supercharger boost problem

[GreenV8S]

Whether you have the throttle upstream or downstream of the blower, it will still benefit from having a bypass. In some respects having the throttle upstream can make the rotor heating problem even worse because the blower is still generating heat it is just doing it in a thinner environment with less cooling to the rotors. But that's something that can wait a few weeks until you've got the thing running.

[kenmorton]

A good book on supercharging:

Supercharged by Corky Bell (ISBN 0-8376-0168-1)

covers pretty much everything from initial design right through to a worked installation. Well worth getting a copy if your doing your own thing.

[chuntington101]

Crofty2011 said:

Thanks Chris, yes I already have PPC because I'd heard about the articles and will send them some photos at some point (if I can get it to work).They focussed on types of supercharger etc but little on actual fitting and any other bits that were needed (I guess they wanted to talk about other things as well as superchargers!!). Is there a rule of thumb when talking about superchargers/turbos ie when talking about them you start from the engine and work back towards the filter? If so then mine will be set up throttle body/bypass valve/intercooler/supercharger/ air filter - which I think is the way the mini is set up (and what you are descibing)??

no the MINI cooper S system is, air filter-throttle body-superchager-intercooler-bypass valve-intake manifold...

this puts the throttle body up stream of the supercharger. if you look at other supercharged cars you will see the set up is the same. as said before it welp with pumping loss and also reduces stress on the blower.

i was thinking about it this morning (sad i know! lol). if you look at the supercharger it only has 1 fereance to the engine, and that the speed of the engine. so what is the supercharger doing at 6k rpm?? its pumping flat out and moving as much air as you ahve pullied it for.....but the throttle (in your set up thats the next thing it comes to) is closed! so you see the boost spike. basically the supercharger is trying to blow the throttle blade out the way.

now if you swap the 'charger and throttle around what happen then?? well you are at 6K but with a closed throttle, the 'charger is basically choked by the throttle and you see no boost. you are not getting the boost spikes (that might be blowing off intercooler piping), the 'charger is under MUCH less stress at closed throttle and you will have longer belt live (due to les stress on the 'charger).

as someone said a bypss valve will help. if setup right (make sure you get one that seals correctly, its a comon problem on the MINI, or you leak boost at WOT) then at low rpm or low throttle you wont see any boost. this will help with fuel.

now what you will need if you keep it the way you have it now is a blow off valve. this will stop the boost spikes by venting the air. its not the best way, something else to leak or go worng, but it would stop you putting the blower under soo much stress.

hope this hleps some mate. have you got any pics of the setup?? sounds like a really cool project.

Chris.

[chuntington101]

GreenV8S said:

Whether you have the throttle upstream or downstream of the blower, it will still benefit from having a bypass. In some respects having the throttle upstream can make the rotor heating problem even worse because the blower is still generating heat it is just doing it in a thinner environment with less cooling to the rotors. But that's something that can wait a few weeks until you've got the thing running.

so what about with the throttle downstream?? closed throttle (like you said above) will result in 14psi (i think the figures he was getting before) boost presure between the blower and the throttle. that will casue ALOT more heat than what you would get with the upstream throttle. also the MINI blower is out of its efficeny at anything above 13psi so if the boost spikes higher then its creating even more heat.

Chris.

[Busa_Rush]

chuntington101 said:

GreenV8S said:

Whether you have the throttle upstream or downstream of the blower, it will still benefit from having a bypass. In some respects having the throttle upstream can make the rotor heating problem even worse because the blower is still generating heat it is just doing it in a thinner environment with less cooling to the rotors. But that's something that can wait a few weeks until you've got the thing running.

so what about with the throttle downstream?? closed throttle (like you said above) will result in 14psi (i think the figures he was getting before) boost presure between the blower and the throttle. that will casue ALOT more heat than what you would get with the upstream throttle. also the MINI blower is out of its efficeny at anything above 13psi so if the boost spikes higher then its creating even more heat.

Chris.

With the throttle downstream and the bypass valve oppen there's no boost being generated, the sc is just spinning up ready to boost when the bypass valve is closed by the throttle being opened slightly.

The benefit of this is that cold air is drawn through the sc and the intercooler if there is one, which aids cooling of the whole caboodle. You only generate significant heat when boost is being generated.

Edit to add that the throttle upstream of the sc might benefit efficiency, not sure, maybe there are reduced losses ? BMW might have done it for reduced fuel consumption/emissions etc or maybe more manageable control of throttle ?

Edited by Busa_Rush on Monday 12th May 09:46

[AOJ]

Boost gauge to be fitted after the Throttle body

On tick-over the Throttle flap is closed so it will have much higher pressure between the charger and Throttle Body as the air flow is restricted.

[Mave]

Busa_Rush said:

chuntington101 said:

GreenV8S said:

Whether you have the throttle upstream or downstream of the blower, it will still benefit from having a bypass. In some respects having the throttle upstream can make the rotor heating problem even worse because the blower is still generating heat it is just doing it in a thinner environment with less cooling to the rotors. But that's something that can wait a few weeks until you've got the thing running.

so what about with the throttle downstream?? closed throttle (like you said above) will result in 14psi (i think the figures he was getting before) boost presure between the blower and the throttle. that will casue ALOT more heat than what you would get with the upstream throttle. also the MINI blower is out of its efficeny at anything above 13psi so if the boost spikes higher then its creating even more heat.

Chris.

With the throttle downstream and the bypass valve oppen there's no boost being generated, the sc is just spinning up ready to boost when the bypass valve is closed by the throttle being opened slightly.

The benefit of this is that cold air is drawn through the sc and the intercooler if there is one, which aids cooling of the whole caboodle. You only generate significant heat when boost is being generated.

Edit to add that the throttle upstream of the sc might benefit efficiency, not sure, maybe there are reduced losses ? BMW might have done it for reduced fuel consumption/emissions etc or maybe more manageable control of throttle ?

Edited by Busa_Rush on Monday 12th May 09:46

Isn't the bypass valve set up to open at the required max boost level, so essentially you are always generating boost?

[GreenV8S]

Mave said:

Isn't the bypass valve set up to open at the required max boost level, so essentially you are always generating boost?

Normally, it's just the opposite: the bypass is closed when the engine is at rest, and opened by vacuum in the inlet manifold. So it opens when the throttle is closed, and closes when the throttle is open. If you see what I mean! The purpose is to remove the pressure differential across the blower when no boost is required.

[Mave]

GreenV8S said:

Mave said:

Isn't the bypass valve set up to open at the required max boost level, so essentially you are always generating boost?

Normally, it's just the opposite: the bypass is closed when the engine is at rest, and opened by vacuum in the inlet manifold. So it opens when the throttle is closed, and closes when the throttle is open. If you see what I mean! The purpose is to remove the pressure differential across the blower when no boost is required.

Doh! Thanks for the clarification

[Busa_Rush]

Mave said:

GreenV8S said:

Mave said:

Isn't the bypass valve set up to open at the required max boost level, so essentially you are always generating boost?

Normally, it's just the opposite: the bypass is closed when the engine is at rest, and opened by vacuum in the inlet manifold. So it opens when the throttle is closed, and closes when the throttle is open. If you see what I mean! The purpose is to remove the pressure differential across the blower when no boost is required.

Doh! Thanks for the clarification

You also adjust the spring tension in the valve to make sure it opens at the right time, can fine tune it pretty well so a steady cruise where the vacuum is low allows the valve to open a small amount, so you get a smooth transition between boost and off boost.