The theory about lightened flywheels and top pulleys seems ok to me, - free revving, faster spool up etc, but then I remember that my engine is trying to push well over a tonne of car at high speed, so why does spinning a few kilogrammes of stock spec metal make so much difference?

 

Can anyone explain it to me??

well for example 1 kg off a flywheel is the same as removeing 10kg off the car, thats not to scale but you get the idea. It basicly means that the engine is in effect seeing 10 kg off the wieight of the car.

 

Did that make sense??

The the engine is pushing well over a tonne, but it has gears to do that. To really see how much it is pushing you should try to pull off in 4th gear on a manual, as that is 1:1 ratio. The engine would stall or you would rip the hell out of your clutch and would pull away very very slow.

 

Its as simple as if you had hold of the 13lb7oz standard pully and the 1lb14oz pulley, you should throw the lighter pulley probably 5 or 6 times further because its lighter. Same with a fly wheel, you would be able to throw a lighter one further because it is lighter.

 

The engine can move a 1.5 tonne car, not because of the engine power but because of the gearing. I can push my car and I dont have 300bhp ;)

 

I think you are also failing to realise that at low revs ie. idle to 2000 rpm the engine has very little power where over 11lb of pulley difference and 10lb of flywheel does make a difference and it makes a difference when the engine revs are coming down. A heavier object will have more force when spinning at the same speed of a lighter one, so the heavier object will need more force to slow down. Same with spinning up. The heavier objects need more force to spin up.

You need to remember that engine designers dont put in heavy pulleys and flywheels because they're too stupid to use lightweight materials. They do it because it is the best compromise. There are harmonic vibrations induced in crankshaft depending on rpm and clever use of mass in the pulley and flywheel damps this out and makes for a smoother engine thats more road useable. Sure you can get more power by changing these components but there is always a cost somewhere else. Smoothness, quietness, crankshaft journal wear etc Theres no free lunch.

You need to remember that engine designers dont put in heavy pulleys and flywheels because they're too stupid to use lightweight materials. They do it because it is the best compromise. There are harmonic vibrations induced in crankshaft depending on rpm and clever use of mass in the pulley and flywheel damps this out and makes for a smoother engine thats more road useable. Sure you can get more power by changing these components but there is always a cost somewhere else. Smoothness, quietness, crankshaft journal wear etc Theres no free lunch.

Exactly right and there is definately a harshness when using the underdrive pulley :(

I'd be a bit concerned by that harshness to be honest. The damper is there to do just that - damp harmonics on the crank.

On some engines (alfa 6's for example) the crank will actually break if you remove much weight!

There is a difference between removing weight and getting a new pulley.

 

To be truthful there are very few modification which will add more power with out making something else go worse.

I'd be a bit concerned by that harshness to be honest. The damper is there to do just that - damp harmonics on the crank.

On some engines (alfa 6's for example) the crank will actually break if you remove much weight!

I must admit I have been tempted to put my old one back on , I suppose the way round it would be to get the crank properly balanced with the pulley etc all bolted on , that way there should not be an issue.

I must admit I have been tempted to put my old one back on , I suppose the way round it would be to get the crank properly balanced with the pulley etc all bolted on , that way there should not be an issue.

 

 

It's not about balancing as such, that is taken care of by the weight of the crank webs, rods, pistons and gudgeon pins etc. Assuming it's a evenly distributed weight then the actual mass does not affect the balance of the crank, however, the point at which the mass is located and the quantity will affect the harmonics.

 

I suspect that most of the claimed gains are from rotating the pumps & alternator more slowly, rather than from the reduction in the pulley mass.

 

I suspect that most of the claimed gains are from rotating the pumps & alternator more slowly, rather than from the reduction in the pulley mass.

 

no, on a zed most of the gains are from the reduction in rotational mass, the underdrive gains are quite small as they dont underdrive by that much really.

 

i agree there is always a compromise, but with manufacturers its usually to do with cost!

 

when i fitted my lightweight flywheel everyone bleated on about reducing the smoothness of the engine & making it harsher to drive etc. in actual fact i found no evidence of any of that. just as smooth, not harsh - just picks up a little quicker now :)

I have been DaveW's car and found no difference in the smoothness.

 

When dont forget the car was made lighter pulleys where proably more expensive than now. It was 15 years ago since the first Z was produced. Materials have got cheaper and stronger and the machines to make these things would have got better and cheaper too.

From my understanding, the balance isn't the issue, its to do with needing the mass to intefere with the natural harmonics of the crank, caused by flex under rotation.

