supercharger question
Turbo Mini Forums

Right, if i had the throttle after the blower what do you need in line to vent pressure? Also how would you work out pulley sizes to get the right pressures out of the charger? is there a guide some where for figgering all this out?

Cheers Peeps
Thanks
Alex.

I suggest using a bypass valve that only closes above a certain throttle opening. This is how most the OEM systems work.

So until you want boost the blower just recycles the air.

Calculator here:

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Actually, I know I keep recomending the Sprintex calculator, but I've only just had a good look at it.

Its overly simplistic and should only be used as a general guide. It does not take into account of intercooling. Given that Intercooling can add 20% to your airflow and power, then you could be miles out.

The proper way to do this is to calculate your air flow as you would do for a turbocharger, taking into account compressor efficiency and intercooling etc. Then use a compresor map for the supercharger chosen. That will give you a speed to run the supercharger and an efficiency to feed back to check your calcs.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

How does the bypass valve work? is it on a thorrotle sensor or just it work on the pressure in the inlet? I assume a washgate would be a way of doing it but not very advanced.

I really should think about an intercooler shouldn't i. by the way this isn't for a mini, my mini's gearbox can't take anymore at the moment. Building my own charger set up for my mx5 but building it my self seems to make me a black sheep on the mx5 forums. they seem to prefer throwing cash at the problem rather then working it out for your self.

Thanks
Alex.

Read up now about the bypass valve and it all seems pritty simple bit of kit. Cheers Axel, Just got to messure my pulley thats on the engine and get my thinking cap on.
Cheers.
Alex.

I have not yet decided how to control my bypass valve.

I could make it spring loaded to open and use the last bit of throttle travel to close it using an extension to the throttle cable.

Or I could spring load it to close and use manifold vacuum to open it with an actuator.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

The unit i found, ran from vacum off the inlet manifold after the throttle and bypassed air from the out let of the supercharger back in to the filter side of the charger. I have do some more reading and worked out i want to run about 5psi on my 1839cc engine.

1839cc?!?

its an mx5 lol

right i belive i have worked out my charger pulley should be 72.41mm but thats using axels link, how do i account for intercooler and the like? I want 5psi ish but it doesn't matter if its alittle more. my drive pulley off the engine is 126mm.

Are you using an M45?

How good is your intercooler? Is it a huge front mounted jobbie or buried in the engine bay with no air flow?

Edited by Paul S on 16th Oct, 2007.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Thats the plan ( M45 is the one of the Bmw thing right?) No idea how good the intercooler is, not got one it should be a goodish sized thing infront of the rad if all goes to plan.

Assuming a 25 deg C inlet temp and a 60% compressor efficiency, the outlet temp would be 75.8 deg C.

Put it through an Intercooler at 80% efficiency, it should come out at 35 deg C. This represents an increase in the charge density of 6.2%.

Therefore, in theory, you should run the blower 6.2% faster to achieve your 5 psi boost with the intercooler. You should also get 6.2% more power.

However, I dont agree with the Sprintex calcs. I'm not sure what engine volumetric efficiency they use to calculate the air flow but it comes out very high.

I've calculated an air flow of 380 m3/hr intercooled, but Sprintex have 446 m3/hr which seems to assume 100% VE.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

right that made some sence to me, so if i work out the pulley size for 6psi then chuck it though an intercooler i'll get get some were around 5psi, this doesn't have to be very accuarte as im not changing the fueling systerm or anything with the ignition. right once the mini is on the road again (for the summer) I'll put the Mx5 in the garage and start work on it. any one know where to get hoses for the inlet cheap?