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Discussion Starter · #1 · (Edited)
This thread is to provide STI enthusiasts with information about the ACPT Carbon Fiber Driveshaft. The original thread accumulated close to 1,000 posts, making it very difficult for new comers to research and learn the latest about this product without spending 3-4 hours to read every post. I encourage those who have not commented in detail about their experience with this modification to post here now that more and more people have purchased this unit.

The purpose of this thread is not only to allow people to post their feedback about the driveshaft but also to summarize what has transpired over the last year since that thread was created on June 21, 2005. Originally, IWSTI member RDCR started the thread after he single handedly tracked down a company he trusted to build him a carbon fiber driveshaft (here are some pics). ACPT indicated that their driveshaft produced a 5% gain across the entire RPM range, which is unlike many of the peak performance gains reported by other aftermarket parts manufacturers.

While nobody has dyno tested and verified this claim (though HSPN Networks is about to put this claim to the test), virtually every member that has since installed the ACPT carbon fiber driveshaft has reported positive feedback.

Edit: [email protected] said he has several of these coming available for those interested in a group buy if you are interested.

Here is Mike's first report.

Rdrcr said:
The ACPT CF driveshaft weighs 13.5lbs, compared to 24.5lbs stock.
Rdrcr said:
You can feel the acceleration difference on takeoff and when the car is moving. It is not really noticable when you are giving the car at light throttle. When you press the throttle to accelerate, the rpm's jump! The car screams to redline! It can be felt and is noticable in each gear change. The car engages each gear smoother and more positive than before. On the freeway, the car will lose speed faster now with the CF driveshaft installed. If you take you foot off the accelerator, speed quickly goes down(a characteristic it did not do so quickly stock).
After reading about Mike's results, I decided to order one even though I had not taken a ride in his car. Mike later reported a ring that began to appear on the driveshaft because of very minor contact with the rear diff plate.

Rdrcr said:
I talked with ACPT today about the rubbing issue. They informed me that it is entirely cosmetic and that it has absolutely no effect on the strength of the driveshaft. Their STi is showing the same "ring" in the same location as mine.

The only way around this rubbing issue, is too remove the driveshaft protection plate after install or too grind down the edge of the driveshaft protection plate. I am going to do neither and just run with it!

He also told me, with other applications, like the Toyota Supra TT, they have had similar issues around the same areas. The Toyota's are running over 1,000 whp with no ill effects with the same "ring".

I trust their knowledge and reputation. I will continue to drive my car hard, on the road and track.

I will soon be visiting the 1/4 mile track and next month, Willow Springs Raceway!

Mike
Mine arrived and I installed it to only give it two thumbs up. With a turboback and engine management, the STI was even more intoxicating to drive with the driveshaft. Many IWSTI members began to show some real interest in a group buy, which I worked on with ACPT and Kingofimports.com.

Before the group buy went through, Ben got a ride in Mike's car.

Ben said:
I drove Mike's car and I have to say I was very impressed. His car really felt more athletic and shifting was smoother. All I could think about while I was driving was, "Man I wish I had this driveshaft with my power (Catless 3" TBE + AP Stage 2)...that would be an insane combo."

In our "quasi-drag race" of about 20-80 mph, his car definitely seemed faster than a stock STi. He had Kevin as a passenger in his car and I had no passengers in mine, and my car really wasn't much faster. I think I pulled 1-2 car lenghts and then he just held. I couldn't shake him and although he wasn't gaining, he wasn't going to drop any more car lengths either. Typically with stock STi's I pull the same 1-2 car lengths but then gradually start pulling further and further ahead as the speed increases. This was certainly not the case with Mike's STi!

The main thing that really appeals to me about this driveshaft that no one has really commented on is that you gain a PERCENTAGE increase in horsepower. It's not like other mods where you get X horsepower, getting X% more horsepower is incredible. Essentially, the more power mods you do to your car the more benefit you will get out of the drive shaft. You might only get 10-15 hp out of it on a stock STi, but you could easily get 20-25 out of it with other mods ;).

