Effectiveness of a Lightweight pulley
 

So I've been reviewing parts regarding a lightweight pulley for the crankshaft and I've seen a few reviews saying that it seems to be pretty amazing. But I have two questions, first off have we had any dyno results indicate an appreciable gain in WHP/WTQ? (I'm not even sure it would show up on the Dyno but I would think anything that facilitates faster revs and acceleration should also show up on a Dyno)

And secondly, I've read a lot about harmonic balancers and how going with a lightweight crankshaft pulley can destroy your crankshaft bearings... Is this the case on our car? (I would imagine it would be somewhat different since it is an H4 instead of an I4)

Sorry if this question was already asked and thanks for all your help!

It has been asked, but there is never really a clear cut 'yes' or 'no' (Unless there is, and I just get bored reading through several dozen conflicting posts).

It's a mod I wouldn't mind doing, so I'm really interested in a definitive answer. I plan on having my FR-S a long time (When the damn thing finally shows up that is), and while I want to mod and have fun with it, I'm not interested in destroying my motor from the inside, just for a little quicker spin up ;)

Here you go...enjoy!

http://www.ft86club.com/forums/showthread.php?t=12450

No, it is not a problem on the Subaru engine and No it won't give you a lot of HP or Torque on the dyno BUT it does help free up rotational restriction so the engine revs easier and and therefore builds energy faster...and better gas mileage although YMMV.

No offense, but I'm four pages in, and still reading an awful lot of speculation >.<

Edit: Just found Jeff's post on page 5, and yes, that does make me feel better ;)

AP's pulley shows a significant increase in hp and tq on their dyno.
http://www.ft86club.com/forums/showthread.php?t=13011

Not sure why this is the case.

That dyno is the pulley, header and crosspipe all together....

Post #3 shows pulley only...

Holy crap... if I am reading that right though, they are putting down almost 170 max HP at 'stock' and then the pulley is boosting it to 186~ !?

Everything I've seen of stock Dynos are seeing about 160 stock... But that pulley seemed to give more power than the whole exhaust system.

170whp is not that odd, I have seen a few read that high. I do find the numbers on the pulley a little strange however...

Everyone seems to say that you can't see the pulley on a Dyno... But that makes almost no sense. Anytime you lower the weight of your drive train you improve WHP right? And more over, with something like a pulley that is on the other side of your engine, it would improve crank power as well?

Because magic.


I can't wait until Perrin dynos their pulley.

It won't make the engine produce more power, but can show a little on a chassis dyno. However, the weight if VERY close to the centerline of rotating mass, and we aren't talking about a lot of weight so I do find a ~50% reduction in driveline loss under acceleration to be a bit unbelievable still from just a pulley. There are so many other components involved that I just find it very hard to believe.

I've seen lightweight pullies dynoed before, and have never seen any sort of WHP increase like Vivids.

Vivid's #s have been in question since their first pull. It's not a good idea to use their dyno results as a benchmark for anything.

That said the link above with the Perrin post on pg. 5 helps clear up most questions.

my bad, the last time i saw that thread the post with JUST the pulley wasnt there. so, i didnt even look further down :P

Yeah I finally slugged through that whole thing and Perrin seems to feel super confident due to past H4 motors from Subaru. I might give it a try in the near future, if I do I will definitely post my experience up in the forum.

That. The engine "feels" peppier and more alive simply because it can spin faster. You're not "making" hp as much as you're "unlocking" it in basic, unscientific terms. You should be able to feel a difference in the speed of revs falling/rising, not in acceleration or power. It might feel like you're accelerating faster, but you're just revving faster and shifting faster due to that.

You've mentioned that on a Mustang Dyno you can adjust the parameters and affect the indicated WHP. Now does this bump up the indicated gains, too? So we should look at the % instead?

Ie: on your example of 240 WHP baseline on an 'adjusted' MD, parts changed gain an indicated 12 WHP, but if the same dyno gets readjusted and baselines at 150 WHP, would the parts change indicate a 12 WHP increase (absolute increase) or 7.5 WHP (relative increase)?

I've had a Perrin pulley on mine now for about a week and a half and can vouch for the car "feeling" peppier and it seems to rev quicker. I would describe it as not making any power as well, but instead of having a 15% drivetrain loss, it may now be a 13% loss. *DISCLAIMER* those are just random numbers and I have no scientific data to back it up. /DISCLAIMER

If anyone can offer a dyno, I'd be happy to drive, within a reasonable distance, and bring the stock pulley with to see if in fact there are any WHP changes. :thumbsup: I do have Visconti's STG1 tune on my car, but the pulley would be the variable.

Ruskymx

I think it depends on the dyno whether or not you see any changes. For example, lightweight wheels will show a slight HP advantage on inertial dynos; could be similar for this type of thing. All the consumer really needs to understand is that there's a heavy thing spinning and we made the heavy thing slightly lighter, thus it should spin faster. That should make sense to 99% of people.

i hope im not sounding stupid right now.... if the car is moving and its revving FASTER, it should mean that the car is accelerating FASTER as well... right?

Read more carefully; if you are accelerating quicker it's not due to POWER it's due to being able to SHIFT faster due to a LIGHTER rotating assembly.

But the point I am getting at is, if it takes less energy to rotate the drivetrain, doesn't it cause the drivetrain to lose less power and thusly make a noticeable change in power being put down to the wheels?

