Pulley kit have any downsides? Or stick to crank
 

I had a Perrin crank pulley on my last FR-S (totalled by idiot), and it was one of the best mods I purchased (freed up engine, more responsive).
My question is whether I should stick with the Perrin crank pulley or buy a kit?(alternator etc.)Theoretically the lighter the better right?
I heard of problems starting with the full lightweight system, and wondered if anyone has first-hand experience?
My goals are to have a faster revving car, any hp or torque is welcomed.

When I hear about how people can "feel" that the engine is more responsive with a lightened pully, I want to call BS.

If you think about it, it supposedly "reduces" the rotating mass.
However if you consider the alternator, air conditioner, belt, crank, pistons, flywheel, cams, and timing chain, the pulley is a tiny fraction of all of that inertia. (I would bet that the timing chain contributes 10X more than the pulley in rotating inertia).
I seriously doubt it makes any difference at all, much less a difference that you can feel.

Also, when the engineers were trying to shave every single ounce off of this car & engine, WHY would they put a heavy pulley on it? I am guessing it has to do with vibration & dynamic balance.

I would not mess with it UNLESS you are doing a dozen other things that would make a bigger difference.

Good point. Wonder if it's just one of those really good theory but practically useless in functionality. Is there solid data showing engine rev responsiveness stock vs lightweight?

The OP said he felt a difference. I have one and I can feel a difference. You on the other hand apparently do not have one. You start your argument with "if you think about it...". and then you ramble on about stuff you probably know nothing about and obviously have no data to back up. With all that being said. I probably won't mess with the other pulleys on my car due to cost. If it were me, a complete kit would be for cosmetic reasons but I would be interested in hearing of others that could tell a difference comparing just a crank pulley to having all the lightened pulleys. The Perrin pulley by itself makes for a good noticeable improvement for the price.

I think people just write "feel" to get out of the "stock" mind. Honestly, I didn't notice any diff on mine even after I had intake, headers, header-back, 3 pulley set, gates racing drive belt, lighter wheels. So a tune def had helped make me "feel" some diff and doing a "race" from a roll (3rd gear)with a "stock, minus muffler delete" brz on freeway where I pulled on the BRZ hard (buddy's on this forum too)

this debates been going on a long time

the possible advantages of the smaller ancillary pullies shoudl be there

done some measuring up
std crank pulley is 143 OD, alt pulley is 57.5 and water pump is 132

alternator is 130Amp @ 14v = 4.4Hp to turn assuming 55% efficent and due to the pulley ratio its running @ 2.5 x crank speed

so adding 10mm ( Fensport pulley) reduces the ratio to 2.12 so 15% slower = 3.75 Hp to turn so + 0.65hp gain

Water pump std ratio is 1.08 with fensport pulley is 0.94 and water pumps typically take 7bhp to turn so again about 15% slower so 6 bhp to turn so 1 bph gain so in total, you should get about 1.6bhp gain

now this is assuming that you're using 130amp all the time - which you patently are not so in reality your're going to struggle to see a difference on a set of rollers

plus your engine bay will look nicer....


however I wouldn't fit a non damped front pulley as while you can arguably get away with it on a flat 4 its still a nice thing to have in terms of claming down crank torsionals

Umm.... I AM an engineer AND I slept at a Holiday Inn Express last night.

The DEFINITION of moment of inertia is: The Sum of all mass Times the Square of the distance from the point of rotation.

The Pulley cant get ANY closer to the center of rotation (COR).
The Timing chain cannot get any further away from the COR.

Lets say the pulley's mass is approximately 3 inches radius from the COR while the timing chains average distance is 9 inches.

This means that the timing chain is Three times further away making its moment of inertia NINE TIMES more influential on the rotation of inertia than the pulley. Shall I do the calculations for the flywheel for you?

So Yeah you are right, I dont know what I am talking about.....

(Oh And I build racing 4 cylinder Boxer engines for fun - I have three of them at home right now)
http://i366.photobucket.com/albums/o...ownfixture.jpg

meh I'll put those dollars in my piggy bank for a turbo

Look how happy he is :)

http://www.primoclipart.com/files/pr...Clip%20Art.jpg

How to you figure the avg radius from COR for the timing chain? Is it the center of the chain fully extended along the pulleys, or is it factored based off the pulley size amd how far it is from COR on the pulley?

It may not be huge in the scheme of things but using your same calculation examples the intertia is lowered from
14.67 to 2.43 (based on Raceseng Revo pulley). How much does the average timing chain weight? Anything 13 lbs or less and that is at least a 10% drop. Seems some what significant to me.

The other pulleys only give an extra drop in overall inertia of about 1.5, so that I can see as diminishing returns considering the cost is much more significant for complete pulley kits.

But Im only a political scientist and stayed at home last might, so I could be way off base.

I completely made up the numbers to make my point.

All I am saying is that IF you want to reduce the rotational inertia of the engine as a system, starting with the pulley is silly.
It has the lowest return on investment of almost any component being so close to the center of rotation.
The only reason it sells so well is that anybody can do it in a few minutes.

Now IF the pulley gives a different drive ratio to all of the other rotating mass then there could be a noticeable difference.
But do you really want to drive your water pump, AC, & alternator slower to get a fraction of a horsepower gain?

In the type IV race engines, rotating mas can be removed from the crank journals and lightened rods/pistons, flywheel. Then you have reduced rotating AND reciprocating mass. Talk about a difference.

I noticed a difference with my butt dyno, other's as well. But I am not an engineer. Do you happen to own one Stugray?
"weighs just 1.2 lbs, 3.7 pounds lighter than the stock OEM crank pulley. This reduction in weight from the crank shaft is equal to removing more than 100 lbs of vehicle weight"
So says Perrin. I say "feel" not to get out of any mindset, but because I actually noticed a difference for a little over 100$, and that's worth it to me.

Okay if you ^^ say so :) I didn't and I had on as previously mentioned, before tune.

I'm not sure any of these replies are even on topic. The OP is asking if there is any disadvantage/negative effects of going with a full pulley kit like the Raceseng kit (idler, water pump, etc), versus just switching out the crank pulley only.

Everyone needs to stop debating the effectiveness or value of simply replacing the crank pulley.