ATR exhaust
- Thread starter jtgn
- Start date
salvageV6
Daily Driver
- Joined
- May 25, 2001
There should be of course.
But at what power level are you talking about?
Prolly for a mostly stock up to mid 11 combo. (guessing here) the 2.5" might be faster due to less weight.
Not sure when the larger pipes are needed.
I would guess at the horsepower level you will attempt to be at and give them a call.
I do know the 3" crossflow system is quiet on the GN even without a cat. compared to my 2 1/2" Kenne-Bell system on salvageV6 with ss. Ultraflow mufflers, also no cat.
But at what power level are you talking about?
Prolly for a mostly stock up to mid 11 combo. (guessing here) the 2.5" might be faster due to less weight.
Not sure when the larger pipes are needed.
I would guess at the horsepower level you will attempt to be at and give them a call.
I do know the 3" crossflow system is quiet on the GN even without a cat. compared to my 2 1/2" Kenne-Bell system on salvageV6 with ss. Ultraflow mufflers, also no cat.
If you have a 3" downpipe and 2.5" dual exhaust, the downpipe is the choke point in the flow system...a flow restrictor if you will. Dual 2.5" exhaust have a 39% greater flow area than a single 3" downpipe.
So if you have a 3" downpipe you will get no performance gain from a 3" dual exhaust in place of a 2.5" exhaust...in fact you might suffer a bit due to the extra weight of a 3" dual exhaust. However, it will sound different (don't know any details here)....
HTH, Bob
So if you have a 3" downpipe you will get no performance gain from a 3" dual exhaust in place of a 2.5" exhaust...in fact you might suffer a bit due to the extra weight of a 3" dual exhaust. However, it will sound different (don't know any details here)....
HTH, Bob
In pure theory, what you're saying of course would be true, but we live in the real world, and gains are common when making such a change.
Simply because exhaust system back pressure is still reduced even when going to the dual 3" system.
Cross section area isn't the only factor involved, but lot's of folks like to trot it out anyway. It would be if the pipes in question were perfectly straight.
But they're not. Take a look under there. See all those bends and curves? Everytime the flow of exhaust has to make any kind of a direction change, even a subtle one, there's going to be restriction added to it's flow. Restriction equals backpressure.
Backpressure after the turbo is just exactly what you don't want. Not any of any kind (as apposed to N/A engines which seem to like some).
Ideally if one could reduce the post turbo backpressure to ZERO, that would be perfect. But not acheivable in a street car application, so minimizing it as best we can is the best way to attack it. That means mandrel bends, easy curves (as best as can be achieved), larger pipes, if mufflers are used, they should be of the straight through variety, with perforated inserts(not punched), no we're not talking glasspacks here
strikeeagle
New Member
- Joined
- Jun 6, 2001
It wouldn't be even if the pipes were perfectly straight - even straight pipe has pressure loss, due to friction along the wall.
The fact that your DP is X" diameter has NO BEARING WHATSOEVER on the fact that the exhaust system that follows it, however large or small (yes, even if the size of a sewer pipe), has pressure loss.
Per ATR, the performance difference between the 2.5" and 3" at the 11 second level is likely to be small. It's mainly a matter of whether you prefer the so-called "macho" tail pipe look.
I also understand that the 2.5" is quieter.
The 2.5" system used to use aftermarket tail pipe hangers, whereas the 3" uses the factory hangers (much nicer look). However, I recall somebody saying the 2.5" units now possess this feature.
Happy hunting!!!
The fact that your DP is X" diameter has NO BEARING WHATSOEVER on the fact that the exhaust system that follows it, however large or small (yes, even if the size of a sewer pipe), has pressure loss.
Per ATR, the performance difference between the 2.5" and 3" at the 11 second level is likely to be small. It's mainly a matter of whether you prefer the so-called "macho" tail pipe look.
I also understand that the 2.5" is quieter.
The 2.5" system used to use aftermarket tail pipe hangers, whereas the 3" uses the factory hangers (much nicer look). However, I recall somebody saying the 2.5" units now possess this feature.
Happy hunting!!!
Here's the major difference - sound.
The other difference being weight.
The 3" sounds a heck of a lot throatier and deeper to me - a friend of mine has the ATR 3" dual system and it sounds a lot louder than my ATR system, which is 2.5 duals. Neither of us are running cats.
Performance differences would be negligible, if any, in my opinion.
Rich
The other difference being weight.
The 3" sounds a heck of a lot throatier and deeper to me - a friend of mine has the ATR 3" dual system and it sounds a lot louder than my ATR system, which is 2.5 duals. Neither of us are running cats.
