OBX Power Pulley Kit sr20de

Yes readed it also on a forum. G Spec is selling pulleys on ebay. Trusted but they sell only 2. JGY has a 4 piece kit also the "real" unorthodox has a 4 piece kit on ebay.
 
If you`re worried about `here say` issues about removing the OE pully dont do it.
I`ve had an alloy pully fitted for years and years now, along with a lightweight flywheel, and a highly aggressive clutch. The crank must take a good old battering.

ZERO ISSUES.
 
After much examining.. im 95% sure the 3 pulley Set from JGY ( Who i rate highly )... are same as OBX Items.

Now maybe its the same manufacturer?.. but balancing speeds and/or quality control is different.. but we all agree on the Water pump / Powersteering pump / Alternator this is of no real issue anyway.

Personally Im a fan of the original crank as the 'Harmonic' dampener makes sence to me.. However, reportedly 10bhp gains cannot be ignored when on a 300+ BHP SR it could equate to 15/20bhp?..

So here we go.. Cheapest set available as far as im aware.

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These are advertised as not only Under drive pullies but as lightweight..

All alloy construction and smaller in size.. Making sence so far.

Reputed gains widly known to be anything to between 6 ans 12bhp? So im going to get some exact weights and some exact dimentions. From initial examination:

The Crank pully is much smaller & Much Lighter
W/P is slightly smaller and much Lighter
Alt Pump is VERY slightly Larger & Much Lighter
P.S Pump is much Larger and much Lighter.

Gains and drawbacks.

Now less weight is simply better all round, so varying sizes are the factor here.

Crank is smaller

GAIN - Crank has LESS load = more power
LOSS - Crank drives other pullies less = less water pressure, less alternator power, less p/s power

Water Pump is smaller

GAIN - Water pump is Driven More = Better water pressure
LOSS - Extra load = less power

Powersteering is smaller

Gain = less Load = more power
LOSS = Less Drive = Weighter P.S

Alternator is smaller

Gain - Less Load = more power
LOSS - less Drive = Theoretically less charging.


Now im borrowing some Accurate scales for some pretty specific weights.. and then we need the Einstein in the Club to do the Maths and Work out how Large or Small these Gains and Loss's are..

Imo
 
I figured the water pump pulley should be larger so that the pump is spinning slower at high revs to prevent cavitation... gspecs is oversized..
 
i,ve been running a 2 x bigger alt pulley for a couple of years no probs
http://img15.imageshack.us/img15/3429/altvfi.jpg
(albeit with solar assistance, but which is very minimal during winter)
but if you are stuck in traffic with the h/lights, heater etc on, then the battery is literally draining during tickover :eek:
but regarding weight reduction, 1kg from some 4 inch pulleys has fuckall momentum when compared to an 11 inch flywheel :roll:
(ie, lightening the f/w has FAR more affect !

frank
 
frank said:
1kg from some 4 inch pulleys has fuckall momentum when compared to an 11 inch flywheel :roll:
(ie, lightening the f/w has FAR more affect !

frank
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I apriciate your input Frank, but 'fuck all momentum' is hardly some concrete proof.

Ive already said that the Weight loss is a good thing, all round. Obviously

Im running a Lightweight Fly also.

Its the UnderDrive and Overdrive, that im saying we could get some concrete information on.?..

Rather than.. yea it feels faster.

Some ratios would give us somthing we could work with?.. a ratio, therefore givving people a 'relativly' accurate way of worrking out the gains.. irrelivant of their curren't level of tune?

If I get the exact dimentions... anyone here capible of working out load changes?..

Give the Crank 100Lbs of torque over its current Diameter, and give each Ancillery a 10Lb drag. Then with new Sizes and same torque, we can work out a ratio for the gains?..

^would this work^

( Ive a feeling only REALLY accurate information would be acertained if weights were added to each Pully. Giving each a 'Set MASS' Given a constant speed. THEN the work Required to change this speed could be Calculated. THEN the new variables, and a re-calculation and this would give us the Difference in Work/Load/Effort between before and after??? hmmm... Wish I remember Some of my University Math! )
 
centrifugal forces are radius x omega x v squared or something crazy (way over my head :eek:)
and under-driving is only of use if you,re running at higher rpm than the factory assumed surely ? (ie, trackday, and if you,re underdriven during normal use then the waterflow will be insufficient, the steering will be heavy and the battery goes flat)

frank
 
frank said:
centrifugal forces are radius x omega x v squared or something crazy (way over my head :eek:)
Click to expand...