It would actually be interesting to have you guys dyno both cars. This way we could see what the increase in HP is on Mike's stock car (power wise) versus Kevin's car with a Turboback Exhaust and Engine Management.

Anyway, after driving Mike's car I definitely want one.
Of course, Ben could not wait and demanded that we install my shaft in his car so he could test it. I obliged and Ben did not wait long to taunt me that I would not be getting my driveshaft back any time soon:

Ben said:
Oh, and now you want to know about the drive shaft, huh? I couldn't quite get off that easy I guess. ;) Let's just say that you won't be getting your drive shaft back. :D

Anyway, after we installed it and drove for a few minutes I was telling Kevin that the car didn't feel much different. He thought I was crazy, and kept telling me it was much faster than before. After some more driving I realized why it felt about the same as it did before. I had been driving by myself the entire day and right after the drive shaft was installed, Kevin got in the car. Was it really possible that my car felt like I was driving alone when there was actually a passenger in the car? I had to find out, so I dumped Kevin at some random stop sign and took off. Much to my surprise, the drive shaft really made that much of a difference. Once I was by myself I was pretty astonished at how much faster the car was. :D The combination of Cobb Stage 2 (3" Catless TBE + AP Stage 2 map) and the drive shaft is really awesome.

There isn't much I can tell you that Mike hasn't already. The one major thing I noticed was that the Stage 2 feeling of "wow this car got a lot faster" had returned. I doubt that it would appear this way on a real dyno, but atleast on the butt dyno I think the drive shaft FEELS about the same as doing a turbo back exhaust. The car really wakes up (much like it did with Stage 2) and makes driving the car just that much more fun.

Basically, I would look at it like this. For a less than the costs of a turbo back exhaust and an accessport you can get a mod that gives about the same boost in acceleration and fun-to-drive factor, takes less time to install (by a factor of about 5), is more stealthy, and for whatever reason, makes shifting easier. I still have no idea what the deal is with the shifting but it definitely is easier to shift fast smoothly. The only real advantage of Stage 2 is that it will make your car sound a whole lot better ;).
 

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Discussion Starter · #2 · (Edited)
RDCR chimed in after some people expressed some concern about the ring he reported:

Rdrcr said:
My STi has the ring and I will continue to abuse the driveshaft and the car. ACPT is aware of the ring in my car and in their own STi(Ben and Nivek removed their protection plate during install). They have absolute confidence that it will in no way effect the driveshafts strength or longevity. ACPT said if I have any problems with the driveshaft they will replace it at no cost to me.
The first shafts began to make it to the doors of people in the first group buy, they began reporting their feedback.

STInk said:
Wife just called:

It is on my doorstep. Plus I got a Crucial uppipe yesterday. It's gonna be a good weekend!
STInk said:
It is pretty freakin' nice. I won't have time to install it until Saturday, but the joints are Spicer with replaceable bearings, and the shaft has this weird golden sheen. You can look deep into it's eyes.... There are some polygonal shapes in the weave; I can't figure out how it's wrapped, but it sure is cool. Not exactly light, but if it is half the weight of stock than you'd have to notice!
91TB78 said:
Impressions:
First thing, the car feels more agile and shifting is MUCH easier. I noticed that it just feels more "athletic." Does it throw you in your seat? No, but it certainly feels quicker and I noticed that the engine revs quicker and smoother, both up and down, making for quicker acceleration and decelleration. :tup:

Very easy mod once you get acquainted with under your car.
evwoo said:
I got mine 2 days ago and it was in perfect shape. Had it installed by a local shop I go to and it took them 20 mins. No fitment issues at all!

I did not weight the stock shaft, but it felt it was 15Lbs heavier? Anyway, I had an appointment in Huntington Harbor with my client and it was a nice drive down. I noticed it required more pedal effort to maintain speed. maybe it is the lightness and have less inertia. So for long dist driving may be more tiring for the leg( right ).

