Supercharged Phoenix is a go....

[dopdog]

have you been able to get your car back yet? also at the risk of being stupid how do you set/know the boost of the rotrex. I have been looking at my spec but cannot find any info on it.

[jeffw]

No, not yet. We measured the boost after the supercharger and then from the map sensor on the plenum. The C30-94 does a maximum of 1bar (around 15psi) so if you have that charger and you are peaking the revs out at 100K you will have 1bar. To work out your supercharger revs...

(Crank Pulley diameter/Supercharger Pulley Diameter) x 9.49 x Engine RPM = Supercharger RPM

9.49 is the input pulley to compressor ratio with the planetary gearing in the Rotrex. Max RPM for the C30-94 is 100K and the C30-92 is 120K.

[dopdog]

just did a quick calculation and have a 95 mm charger pulley with either 128 or 130 crank, that gives me at 7800 either 997.34 or 101293.26. that helps a lot as I was looking at either upping the revs or maybe a different diff ratio. looks like it will be a diff as this is the max for the engine.

thanks Jeff

[jeffw]

Sounds about right. We have dropped the pulley on mine down to 85mm (from 95mm) and also dropped the redline to 7100. In doing so the car has gained 25BHP and 20 ft lb (2.5 psi increase across the board) at peak revs and has a 20ft lb torque increase throughout. My cams mean the power is starting to go over at 7100 anyway so this is fine for me. Higher lift cams with longer duration would need a larger pulley and higher rev limit.

The next area I need to look at is the intercooler. I have a fixed supercharger boost level of around 17psi at at the charger but we are only seeing 11psi at the plenum. So the car makes 310BHP on 11psi and there is 6psi hiding in the, chinese, intercooler. So most intercoolers drop around 2 psi but mine drops 6 so a change of intercooler is on the cards or, maybe, go to a chargecooler which will drop around 1psi. Each 1 psi increase in boost at the plenum is worth 12BHP at the crank so there is another 48-60BHP in the intercooler....

[matt_gsxr]

Jeff,

Is that logic really correct (i.e. 5psi x 12bhp = 60bhp). I.e. that with a perfect (loss-less) intercooler you will get 17psi?
If that really were the case, then where is the extra air from the supercharger going now?


My guess is that if you decrease the intercooler resistance then you will increase the flow, which will cause a small pressure drop at the outlet of the supercharger. If the supercharger were a constant displacement pump (which is isn't) then the drop would bring it down to 11psi again! As the pump is a rotrex thing I guess the pressure drop will be less, but don't expect to get 16psi. If you have the pressure/flow graph for the rotrex then you should be able to work it out from that.


Matt

[jeffw]

Empirically your statements don't add up Matt. When we connected the supercharger directly to the plenum we got 16psi at full boost (one run only before the temps went through the roof).

[adithorp]

"...then where is the extra air from the supercharger going now?..."

There isn't an actual loss of presure in the intercooler. It's just the poor flow accross it means the induction draws it faster than the air can get through the cooler from the 'charger. If you could run the charger without the induction (you can't,obviously) then the presures would equalise each side of the cooler.

[matt_gsxr]

Empirically your statements don't add up Matt. When we connected the supercharger directly to the plenum we got 16psi at full boost (one run only before the temps went through the roof).

I think we agree more than you realise.

If you get 17psi at the supercharger with an intercooler attached, and 16psi with it plumbed directly into the engine.
That 1psi difference is what I was describing.

Presumably if you made the intercooler even more restrictive you could further reduce the flow and get 20psi or more at the exit of the supercharger, but that isn't real usable pressure. Do you see what I am trying to say?

Matt

[jeffw]

Not really....remember this is not a turbo.

[matt_gsxr]

A picture is worth a 1000 words



With your present set up and at 100k RPM you get 17psi at the supercharger outlet, you are at the red cross.

As you reduce the resistance from the intercooler you will get more flow (and hence power), but the rotation rate will still be 100kRPM, so you need to follow the dotted contour to see what pressure you get.

As far as I can tell this will result in a reduction of pressure as you more towards the blue diamond.



From what I understand improving the intercooler will give you more power. But if this map is to be believed you won't get much of an airflow increase (<10%) so I can't see you getting massive power increases. But I am happy for you to prove me wrong and look forward to the results.