So, I have a n 06 revup mt with a jwt clutch and lightweight flywheel. After 2 years with it I'm looking to change the flywheel, as I dont track the car. I was looking at z1 mid weight flywheel at 21 lbs or their sm 27 lb flywheel. Just curious if the step up from my 15 lb flywheel to the 21 would be a noticeable enough difference or should I just go to the 27 lb?

 

what are you trying to accomplish?

 

I daily my car but I do enjoy spirited driving around town. I would prefer more of a "drag" build. Straight line stuff. Taking off from a red light.

 

The only benefit form a heavier flywheel is the inertia you create from revving from a stop. There is no other benefit or having extra rotational mass

 

But doesnt the heavier whell create torque down low?

 

So I think the point travlee was trying to find out was "Why do you want to go with a heavier flywheel? Something wrong with the lightweight?"

I suspect I already know the answer but just want to hear it from you.

In answer to your original question (and subsequent):

YES, you will definitely feel a difference going from an LW flywheel to a 21# unit. Consider that it's ~40% heavier. But still some 30% lighter than the OE DM flywheel.

Personally, I have installed the JWT setup (plus ZSP HD CSC) on one of the family's cars - clutch, flywheel, wet operators - but opted for the nodular iron version - about 26# - (slight bit lighter than stock but retains the needed inertia for tractibility.) Very happy with the choice.

And NO, a heavier flywheel does NOT generate more torque. That is an old wive's tale from way back. Torque prouction is still solely the responsibility of the engine. However, a heavier flywheel can help to TRANSFER torque better than a lightweight because of physics (the relationship between mass and energy transfer).

They say that "weight is the enemy" in cars; and yes, it is for the most part. BUT, it's a tradeoff between having a LW flywheel aiding engine revs and having a car that behaves correctly in all conditions. Me, I'm NOT a fan of lightweight flywheels due to the driveability deficit in my type of driving. (Have had them on S30s and learned my lesson.) But, were I to track my car, then yes, the pitfalls of low weight inertia devices (flywheel) are negligible and relatively unnoticed on track.

After OP explains why the change desired, I will explain why I disagree with this statement. Let's just say that Newton wasn't wrong about a body in motion.

 

I enjoyed the lightweight flywheel for 2 years now and I'm just ready to go back to a heavier wheel. It's just gotten to be too annoying in traffic and I would prefer a heavier and smoother feel. Also, not having to shift as often

 

You just agreed with it with facts. Put a 500lb flywheel on a car. It's only benefit is getting it spinning from a stop and launching. After that the engine has to work harder to bring it up in the RPM's. Simple science

 

<Mic climbs atop the soapbox>

I knew that "500lb flywheel" example would get used. Hahahaha.

OK, here, note what I said a couple of posts back.... "...they say that "weight is the enemy" in cars; and yes, it is for the most part. BUT, it's a tradeoff between having a LW flywheel aiding engine revs and having a car that behaves correctly in all conditions. Me, I'm NOT a fan of lightweight flywheels due to the driveability deficit in my type of driving."

Key word: "Driveability"

The characteristics that I don't care for on a street driven car have to do with a number of operational gotchas that I've experienced. Mind you, not on a 33; rather, my S30s many many moons ago. And, to make it clear, this is a personal preference; not really trying to dissuade anyone from using a lightweight. Just my perspective based on previous "unsatisfactory use" (mismatch to the application).

Oh, and how I use my cars makes a big difference too. I do not track/AX any longer (last time W2W was nearly 40 years ago!) and I drive my 33 only on nice days and in the hills and valleys where safe to do so. As said, "track car, no issues with using a lightweight."

That all said, my dislike for a lightweight flywheel is all about the tractability. I certainly appreciate the performance benefits of a faster revving engine but as said, not at the expense of how the car behaves where I drive it.... street, highway, hills, blah blah blah.

Here are the actual, experienced, operating factors that detract me from using one:

- NVH increase:
Noise - generally speaking, the CD transmissions (and JK, EA trannies that succeed them) are already noisy. I don't need more gear clatter, particularly while stopped for a traffic light. Even my velvet smooth 4- and 5-speeds got noisier.
Vibration - increased vibration due to lower mass and the aluminum construction giving increased clutch chatter.
Harshness - related somewhat to vibration but I found that gear changes and subsequent acceleration were not as smooth through the same transmission as before changing to a LW FW.

- Rev maintenance forcing change in shifting method - Don't care for the change in shifting smoothness. If I fumbled the clutch/shift, the car let me know; similar to a "bogging" feeling. Sure, human error. But I'm honest in saying I prefer NOT to have to think about what I'm doing at all times. With my stock setup (and with the near-stock-weight iron flywheel on my S30s or DMF on 33), every shift is just an unconscious, muscle memory action in average driving; and when I AM thinking about it at 8/10ths+, it aids in my ability to safely go fast up the hill. There really isn't any high RPM application where I drive. 3rd to 5th gear mainly and under 5k (that's generous too, 5k where I drive can be hazardous to one's health looking over the edge of the road.)

Stop n' go driving was a nightmare (I say "was" because maybe in a modern car, it'd be different... but I doubt it as physics haven't changed in a short span of time, haha). Especially since I grew up in San Francisco, where HILLS are the rule, not the exception. Starting off on said hills was already a "hold the parking brake until clutch engaged" nightmare. With a lightweight, it never even felt like it was engaged. Smooth starts in such conditions were non-existent for the most part.

Relatedly, shifting and maintaining speed (freeway OR through/out of a curve) takes a negative hit. Increased loud pedal manipulation to maintain speeds, rev drops between gears if I don't completely observe shifting etiquette were not only troublesome but not the hot ticket for my aftermarket boosted 280Z. Boost builds under torque and any break in torque delivery killed maximum boost if I wasn't careful. Changed back to a conventional weight flywheel and all was good again for this lazy shifter.

So, overall smoothness is what motivates me; and it was lacking and presume it to still be the case (due to the above). Perhaps as I've aged, I prefer things to work as they were designed to with little room for needing improvement. (Like a fine wine in the proper glass?) That, along with my need to be only semi-conscious at times and not requiring 100% attention is my honest rationale for disliking them.

So yes, a lightweight has its advantages, little doubt IN THE CORRECT APPLICATION; but I don't believe there's enough reason justifying it for a daily/fun weekend car. I just happen to like the engagement smoothness and daily motoring rather than the "set of whole different characteristics". While I'm sure I could get used to it, there's no real point in needing to change. No one is timing me from Hwy 84 to 9 on Skyline Blvd. Haha.

If anyone local wants to change my mind, I'm open. Laff.....

 

He said "drag"
You will have a faster 1/4mile with a lighter flywheel. period.

 

I'm making a new flywheel. It will weight 5 kg (11 lbs) once finished.

 

This made me chuckle out loud! When I drive the Z, it's mostly cruising and it's very rewarding to have no perceptible lurch or abrupt bucking with zero effort, just enjoying the exhaust note. By the same token, I'll probably still do a slightly lighter one when we replace the clutch & think I'll get used to it soon enough.

 

Well to further paint a less than flattering view of myself.... I like smoothness of the OE DMF and the attached ease of maintaining the look that I’m cool. 🤣

But if I were buying another new setup for my car.... NOT paying 8 bills for a DMF alone. For that much, the whole clutch, fly, waterworks as a package.

I’m not just old, I’m cheap to go along with it.