What I felt the benefit was a quicker REV up and smoothness ( maybe the shaft is better balanced and also one piece. It also drop RPM faster so works better down shifting ( engine braking ). My car took on a more agreesive roar that is very nice. Not the deep throaty sound of a after marketing exhaust. My only power mod is a PDE catted downpipe with a Protune on an AP. I plan to dyno the car again when I get the ALK injection in. In its present state, my 05 STI puts out 280 WHP with 316 ftlb of torqueon 91 gas. I will find out if the drive shaft will give me more WHP.

I had some fun on the way home going thru a section I test my car. It is definitely smoother rev up. Does not feel a lot more power, but the engine deliver the power sooner and very evenly. A very worthwhile mod without affecting the reliabilty. Good job Nivek and ACPT!!!:tup: :tup:
stituner420 said:
I've had this mod on for about almost 2 days and I can't believe how well my car is running right now. I almost have 30k miles and its never run as silky smooth. The engine has also acquired an interesting and delicious new exhaust note that I'm really digging. I'm not sure if its my imagination or the fact that it doesn't have to work so hard to get power to the wheels. But it sounds great. I've also got a B&B Catback coming in next week, which should further enhance the boxer grumble. Btw, I'm at 5500 ft elevation so at sea level this mod will probably be even more amazing. You guys that don't have ACPT drive shaft installed yet are going to love it!
On a side note, should I reset my ECU, even though my car is running so sweeet right now?
 

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Discussion Starter · #3 · (Edited)
Alright, that was just a few of the positive things people were saying, but not everyone had the same to say. If you take the time to read through the entire original post you can read into every detail, but basically the first version of the driveshaft caused some vibration in only some people's STIs.

Without any real understanding of the problem, James at ACPT took it upon himself to begin troubleshooting the problem. First, he replaced driveshafts at ACPT's cost. Second, he revised the design of the drivehshaft's yolk, which improved the driveshaft's engagment with the transmission. This solved most of the vibrations reported by some IWSTI members, but a few were still having problems. After sending them new shafts and paying to have the original shafts shipped back for testing, James subsequently identified the fact that those with the remaining vibration issues had one thing in common: They had upgraded their soft engine, tranny, and or differential mounts with hardened mounts, which alone increased noise and vibration a significant amount.

Some of our members tested his theory by reinstalling their stock mounts. These members verified that the vibrations they previously reported must have been caused by these hardened mounts since the vibrations were no longer present. As a result, many of these members opted for the carbon fiber driveshaft over the hardened mounts because of the performance gain they experienced with the shaft.

Now ACPT only sells the updated version and all the old buyers received new shafts or a new yolk to have installed at their local driveshafts.

Jim at SoJDM.com has held a few group buys since ACPT made these design changes to the driveshafts and here are some quotes of the latest feedback and impressive results:

MrTransAm said:
I have '05 STi, let me start off by saying I did read every page of this post and knew of all the issues that people were having with their driveshafts. I have like many others all the possible hardened bushings to be had except for the motor mounts. I left the D/S protection plate off to avoid any issues with rub because I don’t rally and don’t see the need for a few extra pounds anyway. I do have more vibes in the car with the shaft, but definitely see the improvements out weight the vibes. Anyway, yesterday I brought my old accelerometer performance computer to work for some after work data collection. This performance computer was one of the first available many years ago, I found it not the greatest at producing actual times the car was capable of, but more of what a specific mod or alteration would produce in the way of performance enhancement.
Okay, so if you follow me on that, given the data recorded yesterday and the data collected today with the exact same outside temp of 86* F. The data was a best of 3 runs average for ¼ mile and best 3 of 6 zero to 60 runs. Improvements were more than I expected, they were as follows:

0-60 mph improved by .39 seconds.

¼ mile time improved by .56 seconds.
¼ mile trap improved by 4.53 mph.

