OBX Power Pulleys

[tequilla]

Does anybody try to fit these pulleys?

[stargazer30]

Would be interesting to see if they fit a roadster.  I assume these are under drive pulleys of some sort?  I had a set on my focus ST170 and they did a good job of making the car rev more freely and pick up a bit better.

[Tem]

They are for 2ZZ. The alternator pulley will work for sure. The water pump pulley won't work unless you have a 2ZZ water pump.

Not sure about the crank pulley..(I think it'll fit)..

[Wabbitkilla]

10 to 15 bhp just from changing pulleys?

Shiny though

[frogger]

Whatever you do - Don't change the crank pulley for any aftermarket item on a road car!

The ancillary pulleys are fine and would cause no damage - but the stock crank pulley has a harmonic damping effect, and NONE of the aftermarket lightweight crank pulleys do - meaning your engines bottom end will eventually need replacement.  s:flame: :flame: s:flame:  

Lightened crank pulleys are fine for race engines that are stripped down and rebuilt regularly - but thats about it.

Anyway - crank pulley warning over!

Regarding the ancillary pulleys...
They would free up a couple of hp, but would probably need a custom length belt purchasing, also the altenator will not charge at the same rate, and the waterpump will not pump water at the same rate either (both will be less).

Altenator is not usually a problem unless you have all your electrics on for a long time (lights/heater fan/etc...) as only then will usage outpace the charging rate.

Not a clue how the water flow rate would affect the overall cooling - my guess is it would be fine - purely because the coolant capacity of the MR2 is so vast that a slight drop in flow rate is unlikely to negatively affect the cars ability to regulate at the correct temperature. If the same engine can run in a celica with much fewer litres of coolant, then I would have no concerns about the ability to use in an MR2 with a slightly lower flow rate.

[Tem]

Altenator is not usually a problem unless you have all your electrics on for a long time (lights/heater fan/etc...) as only then will usage outpace the charging rate.

The nice thing about alternator is that it can vary it's own output/load. If you're using x amps, it will try to output roughly the same (assuming battery is fully loaded, if not, it will of course try to charge it too). If you slow it down, it just has to work more with less revs than it would do with more revs, but the load stays roughly the same anyway. So the pulley doesn't really make it spin more freely, like it does with water pump. You'll just make it rev less, which can be a good thing, if you have raised the rev limit and a bad thing, if it's too slow to be able to charge enough at idle. Hp-wise there's hardly any difference. And it's even kinda hidden in our engine bay, so it doesn't even make much of a bling bling.

Not a clue how the water flow rate would affect the overall cooling - my guess is it would be fine - purely because the coolant capacity of the MR2 is so vast that a slight drop in flow rate is unlikely to negatively affect the cars ability to regulate at the correct temperature. If the same engine can run in a celica with much fewer litres of coolant, then I would have no concerns about the ability to use in an MR2 with a slightly lower flow rate.

Slower water flow WILL decrease cooling. But it gets more complicated, cause the stock pump most likely cavitates at x rpm and slowing it down will actually increase cooling at higher revs. So if you rev higher than the stock rev limit and keep there for long, you might wanna slow the water pump. Then again, you can't change the pulley on 1ZZ pump anyway and when you buy the 2ZZ pump, it already has a different size pulley than 1ZZ does...and there's hardly any room to install a larger pulley to a 2ZZ pump in 1ZZ anyway, so make sure you do your math before trying it out for the fun of it. Again, not much of a bling bling item in our engine bay either.  s8) s8)  



They do make some power. Not just by slowing accessories, but also by being lighter. Kinda like lighter flywheels. Ppl have measured some 2-3hp increases on dyno with alternator AND water pump pulley, so better not believe any 10-15hp promises.

[cclarke99]

Making the alternator run slower will not save you anything as the controller will just increase the field current to compensate. Even at maximum output (15V @40A = 600W) it uses less than 1hp, so even if you switched it off completely any power gain would be too small to measure.

As far as the water pump goes, the coolant capacity only affects the transient response of the system. A bigger water capacity will soak up additional heat for short periods, but in steady operation if the water isn't flowing fast enough it won't get rid of the heat quickly enough. Without any flow the engine will boil after less than 1 min at 60mph.

I'd be surprised that the pump was designed to cavitate as this can damage them pretty fast - a recent example I saw was destroyed after only 60 hours running. I'm also pretty certain that the output of the pump is proportional to the square of the speed, so dropping the speed will cause the flow to drop a lot more. The trouble is, without the sort of test facilities only people like Toyota can afford, you won't find out any of this until it's too late.

