paying for dyno time. It will at least give you an idea which is the best, just not by how much.
Coordinator :: Alabama Motoring Society & South East
Joined: Nov 2002
Posts: 10,170
Likes: 2
From: Burning-Ham Alabama
From my experience, I was disappointed with my Magnaflow exhaust because I lost power at the low end of the rpm range where I drive most of the time in exchange for a bit of power near redline.
It made driving my MINI less fun when I had a harder time getting the car moving at a stoplight or up an incline.
It made driving my MINI less fun when I had a harder time getting the car moving at a stoplight or up an incline.
4th Gear
Joined: May 2004
Posts: 409
Likes: 0
From: McHenry County, Northern Illinois
Back Pressure Question.
I have heard the "common knowledge" for years that back Pressure will increase Torque.
Why would this be true? What possible benefit to the engine is there of not being free breathing?
I understand why a specific length of pipe can cause better purging at a specific speed, but that is quite a different thing from back pressure.
On a 4 stroke you might find a length where the negative wave and positive wave could help purge / charge during valve overlap.
On a two stroke engine, a properly tuned pipe is in effect a supercharger.
But plain old restriction (back pressure) seems to me to just reduce the engines ability to purge.
Some one said it helps the exhaust valves to close, but the differential pressure across the exhaust valve would need to be very high to make a difference, and restriction would raise the pressure, but not the differential pressure.
Does any one know the reason that some back pressure is believed to be good?
John
Why would this be true? What possible benefit to the engine is there of not being free breathing?
I understand why a specific length of pipe can cause better purging at a specific speed, but that is quite a different thing from back pressure.
On a 4 stroke you might find a length where the negative wave and positive wave could help purge / charge during valve overlap.
On a two stroke engine, a properly tuned pipe is in effect a supercharger.
But plain old restriction (back pressure) seems to me to just reduce the engines ability to purge.
Some one said it helps the exhaust valves to close, but the differential pressure across the exhaust valve would need to be very high to make a difference, and restriction would raise the pressure, but not the differential pressure.
Does any one know the reason that some back pressure is believed to be good?
John
Trending Topics
3rd Gear
Joined: Mar 2004
Posts: 188
Likes: 0
My buddy gave me his one ball exhaust and I installed it a few weeks ago and I felt the low end torque was noticeably lower compare to the stock. I still need to install my alta intake and I'm hoping to get back some of the low end torqe w/the intake. Only other mod I have is the 15% pulley. I read somewhere else that the ECU does not need time to adjust to the one ball mod but I felt the same when I got my pulley installed it took about a week for the performance to be felt. So I'm hoping to put some mileage in the one ball hoping the car will adjust. If not the stock exhaust goes back in. I like my low end torque.
Manufacturer
Joined: Dec 2002
Posts: 995
Likes: 0
From: Oregon
Jdewey,
On an NA car the engine has to work at sucking in the air. So things like back pressure help with keeping the velocity higher which gives you the torque. You are right in that a freer breathing engine will give you more power, but only at the upper RPM. This is because to get more flow the intake and exhaust have to be larger, which in turn loses velocity, causing the loss in low end power. Honda's as do others, use vtec like things that have 2 cam profiles. One for low rpm,(high velocity, low end torque) and another for high rpm,(low restriction, low velocity, high end power). Boosted engines don't need
There are some motorcycles that have valve in the exhaust, that closes under lower RPM, giving you the low end power, then opens at higher RPM.
Then add boost to the mix. Since the air is being forced into the engine, things like increasing port size and manifold size, to a point, do nothing but help. Things like valve overlap actaully hinder performance by letting boost escape through to the exhaust.
YuccaPatrol,
I have heard a few other people having this problem with losing power. But i have seem many dyno plots with the exhausts installed back to back and there is no loss. The loss in power must be in the off boost areas, not the boosted areas. That does make sense then that you lost some off boost power.
But this brings up a good point about tuning. If you install an free flowing exhaust, this generally allows a little more timing to be added across the board. This added timing would bring back some of that lost power and add more everywhere else.
