What's a under drive pulley?

[jpblue1000]

in my circles we fit varied ratio pullies 'underdrive' on engines who spin faster than the manufacturer intended. this in turn reduces the speed of the water pump in particular to a level more akin to what the manufacturer designed. In turn this reduces water cavitation at the impeller maintaining better cooling efficiency. the water pump speed has been returned to 'normal' speeds. secondary the alternator does not like the additional 2-3+k extra revs, reducing its speed lengthens its service life. we have not experienced any real gain in engine performnce maybe 1%. we dont run a/c or p/s but sometimes add external oil pumps.
JP

[turbodewd]

If your car is a daily driver the mod sounds silly to me. I would spend the money on other things, i.e a tune. If youre car is an n/a then youre wasting your time IMHO and should save for an XR6 Turbo and stop dithering at the edges.

If you wana mod your car you either work out what is best for your budget OR choose the kW figure you want and do what best to achieve that.

Under drive pulleys sound over rated to me unless youre doing track work.

[MWTB]

I love it how people try and say 'yeah nah underdrives are **** and worthless and a waste of time and there is absolutely no point installing one' trying to discredit them when everyone that has actually got one says they made more power and that they are happy with the price that it cost them.

I don't quite understand how some people's heads work with their fingers in their ears saying 'no no no I'm not listening' talking about alternators and how reducing their drag can't POSSIBLY net any noticable power gains when the general consensus and popular opinion of people that have underdrives say that it damn well does.

[XR6T0Y]

Originally Posted by turbodewd

If your car is a daily driver the mod sounds silly to me. I would spend the money on other things, i.e a tune. If youre car is an n/a then youre wasting your time IMHO and should save for an XR6 Turbo and stop dithering at the edges.

If you wana mod your car you either work out what is best for your budget OR choose the kW figure you want and do what best to achieve that.

Under drive pulleys sound over rated to me unless youre doing track work.

Why should people with an Na save for a turbo? I could have easily afforded a turbo, but I didn't want one. I'm going to be pushing my NA of 200rwkw when I get the job. Just because a turbo is 'easier', doesn't mean it's better. Id rather have a tough NA then be a sheep and go a turbo

[mike_nofx]

Originally Posted by SpoolMan

Post 14.

One model, produced over 10 years ago.

Why not put them in at least the XR6 models of today?

Edit: I'm hoping my comments aren't seen as being negative, or trolling. My questions/statements are said with genuine interest and curiosity in the subject and I do enjoy reading both sides of the debate.

[jpblue1000]

placebos are a great thing, 'I spent the money' so to make me feel better about my decision I tell myself 'my car performs better', as felt through my ***/ears/fingertips.
our back to back dynoing only proved one thing, the water pump was spinning slower and the water wasnt cavitating. To get real noticable reductions in mass we lighten everything, clutch, flywheel, crank, pistons, rods, balancers/pullies and reduce the size of everything else, small amp alternators or no alternators at all. then balance it all together as assemblies then match these parts to headwork, injector sizing inlet mods, exhaust mods then we begin to see improvemnts worth speaking about.
Id like to see before and after power plots with only the pulley being changed...or a real *** meter plot!
However if the pulley comes with agreat sticker it should be good fopr 8.76 kws

[Zaxx]

What debate Mike ?

the pro's have been spelled out and everyone with one is very happy.

[mike_nofx]

Originally Posted by One Six

What debate Mike ?

the pro's have been spelled out and everyone with one is very happy.

Well the one guy who says he has completed back to back dyno runs claims no increase in power, (not of no benefit, just of no extra power). I assume back to back is without a tune in between? Correct me if I'm wrong jpblue1000.

While another member did see an improvement in power on a dyno, there was a tune first.

But the point you make that everyone is happy, is an excellent point. No matter if there is an increase in power or not, or increased or decreased engine wear or not, as long as it makes you happy that's all that matters.

[Drizz06]

Originally Posted by XR6T0Y

Why should people with an Na save for a turbo? I could have easily afforded a turbo, but I didn't want one. I'm going to be pushing my NA of 200rwkw when I get the job. Just because a turbo is 'easier', doesn't mean it's better. Id rather have a tough NA then be a sheep and go a turbo

Your not wrong mate, I'm sick of hearing people carry on about 'should have bought the turbo'.
If I bought the turbo I may not have been able to afford my new house and solar panels.
But that doesn't mean I can't mod my car if I choose to.

