[JJ18Sniper]

Interested as well!

[rmo55c]

Originally Posted by resonant_evil

i agree with what you are saying about the moment of inertia of rotors and wheels. the further the weight is from axis the higher moi. money better spent, maybe for brakeman rotors at around 10lbs saved a corner. same price even, this is my dilemma (better braking and weight savings). i went to import image and i was looking also.
i think for the cost people really arent looking into this mod before they have some basic mods done. this is not really a beginner mod (even though it could be a good one) due to price.

i think the change in mass is what you are neglecting. if you use slicknick112's numbers then the mass is cut in half. (i am trying to order a drive shaft now but xmas is in the way) since i dont have a cf ds on hand i will assume the diameters are close, which would cut the moi in half also. if you use newtons second law (of rotation) (net external torque = moment of inertia x angular acceleration) you will see with a constant torque, a large change of moi will affect the angular accel. (in this case increase it)
change your angular accel, you change your avg angular velocity, which changes your angular displacement.
all i am saying is physics backs up everyones claims, in this case it is not the distance from the axis it is the total mass loss which effects this feel. there is also the dampening and strength of cf to consider.

This all makes sense - at least from what I can remember about physics =) but that would mean that a flywheel is just as close to the axis as the driveshaft. When I had the prolite flywheel installed, my car definitely had a different feel. Quicker revs, smoother acceleration, and a slightly increased feel of quickness. I think that the prolite is almost half of the stock flywheel, so with that respect, the acpt driveshaft being half of the stock, would have a similar effect. Or am I completely nuts? At least it makes sense to me...

[fourseasonsandles]

Wow.. I think this is the one of the most informative threads I have ever read on this forum. Thank you very much Kevin for putting all of this together.

[Chris]

It seems like most of the guys in this thread are running stock turbos, it would make sense that the benefits would be seen with larger turbos as well, but are any of you running FPGreens or larger?

[Drag-On]

Has anyone received their ACPT driveshaft recently? I have heard they have been having a delay on their recent shipments.

Also, I have read about many people experiencing vibrations from their driveshaft. Is the vibration common problem or just isolated cases?

[JJ18Sniper]

Originally Posted by Drag-On

Has anyone received their ACPT driveshaft recently? I have heard they have been having a delay on their recent shipments.

Also, I have read about many people experiencing vibrations from their driveshaft. Is the vibration common problem or just isolated cases?

The vibration issues seem to be isolated to the older models, that utilized the older yoke. When coupled with the new longer yoke, the issue has been non-existant from what I have seen and heard.

[Chris]

Originally Posted by Drag-On

Has anyone received their ACPT driveshaft recently? I have heard they have been having a delay on their recent shipments.

look about 6 posts above yours

[TheLimitedProject]

Originally Posted by Drag-On

Has anyone received their ACPT driveshaft recently? I have heard they have been having a delay on their recent shipments.

Also, I have read about many people experiencing vibrations from their driveshaft. Is the vibration common problem or just isolated cases?

Mine showed up the 12th of December. UPS didn't bother telling me until I had another delivery the first week of January.

So, I was emailing Josh @ Import Image Online wondering where it was... and it was at the UPS depot the whole time.

Oh well... it's here. Still haven't opened the box, but it's here.

[mtskibum16]

This just made my "wish list" right after I stiffen up all the stock bushings. Very informative.

[Saabaru STI]

Want to finally see proof of the results?

Here's a guy with a modded 2005 WRX. Larger turbo, etc. The dyno he used is a very conservative dyno, which makes the gains that much more substantial.

http://forums.nasioc.com/forums/show...185800&page=25

[mtskibum16]

Looks like good results. It's nice to see back to back dynos.

[pharo]

Originally Posted by Saabaru STI

Want to finally see proof of the results?

Here's a guy with a modded 2005 WRX. Larger turbo, etc. The dyno he used is a very conservative dyno, which makes the gains that much more substantial.

http://forums.nasioc.com/forums/show...185800&page=25

This really clarifies how the shaft helps the whole powerband. I have been debating getting the acpt shaft or just saving the grand towards a turbo swap, but I finally realized that this shaft is such a simple install and basically doesn't require daily driving compromise, which to me is worth the extra power and hassle of a turbo swap. I can't wait for them to come in stock again!

[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 )

[SilverSurfer]

That's actually a good read that you posted a link to Rainmaker....

I will say this, when I went to a streetlite flywheel from ACT which is ~4 lbs lighter than the OEM STi flywheel, I didn't notice much. Of course, that's not a very extreme weight reduction (there are flywheels that cut 9 pounds or half of the total weight of the OEM flywheel). I want to believe that this lightened drive shaft is the cat's meow, I really do. I have faith, and I will probably still get one at some point.... Thanks all for posting good/helpful info.

[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.