Carbon Fiber Driveshaft Discussion

[Roreri]

I'd be curious what people think about carbon fiber drive shafts. I've read some posts here, and materials and posts out on the wider internet, and I know there's a variety of opinions on them from wild enthusiasm to meh. I understand the basics:

Lower Weight--about 30 lbs less, in the middle of the car, translating to effectively about 1.9hp equivalent (For an AllTrac: 3200lbs @ 200hp = 16lbs/hp 3170lbs @200hp = 15.85lbs/hp 3200/15.85 = 201.89 or for a GT-Four: 3200lbs @222hp = 14.41lbs/hp and 3170lbs @222hp = 14.28 lbs/hp 3200/14.28 = 224hp). $1400 for a 1.9 or 2 hp gain is not anything to write home about.

Lower Rotational Mass, resulting in (very slightly) more power translated to the wheels. This is not a huge factor as the driveshaft is a small portion of the vehicle's total rotational mass. Plus the drive shaft is a small radius. It seems like lighter tires and wheels would be a better way to get at this--I have a tire/wheel setup that I think is 32.5 lbs each, which is pretty good based on what I've seen.

Better Harmonics, resulting in less noise, vibration, and harshness, and less felt engine shock. This might be the best actual benefit.

Here's a discussion about how not to get too terribly excited about rotational mass and the benefits of a carbon fiber driveshaft:

https://www.w8ji.com/rotating_mass_acceleration.htm

I know there was a group buy organized with ACPT, a long time ago. I'm curious what folks who have a carbon fiber driveshaft think about them.

 

[underscore]

You do also restore a little bit of lost power by removing the center support bearings and extra joints that the stock driveshaft has. The shock factor of picking it up and feeling how light it is compared to the stock driveshaft is cool, but I wouldn't be surprised if the gains are pretty insignificant. I bought mine on a whim for the group buy price but I don't think I'd bother buying one again unless my stock driveshaft was beyond repair and I couldn't find another.

 

[CMS-GT4]

I would expect the stock one to have more dampening qualities than the CF version.
Ripley mentioned that with a rear clutch-type LSD there can be a jolt that is sometimes felt.

I'd consider the CF version if I could get it for a fair price, but it is low on my list of mods.

 

[CTechBlueDragon]

Pretty much a last resort to lose weight for a serious timed race car. The stock shaft is designed the way it is for several reasons. I don't understand them all but I would think the one piece will stress things more and actually add noise and vibrations. Does anyone know if the rally cars used a one piece or stock style shaft? Probably one of the worst money to result ratios of any mod.

 

[Roreri]

I raised this question ambivalent but skeptical. As I said, $1400 for 2 felt hp is nothing to write home about. This above is some straight talk on the subject.

While one way of looking at the carbon fiber driveshaft’s lower weight is as a last resort weight reduction measure for a serious timed track car, another way to look at it is as an admittedly expensive way of reducing weight in a car that isn’t going to be gutted to reduce or balance weight. Since my strategy doesn’t delete the ac, toss out the seats and the dashboard and grind out the sound dampening, and that sort of thing, lighter components are the only real way to cut weight and affect distribution.

I have resolved to my satisfaction (barring any dissenting views) that this would be a high cost low payoff move. The amount involved could be spent on a set of carbon fiber front fenders that would save anywhere from 13-20 lbs off the front of the vehicle. Or spent as part of a turbo and intercooler upgrade that could yield significant power gains. Or I could hire a trainer and lose 30 lbs of suet (or just hit the road and lay off the seconds for free).

I haven’t really addressed my strategic approach to my GT-Four (which is ?? lbs lighter and has 22hp more nominal power than a USDM AllTrac). I’m going to avoid mods on its aging Gen2 3S-GTE in favor of weight reduction. Eventually, when necessary, a new motor, whether a Gen4 3S-GTE, a 2GR, or something exotic (who knows what the state of electric conversions and battery tech will be in 10-15 years).

I’d like to examine the spectre raised that a carbon fiber driveshaft might induce noise vibration or harshness.

Underscore: Doubts about whether it’s improved thrust to weight or wheel horsepower aside, have you experienced any negatives? It’s been some years since you installed it if I’m not wrong. Do you feel like it was a bad decision?

 

[zaluss]

The primary factor in my decision to buy the ACPT carbon driveshaft was that, at least at the time, carrier bearings were NLA for the ST165. I was originally going to see if I could get a steel 1 piece made but then this group buy popped up.

Mine weren't bad but I know they would be eventually.

That said I've had mine installed since 2016 with about maybe 3000~ miles and I don't regret the purchase though I think that I've now seen available replacements for the carrier bearings somewhere. For my intended use it was certainly overkill since I don't track the car.

 

[celi703]

I got the ACPT one on my alltrac. I bought it from a member here a few years ago because I could not find the carrier bearings that were going bad on the stock one. It was very light and pretty straight forward to install. The biggest difference I noticed was better acceleration and less noise compared to the stock one.

 

[underscore]

Underscore: Doubts about whether it’s improved thrust to weight or wheel horsepower aside, have you experienced any negatives? It’s been some years since you installed it if I’m not wrong. Do you feel like it was a bad decision?

It's hard for me to say because when it was installed I had a bunch of other work done at the same time, and the car was at the shop for 2.5 years (ugh) so I can't actually say what of the negatives my car now has come from the driveshaft lol.

As for whether it was a bad decision, when I bought it I had zero real plan for the car and was just throwing random cool parts at it, which isn't really an ideal way to build a car. It was an impulse buy because I saw it come up for the original group buy price of $800, rather than the $1400 they now cost for some reason, so I grabbed it. Bear in mind of course that thanks to currency conversion and taxes the driveshaft would now cost me $2000 CAD before shipping, which is what I paid for the whole car when I bought it, so it's hard for me to recommend it to someone lol.

tl;dr - if your situation warrants having one they seem to be well made. In hindsight, with what I actually do with my car it's completely unnecessary and therefore was a waste of money that I wouldn't repeat if I was restarting my build from scratch.

 

[Roreri]

Fair enough. Thanks for sharing your thoughts on this.

I think from the comments I've seen it's an endgame nice to have component for a car that's being built for competitive purposes.

Or...

It's a bit of spiff and overkill but a way to drop 30 lbs.

I could see how getting one for $800 instead of $1400 would be different. Then again that was $800 when $800 was worth something...

Right now I'm throwing other sorts of parts at my GT-Four. AC Compressor, Condenser Dryer, Coilover set, C/F Hood, Fuel Pump. There's lots of other priorities.

@celi703, since you're right here in NoVA, we ought to link up before I move this summer. I wouldn't mind seeing what your ride is like, and maybe riding along and listening to see whether your driveshaft is quieter or louder or softer or harsher or what. I'll send you a PM.

 

[underscore]

To their credit at least the price has stayed at $1400 since then, which is nice.

Also something I forgot to add, which kind of counters everything else I said: if it's a part that you're not 100% on, but you think you *may* want it one day and you have the funds/space to store it, get it while you can and worry about the rest later. Several mods or spare parts that I kept putting off because they were "always available" have ended up becoming discontinued with little or no warning and are now hard/impossible to find and far more expensive than they were originally. You also have the benefit of living in the land of higher population density and cheaper shipping so you can sell it fairly easily should you change your mind later on.