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??

Can't really comment on the pulley... but the flywheel is a compromise between cost, availability, driveability, and response. Since the car was designed cost will have come down and availbility will have gone up, so that's one reason the car might have had a lighter flywheel as stock in the first place.

 

The flywheel smooths things out so you can't feel each cylinder pushing the car along one stroke at a time. It also helps to avoid sudden changes in engine speed. The smoothing effect of a lighter flywheel is less, but...

 

A brick that's spinning at 60rpm is twice as hard to stop as a brick spinning at 30rpm, even though it's the same brick in both cases. Anything spinning at 6000rpm will be a bugger to stop, even if it's just a yogurt pot lid.

 

In other words, at the top of the rev range the biggest factor is rpm - you could have a yoghurt pot lid in there but it would still smooth things out nicely. At the bottom of the rev range the weight of the flywheel is more important - so a lighter flywheel affects things considerably down the bottom. This has several consequences:

 

1) the car will NOT be as smooth - no creeping in traffic jams at 1000 revs

2) Spinning the flywheel up to the top of the gear will take less energy overall. If you're using less energy over time, this means power - so less energy into the flywheel = more power into the transmission = more horsies at the wheels.

3) At the bottom of a gear the weight is an important factor, so you'll notice the engine taking less effort to spin it up. In other words, better pickup and response.

 

You can also change engine speed faster:

- which is obviously good for upshift and downshift

- but changing engine speed quickly isn't always, for instance, when you're trying to creep on the clutchyou're relying on the engine pulling - with a lighter flywheel there's more of a tendency for the engine to drop to road speed rather than road speed climbing to engine speed.

 

(Should say mass not weight, but for the sake of readability... and doesn't really matter unless you're planning to drive on the Moon. :-) )

 

(Yes, I have a Fidanza!)

i also have a fizanza & really have not noticed any difference at all in smothness or driveability!!

i also have a fizanza & really have not noticed any difference at all in smothness or driveability!!

 

Wot, even round multistoreys and so on?

 

Anyway, I'll have a direct comparison soon - new Z currently has stock on but will have Fidanza by next weekend. :slap:

Like DaveW I have both flywheel an pulley and I can tell you that driveability is excellent. Sure it is slightly different but after a couple of days you dont notice anymore and it feels like it has always been like that. Apparantly the damper on the Z is a torsional damper and not a harmonic damper there is a difference, most of the scare stories come from the BMW community who warn about using them on the straight 6 engines, because the Z is V6 it has a much shorter crank and will not suffer as much torsional flex as cars with a longer crank. Anyone is welcome to try my car at one of the meets this year if your undecided on driveability. Remember unerdrive pulleys are have been around for thousands of years in Yank V8 tuning circles so I think they must have proved their worth.

Paul

Sure it is slightly different but after a couple of days you dont notice anymore and it feels like it has always been like that.

 

That's fair... agree with that.

 

You're right, boxers have crank problems full stop. Another reason for Z over Supra. :D

Hi,

 

The UD pulley can have negative effects on the crank, this is because they are not dampened. Also the underdrive pulleys have a smaller diameter, meaning that things like the water pump will rotate less, causing the engine to run hotter! I believe steve e took his set off due to this!

 

The only lightened pulley is the Fischer pulley, this maintains the original diameter of the oem pulley and is dampened throughout the rev range!

 

I also have an OS lightened flywheel and have no problems with maintaining 750rpm idle and creeping forward in traffic!

 

The engine is definately more freely reving with these items, the only downsides being the drop in revs is quicker, and slightly increased tendency to stall!

 

To explain how these items work, if you were running and placed some ankle weights on it would make it more difficult to run, if you took those weights and put them into a rucksack on your back it would be easier, it is the same principle with the engine!

mmm, so is the group buy that Smithy is organising for Fischer pulleys?

or am I right in thinking not, as he'ssupplying belts with the set?

C'mon you guys that already have underdrive pulleys. What is the concensus? There are a few of you saying yes, but which type do you have? Is it only Topless that has the Fischer and if so, do the rest of you all have the SGP types?

Fischer is not underdrive, underdrive as the name suggests have smaller diameters for racing cars worried about stressing the ancillaries like alternators too much, also to reduce the weight, the fischer is lightened!

 

If you want info about underdrive puleys affect on cranks and engine temps search on TT.Net? I don't think enough people have them in this country to constitute effective feedback!

Gotcha,

So what is the problem with an underdrive, sounds like a good idea to me, Mark.

...and I hear just about every stateside zed has them???

I mailed a friend in the states about them and this was his reply - "I have one on my NA motor, and really like it. Much better throttle response in gear and a quicker rev all around. There's been a lot of debate about them though, because the OEM pulley incorporates a harmonic balancer which can quell crankshaft vibration, and the lightened pulleys don't have this. On the NA motor, being relatively lightly stressed, this is not really a concern, but given the elevated stress on a TT motor, especially a modified one, there is concern that use of a non-harmonically balanced pulley could accelerate wear and tear on the motor's internals, and could lead to engine failure. I haven't seen a concrete case of this yet, but there's a lot of discussion about it. Overall, since it's only about a 10hp gain, you may as well skip it in the event that the lack of the balancer is something to worry about. The way I see it, 450 hp will feel exactly the same as 440hp, and that means that the possibility of damage to the engine isn't worth the risk for a gain you won't feel. If you want to lighten up the drivetrain, do a lightened flywheel - you'll definitely feel that and won't run the potential risk that an underdrive pulley may give you"

 

Vijay