[grim09]

Originally Posted by RainMaker

Guys, that dyno result is absurd. A lightened object will take a uniformly lessed amount of torque to increase the angular velocity (ie NOT a big gain in the midrange and none at the top).

What you see in that graph is typical of added ignition. More power in the midrange, but at the top the turbo can only move so much air (power). I dont know what happened in between the two tables, but if it was going to change, it would have changed exactly like a lightened flywheel or a underdrive or lightened pulley effect the dyno.
(for example: http://www.marchperf.com/superford1.html )

Unfortunetly Rainmaker, I just dynoed that WRX yesterday with a before and after of the ACPT carbon fiber driveshaft and there was a significant gain in the midrange and at the top of the RPM range. Basiclly, he was able to acheive max horsepower a couple thousand RPM sooner than before and although it does not change your peak horsepower or torque, the car showed about a 5% increase across the graph. At the top it was a 16 whp difference.

[mtskibum16]

I don't even see how people are arguing against this driveshaft. Lighter rotating drineline mass = better. PERIOD! The engine doesn't have to use as much power to spin a lighter object; that power can then be used elsewhere ie: to accelerate the car. Whether this power shows up on the dyno screen or not is irrelevent because the power and extra acceleration are there whether any wants to believe it or not. You can't argue with physics.

[grim09]

[rmo55c]

Originally Posted by SoJDM.com

Lightened rotating driveline components (Flywheels, driveshafts, etc) allow engine speed changes to be more rapid. That means some, however slight or large, acceleration improvement without a change in horsepower.

For instance the lighter the flywheel is, the less energy it stores at any given RPM. If not making dragstrip starts, you want the lightest flywheel possible so the engine is not spending so much time spinning up a heavier mass. When making dragstrip starts, theory says heavier flywheels will cause the tires to break loose in a more controlled manner launching better because of the higher energy stored in the flywheel.

The jump off the line utilizing a heavier flywheel means traction is more easily controlled than with a lighter flywheel. Meanwhile the identical car in the next lane with a lightened flywheel might have a less controlled start (usually slower) but may make up for this by accelerating quicker down the rest of the strip - less mass to spin up while accelerating. Also, know that 5 lbs. off a flywheel or other rotating driveline component is not the same as taking your six-pack off the front seat. It is much more magnified at the flywheel because of rotating mass considerations. I believe for AWD cars, there is so much traction available that the heavy flywheel's advantage at the launch is much more limited.

Eliminate standing starts and the lighter flywheel is going to be faster. Better for rolling starts and/or road course work. This theory works the same for driveshafts except for standing starts there is no advantage to extra weight because it is not rotating. So a lightened driveshaft is a benefit in all situations compared to a flywheel.

Well stated. To further this point, when I put in my prolite flywheel, which is half the weight of the stock flywheel approximately, I had no problems with quick starts. I think that the AWD and the ability to rev high and spool up the turbo has allowed for the lightened flywheel to have a negligible impact on a launch. Additionally, the flywheel does help with engine revs, acceleration (minimal though), and smoothness of the car during acceleration.

[RainMaker]

Originally Posted by grim09

Unfortunetly Rainmaker, I just dynoed that WRX yesterday with a before and after of the ACPT carbon fiber driveshaft and there was a significant gain in the midrange and at the top of the RPM range. Basiclly, he was able to acheive max horsepower a couple thousand RPM sooner than before and although it does not change your peak horsepower or torque, the car showed about a 5% increase across the graph. At the top it was a 16 whp difference.

Then post it! If there were no other changes other than the shaft, and no tuning was done, thats a solid result in the plus column.

Right?

[ValvetrainEngineer]

I don't have time to read the whole thread, but here's my results from some time ago, posted in previous carbon DS threads...

http://www.iwsti.com/forums/attachme...5&d=1161714992


Here's my dyno comparison of carbon fiber vs. stock driveshaft. This is back when I was AP stage 2; same dyno, about 2 weeks apart (Nov '05). I had posted the results in the original driveshaft thread, but they got buried quickly. Peak gains are about 9 ft-lbs. and 5 WHP.

[RainMaker]

Originally Posted by mtskibum16

I don't even see how people are arguing against this driveshaft. Lighter rotating drineline mass = better. PERIOD! The engine doesn't have to use as much power to spin a lighter object; that power can then be used elsewhere ie: to accelerate the car. Whether this power shows up on the dyno screen or not is irrelevent because the power and extra acceleration are there whether any wants to believe it or not. You can't argue with physics.

Im not arguing with the shaft. If someone gave me one for free, I'd be very excited to put it on...
For the <10fllb and <13awhp I *expect* it to really make, I'd be willing to pay .............ehhh...........$400.

But it's not.... it's $1100+

I think alot of folks spend the $1100 based on posts of personal revolution, and then when they get it, they work hard to justify their $1100 expediture to themselves.

Chris

[ValvetrainEngineer]

Originally Posted by mtskibum16

I don't even see how people are arguing against this driveshaft. Lighter rotating drineline mass = better. PERIOD! The engine doesn't have to use as much power to spin a lighter object; that power can then be used elsewhere ie: to accelerate the car. Whether this power shows up on the dyno screen or not is irrelevent because the power and extra acceleration are there whether any wants to believe it or not. You can't argue with physics.

Nobody doubts the physics concept, that's fairly simple to understand. What is challenged is the actual calculation - just how much effect is there. When you look at it, this benefit is small compared to the flywheel. Much greater rotational inertia in the flywheel, which spins much faster (7k rpm). The carbon DS is not a great cost effective mod. It's best if you've done most other things already and are looking for some additional benefit.

And the benefit isn't just power - need to consider the lower weight effect on braking and handling (again small, but adds up). That being said, I'm a big fan and would do it again!

[RainMaker]

Originally Posted by ValvetrainEngineer

I don't have time to read the whole thread, but here's my results from some time ago, posted in previous carbon DS threads...

http://www.iwsti.com/forums/attachme...5&d=1161714992

Perfect... exactly the type of results I expect. (Other than the typical STi torque variances dyno to dyno...) a consistent torque gain and a (roughly) slowly increasing HP gain. Roughly 3-8 hp.

Exactly what I would expect, and exactly what physics theorizes should happen.

thanks,
Chris

[SilverSurfer]

So if I do a lightened pulley and a CF driveshaft at the same time I'm guessing this should definitely be something to feel "in the seat of the pants"....

[slicknick112]

Originally Posted by SilverSurfer

So if I do a lightened pulley and a CF driveshaft at the same time I'm guessing this should definitely be something to feel "in the seat of the pants"....

Without a doubt. You'll "feel" the benefits immediately, especially when your cruising on the freeway at 60 behind someone that needs to be passed and you don't need to down shift out of 5th or 6th to get by him in a quick manner. In my experience, 5th and 6th gears are now just as fun as 1-4.

[rmo55c]

I really want the cf driveshaft to compliment my flywheel. I can't even imagine what its going to feel like with the loss in weight on a cf driveshaft, prolite flywheel, 2 piece front rotors. Still debating the idea of a pulley - but have never been too fond of them.

Just have to save a grand now =)

[JJ18Sniper]

How much longer are these out of stock for?

[grim09]

Originally Posted by JJ18Sniper

How much longer are these out of stock for?

contact jim@sojdm.com they should have some now and more with in a week.

[mtskibum16]

Have any of you checked out the recent aluminum DS thread? Seams interesting. If it turns out to be built well then it might be a good solution for those that can't justify $1000+ for the CF one. The DS costs around $500 and it is even a lb or two lighter than the CF one.
Installed my aluminum driveshaft! (update post #34)