[Tem]

I'd be surprised that the pump was designed to cavitate

Actually many stock systems cavitate, at least they used to in late 90's/early 2000. I'm not sure about ours, but I'd be surprised, if it didn't. It's not really an issue, cause you rarely run the engine near redline for long. Even on a track, when you keep hitting it, you'll keep away from it from some time after you change gears.

I'm sure you already know this, but the issue with mechanical water pumps is that it has to spin fast enough at idle to keep the engine cool even while standing still in traffic on the hottest summerday. And with the redline being roughly 10 times that, it equals the pump going 10 times faster as well and like you said, it's not even linear to the flow. And too fast flow will also decrease the cooling capacity. Cavitation is a (cheap, but poor) way to limit the flow.

If you raise the rev limit to 9000rpm and keep the engine between 6000-9000rpm, you overheat pretty quickly. But slowing the pump down keeps the engine cool.  s8) s8)

without the sort of test facilities only people like Toyota can afford, you won't find out any of this until it's too late.

That's very true. You should be able to spot cavitation on the temp gauge though, but you do need to keep in that range for some time. And don't count on the stock gauge, it's useless.  s:lol: :lol: s:lol:

[frogger]

the coolant capacity only affects the transient response of the system

the output of the pump is proportional to the square of the speed

Engineer by any chance?  s:lol: :lol: s:lol:

[tequilla]

Thanks for all replies...I read many topics about lightened pulleys and I'm not still decided if I'll try them on my new rebuild engine. They should be the perfect accessory for lightened crankshaft and flywheel...

[frogger]

Sorry to keep on with the doom and gloom lol.   s:lol: :lol: s:lol:  But...

Actually a lightened pulley is actually the WORST thing to combine with a lightened flywheel, let alone a lightened crank.

An engine exerts very high forces upon the crank as each cylinder fires, and on all engines this is not a smooth process - especially on 4 cylinder engine like the 1ZZ. A large mass like the flywheel serves to absorb the energy transferred to the crank and effectively 'smoothes out the shocks'.
As an extreme example, with no flywheel at all, a gearbox connected staight to a crank, with no flywheel between, would be a very jerky thing to attmept to drive! As you increase the mass of the flywheel from this point, there becomes a point at which the mass of the flywheel (or technically the moment of inertia of the flywheel, which is the mass multiplied by the radius of the flywheel squared) is sufficent enough to smooth the 'shocks' entirely - and in purchasing an off the shelf lightweight flywheel you will be moving down towards the point at which the 'shocks' are not smoothed out, or less smoothed out.

In any case, by reducing the energy that the flywheel can absorb, the 'pulsing' forces of the crank will be greater and result in a higher level of vibration - which crucially, will normally be absorbed by the stock crank pulley/harmonic damper combo. This setup (lightened flywheel, stock crank pulley) is ran by many members with no ill effects. But no harmonic damper, no safeguard.

I too have read more forum discussions about lightened flywheels than anyone would think possible, and also discussed the effects of lightened flywheels at length with a professor of automotive engineering a fair while ago.

What I'm getting at essentially is - if you lighten the flywheel, it's absolutely more necessary than ever to maintain the mass of the harmonic balancer.
Even more necessary again if you're thinking of increasing the engines power at all (thus increasing force exerted upon the crank in the first place)

Overall though, I think the best most succinct comment on lightened crank pulleys I've ever heard is "why risk a spun bearing or an engine rebuild for something with such small gains in the scheme of things?"

One thing I would recommend though is - give your stock crank pulley to whoever is lightening/balancing your crank to get the balancing of the crank as a whole spot on.  s:D s:D

[cclarke99]

Engineer by any chance?

- yes - sorry I got a bit carried away there.
Interesting stuff about flywheels, etc. To give some idea of how important the damper is, they have been known to melt the damping material where they are absorbing so much power. Lightening the flywheel does have quite an effect on the 1st gear acceleration - Vizard quoted an effective weight saving of 17kg on the car for every 1kg off the flywheel. This was for a Mini which is low geared and with, I would have thought, a much heavier flywheel in standard form - the MR2 feels like the flywheel is about as light as you'd want it already. On my old Mini it did have a noticeable effect on the acceleration or at least the ability to spin the front wheels. As for the pulley, the equation above says it all, any weight you take off such a small diameter item will not make a significant difference.

[ChrisGB]

People think of a crankshaft as a solid item, but in service, it flexes and "winds up / whips back". How I understand it is that the harmonic damper is there to reduce the velocity of the whip back effect so that the big end bearings don't get hammered on the side opposite the oil wedge. For example, cylinder 1 (furthest away from the flywheel) fires and applies a twisting force to the crank. This twisting force is partially resisted by the damper which also absorbs some of the travel. As the firing force comes off the crank, the crank tries to unwind the twist. The damper has prevented the twisting force becoming as large as it would be undamped, but now holds onto some of the energy and slows down the rate that the crank untwists. For the minimal gains that may or may not be had, I would not risk it.

