Originally Posted by jammy86
Hey all, need some help for a uni project. I need some method of limiting boost, possibly at 1psi upto 7psi (though i doubt we'll use it more thtn 4psi max.). Its using a supercharger so we cant use a waste gate. What options does this leave me with? Bleed values? Boost controllers? I know little about these and was wondering if anyone could shed some light? we're going to be using a centrafugal type compressor (same as a trubo) which wont boost till ~20k rpm, but then will run all the way upto probably 100k. this means that the boost isnt going to be constant and so it cant just be leaked off at a fixed rate. We need to be able to change the amount of boost it holds easily as we'll be running it probably at 3 different levels throughout the event it will be in.
Anyone got any ideas?
Cheers
JAmes.
The amount of boost run on a supercharger can be changed through the size of the pulleys involved (think of gearing on a mountain bike...).
Now, to make it easily changed is less easy...
The one thought that immediately springs to mind is to have a quick release pulley on the crank, a quick release pulley on the charger and a tensioner in the middle. To change the boost through a pulley ratio, all you'd then need to do is take the tension off, release the pulleys and the belt and change them. If designed properly i see no reason why that couldn't be done in under a minute.
The other, slightly more tricky option is to develop a wastegate type setup before the throttle body. An external wastegate would probably be your best option but you'd need to change the spring rates inside and if time is going to be an issue, you'd need 3 wastegates all with different spring rates and then be able to mount them on V clamps so you'd be able to unclip the clamp and change the wastegate.
The rough as hell way to do it would be to introduce a controlled boost leak into the equation - fitting either a mechanical or electronic bleed valve into the boost control would allow you to 'leak' unwanted pressure - but i'd not advise this as a primary choice...
Thats the beer induced thoughts off the top of my head - hope it helps.
Oh, and having just re-read your first post - i should point out that you would be using bleed valves/wastegates etc in a much different sense than their normal application.
External wastegates normally vent exhaust gases to prevent the gases reaching the turbine wheel of the turbocharger, i'm suggesting you use them to vent unwanted boost pressure.
Bleed valves are normally used to fool the actuator into seeing a lower pressure than is actually being achieved, again, i'm suggesting you use it to vent unwanted boost to atmosphere.