Just beginning to put together parts necessary for a compound system, should i start with one or two wastegates, one on each turbo?
There's no easy answer to that question. What works and doesn't work depends a lot on how you route and position the gates. I've outline a couple of arrangements that have worked for me, and at least one that has not. I'm sure others can share what has worked for them as well. For generic guidelines though it's usually safe to assume that you need a LOT of wastegate bypass on the small turbine if you route it to the big turbine inlet, as you typically would. Two 44s or one 60mm would be typical here, with pros and cons to each option there. The big turbine is much easier to bypass, just treat it the same way you would as a single (large gate to run less of its capacity, small gate if you intend to use most or all of its capacity).Just beginning to put together parts necessary for a compound system, should i start with one or two wastegates, one on each turbo?
Tnx for taking the time for such a good answer.turbine choke flow is clearly important for making this work. The problem is that we can rarely choose a turbo based on that. The small turbo has to be chosen for the required spool, and for SI engines in particular, and that always means a turbine that is going to choke and require a lot of wastegate bypass. Diesels have more leeway here.
Hopefully something in there helps.
Again, I regret that my turbine knowledge is limited, but as I understand things, when the turbine/housing chokes, that doesn't mean it won't admit more shaft RPM. It will raise back pressure, which will then force more mass flow through the same restriction/choke point, which will raise shaft speed. A turbine side that provides more choke flow will operate with a lower back pressure (at the expense of spool, usually). The wastegate can really only bypass what the turbine does not require to generate shaft power to drive the compressor to what you're asking of it. That's a pretty loaded statement there, but it's key to understanding what the wastegate is really doing. If you understand that you can't simply open the WG more to reduce back pressure without boost falling, you probably get it. You can look at the WG position or WG bypass as the result of the turbine wheel, turbine housing, and work you're asking of the compressor, rather than the cause of it.And if HPT choke's, does it allow more shaft RPM still ?
Or try to ask it other whise.
If HP turbine choke's and you have great bypass capabilitys.
Are you still able to flow more LPT vollume on the intake site still ??
Yea I was thinking it would be too big / close in size to the s/c, but I have dynos showing the 8374 making 28psi by 3200 rpm on a TWO rotor (13b). So my reasoning was that the same turbo would spool 50% quicker on a 3 rotor (20b). I guess the next size down would be the EFR 7670, but I'm a bit worried it would be too small turbine-wise. Ur right tho, a larger s/c would be sweet, unfortunately the the C38R is the biggest compressor Rotrex offers.Those probably are too close in size. If you can spool the 85 lb turbo it will work but it doesn't seem worth dragging the SC along for the right for another 200 hp. I would consider a small turbo or quicker spoo if that SC is enough power, or a larger SC if that 85 lb turbo is easy to spool and you need more power. Always a judgement call with this stuff based on what you really need it to do.