Now, keep in mind that my car ran a best on a 71* day of 13.32 @ 102.23 mph
This was when the car was bone stock.

Again, now with the car being Cobb Stage 1 map and the improvements of the data above with the Carbon Fiber D/S installed, I would think the car would be very capable of:

High 12s @ 105+ on a hot day like today, just think, .this will improve with TBE and Stage 2 mapping and then a protune. WooHoo!

The driveshaft will always be allowing more of the future mod power to the ground; you can’t go wrong with this mod my STI brothers.

The car was totally different from yesterday on the 90+ temp days to this mornings 67 degree start; the car could not be described as anything other than a raging bull. I actually surprised myself on a 4th to 3rd shift for a truck passing, the car was gone so friggen fast I spoke aloud words of joyful profanity.
MrTransAm said:
Thought you guys would like to know how the Carbon Fiber driveshaft does at top speed. The only vibe I really get is a mild harmonic transition at 65mph,.it is gone at 67mph. When I say mild,..I mean this DS is to much of a gain to even care about the vibe lasting for 2 mph. I just don't stay at that speed,.I avoid the vibe.


http://media.putfile.com/ACPT-CF-Driveshaft-high-speed-check

MrTransAm said:
Rdrcr said:
It’s been over a year since the ACPT CF DS has been installed in my ’05 STi.

To date, this has been the best and most favorite performance modification that has been added to my STi. I have experienced no problems with this modification and it has performed flawlessly this past year both on the street and track. With the driveshaft installed, I have logged over 1,800 track miles through private and open track days and nearly 8,000 spirited street miles. The car has also experienced speeds in excess of 150mph and countless back to back laps with speeds over 130mph without incident.

I have only encountered two minor drawbacks with the CF DS. The first, being the “wear ring” that was caused by very slight contact with the driveshaft protection plate. Second, the car has a hardly noticeable vibration at 120mph that is completely gone within less than a second as you accelerate past 121mph.

Both, in my opinion take nothing away from the benefits of this modification. I recommended the CF DS in the beginning and I still recommend it over one year later. :tup:

Mike

BrewPubeaver posted some feedback with pics:
http://www.iwsti.com/forums/showpost.php?p=763405&postcount=928

RacerXS said:
Just had my shaft installed yesterday, it's everything it was built up to be. Definitely worth the $$......
MrTransAm said:
I have some good news about my driveshaft installed. For me anyway.
Anyhow,.As some of you had known,.I had what could only be described as a harmonic transition vibration that would show up at 65 mph,.didn't matter what gear. Would leave at 67-68 mph or at 62 and below mph. I ordered up the Turn in Concepts Klunk killer set:



Now,..I already had the outrigger bushings from Whiteline and found that the guys I had put them in did so incorrectly. Agghh!! Dickheads! I thought something wrong after I found a contact hit on the driveshaft from the upper part of the differential crossbeam. They had used the thicker poly bushings that are meant for the Foresters. I now have the proper bushings installed after the 15 minutes it took to do. Now the great news is the other part of the kit and a little harder to install,...
The TiC Rear Diff Mount Bushings,..they have stiffened up the diff so nicely that the 65 mph vibration has left the car,..I HAVE NO,.I repeat NO vibration form the car after this install,..I am very very pleased spending the $70 on this kit.
MrTransAm said:
There was a definite increase in acceleration for me. The car is very quick to react to the throttle now,..my fourth gear really seems to pull harder now.
My wife noticed the difference in the passenger seat,..she said the car just felt lighter and quicker in it's speed reaction. If fact every person that has driven or been driven in my car says there is a big difference from before the CF D/S,...I go Stage 2 on Tuesday,..I can't wait to feel it then. A trip to the drag strip will follow shortly.
jasv11 said:
I saw an increase of 4 to 8 hp and 4 to 8 lbs torque on my GTpro over 4 runs before install and then after. The other benifit is the car doesnt herky jerky shift anymore, its alot smoother. I have no vibrations at all from it on my 06. I have all stock mounts (tranny and rearend)

