High performance clutch question

[love2scoot]

I just got a high performance clutch with 2000 rpm springs and main spring.i currently have 5 Gramm roller weights in it that were stock.now that I have stepped up to a high performance clutch should I change weight size and if so where should I start gram wise?

[90GTVert]

Not really because of the clutch or clutch springs, but because of the stiff main/torque/contra spring you will likely need to use heavier rollers/sliders to keep RPM in check. A stiff contra spring resists the force of the rollers more, so rollers need to be heavier to counteract it. Either that or swap a softer contra spring into that clutch assy.

[GrumpyUnk]

It sure is easy to get into circular brain puzzles with all the parts involved. The explanation made perfect sense.
Now try to figure out what to do if you get more torque/hp from the engine fed into the variator. You want a bit more weight so the extra power doesn't shove the revs to the redline, but keeps them 'in the torque curve', which has moved and expanded(wider range of rpms having actual torque). 90GT did a series on tuning that is on youtube that gives a real documented with numbers(who needs stinkin' numbers...) examination of weights, clutch springs, and torque springs. Oy. Too much to consider, so I'm just going to go 'in the middle' and hope for the best.
I think the 2000rpm springs start to engage the clutch at that speed. Higher or lower engagement would depend on weaker or stronger clutch springs respectively(the springs that keep the clutch shoes from expanding out and rubbing on the inside of the clutch 'bell'). The choice depends on your engine output, and desired effect, quicker acceleration or higher top speed, which is linked(surprise) with the variator weights and style(roller or slider), which are ALSO linked to the strength of the torque spring(stronger will fight 'upshift' of the CVT, weaker will allow the variator to win, and kick to the higher gear ratio sooner).
Whattamess. Question is, what do you want to do? Accelerate faster or have a higher top speed, or, even more complex, what mods to the engine are done or planned? If you went to a BBK, or performance cam, or a larger bore carburetor, or a mix of those, with or without replacing the cylinder head at the install of the BBK, you'll get more power(expected, anyway), more torque, and a significant change to the hp/torque curves over the rpm range. Suggested peak operating rpm is around 8k, from what I read. You want your 'cruise' speed to keep the rpms at or below that number. You want your rpms under acceleration to follow the same rule. If you add hp/torque, the variator weight vs clutch engage rpm vs torque spring 'upshift' force have to be changed, more or less in synch, or you'll get lots of rpm with slow performance, or at the other end, quick engage, quick 'upshift', and higher top speed. Again, oy. Whatta mess.
I'd say you want variator weights that match hp/torque enough to squeeze the belt out to near the max diameter of the variator. Check using a 'magic marker' line from the center out to the rim, drive, and see where the belt rode at its max.
You'd want the torque spring to allow variator upshift(out to max diameter) reasonably, so the engine didn't bog(too soon upshift because of weak spring), or scream(too strong a spring, the engine can't get the variator expanded to allow upshift).
Clutch springs change the rpm where the engine power starts to get transferred to the output shaft. Weak springs will engage the clutch at lower rpms. Stronger springs will hold off the clutch, and 'lockup' to higher rpms. If too weak, the engine will be 'loaded' before it gets into its torque range. If too strong, the engine will be revving like a hummingbird, and you'll be going nowhere, as the clutch springs are not pushed against the inside of the bell, and are likely slipping until rpms get 'up there'.
I don't have the roads where I could do the tests that were documented, so I learn vicariously from 90GTvert, who has spent a load of time and effort doing the experimentation. Last thought, don't go to extremes of any portion as it will or can bias results so much you don't know what is causing slow speed or acceleration, etc.
tom

[90GTVert]

Mar 9, 2018 11:26:22 GMT -5 GrumpyUnk said:

I think the 2000rpm springs start to engage the clutch at that speed.

RPM rated springs are intended to raise RPM by the rated amount. So let's say your stock clutch setup engages now at 3,000RPM. If you install 2,000RPM clutch springs, the rating is saying it should now engage around 5,000RPM. That's in an ideal circumstance. It's really not that simple because they don't always react the same way in each setup. Each brand of spring may be stiffer or softer than the next too, to add to the fun factor.

Simplistic thinking is to just consider them softest to stiffest.

Softest Stock>>>1,000RPM>>>1,500RPM>>>2,000RPM Stiffest



Again a simplified approach to CVT tuning :

Use the softest contra spring that is stiff enough to control the belt. Stock works OK for stock. BBKs you prob want a little stiffer, like 1,000RPM or possibly more in some cases. I often use 1,000RPM for even stock, simply because I can buy aftermarket springs from the same brand and have a replacement of similar stiffness. If you buy any ole stock replacement, it can vary considerably. So pick say an NCY 1,000RPM spring and then buy an NCY 1,000RPM spring every time. Write down part numbers if you can to make it simple to be certain you get the same spring.

Then tune with sliders to get the right performance. Rollers are fine too, sliders last longer for me and may improve performance in some cases so I don't bother with rollers anymore.

Set the clutch up for best launch from a stop. Don't focus solely on RPM. Watch the belt as the clutch is engaging. If the belt is transitioning through ratios on the pulleys before the clutch engages, use softer springs.

The goal of all of this is simply put to keep as near peak output of the engine at all times when WOT. Don't expect to never hear RPM change. Aftermarket components with different angles on various bits and other design changes can tighten up the rev range that the CVT stays in.


CVT tuning is certainly more complicated than that if you demand the best result, but those basics can be applied to get a good result in most cases. Also note, CVT inspections and cleanings are important and you must keep and eye on the condition of the belt as well to avoid failures or perfomance issues.

[love2scoot]

Ok so here goes ,I put the new clutch assembly on has all be hardware new 2000 rpm clutch and contra springs.i put 10 gram roller weights with it and a new belt.i still broke a belt again the clutch shaft is solid with no play at all seals are in great shape.what could still be causing my belts to break?and thank you guys for all previous help and future help.this situation has me so baffled



Thanks again
Chris

[oldgeek]

Cheap Belts are usually the culprit.