Im a bit bored - so searching the net for a simply to use model. lol

frank said:
and under-driving is only of use if you,re running at higher rpm than the factory assumed surely ? (ie, trackday,
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The forces ( drag or changes of Centrifugal inertias ) act across the full extent of any changes in Speed?.. therefore ALL accelleration is affected.. low end and high end...

To me it stands to reason that the higher the RPM the more negligable these loads become?.. although theoretically it should be equal across the board?

frank said:
and if you,re underdriven during normal use then the waterflow will be insufficient, the steering will be heavy and the battery goes flat)

frank
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You need to read my 1st post with the info frank. The Water pump is the only one smaller. Other than the crank. Wether this Reduction in size counteracts the CRANKS reduction in size would have to be worked out, and we would be left with a small increase or a small decrease in flow.

The alternator can easily be reduced in Rotation by a small Degree..

The power steering is interesting however as at idle it would be at its heavyest.. as a small increase in RPM would make up for the defecit in terms Steering wheel Effort.?..
 
kristian said:
The power steering is interesting however as at idle it would be at its heavyest.. as a small increase in RPM would make up for the defecit in terms Steering wheel Effort.?..
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is,nt the p/s pump governed tho kristian , ie, only actually pumps when pressure is needed (so the factory "gear it" so that full pressure is avaliable even at tickover)
and the sole reason for lighter f/w,s ect is for exceleration surely (ie, you dont actually "gain" any power, its just akin to removing weight from the car :)

frank
 
frank said:
is,nt the p/s pump governed tho kristian , ie, only actually pumps when pressure is needed (so the factory "gear it" so that full pressure is avaliable even at tickover)
frank
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Interesting point.. it makes the maths even more complicated. I think its reasonable to dismiss the Varying loads do to it being not really suitable to have

'this pully set will give you an extra 3% bhp when driving in a straight line, and only 2% when cornering'..

Though you are correct.. I meant when a load is applied from the PS pully.

frank said:
and the sole reason for lighter f/w,s ect is for exceleration surely (ie, you dont actually "gain" any power, its just akin to removing weight from the car :)

frank
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There is a big difference though bud between the FLY wheel and the crank pully..

A lot of people have the conception that they are the same.. due to rotating Mass on the Crank.

This is true. but the Flywheel DOESNT DRIVE anything.. its simply a dead weight.. The crank Pully is affectivly pushing and pulling, in addition to being a dead weight.

In terms of the cars acelleration or changes in Inertia. A lighter fly does obviously reduce an amount of dead weight.. but the RPM of the engine or WEIGHT of the crank is also affected in a different way.

The sole reason for a flywheel in the first place is simply to give an preferred 'NON load' rate of inertia. By having a Dead weight to counteract any sudden change in speed on the free reving engine.. this makes the engine Free rev up at a certain rate. ( eg motorbike engines rev very quickly.. )

... also steadies the idle.. and is useful with the clutch.. ( another topic )

The Crank pully is a participent in this cycle but its 2nd the the leverage forces applied to it... or the load placed on it.

Hope this is some useful info.
 
kristian said:
This is true. but the Flywheel DOESNT DRIVE anything.. its simply a dead weight.. The crank Pully is affectivly pushing and pulling, in addition to being a dead weight.
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the f/w is driving the car lol :P (via the clutch assy)
and these 6-12 hp claims are bollox, a 65amp alternator consumes about 1hp (65a x 12v= 780watts = 1hp) and thats if the battery is flat and full revs (if the battery is at normal voltage then the regulator in the alt drops it to a trickle charge)
the p/s pump is probably about 2hp (when steering) and probably 1/10th of that on the straight
the waterpump draws about 1/2 a hp full chat
so all together (flat battery/full lock/6krpm) they total about 5hp with belt losses
and if an underdrive setup drops the gearing by about 20%, then thats a 1hp saving :roll:

frank
 
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