Bottom Pulley - larger diameter available?

[the beard]

My current pulley (tow vehicle) is 171mm diameter.  I am after something slightly larger as the van does 2,700 revs at 60 mph towing and am looking to increase fan speed slightly.

If I get a piece of string around the deepest part of the groove that the fanbelt runs in, I get a circumference (minimum) of 46cm.  The top pulley (stock) is 23cm circumference (where the fanbelt runs) so for every turn of the lower pulley the fan turns approx twice as fast.  This means that for a stock VW engine pulling up to max say 4,000 revs the fan (stock) turns up to 8,000 rpm!

Anyway I am looking for a bottom pulley that is say 1cm wider in diameter - it will still fit above the breastplate (just) with the fanbelt on.  If I've done my maths right my current fan speed of 5,400 will increase to just over 6,000 rpm so around a 10% speed increase - still well within the stock VW fan speeds.  If I can find one then I am also going to have to get a Porsche top pulley to fit a stock fanbelt on both, which again will increase my fan speed but should still be well within safe limits.

I have been told Berg new pulleys are slightly bigger in diameter although there's no detail on their website.  Wondered if anyone has any actual measurements above 171mm diameter/46cm circumference.

Pulley I have now is a fairly light aftermarket one but in stock size.  Doesn't necessarily have to be anything thick and heavy as not revving much.

Cheers
Phil

[benssp]

Hi Phil, i'll measure my new Berg pulley when i get home(bought in october)

i'll send you an email tonight

[Martin]

if your wanting to run the cooling fan faster put a longer belt on it and run more shims in the top pulley, this makes the belt run a little deeper in the pulley making it seem smaller than it actualy is, this will speed it up. Failing that i can make you a larger bottom pulley.

is the motor getting to hot?


Martin

[The Ideaman]

Why not use a 356 top pulley?

[Martin]

Why not use a 356 top pulley?

Did't think of that! , lol

[dirk zeyen]

hi martin,

shorter belt!!!
shorter belt means smaller diameter on the top pulley and yes you need more shims

dirk zeyen

[richie]

Phil,as mentioned you can use the 356 top pulley which is smaller diameter giving you the increased fan speed you are looking for,
or just drive it faster=more RPM

cheers riche

[Martin]

hi martin,

shorter belt!!!
shorter belt means smaller diameter on the top pulley and yes you need more shims

dirk zeyen

ok, it must be idiot day for me today!


Martin

[stealth67vw]

AC.net sells a larger diameter bottom pulley.

http://www.aircooled.net/new-bin/viewproductdetail.php?keyword2=ESM0038&cartid=0209200989445524

[Bruce]

36hp bottom pulley is about 184mm in dia.

[the beard]

In fact when I mentioned the Porsche top pulley I was thinking of the 356 one - think I will start by trying that on there.

Ben - any result on the measurement of the Berg pulley?

Martin - she runs at 210 towing in hot summer, but I've had to remove my internal ducting to the oil cooler fan because of the new headliner (no room left) and will make an under chassis ducting system in future but this is to counteract the loack of cold air blast to the fan otherwise I reckon she will run at above the 210.  Seeing as it's a 10 hour round trip and I'm hoping to make plenty of trips I want to do the best for the longevity of the motor.  My understanding is that optimum oil temp for maxium lubing is approx 180-190F?

John - thanks for the tip, that aicooled.net pulley is a heck of an good idea however I have full flow so unfortunately wouldn't fit my motor,  It looks about a full inch wider than the stocker!

Bruce - I just measured an original 34 horse pulley and it comes out at 169mm width although the circumference where the fan sits is 48cm so slightly bigger.  Looks like VW used a much larger pulley for the extra 2hp motor, another 15mm wider which actually could be perfect for mine.

Richie - The motor's up to more towing speed but the steering box on the split ain't!  I see rack and pinion in the future......

Cheers all
Phil

[benssp]

Hi Phil, sorry my vernier only goes upto 100mm

the trusty tape measure gave me 7" diameter/178mm

[Bruce]

Bruce - I just measured an original 34 horse pulley and it comes out at 169mm width ......

Just to clarify, I was referring to the pulley from a 1200, 30bhp engine, not the later 34bhp engine that we call a 40hp.

[Neil Davies]

Richie - The motor's up to more towing speed but the steering box on the split ain't!  I see rack and pinion in the future......

Cheers all
Phil

Valley Gas Speedshop (Jimmy Hibberd with the blue '33 Willys from the Gasser Circus) does a kit I believe. Worth lookin into!

[the beard]

Yep they do a rack and pinion - disadvantages are cost and you have to drill through the front valence to clearance the mechanism.

Unlike the Creative kit which is nearly half the cost and requires no machining however the turning circle is dreadful, the stock height steering column is too low (skinned knuckles) and it doesn't auto centre after you turn (nightmare) so basically pants overall.

[stretch]

Race Shack have a rack and pinion system as well.  The 'G Rack' I believe it's called.  Might be worth giving them a bell.

[GreenTom]

You could try with BMD pulley (STD diameter bottom and the smallest they have in offer - maybe the one from dry sump system) should help.