I didn't really understand the explination the guy gave me at the time, but apparently at the flywheel end, the same is not true as the drive to the box etc. gives a similar effect

From my understanding, the balance isn't the issue, its to do with needing the mass to intefere with the natural harmonics of the crank, caused by flex under rotation.

 

yeah, there is always a slight issue with that, from the power pulses from each combustion cycle. would have thought it would be more than acceptable on a V6 tho

Yeah, you'd think so as the crank is shorter too.

TBH, loads of people in the states seem to run these, you've just got to decide if it's worth the risk.

The other thing to bear in mind is it's not mass reduction that has the effect, but mass * r^2, so if the diameter is relatively small (like a pulley) it has much less effect than if it's big like the flywheel.

It may effect the car some where, but the damage it is causing may be so slow that that we will never see the damage in the cars life time. It may take 10 year before it happens.

All I can say is if you have the underdrive pulley, get a lightwwight flywheel next time you're changing the clutch. Their combined effect is amazing, my Z has never pulled this strongly before :shock:

well i have the f/w already - so thats it im getting the pully!! :D

Exactly right and there is definately a harshness when using the underdrive pulley :(

 

Have to disagree m8. I'm running an unorthodox UD pulley and makes no difference.

However........ I did have the con rods and crank all balanced at the same time. Which may iron out any unwelcome vibes you're getting.

 

Si.

Bagin maybe your pulley is slightly misshaped. Where did you get it form and where did you other guys get yours from where you feel no harshness ?.

 

I'm up for a flywheel and underdrive pully :D. Group buy anyone ?

 

I'm up for a flywheel and underdrive pully :D. Group buy anyone ?

 

LOL!! funny you should say that Stu!! - watch this space ;)

Have to disagree m8. I'm running an unorthodox UD pulley and makes no difference.

However........ I did have the con rods and crank all balanced at the same time. Which may iron out any unwelcome vibes you're getting.

 

Si.

Willy , you have just stated that you had everything balanced so you probably will not have any vibration . STU , SE fitted mine , there is no vibration as such just a growl at a certain RPM which dissapears higher up the rev range , which is exactly the same as Daves

mmmm. Sorry I asked now!

My cars going to have the engine out for new tubs soon, so I have the option of fitting clutch and flywheel 'on the cheap' so to speak. Then I heard that fitting the pulley too was a good idea for faster response. Didn't really want to make the car sound any nastier as it already has a real 'rorty torty' rasp at peak power (maybe I do need a silencer after all!)

 

BUT I certainly don't want to have a lumpy ride and vibration, so can anyone tell me what the risk of this might be - I don't want to be balancing cranks and stuff after this big bill!

mmmm. Sorry I asked now!

My cars going to have the engine out for new tubs soon, so I have the option of fitting clutch and flywheel 'on the cheap' so to speak. Then I heard that fitting the pulley too was a good idea for faster response. Didn't really want to make the car sound any nastier as it already has a real 'rorty torty' rasp at peak power (maybe I do need a silencer after all!)

 

BUT I certainly don't want to have a lumpy ride and vibration, so can anyone tell me what the risk of this might be - I don't want to be balancing cranks and stuff after this big bill!

Nigel go on to TT. net and do some reading mate then make up your own mind

 

Ryan

for anyone interested in a lightweight pulley & belt kit see here as iv arranged a group buy from Smithy on these!

 

come on guys, you know you want one ;)

Nigel go on to TT. net and do some reading mate then make up your own mind

 

Ryan

 

 

Ryan, my guess is that you've done the reading too, and you're the one with the 'less than ecstatic' opinion on all this. I've had mixed reactions (from this thread obviously - but from other independent sources too). 20+ extra BHP sounds worth having to me, but is it hit and miss with regard to the quality of the finished ride?

Ryan, my guess is that you've done the reading too, and you're the one with the 'less than ecstatic' opinion on all this. I've had mixed reactions (from this thread obviously - but from other independent sources too). 20+ extra BHP sounds worth having to me, but is it hit and miss with regard to the quality of the finished ride?

 

Nigel I did lots of reading before having my pulley fitted and came

to the conclusion , that to date no one could prove that there engine

has failed using this product.

 

I am very happy with the gains that I have got using the pulley

probably even more as I have had my AC removed to so thats one

less belt to pull.

 

there is nothing wrong with the finished ride , most people that go in

car love the sound that the pulley has given it.

 

Time will tell i suppose.

 

Ryan