I understand of course that changing anything in the drivetrain doesn't cause the explosions inside the engine to explode harder (I.E. more oxygen and fuel) resulting in 0 ACTUAL power gain, but the act of freeing up inertial mass in the powertrain should result in putting more power down to the wheels right?

Think of the engine as having to put power to the crank pulley. Its heavy and the engine cant rev up and down as fast. With a lighter one the pulley has less rotational momentum so less power is required to get it up to speed. IE less power loss from the engine to the driveshaft.

I think it should be more like the fact that there is less rotational mass, that it allows it to spin up faster, not spin faster as a result. It would only reduce the work needed thus improving the time. Not the speed.

AMIRITE?

thats what im saying. but you were saying that you wont feel quicker acceleration with a pulley... im confused.

Yes, that's more correct.

Read what others are saying, it may be more suited to your understanding. You MAY notice the revs climbing faster in gear, but you'll notice it way more when shifting. You're reducing a minuscule amount of drivetrain loss...as another poster said, you're not feeding more oxygen or anything like that; you're not MAKING more power. This mod is more about feel than performance, in my opinion.

So, the end result is that you won't really get any appreciable amount of power freed up from this mod, however, when in neutral especially, your revs will build up faster. If we examine the rotating mass while the clutch is pushed in or the car is not in gear we see that it is likely fairly low. Something like 20lbs for the pulleys, 30 lbs for the flywheel assembly, and probably 40 lbs for the crankshaft and pistons. That is ALL that is spinning when the car is not in gear.

If we take the crankshaft pulley and reduce it from 4lbs 14 oz to 1lb 4 oz (Or whatever the specs were) we see a massive shift in mass while the car is not in gear. Losing 3lbs from a 90lb assembly is pretty darn good, and once more, it is from a part that is directly and always engaged. If I recall correctly, when the clutch is pushed in all you have rotating is the flywheel and the crank + any accessories, so with only the oil pump and alternator we are probably looking at more like a 60~ lb assembly which means 3 lbs is 5% improvement.

But if we look at the actual engagement, I.E. when we have the car in a gear and the engine is having to turn all of the components + move the weight of the car we realize it's only about 3 lbs in a 2600 lb contraption. That said, rotating mass is worth a bit more, but it would probably only be the equivalent of pulling 15~ lbs of static weight. (That is entirely based on a spitball effort and in no way should be used as gospel)

I think that sums up the discussion... /thread!

Oh and also, an argument could be made about it allowing the car to maintain torque a bit longer since the parasitic loss would be lowered, but to see any real effect you would probably need to do quite a bit of internal work as well.

A light pulley and a lighter flywheel are obviously the two easiest ways to achieve a lighter rotating assembly; often people say they have to practically relearn how to drive the car when they get a lighter pulley due to how much faster revs drop between shifts. Now lighter pistons, valves, valve springs, rods, and a billet crank will definitely make a difference...but who's going to do that.

I would imagine that if one played with the calibration or the parasitics, any gain would be a larger % than on an accurate dyno, but I have never tested the same part before/after two different dynos so I'm not sure.

Noticable? Not in my experience on ~200hp 4 cylinder NA cars. I've never seen more than fairly normal variance levels of change.. ie a couple of HP.

The claims we are talking about here are eliminating ~50% of the entire driveline loss through a pulley.

Part of gains showing on a dyno depend on how the dyno is operated.

On a Dynojet you pretty much just do acceleration pulls, so you will a gain from ANY rotating mass reduction. They measure power based on the time it takes to accelerate a drum of known mass. Light wheels will show a gain. Flywheel will show a gain and pulley will show a gain. How much depends on the weight loss, where the weightloss is (outside of large diameter is better) and how much the part has to accelerate (pulleys and flywheels at engine speed take more than wheels which are slower because of gearing).

However on resistance or brake types that make the motor fight a resistance and hold rpms, you generally won't see rotating mass gains unless they are doing acceleration type pulls.

In real-world acceleration the lighter rotating mass will make an improvement from less power being wasted on accelerating the drivetrain.

This is all very true.

Like what was said in the other thread, noticeable gains in the FIRST TWO GEARS. this is due to the eng accelerating the entire car at a high enough speed that the small weight change in the pulley has an effect on overall dynamics on acceleration. As you go higher in the gears the effects of the light weight pulley becomes marginalized to 0 as the acceleration of rotating mass becomes minimal.

Remember, drive tran mass lost performance gain is realtive. The pulley is a very small component in a massive assembly compairtive speaking, the 1 lb gain will not have a noticeable effect since te bulk of the mass is still here.

Hence any gain that is able to be pickup by the dyno will most likely be dismiss as test variation.

Very good point that people tend to miss. As I stated in te other thd. The gain by pulley and flywheel is your increase in angular acceleration, not velocity.

There is no double a measurable performance gain. However you will not be able to verify it though the traditional measuring means like dyno.

The easiest way to see the gain is to go and rev someone else's car with this mod

So at the end of the day, what is the benefit of spending money on this?

im doing a dyno this coming sat on the lightweight pulley..going to a do a stock pull with visconti tune and then a pull with the pulley and visconti tune..we'll see if the pulley shows and it will be a on a mustang dyno

decreasing rotational mass and increasing throttle response.