The problem is in the mini world, everyone relys on other peoples tuning. What are the base maps in the ECU, and how are they being modified and where? Maybe the chips tuned for your intake SC pulley and exhuast really aren't as good as they could be. I have seen many dyno plots of chips that do nothing but change the topend HP and increase redline. What we need is a user tunable ECU. Sorry this just turned into a ECU tuning thread. Maybe that is what we need to start.
On an NA car the engine has to work at sucking in the air. So things like back pressure help with keeping the velocity higher which gives you the torque. You are right in that a freer breathing engine will give you more power, but only at the upper RPM. This is because to get more flow the intake and exhaust have to be larger, which in turn loses velocity, causing the loss in low end power. Honda's as do others, use vtec like things that have 2 cam profiles. One for low rpm,(high velocity, low end torque) and another for high rpm,(low restriction, low velocity, high end power). Boosted engines don't need
There are some motorcycles that have valve in the exhaust, that closes under lower RPM, giving you the low end power, then opens at higher RPM.
Then add boost to the mix. Since the air is being forced into the engine, things like increasing port size and manifold size, to a point, do nothing but help. Things like valve overlap actaully hinder performance by letting boost escape through to the exhaust.
YuccaPatrol,
I have heard a few other people having this problem with losing power. But i have seem many dyno plots with the exhausts installed back to back and there is no loss. The loss in power must be in the off boost areas, not the boosted areas. That does make sense then that you lost some off boost power.
But this brings up a good point about tuning. If you install an free flowing exhaust, this generally allows a little more timing to be added across the board. This added timing would bring back some of that lost power and add more everywhere else.
The problem is in the mini world, everyone relys on other peoples tuning. What are the base maps in the ECU, and how are they being modified and where? Maybe the chips tuned for your intake SC pulley and exhuast really aren't as good as they could be. I have seen many dyno plots of chips that do nothing but change the topend HP and increase redline. What we need is a user tunable ECU. Sorry this just turned into a ECU tuning thread. Maybe that is what we need to start.
Banned
Joined: Jul 2004
Posts: 1,848
Likes: 1
From: City of Angels, Cali
I just thought I should post this...
I installed a JCW Exhaust last week. Since then, my car does not pull like it used to when in 6th gear, at 3k rpm. That is a fact, I know my car. The difference is dramatic, which makes me
because I LOVED pulling in 6th. (I was like GO 1.6 litres, yeah!!!!!!)
On the other hand.... it pulls slightly faster when redlining, 2-3-4, and I swear I feel it lurch forward even more after 5k rpm.
I installed a JCW Exhaust last week. Since then, my car does not pull like it used to when in 6th gear, at 3k rpm. That is a fact, I know my car. The difference is dramatic, which makes me
because I LOVED pulling in 6th. (I was like GO 1.6 litres, yeah!!!!!!)On the other hand.... it pulls slightly faster when redlining, 2-3-4, and I swear I feel it lurch forward even more after 5k rpm.
supertrapp and mania header data
interesting"historical" data on backpressure, torque, etc.
http://www.mini2.com/forum/showthread.php?t=52991
http://www.mini2.com/forum/showthread.php?t=52991
Manufacturer
Joined: Dec 2002
Posts: 995
Likes: 0
From: Oregon
camelpilot,
The mini's ECU may have some sort of "speed Limiter" when you are in 6th gear. We know the Mini has a fuel cut at a certain speed, but maybe they do some other things like pull extra timing in 6th gear when there is more boost than normal seen? Using what i saw in previous Dyno runs with exhaust systems, and the ones posted on mini2, you shouldn't have lost any lowend power. But these dyno runs were done in 4th gear most likely so there is no way to know if there is something weird going when it 6th. Seems wierd though, maybe it was really hot that day?
flybot2160,
Those graphs are very good, it shows how the larger diameter, and freer flowing exhaust on the MCS doesn't hurt power down low. Also shows how the header doesn't loose low end, but gains top end, most likely from the freer flowing cat. The changing of the discs doesn't really show much change in WHP. 2WHP from run to run is a normal varience, so some of the valleys and peaks can be disregarded. What would have been really cool to see is the supertrap with nothing bolted into the end, just a straight pipe!
