Exhausted Opinions
12-03-2007, 07:17 AM
#21
1.5 BAR
Join Date: Jul 2007
Posts: 752
Re: Exhausted Opinions
at low rpm when you step on it, the exhaust is flowing plenty to offer no restriction to the turbo, and thus a near ideal pressure drop, all this exhaust sizing is done for peak output. response difference would be almost completely zero.
12-03-2007, 10:44 AM
#22
Administrator
Join Date: May 2005
Posts: 78
Re: Exhausted Opinions
Originally Posted by fe3tcourier
at low rpm when you step on it, the exhaust is flowing plenty to offer no restriction to the turbo, and thus a near ideal pressure drop, all this exhaust sizing is done for peak output. response difference would be almost completely zero.
pressure drop is key. The restrictions of the tailpipe are somewhere around: the cat (60%), the muffler (30%), and the tubes (10%).
High flow cats and zero restriction mufflers are key.
Measure the turbine exhaust housing outlet for diameter. That should be the first 10-15 inches of the downpipe. From there, expand it 1/2 inch, run another 10-15 inches and expand another 1/2 inch. My exhaust starts at the turbo at 2.25" and ends at 3", stepped to 2.5" and 2.75" in between. The difference between that system and my previous 2.25" catback (same downpipe) is almost 1000RPM faster spool....
12-03-2007, 11:35 AM
#23
1.0 BAR
Join Date: Mar 2007
Posts: 247
Re: Exhausted Opinions
So a 3'' from the turbo will make the car boost 1250rpm earlier?
in my country all the big guns run a 76mm but it cost 2 months wages. so most cheap skates like me run a 63mm which is only a weeks wages.
what performance am i missing out on, now that we have proof less back pressure = more power/faster spool time/more response.
in my country all the big guns run a 76mm but it cost 2 months wages. so most cheap skates like me run a 63mm which is only a weeks wages.
what performance am i missing out on, now that we have proof less back pressure = more power/faster spool time/more response.
12-03-2007, 12:17 PM
#24
Administrator
Join Date: May 2005
Posts: 78
Re: Exhausted Opinions
Originally Posted by Schwitzer Turbo
So a 3'' from the turbo will make the car boost 1250rpm earlier?
in my country all the big guns run a 76mm but it cost 2 months wages. so most cheap skates like me run a 63mm which is only a weeks wages.
what performance am i missing out on, now that we have proof less back pressure = more power/faster spool time/more response.
in my country all the big guns run a 76mm but it cost 2 months wages. so most cheap skates like me run a 63mm which is only a weeks wages.
what performance am i missing out on, now that we have proof less back pressure = more power/faster spool time/more response.
Just like your intake manifold tapers in to increase the velocity, the exhaust should taper out. A 3" DP on a turbine with a 2" exit will probably cause turbulence and impede flow as the exhaust gases get lost in the mix filling up a large void.
the general rule is simply: Back pressure in an exhaust system is evil.
the difference in 2.5 piping and 3.0" is trivial, however the cross-directional area is 80% larger....
The people working for 2 months with 3" exhaust most likely get paid 1/10 the amount of the people working 1 week.
It's quite possible my 3" catback may or may not give me any extra benefits of a 2.5". The something like $20 difference in the final cost was enough to go bigger.
12-03-2007, 01:18 PM
#25
1.0 BAR
Join Date: Mar 2007
Posts: 247
Re: Exhausted Opinions
Originally Posted by Braineack
Just like your intake manifold tapers in to increase the velocity, the exhaust should taper out. A 3" DP on a turbine with a 2" exit will probably cause turbulence and impede flow as the exhaust gases get lost in the mix filling up a large void.
the general rule is simply: Back pressure in an exhaust system is evil.
the difference in 2.5 piping and 3.0" is trivial, however the cross-directional area is 80% larger....
The people working for 2 months with 3" exhaust most likely get paid 1/10 the amount of the people working 1 week.
It's quite possible my 3" catback may or may not give me any extra benefits of a 2.5". The something like $20 difference in the final cost was enough to go bigger.
12-03-2007, 01:21 PM
#26
Administrator
Join Date: May 2005
Posts: 78
Re: Exhausted Opinions
Originally Posted by Schwitzer Turbo
What i just upgraded my Tb from a 54mm to a 70mm was that a ---- up?
no, the individual runners still taper down in diameter as they enter the head. You're simply allowing more airflow volume to enter into the manifold.