Light weight flywheel is at the other end of the crank and although the crank is mated to it, when under power, it is also mated to 1000Kg of car, so changing the weight of the flywheel should have negligible effect on the crank resonance. There are various estimates around for the effect of light weight flywheels. In a short geared high revving engine, it can be as much as 40Kg equivalence per Kg removed in 1st gear. Equally important is where the material is removed from. Making the outer edge light is good, making the middle light much less so.

How the reduced weight of a flywheel would affect gearbox life is another matter. Certainly in diesel engined cars, they only get away with such big outputs on relatively small gearboxes due to the effect of the dual mass type flywheel.

Chris

[frogger]

it is also mated to 1000Kg of car, so changing the weight of the flywheel should have negligible effect on the crank resonance.

Didn't think of it like that. Good point!

So it seems flywheel weight reduction is fair game up down to the point at which you reduce the moment of inertia below the req'd minimum. which any off the shelf item isn't likely to go below i guess.

[Anonymous]

i have Ralco RZ crank and alternator pulleys.. No issues..

 m http://www.coolcarpartsonline.com/alumi ... pulley-set m

[frogger]

Yet

[Anonymous]

I'm glad this subject has come up as I need to change my crank pulley as I have a small oil leak coming from it due to a groove being worn into it from the washer/gasket so looks like I'm going to have to buy a genuine Toyota pully at £150+.  s:cry: :cry: s:cry:

[frogger]

I don't fully understand how the pulley would be solve a leak  s:? :? s:?  isn't the crank oil seal completely seperate?

That said, if the pulley is really in need of replacement, I guess £150 isn't tooo bad, but the crank pulley is pretty easy to swap out so long as you can get enough torque onto the bolt (sounds easier than it is mind!) so you could try a 2nd hand one - plenty of them knocking about on knackered 1ZZ blocks!

I would offer you mine, but unfortunately my recon engine came without crank pulley so needed to reuse my original one.

[Anonymous]

So on an averagely driven engine (say 10K miles a year, 50% motorway 50% B-road blasting) by how much would a lighter crank pulley reduce bottom end lifespan? Are we talking you'd destroy it within 5K miles, or it might need doing after 50K? I know every engine is different and everyone drives differently yada yada yada, I'm just after a rough guesstimate.

[spit]

I don't fully understand how the pulley would be solve a leak  s:? :? s:?  isn't the crank oil seal completely seperate

The seal works by mating with the face of the pulley. Its low pressure in the camchain housing, but the housing hole is bigger than the shaft (and locating pin) that the pulley attaches to.

Good chance that LoB's seal is fubarred though. Bryan - I may have one kicking around somewhere.

[Anonymous]

My garage has tried a new seal which has reduced the leak but say a groove has been worn in the pulley allowing a small amount of oil to leak out so a new pulley is required.

[frogger]

In which case, failing buying a new one at £150+, or a 2nd hand one... I'd be tempted to go for a 3rd option of welding up the groove and getting a local machine shop to turn the welded area back down to a true flat surface, so long as it aint more than getting a 2nd hand one sent out... Not that I'm tight or anything...  s:roll: :roll: s:roll:

[Tem]

So on an averagely driven engine (say 10K miles a year, 50% motorway 50% B-road blasting) by how much would a lighter crank pulley reduce bottom end lifespan? Are we talking you'd destroy it within 5K miles, or it might need doing after 50K? I know every engine is different and everyone drives differently yada yada yada, I'm just after a rough guesstimate.

Many have driven several dozen kmiles with one, so it surely doesn't break anything that quickly. It might not even be any issue at all during stock engines lifespan. Some go as far as saying it's not really a major issue on a 4-cylinder car. I believe in it "it does some damage over time", but can't say anything definite. Kinda like knock. It might or might not kill an engine. I've had audible knock several times, but yet nothing broke and there were no signs at all on the engine internals.

But say you're revving to 9k and already pushing the stock stuff a bit beyond their limits and you probably don't want any more stress on any parts.  s:? :? s:?

[Anonymous]

Nice one, thanks for that Tem. I think working on the principle that you might lose 10% of the engine's normal lifespan but gain a few extra ponies, it's not something that I'd ever worry about should I put one on any car I own.

[ChrisGB]

It is one of those things that is like asking how long is a piece of string. The more drastic effect of changing the damper can be the crankshaft snapping completely due to metal fatigue.

A comprehensive article here for those with time to digest it:

Torsional dampers