The mini's ECU may have some sort of "speed Limiter" when you are in 6th gear. We know the Mini has a fuel cut at a certain speed, but maybe they do some other things like pull extra timing in 6th gear when there is more boost than normal seen? Using what i saw in previous Dyno runs with exhaust systems, and the ones posted on mini2, you shouldn't have lost any lowend power. But these dyno runs were done in 4th gear most likely so there is no way to know if there is something weird going when it 6th. Seems wierd though, maybe it was really hot that day?
flybot2160,
Those graphs are very good, it shows how the larger diameter, and freer flowing exhaust on the MCS doesn't hurt power down low. Also shows how the header doesn't loose low end, but gains top end, most likely from the freer flowing cat. The changing of the discs doesn't really show much change in WHP. 2WHP from run to run is a normal varience, so some of the valleys and peaks can be disregarded. What would have been really cool to see is the supertrap with nothing bolted into the end, just a straight pipe!
Thread Starter
|
5th Gear
Joined: Nov 2004
Posts: 890
Likes: 0
From: Rutherfordton, NC
Originally Posted by camelpilot
Will removing the resonator give you any hp gains? Anyone know?
Jeff:
Thanks for the reply!
Jeff:
Thanks for the reply!
5th Gear
Joined: Feb 2005
Posts: 928
Likes: 0
From: Raleigh, NC
I guess I'm all alone over here in the corner.
My opinion:
Backpressure is never a good thing. It's just one of those myths that is so widespread it'll never go away.
Maintaining exhaust velocity is important however. The higher the velocity the better the performance. I'm hoping noone will dispute that. A larger than optimal exhaust can hurt performance, but I contend that it's not because of a lack of "backpressure", it's because you no longer have enough gas to maintain flow. You introduce turbulence and excess cooling.
I am confident that a 3" exhaust on the Mini will show considerable improvements across the RPM range. It will be some time before I have the dyno graphs to back it up - and when I do, it'll be a no-bend exhaust so the additional variable will make for a poor comparison.
Anyway... what do I know... I'm just a little unhappy with statments like "backpressure gives torque".
My opinion:
Backpressure is never a good thing. It's just one of those myths that is so widespread it'll never go away.
Maintaining exhaust velocity is important however. The higher the velocity the better the performance. I'm hoping noone will dispute that. A larger than optimal exhaust can hurt performance, but I contend that it's not because of a lack of "backpressure", it's because you no longer have enough gas to maintain flow. You introduce turbulence and excess cooling.
I am confident that a 3" exhaust on the Mini will show considerable improvements across the RPM range. It will be some time before I have the dyno graphs to back it up - and when I do, it'll be a no-bend exhaust so the additional variable will make for a poor comparison.
Anyway... what do I know... I'm just a little unhappy with statments like "backpressure gives torque".
Originally Posted by ALTA2
...... changing of the discs doesn't really show much change in WHP....
4th Gear
Joined: Nov 2002
Posts: 529
Likes: 0
From: Irvine, California
I think that, in the case of a MINI with a stock header, the exhaust's backpressure isn't a concern. Basically, it should be as free-flowing as possible. The header is the restriction in the system.
See here for an example of what I'm talking about:
http://dinancars.com/whitepapersFile.asp?ID=3
They also have an interesting discussion of harmonic dampeners, but that's for another thread:
http://dinancars.com/whitepapersFile.asp?ID=5
See here for an example of what I'm talking about:
http://dinancars.com/whitepapersFile.asp?ID=3
I’m fairly certain that many of you have been exposed to a “bench racing legend” that would have you believe that increased backpressure will improve low rpm power and that low backpressure will increase high rpm output. Nothing could be further from the truth. An exhaust system is sized for maximum flow at wide-open-throttle and peak rpm. All exhaust systems are “oversized” for lower engine speeds (rpm), as backpressure is so insignificant that it can’t even be measured. Less back-pressure always results in more power at higher rpm, with no negative effect on lower engine speed performance. The amount of power that can be extracted from an engine at a given rpm as a result of exhaust design is really limited by the exhaust manifold or header. After the header, less backpressure is always better.
http://dinancars.com/whitepapersFile.asp?ID=5
Well I'm also fuzzy on the theory behind low backpressure equals low torque, but I can tell you I just removed a Quicksilver exhaust for one reason being I did notice a drop in low-end torque (butt dyno). With it on I had to add more gas for 1st gear take-offs. I'm back to stock exhaust and the MINI is easier to take-off.