To those looking for power! Simple answer is yes, the under drive will increase power even if its bugger all. After all $300 is bugger all money when it comes to increasing power.

[jpblue1000]

mike you are correct, no measured increase in either HP or torque as a result, this was on a heavily modified race engine (2L) as described so already at its maximum hp/cost potential, we were suffering inneficient water movement through the engine as the pressed metal water pump impellar is poorly designed and at 7, 8 and 9 k it was cavitating. and cavitated water boils easier! and more readily, we have since moved to cast metal impellar from Mr Cosworth and improved the situation further. In my opinion it didnt do anything HP related, It did however help the longevity of the engine, thus to make you all happy, made HP for longer thus more horsepower per hour! hows that.
JP

[Bossxr8]

Originally Posted by mike_nofx

Why dont manufacturers fit them as standard?
If there is 5-10 extra kilowatts to be made, for no real loss, and for no extra money... They'd be mad not to???

note: I know manufacturers dont always fit the best parts from factory, but thats usually to save money. It wouldnt cost more for a lighter balancer.

In a way manufacturers are now doing there own thing to reduce parisitic losses like underdrive pullies do, such as low drag alternators, variable flow oil pumps and even replacing pumps with electric ones to remove drag off the engine and decrease fuel consumption.

Originally Posted by mike_nofx

Well the one guy who says he has completed back to back dyno runs claims no increase in power, (not of no benefit, just of no extra power). I assume back to back is without a tune in between? Correct me if I'm wrong jpblue1000.

While another member did see an improvement in power on a dyno, there was a tune first.

But the point you make that everyone is happy, is an excellent point. No matter if there is an increase in power or not, or increased or decreased engine wear or not, as long as it makes you happy that's all that matters.

I've seen at least 3 or 4 dyno before and after with the pullies and never have I seen one not make extra power.

[SpoolMan]

Originally Posted by mike_nofx

One model, produced over 10 years ago.

Why not put them in at least the XR6 models of today?

Edit: I'm hoping my comments aren't seen as being negative, or trolling. My questions/statements are said with genuine interest and curiosity in the subject and I do enjoy reading both sides of the debate.

Replied to your question where an answer was written a few posts back.
not interested in researching if there being used now as an OEM spec.
I have fitted under-drives on my last 2 N/A vehicles and I would do it again without hesitation, if you can fit yourself without having to pay fitting charges very good value for your mod buck..

[Kable72]

I can tell you right now, an underdrive is going on my XR6 as I put one on my old BA and would do so again.

[335POWER]

Sorry to bump an old thread, but I've decided I'm gonna get the under drive pulley installed on my car soon, by Bruce Heinrich, and once it's done, he's gonna put it on the dyno to see if it's worth tuning to get more power of it

[Kable72]

Always worth tuning mate. Even if you don't make much more power from it, your car will love you for it.

[Crazy Dazz]

Umm, not sure how some could claim that ALL XYZ V8’s were fitted with an “underdrive.” If Every car comes with the same configuration then it’s NOT an UNDERdrive.

The rate at which these ancillaries are driven is essentially a compromise, based upon estimated operating conditions, and to some extent “worst case” scenarios. Eg the water pump must turn fast enough at idle for a car trapped in a traffic jam on a stinking hot day with the aircon running flat chat. So IF you underdrive the water pump, you might have to watch your temp in those conditions. On the other hand in Canberra and have your heater running on most days, then it’s not such a problem. So yes, if you plan on operating your engine on average at higher revs, then “underdriving” your ancillaries is an option.

Underdriving your alternator won’t achieve much. The drag is determined by the electrical load. Obviously operating high drain electricals at prolonged idle isn’t advisable, but few people do that.

Underdriving your aircon will achieve practically nothing. Your aircon clutch should disengage at WOT anyway.

Underdriving your PS, WILL cause lower pressure at idle, so you may find parking a bit heavier. There probably are legitimate savings at higher RPM, because generally once you hit a certain pressure, the bypass opens up, so you’re wasting power pumping the fluid around in circles at pressure.

[Road Games]

[Legit290]

My under drive kit came with a larger pulley for the water pump so I don't think it would cause cooling problems.
Fitted mine in about 40 mins and two beers with mechanic mate looking over my shoulder and calling me names. It was one of my first ( of many ) mods and one of the cheapest at about $230.