Not hardly. It's unsprung because it's designed to work with a dampened flywheel. It doesn't need damping springs, and the lighter disc puts less load on the synchros when shifting gears. Exactly the same as a stock MkIV Turbo Supra. It's not cheap or cheaply made. It's a stock clutch with stiffer springs in the pressure plate. That's all.

 

Well with a billet flywheel such as the subject of this thread, you will definitely want a sprung clutch if you want to maintain any comfort in your shifting.

The weight/load difference of a sprung VS unsprung clutch is virtually negligible when comparing the weight difference of a 40+ lb flywheel to this Fidanza unit.

Also keep in mind that weight is not the issue, inertia is. The closer to the center the mass is, the less inertia it has. So the 20 extra pounds in the flywheel that are further from the center of rotation add a gratuitous amount of inertia compared to the inertia from the extra pound or 2 from the hub of the clutch (smaller radius=less inertia).

There is virtually no load increase on the synchros when using a sprung clutch also due to the reduced shock absorbed by the dampening springs in the hub. Also lightening the mass of the rotating components of the engine decreases the load on the synchros unless you are rev matching PERFECTLY before engaging the clutch, as the engine has to adjust to RPM of the transmission.

 

You've obviously never rebuilt a transmission. I have.







Your analysis is lacking some facts. The flywheel's weight has absolutely nothing to do with loading on the synchro unless you don't know how to shift. The only piece of the clutch rotating with the transmission when the synchros are working is the friction disk. As LuK clearly states on their website So your insistence the springs don't affect this is just plain wrong. If you get rid of the damping system in the flywheel by going to a solid piece for lighter mass, sure, you want to put springs in the disk to reduce driveline shock, but it will be at the expense of accelerated synchro wear. There is no way around it.

Would I buy the Fidanza if I had a 250M? Yes, in a second. But don't be passing off half truths and untruths about the effects or consequences of this choice.

 

I've rebuilt my Subaru's transmission with only the help of a few friends and I've rebuilt several Escort transmissions, but no, I've never rebuilt a Toyota or Lexus transmission.

All I'm trying to say is that any synchro wear issues from the small amount of inertia added by using a sprung hub, are completely insignificant.

Also, if there were any significant issues with sprung hubs and synchro wear, then 95% of the worlds manufacturers would not be using them every day.

 

This thread is getting spicy I like it.... feel free to shoot me an email if you guys have any questions

 

I wouldn't say spicy, lol.

I'd say we can all agree that The Fidanza FW + sprung clutch is a better solution for performance than the OEM setup.

Shawn, feel free to chime in on any of the technical aspects, or get one of your engineers to Chime in. I'm just a dude with a BSME who knows a bit about how things work, I've never actually done R&D on a particular clutch system.

 

That's not a Lexus or Toyota gearbox. It's a Getrag 233, AKA Toyota V160. I rebuilt it by myself after a drawn out battle with TMUSA over getting the manual. There are significant issues with synchro wear, and the reason you don't hear about them is because many transmissions were designed with a spring or rubber damped clutch in mind. The engineer expected the synchro would need a little more surface area and mass to deal with shifting. Not so in these gearboxes designed for dual mass flywheels. That Getrag 233 makes a horrendous noise at idle with a solid flywheel from the synchros rattling - regardless of whether the hub is sprung or not. Another interesting factoid:



This is what first gear in the 233 weighs- 1.854 kg, 4.07 lbs. Getrag has a "triple cone" synchro for this gear and the other three gears behind the midplate in the gearbox. They do this to reduce the overall mass and provide a great deal of braking surface area for a gearbox intended to be used behind a fully dampened flywheel. Gears are heavy and turning at a different speed than the shaft. That's why synchros exist. So when that synchro applies braking force to the gear to make the gear's speed match the shaft's speed, the mass of the gear and the mass of the shaft - including the friction disk - have to be accounted for by the engineer if the OEM service life is going to be maintained. Changing either the gear or the shaft/disk assembly will change the service life.

And again, no argument about whether or not to add the springs - the gearbox will definitely appreciate any damping you can give it, but anyone running this stuff hard needs to expect there may be long term consequences like replacing synchros more frequently.

 

So you're saying the transmission is just an inferior design?
I doubt it's that different from so many other transmissions (read virtually every other transmission, ever) that have NO issues with sprung hubs causing significant synchro wear. If there were really any significant issues with synchro wear caused by sprung hubs, then so many OEM hubs would not be sprung.

Also if you think there is a real issue here, then we should engineer a disk with a MUCH smaller diameter, because that presents a MUCH larger increase in inertia, and there is no issue with synchro wear when many people get oversized clutch/flywheel combinations.

Let's get technical.
The mass of the disc itself is about 1.25kg and I'll be generous and assume that 750g of it is the hub assembly. The radius of the hub is about 60mm. Since we don't know the specific distribution of the mass of the hub, we'll have to create a range. Best case scenario, the mass is located fully on the center of the hub, with a radius of 20mm; the formula would be MR^2 (R being only 20mm in this case). Realistic scenario, the mass is spread evenly from the center to the edge. The inertial formula would be 1/2MR^2 (R=60mm). Worst case scenario, the mass is fully located on the outside edge of the hub; the inertial formula would be MR^2 (R=60mm).
Case 1 (minumum) inertia=3.00E-4 kg*m^2
Case 2 (realistic) inertia=1.35E-3 kg*m^2
Case 3 (maximum) inertia=2.70E-3 kg*m^2

The OEM hub is likely less than 500g lighter than the sprung hub, so again being generous, we'll say the hub mass is 250g:
Case 1 (minumum) inertia=1.00E-4 kg*m^2
Case 2 (realistic) inertia=4.50E-4 kg*m^2
Case 3 (maximum) inertia=9.00E-4 kg*m^2

The inertia of the rest of the disc (assuming 240mm diameter) is 2.7E-3 kg*m^2 and the inertia of the rest of the shaft (~2.5kg, 20mm radius) is ~8.0E-4 kg*m^2.
These 2 combined are 3.5E-3 kg*m^2.

The total inertia for the unsprung setup:
Case 1 (minumum) inertia=3.6E-3 kg*m^2
Case 2 (realistic) inertia=3.95E-3 kg*m^2
Case 3 (maximum) inertia=4.4E-3 kg*m^2


The total inertia for the sprung setup:
Case 1 (minumum) inertia=3.8E-3 kg*m^2
Case 2 (realistic) inertia=4.85E-3 kg*m^2
Case 3 (maximum) inertia=6.2E-3 kg*m^2

Seems pretty insignificant to me when considering the inertial increase from going to a twin disc setup, or the reduction in inertia from switching to a pucked clutch.

Your fear mongering is unwelcome here.

AND, if you're really THAT convinced that there will be ANY issue with synchro wear, just buy a stage 3 (pucked) or stage 4 (unsprung and pucked) clutch.

 

Yes. The gearbox in the 250 is an inferior design. I've said that a number of times on this forum.

 

T56 swap?

 

i hate waiting!!!!!!

 

don't we all!

Don't forget, only 2 more days to get the special deal on this FW!

 

Tomorrow is the last day to get the group buy pre-order pricing!

 

I just noticed this post.
You don't know how wrong you are.

I've had a stage 2, 2+ and 3+ in my car and I can tell you that the 3+ was the easiest of them all to drive.

 

REALLY? I had the HKS triple plate in my car. Right after an RPS "Carbon Claw." More metal doesn't make the clutch easier to street drive. Works great at the track. Sucks at a light with a cop next to you.