This is just to satisfy my own head about his things work. I trust Mark and his expertise and he is the one tuning my truck to keep the magic inside the block.
Disclaimer finished, I am super close to getting back on the road and I am trying to educate myself on my first compound turbo setup. Specifically, I am thinking about how they share the load and where they can both operate efficiently while doing so. I've read rules of thumb kinda posts about wanting the setup that I have to supply the total boost 50/50, etc. I got hung up on the p/r math but figured out my mistakes and I think (hope!) that I have a decent grasp now. That said, when I look at the maps of the stock IHI and the S475, I don't see where the 50/50 recommendation is working for me. I've also read that you want to have both turbos at about the same pressure ratio, and that makes some sense. I suppose that you might want to play around with the contributions of each to find where the setup is most responsive, but the compressor maps and the p/r should perhaps dictate the playing field boundaries to avoid catastrophe or poor performance from surge etc.
My build: 2002 Lb7, SBE, 12mm pump, 65 over SACs, stock port/polished IHI and box stock S475 t6 1.32 a/r.
I am guesstimating max tune will have arguably about 45psi. I live at about sea-level.
(45psig+14.7psia)/13.7psia= 4.36 p/r
Primary making 15psi is a 2.17 p/r (halfway up the first island on the compressor map).
Secondary picks up the rest and delivers 30psi more. 2.19 p/r (halfway up the first island on its map).
Doesn't that seem better than 50/50 where the primary is at 2.72 (just leaving it's most efficient "island" on the map), and the secondary is at 1.64 (just below it's greatest area of efficiency on its compressor map)? Or is the 50/50 because the BTDT guys know that this is where everything responds best and it's within acceptable limits?
Just curious
Disclaimer finished, I am super close to getting back on the road and I am trying to educate myself on my first compound turbo setup. Specifically, I am thinking about how they share the load and where they can both operate efficiently while doing so. I've read rules of thumb kinda posts about wanting the setup that I have to supply the total boost 50/50, etc. I got hung up on the p/r math but figured out my mistakes and I think (hope!) that I have a decent grasp now. That said, when I look at the maps of the stock IHI and the S475, I don't see where the 50/50 recommendation is working for me. I've also read that you want to have both turbos at about the same pressure ratio, and that makes some sense. I suppose that you might want to play around with the contributions of each to find where the setup is most responsive, but the compressor maps and the p/r should perhaps dictate the playing field boundaries to avoid catastrophe or poor performance from surge etc.
My build: 2002 Lb7, SBE, 12mm pump, 65 over SACs, stock port/polished IHI and box stock S475 t6 1.32 a/r.
I am guesstimating max tune will have arguably about 45psi. I live at about sea-level.
(45psig+14.7psia)/13.7psia= 4.36 p/r
Primary making 15psi is a 2.17 p/r (halfway up the first island on the compressor map).
Secondary picks up the rest and delivers 30psi more. 2.19 p/r (halfway up the first island on its map).
Doesn't that seem better than 50/50 where the primary is at 2.72 (just leaving it's most efficient "island" on the map), and the secondary is at 1.64 (just below it's greatest area of efficiency on its compressor map)? Or is the 50/50 because the BTDT guys know that this is where everything responds best and it's within acceptable limits?
Just curious
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