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MRSHIRO

240mm clutch disc on 250mm flywheel (performance cheap trick)

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Hi Guys,

 

This may have been coverd already. If it has please excuse me.

 

I've been researching Z31 flywheels and clutch/pressure plate setups. I've got a Shiro I'm restoring and figuring out the flywheel/pressure plate/clutch disc combinations has been interesting.

 

The pressure plates for the 240mm and 250mm flywheels are not interchangable (the pressure plate bolts holes and pins are further out on the 250mm flywheel. The stock 240mm pressure plates/clutch setups are known to generally hold better than the stock 250mm pressure plates/clutch setups. There are new stock-ish 250mm flywheels available (Rhino etc.) as opposed to no new stock-ish 240mm flywheels (they maybe out there I just could not find them).

 

So, here is my solution, I'm going to use a 240mm clutch disc with a 250mm pressure plate on a 250mm flywheel. Using slightly smaller disc clutches on slightly larger pressure plates is an old school perormance trick that was used back in the 60's and 70's on muscle cars. The theory being that applying the same pressure to a smaller area makes for greater presure between the flywheel and clutch surface.

 

Yes I know the lightened flywheels are a lot of fun, I've had them on stroked L6s. Yes I know that Centerforce now has a dual friction clutch/pressure plate setup for the 250mm flywheel (bit pricey though). Yes I've read about using 90-96 300ZX pressure plates and 350ZX pressure plates on the Z31 250mm flywheels.

 

My set up will be a 240mm Centerforce Dual Fricton clutch disc, stock 250mm Exedy pressure plate, new stock-ish Rhino 250mm flywheel. I'm building the engine to 400 hp, and want a clutch set up capable of holding up to occasional burn outs, while keeping the pedal pressure stock as this will be my daily driver and I plan to put a lot of miles on it.

 

Anyway, for you guys with tight budgets and you guys using their Zs as daily drivers this might be a option. I've fitted this combo up and everything matches up. I haven't installed yet, but I'll post results when I do. So wait for me to post the results before doing this setup yourself.

 

If anyone else has done a similar setup, I'd like to hear about your results. I'd also like to hear from folks that are using the 90-96 300zx and 350ZX pressure plates and clutches on stock Z31 250mm flywheels.

 

Sorry for the length of the post, thanks for your interest.

 

 

 

 

 

 

 

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Using slightly smaller disc clutches on slightly larger pressure plates is an old school perormance trick that was used back in the 60's and 70's on muscle cars. The theory being that applying the same pressure to a smaller area makes for greater presure between the flywheel and clutch surface.

 

Heresay, and BS. If that were to make any sort of sense, or have any performance advantage- I would run the smallest pads on the largest brake calliper I could find and out-brake everyone with this new secret performance trick, borrowed from the 60's and 70's.

 

Sorry, but it just doesn't make sense.

 

The only reason why earlier 240mm Z31 discs held better than any 250mm disc were due to the AFTERMARKET options only being available in 240mm option because the 1984-1986 models, turbo and non-turbo alike, were equipped from factory with 240mm assemblies.

 

This is stated in the 1984-1986 FSM on page CL-10. It is identified as Clutch Disc Model 240TBL, and Clutch Cover model C240S. 

 

When the 1987 Z31 300zx came out with the uprated FS5R30A transmission, Nissan sized them up by 10mm. The N/A models remaining @ 240mm like their turbo and non-turbo predecessors. This is stated in the 1987-1989 FSM on page CL-10. It is identified as Clutch Disc Model 240TBL, and Clutch Cover model C240S for the non-turbo, and 250TBL / C250S respectively, for the turbo model with the beefier transmission.

 

It is not cost-effective for a company to make new templates and produce new discs for an extra 5mm on either end of the disc. For no other reason is the 240mm available through aftermarket suppliers who manufacture clutch assemblies with higher holding capacity. Nissan upsized their units because they did not increase the harshness of the clutch engagement- they kept it relatively the same as the 240mm version by equipping the unit with more friction area, but using the same friction compound. For an aftermarket setup, the extra 10mm is almost negligible. 

 

If I handed you a box of 250mm clutch discs and put one 240mm in there, you would never know the difference, even if you went sorting through them. The hub splines on virtually all Nissans are the same too, so any 240mm disc from a Z31 will work on a Z32/33/34 provided the center spring/hub is the same depth, and the friction pads are of the same thickness.

 

The FS5R30A is the predecessor to the Z32 RS5R30A, and is virtually the same, internally. Thus the Z32 engines backed by MT transmissions are all equipped with 250mm discs. Also, the FS6R31A is fitted with a 250mm clutch disc from factory in the Z33/34 because it is the successor to the R30A series transes.

 

The added 5mm on either end of the disc does not contribute a HUGE amount, but you can use a 250mm flywheel like a Fidanza, or SouthBend Clutch, and you can buy a 240mm or 250mm disc, and pressure plate. Someone correct me if I am wrong, but the Fidanza flywheel should accept both 240 and 250mm discs and pressure plates.

 

You will get the increase in clamping load from having an uprated pressure plate, you will get the increase in friction surface due to the extra 10mm overall disc OD (which is not anything to write home about), and you will get the increase in holding power through use of better friction material like "Feramic" button type pucks- which, combined with the increase in clamping load, is the most important part of the assembly, and the part that makes the biggest difference.

 

The main reason why there are many 250mm options nowadays is most likely because Nissan does not use the 240mm disc on any higher powered vehicles now as a low-cost/low-model option, so now it doesn't make sense for them to go "backwards" so to speak, and since the flywheels are different heights, different bolt patterns, and the ring gear offset is in a different place, they had the chance to redesign everything @ 250mm with no 240mm option.

 

I would try the South Bend Clutch option, as I have used their old "stage 4" model, which is equipped with a 350z pressure plate, and a 250mm disc, and it should be fine on your "Rhino" 250mm flywheel. It's also very drivable.

 

You can use your current setup. It should work fine... but 400hp out of a VG30/33 makes gobs of torque. Don't expect a stock pressure plate to make full use of the uprated disc friction pads. If anything, it will slip and glaze the pads too easily, and then you're left with three pieces of junk rather than one.

Edited by Careless

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