I havent been back to the drag strip for a while so I will be interested on the new times with it.
vodka said:
I got mine on the car about 2 weeks ago. 06 STI. Flawless install, and no problems yet. Highway cruising and above posted CA speed limits = OK as well. No vibrations or anything of the sort. Highly recommend this mod. The car accelerates noticeably quicker now, and shifting is so smooth. :tup:

nhsilversti said:
another update

well my cars issue is getting much closer to being resolved but, its still not quite there. as i type the car is at a driveline shop. they found a misalignment on the rear diff, the diff was to high. i have no idea why or how this happens without being in a very bad wreck which i have not yet been in. as of now with the diff spaced down and the outrigger modified, there is still a "vibration" starting at 55 and it gets slightly worse the faster you go. prior to this i would start to feel a "shake", notice not vibration, at 60-65 that would increase the faster you go up to 85 which was the MOST i would push it as the car felt like it was going to explode. they are going to pull the shaft out and recheck the balance, even though the shaft was fine in another car.

i will update again when i get the car back, hopefully sometime wednesday.


NEW FOLKS, DO NOT LET MY PROBLEM STOP YOU FROM GETTING THIS SHAFT! IT IS A PROBLEM WITH MY CAR! DO A SEARCH UNDER MY NAME ON HERE AND YOU CAN SEE WHAT ALL HAS BEEN DONE TO CORRECT THE PROBLEM. PLEASE DO NOT PM ME WITH HAVE YOU TRIED THIS OR THAT.

FINAL UPDATED ADDED AT REQUEST OF nhsilversti:
First and foremost even with all the trials and tribulations I would buy and recommend ACPT for your cars drive shaft needs. I cannot pass on enough thanks to ACPT for their commitment to helping get this resolved.

The car, as expected, is now a “free” moving beast! The slightest amount of movement with the car reveals an ease of movement. By that I mean the car move effortlessly. As some of you know I have the PPG 1-4 straight cut dogbox, the trans LOVES the DS. You can easily feel the smoother shifts and hear much less whine from the trans. Prior to the ACPT DS I would launch the car at 6K and get 10 of so feet of wheel spin. With the DS installed a 5-5.5k yields about 50 feet of rubber stripes if you keep your foot in it. Looks like I have to relearn launching the car. I would describe the seat of the pants “feel” of the improvement on my car like this: I feel like I have gone from a stock vf39 to an FP Green. In reality I have the FP Green so I don’t know what to compare it to, gt35r? The throttle response is vastly improved, makes the car feel more nimble.

I am going to make a short video of the launch to prove the length and ease of wheel spin utilizing this setup. I hope to have it up by the weekend. btw this is done on 235/45/17 aziens, not some hard small all seasons.

ted
RacerXS said:
I installed the shaft about a month ago, initially I was getting a little vibration ONLY when I let off at high RPM's (above 4K) while traveling 70 MPH or higher & it would last a few seconds.
I installed the rear diff, outrigger & transmission cross member bushings as well as the whiteline subframe locking bolts.........now there is NO vibration at all from the shaft. A little more NVH, but not as bad as you would think.....esp since I have the Cusco engine & tranny mounts too.
Sleeper in Seattle said:
I just got mine installed with the help of a friend and his lift at his shop. All in all it took about 25 minutes. I have a cobb catted downpipe mated to a stock midpipe and exhuast, and we were able to just unhook the exhaust hanger and squeeze the driveshaft in. It would have been easier to remove the midpipe, but my friend said it didn't have to be removed- and he's stubborn.....
As for first impressions:
I only have about five miles on it, but there feels like there is a lot more torque and the car feels like it accellerates a lot faster now. It is similar to the feeling of when you first go stage two. It puts a smile on your face!
I am driving for 8 hours on long road trip tomorrow, and I will give more feedback when I get back.
So far, I'd almost say that this is a better mod than going from stage one to stage two. It's more expensive, but car tach and speedometer seem to move a lot faster.
More impressions later.
Oh, yeah, there are no descernable vibrations up to about 110mph.
James
 

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Has anyone outside of "evwoo", noticed that it required increased pedal pressing to maintain speed? I would consider this an inconvience for highway trips.
 

