Lightened CV's?
 

Have any of you had your CV's lightened? Does it help at all other than to lighten one's wallet?

I toasted another CV boot at the track yesterday, and I'm nearing the point where I'm just going to have to replace them - there's only so many times one can fling all the grease out before one has to replace the part.

SmartRacing does it for $50 per joint; I'm guessing there's other places that can do it cheaper. If I had a lathe...

How about their tubular axles?

http://www.smartracingproducts.com/ProdCat/Drive%20Axles%20and%20Parts/Drive%20Axles%20and%20Parts.htm

http://www.smartracingproducts.com/P...s/CVJoints.jpg

what is the benefit from this? I was always told that the CV is the weak spot of the drivetrain...would this make them weaker?

While removing weight never hurts from a performance standpoint, I'd like to see some quantitative evidence that making CV joints lighter really makes a difference. Mass moment of inertia is the important quantity here, and I don't see a CV joint being a big contributor to the overall mass moment for the whole system. Hold a CV joint in your hand and spin it about it's axis of rotation - not too much resistance to spinning. Do the same thing with a pressure plate....

Mike

I guess if your racing in ALMS it might help. Otherwise, I think your money can be spent better in other areas. I actually have a spare driveshaft for times like this. It's really helpful at the track because you can just install the spare and worry about replacing the broken boot in the comfort of home. This also saves getting CV grease everywhere.

Cheers, James

Less rotating mass = faster accel and braking. I was looking up something else on their site and found these, which got me to thinking (never a good thing).

I've never broken a CV; what is the common failure mode? My guess is that it would be the little cage.

Does your 1977 body still have the 100mm CVs or did you change to the late'85 108mm CVs with the 3.6liter conversion?

Whatever was stock on it's 12/76 build date; the later ones are the welded ones, right? I don't have those.

While I violently agree <g>, "faster accelerating and braking" is a relative thing.

Removing 5lbs from your car would result in "faster accelerating and braking", but would you notice? No.

Mike

That's why I asked; Now I'll take the $200 and get an e-ram cool collar cup holder air freshener for my H2

I believe IROC was noting that the CV shaft is rather thin, so the rotating mass is very close to the center of rotation and negligable. If the SM product is a hollow tube that would definitely strengthen it, but accelerating a little mass far from the center of rotation is the same as accelerating a larger mass close to it, and the weakness is still in the joints.

maybe the 935 version would be nice...if I remember right they are made from titanium. =o)

http://66.34.72.138/gallery/image/9398.JPG

Is that a rubber dampener to relieve driveline shock in the middle of that axle? Normal 911 axles can change in length as the suspension goes through its travel, how does the 935 accomplish or compensate for this change in geometry?

SRP is a very competent high end co. - like Wevo IMHO. I don't think they would offer it unless it was worth it -- for some.

This is expensive and not the first choice of things to do. It depends on where you are in the Church of Light (Weight's) pantheon.

The founder, Craig Watson, is an engineer (they are all over the 911 scene - aren't they?). You could contact him and ask for his opinion. I'd ask -- at what flywheel wt. does this start to be important.

You need to consder two factors re effective wt. -- 1. the radius from the center of rotation, but 2. the rate at which the roatation changes.

For overall wt. loss, the wt. is near the rear, but low to the ground.

If they hollow the shafts and lighten the CVs themselves, I think the savings is about 11 lbs. if I remember right.

Yes - the rubber dampener was to take out the driveline shock.

The standard u-joints were for reliability and strength. The Ti tubes were for better torsional strength (than Al) and reduced mass moreso than inertia. Throw that big rubber dampener on there (can't remember what it's called at the moment) and the inertia was about the same, if not higher than, a production CV axle.

The 935s that used these axles (all had the upside down trans) didn't have a lot of suspension travel. The linear motion of the axle was accomplished using the splined end of the axle in the mating end of the splined wheel hub.

These 935 axles, along with the upside down trans beginning with 935/78, were developed because the earlier 935s had a nasty habit of eating CV joints during the endurance races - partly due to the ever increasing HP/torque and the continuous development of getting the car lower to the ground (radical axle angles). CV axles changes were taking way too long in the pits during the enduros, so with this design it was 4-bolts at the trans output flange, slide it out of the hub, slide the new one in the hub, and replace the 4-bolts.

BMW calls them "Guibos" and they are located between driveshaft and tranny on RWD and F d-shaft and transfer case on AWD. Maybe Porsche calls them the same.

Jason

Guibo

The outer CV joint is unsprung weight as is half of the drive shaft. So, these measures offer a tripple-whamy. They reduce, in order of importance, 1). unsprung weight, 2) weight from the back of the car , and 3) rotating weight. It only makes sense because it works from so many perspectives.

-Scott

Here's what you need Thom;)
http://forums.pelicanparts.com/uploa...1095277881.jpg