Rear Mount Hot Side pipeing, help
10-21-2009, 06:48 AM
#11
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IMO... cut as much of the 3" off as you can and do it all in 2 1/2. Also, wrap EVERYTHING pre-turbo with header wrap. Mount the turbo as close to the motor as you can. Turbos NEED hot, high velocity, exhaust gas to make them work as efficiently as possible. Remember, I has a STS for 2 years before I went front mount. 
Making boost and pretty fast does not seem to be an issue here.
I think if you run 3" back to the WYE and then a foot or two of single 2 1/2" you should get all the acceleration in velocity that you need without any restriction to that point. Wrapping the pipes will help to keep heat in as well. It is also in your choice of A/R for the turbine and where you want to see boost. The Allison may also be robbing boost a little with its choice of gear ratios not loading up the turbo fast enough and the fact the 8.1 has a lower red line and more internal mass to spin up. Also the fact the 8.1 is tuned for torque not for speed.
I hope it works for you this time.
10-21-2009, 09:19 AM
#12
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Well that is probably true but I am not changing mine to find out. It costs to much....
Making boost and pretty fast does not seem to be an issue here.
I think if you run 3" back to the WYE and then a foot or two of single 2 1/2" you should get all the acceleration in velocity that you need without any restriction to that point. Wrapping the pipes will help to keep heat in as well. It is also in your choice of A/R for the turbine and where you want to see boost. The Allison may also be robbing boost a little with its choice of gear ratios not loading up the turbo fast enough and the fact the 8.1 has a lower red line and more internal mass to spin up. Also the fact the 8.1 is tuned for torque not for speed.
I hope it works for you this time.
Making boost and pretty fast does not seem to be an issue here.
I think if you run 3" back to the WYE and then a foot or two of single 2 1/2" you should get all the acceleration in velocity that you need without any restriction to that point. Wrapping the pipes will help to keep heat in as well. It is also in your choice of A/R for the turbine and where you want to see boost. The Allison may also be robbing boost a little with its choice of gear ratios not loading up the turbo fast enough and the fact the 8.1 has a lower red line and more internal mass to spin up. Also the fact the 8.1 is tuned for torque not for speed.
I hope it works for you this time.
10-22-2009, 01:55 AM
#16
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Ender06 if I had single rear mount I would have merged the 2 3" exhaust pipes as soon as the driver side crossed over to the pass side and ran only 1 single 3" pipe to rear turbo and ran .95 A/R on turbine. Need to minimize pipe volume on hot side to keep as much Heat (Heat is energy) as possible. On the cold side I would have run a single 2.5" to the Intercooler(less volume to pressurize the less lag). Use factory Exhaust manifolds and wrap as much as you can with wet heat wrap. 
Word of warning when you have the pipes welded make sure they are slip fit only before welding...welding slag of any sort = damage to Turbine Blades
Word of warning when you have the pipes welded make sure they are slip fit only before welding...welding slag of any sort = damage to Turbine Blades
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