Again, non-scientific, but I did have it on for a month. Long enough to notice a change when I swapped back.
Again, non-scientific, but I did have it on for a month. Long enough to notice a change when I swapped back.
Your not alone
Originally Posted by JeffS
I guess I'm all alone over here in the corner.
My opinion:
Backpressure is never a good thing. It's just one of those myths that is so widespread it'll never go away.
Maintaining exhaust velocity is important however. The higher the velocity the better the performance. I'm hoping noone will dispute that. A larger than optimal exhaust can hurt performance, but I contend that it's not because of a lack of "backpressure", it's because you no longer have enough gas to maintain flow. You introduce turbulence and excess cooling.
I am confident that a 3" exhaust on the Mini will show considerable improvements across the RPM range. It will be some time before I have the dyno graphs to back it up - and when I do, it'll be a no-bend exhaust so the additional variable will make for a poor comparison.
Anyway... what do I know... I'm just a little unhappy with statments like "backpressure gives torque".
My opinion:
Backpressure is never a good thing. It's just one of those myths that is so widespread it'll never go away.
Maintaining exhaust velocity is important however. The higher the velocity the better the performance. I'm hoping noone will dispute that. A larger than optimal exhaust can hurt performance, but I contend that it's not because of a lack of "backpressure", it's because you no longer have enough gas to maintain flow. You introduce turbulence and excess cooling.
I am confident that a 3" exhaust on the Mini will show considerable improvements across the RPM range. It will be some time before I have the dyno graphs to back it up - and when I do, it'll be a no-bend exhaust so the additional variable will make for a poor comparison.
Anyway... what do I know... I'm just a little unhappy with statments like "backpressure gives torque".
6th Gear
Joined: Apr 2003
Posts: 3,957
Likes: 2
From: a canyon, south Bay Area
Having gone to a 2.5 catback that is essentially straight all the way back(battery box removed), I can tell with certainty that my MCS became faster by noting my times and speeds achieved at various points on a rural road where I live. She feels no faster off the line, and I have less boost, but I'm convinced that it was wise move. I might consider replicating this set-up with a 3" system, but then I would need a specially designed center pipe. Our center pipe in the tunnel is not straight per se, as it has drop-off of a couple inches when it enters the rear tunnel.
2nd Gear
Joined: Jan 2005
Posts: 74
Likes: 0
Originally Posted by ALTA2
Jdewey,
On an NA car the engine has to work at sucking in the air. So things like back pressure help with keeping the velocity higher which gives you the torque. You are right in that a freer breathing engine will give you more power, but only at the upper RPM. This is because to get more flow the intake and exhaust have to be larger, which in turn loses velocity, causing the loss in low end power. Honda's as do others, use vtec like things that have 2 cam profiles. One for low rpm,(high velocity, low end torque) and another for high rpm,(low restriction, low velocity, high end power). Boosted engines don't need
There are some motorcycles that have valve in the exhaust, that closes under lower RPM, giving you the low end power, then opens at higher RPM.
Then add boost to the mix. Since the air is being forced into the engine, things like increasing port size and manifold size, to a point, do nothing but help. Things like valve overlap actaully hinder performance by letting boost escape through to the exhaust.
YuccaPatrol,
I have heard a few other people having this problem with losing power. But i have seem many dyno plots with the exhausts installed back to back and there is no loss. The loss in power must be in the off boost areas, not the boosted areas. That does make sense then that you lost some off boost power.
But this brings up a good point about tuning. If you install an free flowing exhaust, this generally allows a little more timing to be added across the board. This added timing would bring back some of that lost power and add more everywhere else.
