-Boostjunky-
Boost-A-Holic
Ok, I hope to spark up an interesting conversation here, and get some good insight from members of the forum that have been down this road, and actually have some factual information (be it derived by personal experience, or by laws of physics). The topic of conversation is, as stated in the title, sizing compound turbo setups.
The way I understand things is that the drive pressures (which will cause high EGTs) are a HUGE concern when running compounds, and this due to the fact that you are running through 2 different turbine housings. One of them is going to be significantly smaller than the other, so this is the one that should be VERY carefully sized.
Now, I've been personally kicking around the idea of running compounds on my truck (it's a virtual certainty that I will be in the near future). In talking with a guy that works at Industrial Injection, I suggested that I would be interested in a final power output of around 800 whp (uncorrected @ 4,500 ft elevation).
In order to accomplish this, I figured an S480 would certainly be up to the task. I would REALLY like to keep the truck driveable and have as little lag as possible. As such, I thought about using a 62/71/14 as the small turbo in the setup.
What I'm hearing from my friend at II, however, is that this is a mis-match and that it will run HOT, and that a better match would be a 64/71/14. This intrigues me and has brought up the following questions/thoughts:
1) The primary determining factor of how hot the EGTs are going to get depends mostly on the backpressure (drive pressure) in the system (not taking into consideration fueling).
If this is true, then a 62/71/14 vs a 64/71/14 should yield the EXACT same drive pressures, being that the turbine wheel is the exact same diameter, and the turbine housing is the same size. I can only assume that the wastegate is also the same size for both turbos, and when it comes right down to it, how much the wastegate flows is going to be critical, since it will be full open once the big guy takes over.
2) The compressor housing size between the two (62 vs 64) is minimal. 2mm on the inlet, and virtually identical on the outlet. So, there should be little to no difference in restriction of the compressor housing.
3) If I can spool up more quickly, that will mean less time for heat to build up due to being overfueled while TRYING to spool up.
So, all variables accounted for, it would seem to me that this would be a win win situation, and that the 64 would only exaggerate lag and initial heat-up (during spool).
Ultimately, the power potential of the setup is determined by the big turbo, being that once you've spooled the big guy, the little guy is just along for the ride! He's no longer contributing to the "power making business end".
Am I correct in my observation, here? Or am I way off base? Can someone set me straight? I'd really appreciate any and all input!
The way I understand things is that the drive pressures (which will cause high EGTs) are a HUGE concern when running compounds, and this due to the fact that you are running through 2 different turbine housings. One of them is going to be significantly smaller than the other, so this is the one that should be VERY carefully sized.
Now, I've been personally kicking around the idea of running compounds on my truck (it's a virtual certainty that I will be in the near future). In talking with a guy that works at Industrial Injection, I suggested that I would be interested in a final power output of around 800 whp (uncorrected @ 4,500 ft elevation).
In order to accomplish this, I figured an S480 would certainly be up to the task. I would REALLY like to keep the truck driveable and have as little lag as possible. As such, I thought about using a 62/71/14 as the small turbo in the setup.
What I'm hearing from my friend at II, however, is that this is a mis-match and that it will run HOT, and that a better match would be a 64/71/14. This intrigues me and has brought up the following questions/thoughts:
1) The primary determining factor of how hot the EGTs are going to get depends mostly on the backpressure (drive pressure) in the system (not taking into consideration fueling).
If this is true, then a 62/71/14 vs a 64/71/14 should yield the EXACT same drive pressures, being that the turbine wheel is the exact same diameter, and the turbine housing is the same size. I can only assume that the wastegate is also the same size for both turbos, and when it comes right down to it, how much the wastegate flows is going to be critical, since it will be full open once the big guy takes over.
2) The compressor housing size between the two (62 vs 64) is minimal. 2mm on the inlet, and virtually identical on the outlet. So, there should be little to no difference in restriction of the compressor housing.
3) If I can spool up more quickly, that will mean less time for heat to build up due to being overfueled while TRYING to spool up.
So, all variables accounted for, it would seem to me that this would be a win win situation, and that the 64 would only exaggerate lag and initial heat-up (during spool).
Ultimately, the power potential of the setup is determined by the big turbo, being that once you've spooled the big guy, the little guy is just along for the ride! He's no longer contributing to the "power making business end".
Am I correct in my observation, here? Or am I way off base? Can someone set me straight? I'd really appreciate any and all input!
op:good stuff here