Performance differences would be negligible, if any, in my opinion.
Rich
Rick Krupa
New Member
- Joined
- May 26, 2001
jtgn,
Sound clips can be heard on our site listed below.
Sound clips can be heard on our site listed below.
Friction..which causes back pressure is all about exhaust gas velocity. And velocity is all about pipe diameter. Other friction factors pale by comparision to velocity especially when the specific gravity of exhaust gasses is so small. Coefficients of wall friction are essentially the same for both SS downpipe and SS exhaust. Other factors are length of pipe, number of and radii of bends. These radii are pretty generous and mandrel bent pipes means the wall friction is also low. These other factors are all small which makes the effect of velocity even larger.
Flow rate is calculated by: Q = VA where V is velocity and A is area of the pipe. Let's call the velocity of the exhaust flow thru the 3" down pipe V1...when it goes from a 3" pipe to two 2.5" pipes the gas velocity is reduced by 39%...we'll call that V2. So because of the pipe area changes, the velocity of V2 is 39% less than V1.
Friction effect is calculated by: Wall friction coefficient times (length of pipe divided by pipe diameter) times (Velocity squared divided by 2 times gravity constant).
Because the velocity factor is squared in the friction calculation the net effect of the 39% reduced velocity is a 63% reduction in friction...ie back pressure. Said another way...the back pressure in the exhaust pipes is 63% less than that in the downpipe.
I like to exaggerate a scenario when making a point...think of Hoover Dam...when they crack open one of the valves to allow water to flow thru (around or under) it, the velocity thru the tunnel is very high and so is the wall friction (backpressure)...but after it shoots 50' across the water and ends up in the river flowing downstream the same flow rate in a much larger pipe (the river) and much slower velocity now causes very little backpressure.
Now 63% less backpressure is not zero...so yes there is some additional backpressure added to that of the downpipe...but it is negligible when compared to the downpipe effect. A dual 3" exhaust cuts the exhaust pipe gas velocity by 50% and the friction factor by 75%. I suggest that you cannot emperically determine the difference between 63% less backpressure and 75% less backpressure in a typical 10-13 second car....hence there is no need for the dual 3" exhaust if you have a 3" downpipe.
Most of the above is just theory and calculations...in the real world I don't think the back pressure generated in virtually any aftermarket exhaust scenario even including a single 3" exhaust is significant....weight is the bigger hitter in performance in my opinion...and that isn't too much of a big deal either to most of us.
So it might come down to the "look" and the sound of 2.5" and 3" dual exhaust systems which are the real tangible reasons to choose one over the other.
Regards, Bob
Flow rate is calculated by: Q = VA where V is velocity and A is area of the pipe. Let's call the velocity of the exhaust flow thru the 3" down pipe V1...when it goes from a 3" pipe to two 2.5" pipes the gas velocity is reduced by 39%...we'll call that V2. So because of the pipe area changes, the velocity of V2 is 39% less than V1.
Friction effect is calculated by: Wall friction coefficient times (length of pipe divided by pipe diameter) times (Velocity squared divided by 2 times gravity constant).
Because the velocity factor is squared in the friction calculation the net effect of the 39% reduced velocity is a 63% reduction in friction...ie back pressure. Said another way...the back pressure in the exhaust pipes is 63% less than that in the downpipe.
I like to exaggerate a scenario when making a point...think of Hoover Dam...when they crack open one of the valves to allow water to flow thru (around or under) it, the velocity thru the tunnel is very high and so is the wall friction (backpressure)...but after it shoots 50' across the water and ends up in the river flowing downstream the same flow rate in a much larger pipe (the river) and much slower velocity now causes very little backpressure.
Now 63% less backpressure is not zero...so yes there is some additional backpressure added to that of the downpipe...but it is negligible when compared to the downpipe effect. A dual 3" exhaust cuts the exhaust pipe gas velocity by 50% and the friction factor by 75%. I suggest that you cannot emperically determine the difference between 63% less backpressure and 75% less backpressure in a typical 10-13 second car....hence there is no need for the dual 3" exhaust if you have a 3" downpipe.
Most of the above is just theory and calculations...in the real world I don't think the back pressure generated in virtually any aftermarket exhaust scenario even including a single 3" exhaust is significant....weight is the bigger hitter in performance in my opinion...and that isn't too much of a big deal either to most of us.
So it might come down to the "look" and the sound of 2.5" and 3" dual exhaust systems which are the real tangible reasons to choose one over the other.
Regards, Bob
