350whp on 92 octane - How do I get there?
12-19-2009 | 09:19 AM
#106
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From: Denver
Well the typical rule is to keep exhaust gas velocity below 250ft/sec.
Using:
Airflow / Area = 250
I get ~2.7inch diameter pipe would be the minimum for post turbine... Pre-turbine, we can usually get away with a bit smaller, to help drive the turbo.
-Rogue
Using:
Airflow / Area = 250
I get ~2.7inch diameter pipe would be the minimum for post turbine... Pre-turbine, we can usually get away with a bit smaller, to help drive the turbo.
-Rogue
12-19-2009 | 09:46 AM
#107
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From: Denver
And if anyone felt so inclined, these guys could tell you, with extreme precision, what size and your exhaust should be:
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12-19-2009 | 09:24 PM
#109
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I would think, with the crossover, that erroring on the big side would be better than too small right? A little extra lag is better than loss of boost at the top?
12-19-2009 | 09:32 PM
#110
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From: Denver
Would the crossover ID be any different on our engines between a GT30 and GT35 turbo's (I know the hot side size is what would matter)? Generally speaking....
I would think, with the crossover, that erroring on the big side would be better than too small right? A little extra lag is better than loss of boost at the top?
I would think, with the crossover, that erroring on the big side would be better than too small right? A little extra lag is better than loss of boost at the top?
And generally, pre-turbine its better to error on the smaller side then larger.
So with my example earlier, it would be better to run 2.5" rather then 3".
-Rogue
12-19-2009 | 09:45 PM
#111
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Why would you go smaller?
Didn't this thread say, a few pages ago, that to much back pressure in the crossover was a bad thing?
There's quite a big difference between 2.5 and 3in anyway.... I was thinking on the lines of 2.25 vs 2.5 (or am I WAY over thinking the crossover?)
Didn't this thread say, a few pages ago, that to much back pressure in the crossover was a bad thing?
There's quite a big difference between 2.5 and 3in anyway.... I was thinking on the lines of 2.25 vs 2.5 (or am I WAY over thinking the crossover?)
12-20-2009 | 03:04 AM
#112
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From: Denver
You are over thinking it, lol 
Backpressure is mainly determined by the turbine section of the turbo, much less so the crossover pipe-diameter. The turbine inlet is only so big, and really, going any larger on crossover pipe size does not make a whole lot of sense.
Backpressure is mainly determined by the turbine section of the turbo, much less so the crossover pipe-diameter. The turbine inlet is only so big, and really, going any larger on crossover pipe size does not make a whole lot of sense.
12-20-2009 | 03:21 AM
#114
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From: Denver
A great book to build turbo knowledge is "Maximum Boost by Corky Bell". It has been the staple for turbocharging for years.
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12-20-2009 | 09:57 AM
#116
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I'm also in the camp that thinks that the turbine is the most important aspect of determining the back pressure at the exhaust valve.
So, what would be the significance of modifying the headers, which I've heard about over time?
So, what would be the significance of modifying the headers, which I've heard about over time?
12-20-2009 | 11:14 AM
#117
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From: Phila.
Yes and no. I had a friend tell me recently that worked for Honda superbike race team that exhaust is like black magic. I am no expert on the 944 turbo exhaust but from Power Engineering I know that we calculate pipe diameter and tubing size based on temperatures and fluid being moved.
When you look a sport bikes people buy various tuned exhaust system. Eg Muzzy, Yoshomura, Akrapovic, etc. They don't just have a local exhaust shop weld up a pipe system. Exhaust should all be about tuning to me since thats what streetbikes do.
We do know we are limited by the turbo inlet size so anything bigger than that is pointless. Exhaust also bounces as a wave through the system. Changing shapes and diameters changes tuning properties. Eg equal length headers.
I will dig through some of my PE books and see if I can find something that might anwer that question better. Again I'm no expert but I have been thinking about that for a while since I am in the middle of having my 3.0 built.
Jason
When you look a sport bikes people buy various tuned exhaust system. Eg Muzzy, Yoshomura, Akrapovic, etc. They don't just have a local exhaust shop weld up a pipe system. Exhaust should all be about tuning to me since thats what streetbikes do.
We do know we are limited by the turbo inlet size so anything bigger than that is pointless. Exhaust also bounces as a wave through the system. Changing shapes and diameters changes tuning properties. Eg equal length headers.
I will dig through some of my PE books and see if I can find something that might anwer that question better. Again I'm no expert but I have been thinking about that for a while since I am in the middle of having my 3.0 built.
Jason
It's the same principle with exhausts. I'm not saying you want the crossover diameter to be larger than the turbine inlet, but you might gain some exhaust gas velocity through the turbine by keeping the crossover dia slightly larger than the turbine inlet, then just before the turbine inlet, reducing the diameter with a nice reverse cone pipe (instead of one stepped pipe with a sharpe transition).
12-21-2009 | 11:37 AM
#118
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Is there a way to create a collector with the exhaust to actually pull out exhaust and thus decrease backpressure?
What about some sort of "velocity stack" approach?
What about some sort of "velocity stack" approach?
12-21-2009 | 12:00 PM
#119
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12-21-2009 | 02:07 PM
#120
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i believe this is the same idea as tapered intake runners; the stack gets narrower to increase gas velocity to ensure the steam gets out rather than just hanging around and like you said causing cooling issues. then the larger diameter above the "waist" of the stack probably creates a lower pressure area which the gas below will want to flow to.