The most common misconceptions that tuners have (Write Up)
Senior Member
Joined: 06-28-06
Posts: 12,577
Likes: 2
From: Canada
well done adam.
+rep
I especially appreciate your explaination on exhaust velocity.
We have had a few issues lately on the whole "3 inch is the greatest" debate.
Hopefully this will help people understand that bigger doesnt always mean better.
+rep
I especially appreciate your explaination on exhaust velocity.
We have had a few issues lately on the whole "3 inch is the greatest" debate.
Hopefully this will help people understand that bigger doesnt always mean better.
New Member
Joined: 06-30-07
Posts: 54
Likes: 0
From: Bristol, PA
for the most part, dead on. I do have to comment on one of your items however.
Some motors really do benefit from a bit of back pressure in the exhaust (mostly newer ones). It helps with scavenging (which is the name for the vacuum that forms behind a pulse of exhaust gas that helps to pull the next pulse out of the cylinders).
However, I will say that stock exhaust set-ups do create WAY more back pressure than is actually needed - and most after market systems will still create enough of that back pressure anyway (the only way to really get rid of back pressure all together is to have no exhaust at all, which is something you wouldn't want to do anyway for a multitude of reasons)
Some motors really do benefit from a bit of back pressure in the exhaust (mostly newer ones). It helps with scavenging (which is the name for the vacuum that forms behind a pulse of exhaust gas that helps to pull the next pulse out of the cylinders).
However, I will say that stock exhaust set-ups do create WAY more back pressure than is actually needed - and most after market systems will still create enough of that back pressure anyway (the only way to really get rid of back pressure all together is to have no exhaust at all, which is something you wouldn't want to do anyway for a multitude of reasons)
Thread Starter
Senior Member
Joined: 01-05-06
Posts: 10,877
Likes: 2
From: East Brunswick, NJ
for the most part, dead on. I do have to comment on one of your items however.
Some motors really do benefit from a bit of back pressure in the exhaust (mostly newer ones). It helps with scavenging (which is the name for the vacuum that forms behind a pulse of exhaust gas that helps to pull the next pulse out of the cylinders).
However, I will say that stock exhaust set-ups do create WAY more back pressure than is actually needed - and most after market systems will still create enough of that back pressure anyway (the only way to really get rid of back pressure all together is to have no exhaust at all, which is something you wouldn't want to do anyway for a multitude of reasons)
Some motors really do benefit from a bit of back pressure in the exhaust (mostly newer ones). It helps with scavenging (which is the name for the vacuum that forms behind a pulse of exhaust gas that helps to pull the next pulse out of the cylinders).
However, I will say that stock exhaust set-ups do create WAY more back pressure than is actually needed - and most after market systems will still create enough of that back pressure anyway (the only way to really get rid of back pressure all together is to have no exhaust at all, which is something you wouldn't want to do anyway for a multitude of reasons)
You're most welcome.
Last edited by NJHK; Jul 23, 2007 at 12:03 AM. Reason: Automerged Doublepost
Thread Starter
Senior Member
Joined: 01-05-06
Posts: 10,877
Likes: 2
From: East Brunswick, NJ
Rent me! per hour
Joined: 03-22-07
Posts: 24,161
Likes: 20
From: Still fixing others mistakes.
you need a gold toof.
to increase the scavenge effect on exhaust, start at 3 inch. drop to 2.75 a little ways back. then drop to 2.5
why?
increase in exhaust velocity.
if you think im on crack, look at how head work is done.
to increase the scavenge effect on exhaust, start at 3 inch. drop to 2.75 a little ways back. then drop to 2.5
why?
increase in exhaust velocity.
if you think im on crack, look at how head work is done.
Senior Member
Joined: 02-26-07
Posts: 532
Likes: 0
From: chicago
That was certianly a long Cudos!
Needed more flow equasions and the term "volumetric efficency" defined Both very important in understanding how /why a 4" exhaust Falls on the bad side of the bell curve for performance.
http://www.epi-eng.com/ET-VolEff.htm
that should do it
Needed more flow equasions and the term "volumetric efficency" defined Both very important in understanding how /why a 4" exhaust Falls on the bad side of the bell curve for performance.
http://www.epi-eng.com/ET-VolEff.htm
that should do it
Thread Starter
Senior Member
Joined: 01-05-06
Posts: 10,877
Likes: 2
From: East Brunswick, NJ
That was certianly a long Cudos!
Needed more flow equasions and the term "volumetric efficency" defined Both very important in understanding how /why a 4" exhaust Falls on the bad side of the bell curve for performance.
http://www.epi-eng.com/ET-VolEff.htm
that should do it
Needed more flow equasions and the term "volumetric efficency" defined Both very important in understanding how /why a 4" exhaust Falls on the bad side of the bell curve for performance.
http://www.epi-eng.com/ET-VolEff.htm
that should do it
Senior Member
Joined: 02-26-07
Posts: 532
Likes: 0
From: chicago
I want a mufler like the new vettes with a butterefly valve hooked to the vacuum to controll the Back Pressure on the cars exhaust. With the proper diamiters you could prolly float your entire HP band 1 or 2 hp 2-3 tq across the chart. More if you get the biggest size pipe you car could handel WOT. heh variable exhaust outlet diamiter is like a whole new lvl of cool.
Last edited by Evil C; Aug 6, 2007 at 03:09 AM. Reason: The monkey in my head told me to
Senior Member
Joined: 11-26-06
Posts: 791
Likes: 0
From: Cincinnati, OH
well-designed stepped headers use a series of increasing diameter pipes from the collectors which allow for this pressure difference. natural harmonics of the pipes help, too.
