G40 lader limitations.

[Varley]

Been thinking about trying a smaller pulley on my G40 charger which has got me thinking about the implications of such a move..

What is it exactly that determines how soon it would need a rebuild?

Is it simply that the increased rpm means proportionatly shorter service intervals or is it that the boost pressures involved when it's spinning that fast causes additional damage to the seals/bearings etc or is it a mix of the two?

Reason I ask is that with my setup (Full blend charger, 65mm pulley, PSD intercooler, larger throttle body, big valve head, 1473cc) the pressure in the system is reduced from a standard setup significantly, sub 10 psi on my gauge.

If it's the boost backpressure (?) that determines rebuild time then my basic maths would suggest my setup with a 58mm pulley wouldn't result in significantly different boost pressure than a standard setup with a 65mm pulley? Logic then follows that rebuild time would be reduced from how it is currently but in absolute terms still reasonable?

Is my reasoning sound or am I barking completely up the wrong tree?

What difference would running a standalone oil supply setup make?

Cheers!

[PeteG40]

in my opinion it overstresses the bearings and the oil seals. 

steve pitt used to use a 58mm and i watched at a rolling road day as it was held at 6k rpm and  started leaking oil - the oil seals were melted!!!

the other guy i know used a 60mm pulley and after revving it to about 6.5k rpm 4 times the charger grenaded.. Suspect that the top bearings (which are grease filled not oil fed) overheated and seized causing the timing belt to snap.

So basically - you can use a smaller pulley but it can over work bearings and seals and cause failure of both.  In my opinion of course.

The top bearings are actually only £4 bearings...

[hayesey]

personally I think these 1473cc engines need a bigger charger if you want to keep boost pressure up highish.  If it was me then I'd fit a turbo to it but if you want to stay supercharged then a g60 will give you good boost.

you could fit a smaller than 65mm pulley to the 40mm glader but it is working beyond the limits of what they can really take.  I reckon you'd soon get fed up of buying new chargers.

[Varley]

Cheers for the replies guys!

So are we saying that charger rpm determines bearing life and pressure in the system determines seal life? Or that service interval is proportional to rpm full stop?

Is it that the whole system heats up because of the higher rpm which damages the seals? Could you get a 'cooler in the standalone system maybe?

Sure I read somewhere that boost pressure governs charger life in some way?

Pete: Do you mean that a standalone kit wouldn't protect the top bearings? Could these be uprated?

I agree a different charger would make more sense but stay with me... lol

[PeteG40]

top bearings arent oil fed no, not sure about uprated ones... RPM do some which are supposed to be. When i rang them their number was disconnected though.


also the oil seals are hot i think due to the friction of the main shaft on them.

only way of finding out is trying i suppose.

[g40chris]

how can you re-grease the top bearings other than rebuilding it

[Nick_S]

You wouldn't want to use a stand alone oil system with a 58mm pulley. The oil for these is thin enough as it is, so with the extra heat generated with higher RPM's the oil seals will undoubtably fail. Unless you put in a separate oil cooler for that as well, it wouldn't have chance to cool in that short system.

Tricky one as said will be your rev limiter. Too high and the charger RPM's will get too high, and too low will mean risk of bouncing off the limiter with toothed belts. Not a good idea.

Could always look into RS spec ported chargers for more boost. Again there will be reliability issues as with 58mm pulley systems.

[PeteG40]

how can you re-grease the top bearings other than rebuilding it

you can't - you have to rebuild it, they are sealed bearings units.

[PeteG40]

You wouldn't want to use a stand alone oil system with a 58mm pulley. The oil for these is thin enough as it is, so with the extra heat generated with higher RPM's the oil seals will undoubtably fail. Unless you put in a separate oil cooler for that as well, it wouldn't have chance to cool in that short system.

Tricky one as said will be your rev limiter. Too high and the charger RPM's will get too high, and too low will mean risk of bouncing off the limiter with toothed belts. Not a good idea.

Could always look into RS spec ported chargers for more boost. Again there will be reliability issues as with 58mm pulley systems.

i'd have thought that oil temps with a standalone would be much much cooler as it won't go in at 100 degrees+ heated by the engine, that was one of the plus sides of using them.... as well as lower pressure.

[hayesey]

oil temps in the charger with a stand-alone would be much lower than the engine oil which is being heated up by the engine.  Two ways of keeping the oil cool in a stand alone system, one is by having a bigger oil tank so there's physically more oil in it to disperse heat and the other is to incorporate some kind of oil cooler into the system. 

charger rpm and boost pressure both effect the life of bearings and seals and wear and damage to the actual charger parts themselves too.  Running a 58mm pulley on a g-lader isn't a new idea, some of the pitstop lads were doing it years ago, expect charger rebuilds roughly every 1500-2000 miles is all I can say.

[PeteG40]

the charger spins 1.6x crank speed on a 76mm normal pulley.

therefore at 6500rpm= charger spins at 10,400 rpm

76/65 = 17% smaller (ish)

therefore a 65mm pulley is 12,160rpm

a 60mm pulley is 13,173 rpm

a 58mm puley is 13,628 rpm

[Robin]

You wouldn't want to use a stand alone oil system with a 58mm pulley. The oil for these is thin enough as it is, so with the extra heat generated with higher RPM's the oil seals will undoubtably fail. Unless you put in a separate oil cooler for that as well, it wouldn't have chance to cool in that short system.

really?!

that can't be right!

surely it depends on what pump you use for the standalone kit, if you use a proper oil pump then you can use nice bit of engine oil for the lube which shouldn't go past 50degrees ish, if you go for the cheap facet fuel pumps then you'll need to use machine oil which is much thinner but will be the same as hot engine oil at 90ish degrees but with less pressure which helps the oils seal from popping out.

[Nick_S]

That facet pump oil i've seen folk run is piss thin. Heat this up and it will loose viscosity like all oils. Seals are likely to fail by seep/weepage rather than a hydraulic hammer popping failures as seen with engines bouncing on rev limiters.

[Andy]

Henry used to run his PSD standalone with Synta Silver - as did many others. I used 0W30 fully synthetic in mine, nice and stable at higher temps in theory - though with a litre of the stuff circulating it never got hot to the touch.

Seriously doubt even with a 58mm pulley that you'd get much heat into that oil at all, you'd be talking of raising the oil temp by circa 70degC just to get the standalone oil up to lowish 'normal' engine oil temps of 90degC. That's a lot of heat energy for the bearings to generate to do that to 1 litre of oil.

I'd definitely use a standalone, and add a small cooler if I found it necessary. Would give flexibility as to what oil to use for the charger too.

[PeteG40]

I think the point is being missed here.

The worst bearings are grease filled and not oil cooled, so a standalone won't really help them. 

And where the seals went on beavis's was where the shaft touches the seal - friction there burning the seal.  A standalone wont do much in this either if its localised heat from contact.