That's awesome, thanks for that info. Seems like it'll be little or no concern at my power level, especially with a smaller c30. Does it make any sense to run a larger c38 and use a wastegate to blow off extra boost?the C38-series Rotrex units suffer from shaft brakages hitting the often hard rev limiters of Honda engines.
The newest C38R is also improved in this regard, but way to big for your power goal.
There are replacement shafts available with proper chamfers where the shaft diameter reduces towards the turbine wheel.
They put a step change of the shaft diameter in there to lead from the bigger center section of the shaft into the smaller threaded part for the wheel.
The torsional vibrations hitting a hard rev limiter shear them off. The bigger C38 turbines having a larger rotational intertia than the C30 wheels lead to fatique at this spot.
As of 2016 it seems Rotrex have addressed this themself:
View attachment 106107
"A major design change was introduced in 2016 as a direct response to customer feedback. The high-speed spindle shafts in our C30 and C38 range superchargers were redesigned and significantly strengthened to avoid spindle snapping under certain conditions."
"Customer feedback" as in pissed customers thrashing $2k superchargers and within the warranty period dealers having to replace lot's of them.
I do trackdays with a chap that killed 2 C38 of a F20c engined Lotus Seven before the shop downgraded to a C30-94 that then lasted.
So be aware of cheap older kraftwerks kit with C38 SCs. At least map them to not hit the limiter that hard.
The C30 units do not suffer from this. For a K20 or K24 you would want at least the biggest C30-94 unit. This will get you to over 400 crank HP.
The roots or screw blowers are very reliable albeit with a flatter torque curve than a Rotrex. Both will give you as much top end power as you dare. Power essentially climbs continuously to wherever you set the limiter.
Stock 2ZZ tend to brake valves if you rev them higher than 8000 for longer than a few moments. It is very common. With a stock 2ZZ stick to 8k max.
K20a2 are getting harder to come by. K24a3 seem to be plentiful.
Concerning the TVS... My main reason for the rotrex was that it runs cooler. Considering the relatively lower power level that I'm aiming for... I'm guessing I should still be ok with heat on a TVS? Especially if I use their air to water intercooler inside the manifold. I'm typically only doing 20-25 minute sessions at most.
Fitment on the TVS seems simpler:
Rotrex, it looks like I'd have to relocate some bits... engine coolant, reservoir for air to water hex, oil catch can:
Current engine bay with previous TVS removed: