Modifying pullies

[Bender Unit]

Just pondering a way to reduce some weight and rotating mass and was thinking about modifying the stock pullies.

I know you can get aftermarket jobbies but they cost, and I have old stock spares to mess with so want to see if I can get a similar effect for less.

So idea 1, chop the outer row off the stock crank pulley - i dont have AC or PS so its wasted. Advantage is I save some weight, retain the elastomer center to assist with harmonic balance.

Second idea was to get a hole saw and run some holes through the stock water pulley - the stock item weighs chuff all so I cant think the alu version weighs much less the weight saving will make it weigh even less.

Anyone see an issue with any of ths before I chop it it up and find out?

[classic mk1]

Whatever floats your boat matety .

[un1eash]

Wont work, the outer pully is bolted to the crank then the inner pully which is used is laminated/stuck to it.

[Lauren]

I'm not really convinced you'll really gain all that for what are pretty minimal weight savings, even if they do rotate.

[crazylegs]

i had an engineer friend of mine do just what you are thinking. he put the pulley on a lathe and took the air con section off. it made a considerable difference to the weight. it does work the bolt tightens on the inner pulley not the outer. its a free mod and an easy one and a rotating pound or two from the crank cant be bad

[Bender Unit]

Good to hear Crazylegs, will pop it on a lathe and remove the outer row. Checked out the water pump pully and I reckon I can put about 4 good sized holes through it to reduce a bit more weight. Just need to get an electric fan so I can do away with the viscous jobby mounted to the water pump pulley as that’s also going to be a drain. I have a alloy alt pulley.

Lauren, I know it seems minimal weight saving but every little counts when you’re trying to eek so more power out of the 4fag. Also its cheap mods and cheap is good.

Cheers

James

[LimeyMk1]

Might do the same to my MZFE pulley it's f'in massive.

[kaiowas]

trying to eek so more power out of the 4fag.

Don't fall into the trap of believing this will give you more power. It'll give the vehicle a performance increase however it'll increase power output no more than removing the carpets does.

[Tiny]

It will be less mass to move so there will be a Small Performance gain but its not an increase your freeing up power that is lost in the engine but the gains will be minimal.

TBH the only reason i would want to do this would be to fit a shiney Aluminium set that will look better in a fully shiney clean engine in a show car It will look alot better than a rusty old twin pulley not to mention when you look down there and you dont have aircon it does look like there is something missing.

[kaiowas]

You're not 'freeing up power'. That's simply not how the physics works. You're reducing the effective mass of the vehicle (Effective mass is the actual mass plus a compensation for the mass of rotating components)

By reducing the effective mass you'll see improved acceleration as you would with any weight reduction but you'll never see an increase in measured power at the wheels just from fitting a lighter pulley of the same size.

[Bender Unit]

Don't fall into the trap of believing this will give you more power. It'll give the vehicle a performance increase however it'll increase power output no more than removing the carpets does.

That’s why I am doing it to reduce parasitic drag on the engine. That’s the other reason why I am going to remove the stock viscous fan as that is essentially acting like a big wind brake which is robbing even more power. I know it doesn’t give additional BHP as such, just free’s up what’s currently being wasted.

TBH the only reason i would want to do this would be to fit a shiney Aluminium set that will look better in a fully shiney clean engine in a show car It will look alot better than a rusty old twin pulley not to mention when you look down there and you dont have aircon it does look like there is something missing.

One issue with the Alu crank pully is that as its not damped it can lead to accelerated wear on the bottom end. That’s why modifying the stock one is a good idea as it retains the elastomer core and damping ability. Oh and the alu ones are pretty dear and a lot still come with the AC / PS row. Going to remove the 2nd row, shot blast it and then paint it to make it look pretty.

[kaiowas]

Ignoring the fan for a second as it's a seperate issue (removing this will free up a little power but only if the electric one you replace it with uses less power than the drag on the viscous fan is sapping)

Parasitic losses will only be reduced by changing the size(s) of the pulley(s) so that it's spinning the alternator/water pump etc at lower speeds for a given engine speed. Merely fitting lighter ones of the same size will do nothing for you on that front.

[cartledge_uk]

trying to eek so more power out of the 4fag.

Don't fall into the trap of believing this will give you more power. It'll give the vehicle a performance increase however it'll increase power output no more than removing the carpets does.

There is an equation somewhere, I cant for the life of me find it.

but it equates the loss of rotaional mass in approximate real time weight savings.

Yes thats true about the carpets, but in a road car you want to keep the carpets

And in total if you lighten all the pulleys, crank, alternator, camshafts and then lighten the flywheel you can save a LOT of weight, I mean a LOT!

My savings so far
camshaft pulleys 125g each (250g total)
Crank pulley 1050g (supercharger pulley)
Flywheel 3100g
Alternator pulley 25g (not weighed but a guess)

So thats a saving of ~4400g. Saving that much weight let alone that much weight off the rotating components will have a definite seat of pants acceleration increase

And Honda do it on most of their engines, thats how they rev so freely. and spoon sports used to sell lightened everything, even used to sell lightened cam followers!

edited for spelling, as I'm having an inability to spell atm

[cartledge_uk]

Parasitic losses will only be reduced by changing the size(s) of the pulley(s) so that it's spinning the alternator/water pump etc at lower speeds for a given engine speed. Merely fitting lighter ones of the same size will do nothing for you on that front.

Not strictly true, the mass of the turning component has to be accelerated by the power of the engine, by reducing the weight of that component, you are reducing the energy required to turn it, and therefore increasing the acceleration of the component.

newtons laws

acceleration is inversely proportional to mass.

[kaiowas]

Parasitic losses will only be reduced by changing the size(s) of the pulley(s) so that it's spinning the alternator/water pump etc at lower speeds for a given engine speed. Merely fitting lighter ones of the same size will do nothing for you on that front.

Not strictly true, the mass of the turning component has to be accelerated by the power of the engine, by reducing the weight of that component, you are reducing the energy required to turn it, and therefore increasing the acceleration of the component.

newtons laws

acceleration is inversely proportional to mass.

Whilst the reduced mass allows the engine to accelerate faster that doesn't equate to more power.

Power = torque x rpm (x constant to account for units)
At a given rpm you'll get the same torque regardless of how quickly you reached that speed.

[cartledge_uk]

Whilst the reduced mass allows the engine to accelerate faster that doesn't equate to more power.

Power = torque x rpm (x constant to account for units)
At a given rpm you'll get the same torque regardless of how quickly you reached that speed.

Fair point, I miss read the post above about power.

But in summary, 2 cars on a traffic light drag strip, car a has lightened pulleys, car b is standard. Car a will get to the finish quicker (in theory, depending on driver, policeman waiting in a layby etc)

[Mk1Chris]

But in summary, 2 cars on a traffic light drag strip, car a has lightened pulleys, car b is standard. Car a will get to the finish quicker (in theory, depending on driver, policeman waiting in a layby etc)

I think thats the point of it all really, any improvement is still an improvement.

[Tiny]

NST - http://www.nonstoptuning.com/pKitToyCor.htm

They claim a 7-10hp increase from running their lightweight underdriven accessory pulleys Is it really going to be that much of a gain from just losing rotating mass?

[kaiowas]

Yeah, I'm not disputing that there's a performance increase to be had, i'm just warning against talking in terms of power increases as people selling these sort of pullies often do.

As I said before the only way that a different pulley can increase power is if that pulley causes alternators/water pullies etc to be underdriven thus reducing the amount of power sapped by those accesories.

Tiny - see above, it's the underdrive aspect which gives rise to power gains. You get no power by reducing mass.

If you want another way of thinking about it:

Would you expect fitting a CF bonnet give you more power?
What about replacing the undriven wheels with lightweight ones?
What about the driven wheels?
Driveshafts?
Gearbox input shaft?
Flywheel?
Crankshaft?
Crank pulley?

Whilst replacing any of those components with lighter ones will give you a faster accelerating car it's the reduced mass that that allows this. None of them will give you more power. The only difference with the rotating components is that the performance benefit per kilo removed is higher because the mass has to be accelerated both linearly and rotationally for the car as a whole to accelerate.

There are exceptions where lighter engine components can give you more power but these are typically reciprocating rather than rotating parts (such as valves, followers, pistons, conrods etc) the reduced mass allows you to run to higher speeds without increasing the loads involved in acclerating/decellerating those parts.

[Bender Unit]

Whilst replacing any of those components with lighter ones will give you a faster accelerating car it's the reduced mass that that allows this. None of them will give you more power.

Wow boffin off Think this all got a bit technical and a bit too analytical – at the end of the day whilst these mods don’t give you extra “bhp” they do make your car faster – so its worth doing!

Going to have a play on the weekend.