running straight pipe
Professional
Joined: Jan 2006
Posts: 233
Likes: 0
From: New England
RE: running straight pipe
the '03's with the 3.5" turbo outlet get the most out of changing to 4" or larger. There is a TREMENDOUS difference in back pressure, resulting in Tq and HP gains across the board.
ORIGINAL: Sereguial
I don't think either of you two are wrong. It depends on your exact setup, a stock 03 with muffler delete (no cat stock) will have different characteristics then an 05 with muffler and cat delete, since they are both different exhaust diameters and therefore different back pressures. Back pressure is a good thing for low engine speeds and torque (to a point that is); however, back pressure is bad for higher engine speeds and horsepower. As Steve said, in his setup he noticed a lack of torque at low engine speeds and Silverline has seen multiple times a gain in power. This is all a characterisitic of how they drive, Steve (correct me if I am wrong) probably spends more time in either lower RPM ranges or utilizes his entire engine band(and transmission will make a HUGE difference on this), where as Silverline probably uses higher engine speeds.
Getting back to the questions of straight pipes for your specific applications: if you use low end torque a lot, and you don't necessarily do JUST because you tow (depends on how you drive and gearing), you want back pressure. If you use higher engine speeds typically then it is probably good to go with straight pipes. Again, this all depends on your setup, since things like engine tuning will change these effects drastically.
As Silverline said, a more free flowing exhaust will cause lower EGT's, which can help for towing...
This is not a simple one answer situation... I suggest doing what Steve did, try it and if it doesn't do what you want then go with something else. Just remember the "butt dyno" can lie to you
and without monitoring equipment for stuff like EGT's then you will have issues.
BTW Steve: Back pressure hurts turbo spooling... but it does help exhaust flow characteristics at slow speeds (prevents flows from hurting in-cylinder combustion charactersitics such as in-cylinder pressures)
Oh, and had to add this:
I am not trying to step on anyone's toes, just trying to clarify exactly what has already been said and put my 2 cents in as well
I don't think either of you two are wrong. It depends on your exact setup, a stock 03 with muffler delete (no cat stock) will have different characteristics then an 05 with muffler and cat delete, since they are both different exhaust diameters and therefore different back pressures. Back pressure is a good thing for low engine speeds and torque (to a point that is); however, back pressure is bad for higher engine speeds and horsepower. As Steve said, in his setup he noticed a lack of torque at low engine speeds and Silverline has seen multiple times a gain in power. This is all a characterisitic of how they drive, Steve (correct me if I am wrong) probably spends more time in either lower RPM ranges or utilizes his entire engine band(and transmission will make a HUGE difference on this), where as Silverline probably uses higher engine speeds.
Getting back to the questions of straight pipes for your specific applications: if you use low end torque a lot, and you don't necessarily do JUST because you tow (depends on how you drive and gearing), you want back pressure. If you use higher engine speeds typically then it is probably good to go with straight pipes. Again, this all depends on your setup, since things like engine tuning will change these effects drastically.
As Silverline said, a more free flowing exhaust will cause lower EGT's, which can help for towing...
This is not a simple one answer situation... I suggest doing what Steve did, try it and if it doesn't do what you want then go with something else. Just remember the "butt dyno" can lie to you
and without monitoring equipment for stuff like EGT's then you will have issues.BTW Steve: Back pressure hurts turbo spooling... but it does help exhaust flow characteristics at slow speeds (prevents flows from hurting in-cylinder combustion charactersitics such as in-cylinder pressures)
Oh, and had to add this:
I am not trying to step on anyone's toes, just trying to clarify exactly what has already been said and put my 2 cents in as well
Record Breaker
Joined: Apr 2007
Posts: 1,512
Likes: 0
RE: running straight pipe
just reading this makes me think of when i tried straight pipes... they sounded good and loud but i have to say IMO all low end was GONE! it was so bad that i dident want to drive the truck because i felt all the power and speed was gone. i do mostly city driving so top end speed or power never ment anything to me. once i installed an 4" aero XL in the stock muffler spot it was better but still not as fast as stock at the low end so i installed a 22" borla straight thru muffler in front of the aero and i am back to stock feeling pretty much. i did not have gauges at the time so i do not have a diffrence in EGT's. but this is just my $.02 on the subject if it helps anyone out for anything!
Champion
Joined: Feb 2005
Posts: 3,710
Likes: 2
From: Skagit County, WA
Backpressure is never good.
When people say that backpressure is good, they're mistaken. What is necessary and good is exhaust gas velocity. Pipes that are too large lead to slow exhaust gasses. At low RPM, a properly sized exhaust pipe will provide a higher velocity - keeping gasses hot and moving quickly - which improves scavenging. Scavenging of exhaust gasses uses exhaust gas velocity to create a low pressure area outside the exhaust valve, which draws more spent exhaust out of the cylinder and even draws intake gasses in depending on valve overlap.
It's not the backpressure you need, it's the scavenging and velocity.
I put a 'test pipe' in place of my straight through muffler. The muffler is back on. I was fine with the volume, but at mid throttle it was too blatty.
I have a hard time believing that going straight through with stock exhaust negatively impacted power and economy given equal driving habits. It just doesn't make sense.
When people say that backpressure is good, they're mistaken. What is necessary and good is exhaust gas velocity. Pipes that are too large lead to slow exhaust gasses. At low RPM, a properly sized exhaust pipe will provide a higher velocity - keeping gasses hot and moving quickly - which improves scavenging. Scavenging of exhaust gasses uses exhaust gas velocity to create a low pressure area outside the exhaust valve, which draws more spent exhaust out of the cylinder and even draws intake gasses in depending on valve overlap.
It's not the backpressure you need, it's the scavenging and velocity.
I put a 'test pipe' in place of my straight through muffler. The muffler is back on. I was fine with the volume, but at mid throttle it was too blatty.
I have a hard time believing that going straight through with stock exhaust negatively impacted power and economy given equal driving habits. It just doesn't make sense.
