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kenikh kenikh is offline
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Join Date: Feb 2005
Location: North of Exit 17
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Originally Posted by 911st View Post

Yes, equal length is the ideal turbo exhaust for making power!

But, lower volume is strongly correlated with reduced spool time. (See graph at start of this thread.)

I still have not seen a credible source that says equal length reduces spool time over a well designed non-equal system.

This is why I would say making the assumption that any such system will do so is a 'leap of faith' until proven with repeatable tests that control for boost level and AFR.

It could very well be I just could not find any experts that confirm this and am mistaken.

What I have read is that unequal length has the potential to create higher pressure spikes at the turbine that can have the effect of accelerating a turbo quicker.
Admittedly, my understanding regarding the benefits of twin scroll turbos is strictly in the 4 cylinder department; what you said does make sense regarding the impact of pulses on engines with fewer cylinders. The more degrees between each pulse does, at least mathematically, mean that the pulse wave of a given "bang" is less likely to get clipped by the wave of the next "bang", as well as having fewer degrees of overlap of the tails of the waves.

Regardless, all of the Japanese pocket rockets use divided twin scroll turbo with equal length headers and the dyno runs on NASIOC and EVOm all tell the truth in these applications that a pulse tuned turbos spool and transient response are MUCH quicker than the same turbo running merged shorties. That said, the length from head to turbo in these cars is so much shorter than our cars, that the exhasut volume between the two is negligibile, so you get the best of all worlds.

If anyone outh there is running a divided twin scroll turbo in a 930, it would be telling to see the difference in spool between a divided, equal length exhaust and a merged, equal length exhaust on the same turbo (apples to apples). For me, the debate is academic, as my motor is still a long way from built and I am already all-in on the turbo and exhaust selection.

Maybe 9 months from now I will be the one doing the comparison, but until then, I'll hold out hope someone else will.

- 1965 911
- 1969 911S
- 1980 911SC Targa
- 1979 930

Last edited by kenikh; 01-14-2010 at 04:46 PM..
Old 01-14-2010, 04:44 PM
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