The problem is in the mini world, everyone relys on other peoples tuning. What are the base maps in the ECU, and how are they being modified and where? Maybe the chips tuned for your intake SC pulley and exhuast really aren't as good as they could be. I have seen many dyno plots of chips that do nothing but change the topend HP and increase redline. What we need is a user tunable ECU. Sorry this just turned into a ECU tuning thread. Maybe that is what we need to start.
On an NA car the engine has to work at sucking in the air. So things like back pressure help with keeping the velocity higher which gives you the torque. You are right in that a freer breathing engine will give you more power, but only at the upper RPM. This is because to get more flow the intake and exhaust have to be larger, which in turn loses velocity, causing the loss in low end power. Honda's as do others, use vtec like things that have 2 cam profiles. One for low rpm,(high velocity, low end torque) and another for high rpm,(low restriction, low velocity, high end power). Boosted engines don't need
There are some motorcycles that have valve in the exhaust, that closes under lower RPM, giving you the low end power, then opens at higher RPM.
Then add boost to the mix. Since the air is being forced into the engine, things like increasing port size and manifold size, to a point, do nothing but help. Things like valve overlap actaully hinder performance by letting boost escape through to the exhaust.
YuccaPatrol,
I have heard a few other people having this problem with losing power. But i have seem many dyno plots with the exhausts installed back to back and there is no loss. The loss in power must be in the off boost areas, not the boosted areas. That does make sense then that you lost some off boost power.
But this brings up a good point about tuning. If you install an free flowing exhaust, this generally allows a little more timing to be added across the board. This added timing would bring back some of that lost power and add more everywhere else.
The problem is in the mini world, everyone relys on other peoples tuning. What are the base maps in the ECU, and how are they being modified and where? Maybe the chips tuned for your intake SC pulley and exhuast really aren't as good as they could be. I have seen many dyno plots of chips that do nothing but change the topend HP and increase redline. What we need is a user tunable ECU. Sorry this just turned into a ECU tuning thread. Maybe that is what we need to start.
BRING IT AND WE WILL BUY!!!
Manufacturer
Joined: Dec 2002
Posts: 995
Likes: 0
From: Oregon
TonyB,
Your setup would be very easy to test a 3" system on. Straight through to the back must be pretty loud. The loss in boost is perfectly normal with a freer flowing exhaust. Just think at a given RPM the SC is pushing a fixed amount of air. If it is being blocked with the exhaust, more boost. A freind of mine had a cat melt on his SC Integra, and he saw 15PSI, when normaly is was set to 8psi!
We will keep people posted on the 3" system!
Your setup would be very easy to test a 3" system on. Straight through to the back must be pretty loud. The loss in boost is perfectly normal with a freer flowing exhaust. Just think at a given RPM the SC is pushing a fixed amount of air. If it is being blocked with the exhaust, more boost. A freind of mine had a cat melt on his SC Integra, and he saw 15PSI, when normaly is was set to 8psi!
We will keep people posted on the 3" system!
6th Gear
Joined: Apr 2003
Posts: 3,957
Likes: 2
From: a canyon, south Bay Area
The volume (decibels) is really not that bad with my 2.5" straight system. I borrowed a sound pressure meter during my experimentation... It was a tad louder when I didn't have a resonator just behind the cat. This is what I finally decided to use for the first part of my system:
I then had an additional 10 or so inches of 2.5" stainless welded onto this so that the Borla and tip would make for the ideal length for the exit. Also, I needed go back up a couple of inches due to the tunnel drop (middle of above photo), and a Borla Turbo center/offset muffler made this happen beautifully!
This was taken some time ago as your (Alta) rear control arms are now in place
There is certainly room for 3"!
I then had an additional 10 or so inches of 2.5" stainless welded onto this so that the Borla and tip would make for the ideal length for the exit. Also, I needed go back up a couple of inches due to the tunnel drop (middle of above photo), and a Borla Turbo center/offset muffler made this happen beautifully!
This was taken some time ago as your (Alta) rear control arms are now in place
There is certainly room for 3"!