Running Pas Pump And Alternator Faster

[M@tt 77]

At present the pulley on my supercharger is too large to spin at the desired speeds when powered by the current crank pulley.

 

There are 2 options

1) make a new smaller pulley for the SC (not as simple as it sounds, as its not a straight bolt on job, it would need a couple of parts making incorporating a bearing, circlips and a splined collar but certainly doable)

2) make a larger crank pulley

 

now the 2nd option is alot simpler (cheaper ) but it has the added effect that it will mean the PAS pump and alternator are being driven at a faster speed

 

my question is does anyone know whether this is going to damage the items? ie will the alternator be kicking out too much voltage or does it regulate itself to a set voltage once reached regardless or the speed its spinning

 

Will the pas pump pressure be too much? please don't suggest electric PAS as an alternative at the mo, i'd rather look at a solution keeping it as it is

 

Cheers

[Ryan 99]

The alternator contains a regulator and puts out a constant voltage while running, and the PAS pump has a bypas valve inside to stop the pressure getting too high.

 

How much faster would they be turning?

[M@tt 77]

well the current crank pulley is 12.5cm and the standard M62 SC pulley is 9.8cm.

 

So by my calculations the Crank to SC pulley ratio is 2.2 based on it needing to spin 16krpm @ 7200 engine redline

 

therefore 9.8 * 2.2 = ~ 21.5cm new diameter of crank pulley

 

so the devices would be spinnign at (21.5 - 12.5)/(12.5) = 72% increase

 

Alternator Present (12.5/5.8) = 2.15 rev per crank rotation

Alternator New Crank Pulley (21.5/5.8) = 3.7 rev per crank rotation

 

PAS Present (12.5/10) = 1.25 rev per crank rotation

PAS New Crank Pulley (21.5/10) = 2.15 rev per crank rotation

[welshpug 1,657]

what's the original crank pulley for that charger and do you really need to spin it flat out?

[M@tt 77]

I've sent an email to the chap who i bought the SC off to see if he could tell me.

 

I #think# it might be 18.5cm as looking on some Merc forums a popular upgrade seems to be an oversized crank pulley of 21.5cm from what i can tell

[M@tt 77]

just had an email back and the OEM pulley is indeed 18.5cm diameter

 

well by the sounds of it overspinning the alternator and PAS aren't goin to do them any harm (ryan i hold you accountable )

Edited August 25, 2009 by M@tt

[jackherer 543]

well by the sounds of it overspinning the alternator and PAS aren't goin to do them any harm (ryan i hold you accountable )

 

The regulator and bypass valve will (should) prevent any harm to the rest of the car but the alternator and PAS pump themselves may well develop problems very quickly with the bearings etc. However they are both readily available so its worth a go IMO.

[Ryan 99]

Well, they won't fry the electrics, or blow all the PAS hoses, but spinning them that fast may shorten their life.

 

With the current pulley ratios the alternator spins at ~15.5k at redline, and the PAS at 9k. The larger pulley would make these figures 26k and 15k. The alternator should be fine at that speed, although the bearing(s) may wear more quickly. 15k rpm may cause cavitation in the PAS pump and a loss of pressure.

[Tom Fenton 1,542]

Matt stop being a tightwad, and have a proper SC pulley made like we said.........job done once and for all.

[James_R 3]

I'll agree with the shortened life from spinning alts faster, I managed to kill 3 alternators in a weekend ring trip (inlcuding a new refurb'd one) form lapping with the revs up over the 4 day easter bank a while back.

[M@tt 77]

hmm i really fancy keeping the elctrical clutch if possible hence using the larger crank pulley, rather than makign a new SC pulley. But i'm going to have to have a think.

 

Maybe an enlarged Alternator pulley and PAS pulley could be an option?

[welshpug 1,657]

how high does the original engine it was fitted rev to?

[madspikes 41 1 Cars]

Who would have thought fitting a supercharger to a 205 would be hard work!!

 

Like Tom said, I would get a proper pulley made up for the charger. Would one off E45 fit?

 

Arent you going to run into clearance issues running a bigger crank pulley? What about that extra mass spinning at the end of the cranl?

Edited August 25, 2009 by madspikes