Stepped header primaries are becoming very common but the use on a turbo application is curious.
The Rotax/BRP/Ski-Doo 850 turbo has a 'Y' junction 2-into-1 header, & the attached expansion
chamber/diffuser cone pipe - has to be gas-pressure sealed - yet not fracture prone.
Re: 2 stroke thread (with occasional F1 relevance!)
Posted: 29 Apr 2022, 00:31
by gruntguru
Ahh interesting, thanks J.A.W. Does that layout (with or without turbo) function the same as one chamber per cylinder in terms of expansion chamber "supercharging".
Re: 2 stroke thread (with occasional F1 relevance!)
Ahh interesting, thanks J.A.W. Does that layout (with or without turbo) function the same as one chamber per cylinder in terms of expansion chamber "supercharging".
With a 180 degree crankshaft 2-stroke, firing intervals allow for this expedient, but packaging/costs
trump max output/efficiency gains ultimately shown by running individual systems per cylinder.
A larger number of cylinders will allow closer combustion events & synergistic flows accordingly as
gas flow can be timed as continuous, or over-lapping (3 cyl 2-strokes = 6 cyl 4-strokes, pulse-wise).
Re: 2 stroke thread (with occasional F1 relevance!)
Posted: 29 Apr 2022, 05:46
by gruntguru
. . and of course wave supercharging becomes less important when you have a hair-dryer hanging off the side.
Re: 2 stroke thread (with occasional F1 relevance!)
Posted: 29 Apr 2022, 05:56
by johnny comelately
I always understood the step is to prevent the pressure wave going back into the engine.
We have used reverse cones with some success to achieve same .
Re: 2 stroke thread (with occasional F1 relevance!)
Posted: 29 Apr 2022, 06:33
by gruntguru
The two stroke "pipe" is designed for the pressure pulse to go back into the engine (the pulse contains fresh charge not exhaust gas).
Re: 2 stroke thread (with occasional F1 relevance!)
. . and of course wave supercharging becomes less important when you have a hair-dryer hanging off the side.
This would depend on the differential pressure between cylinder and turbine inlet. I assume never as extreme as venting to atmosphere directly, perhaps unless during WGO. Regardless, wave tuning should still be possible, pipe enlargement will lead to a pressure and velocity drop locally. Same for the 'supercharging' wave, maybe there is a small gain to minimizing crossflow beyond what is needed. Less compressor work.
Re: 2 stroke thread (with occasional F1 relevance!)
Posted: 02 May 2022, 13:14
by Pinger
From this:
To this:
No mention of why the turbo was relocated to the end of the pipe.