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JJ18Sniper said:
Has anyone outside of "evwoo", noticed that it required increased pedal pressing to maintain speed? I would consider this an inconvience for highway trips.

I have actually seen an increase in hwy gas mileage when i drive long trips. Plus that is what cruise control is for.
 

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Here's an update!
I have put on over 700 miles on my driveshaft now.
I feel like my car makes power about 1500rpm sooner everytime I get on the gas and seems to grow with the revs.
I went from averaging 16mpg to averaging 25.3. See disclaimer below.
Torque comes on so much quicker now- I find myself looking down at my tach wondering what prm I am at after getting on it. I am usually about 1500-2000 rpm lower than I would think.
Throttle response "seems" a lot faster.
I find myself downshifting a lot less during my normal commute.
All in all, I would have to say this is probably my best mod so far.
Disclaimer:
I got rid of the syms replica and installed RDCR's duckbill trunk. Thanks! I still owe you pictures! And I got Volk 57f 18X8.5 with the bridgstone Pole positions 265/35/18. All of which may have contributed to getting better gas milage.
I would reccomend this mod to everyone!
 

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Sleeper in Seattle said:
Here's an update!
I have put on over 700 miles on my driveshaft now.
I feel like my car makes power about 1500rpm sooner everytime I get on the gas and seems to grow with the revs.
I went from averaging 16mpg to averaging 25.3. See disclaimer below.
Torque comes on so much quicker now- I find myself looking down at my tach wondering what prm I am at after getting on it. I am usually about 1500-2000 rpm lower than I would think.
Throttle response "seems" a lot faster.
I find myself downshifting a lot less during my normal commute.
All in all, I would have to say this is probably my best mod so far.
Disclaimer:
I got rid of the syms replica and installed RDCR's duckbill trunk. Thanks! I still owe you pictures! And I got Volk 57f 18X8.5 with the bridgstone Pole positions 265/35/18. All of which may have contributed to getting better gas milage.
I would reccomend this mod to everyone!
If anything, I would think the larger tires would give you crappier mpg...
 

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BTW, how was the install on this? I have a '06 STI also, and wanted to make sure it was a simple 'bolt-on' operation...
 

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my review:

Mini996TT aka La Mer said:
Driveshaft installed:

Shifting: Shifts are greatly improved. Smoother than ever before. Transitioning between gears is a lovely thing, now. No more herky jerky, i-cant-shift-my-car feelings.

Performance: The time it takes the RPM's to get going, and in turn spool the turbo, is greatly reduced. Because of this, it feels to me that the turbo lag feeling, in turn, has been reduced equally. Up top is similar to the performance down low. The feeling of your car falling off up top has also been reduced. After driving my buddy's B5 S4, I would compare a power similar to that. The power curve has flattened out, rather than a typical turbo lag to boost situation: you wait for the boost to build then hold on as boost increases. Don't get me wrong, it pulls JUST as good, if not better, in boost, but the transition of being out of boost to being under boost is not as big of a shock in contrast.

:tup: to the driveshaft. I'm a happy camper.
 

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Great write up Kevin! After a year of having this installed on my car, it remains one of my favorite mods as well. Increased acceleration across the entire rpm spectrum, easier shifts, more hp to the ground, less weight. I briefly considered selling mine only because I was short on money. I just could never bring myself to uninstall it because I loved the performance gains so much. For those of you lurking on this mod, get in on a group buy, its worth it!
 

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Sleeper in Seattle said:
my best mod so far.
Disclaimer:
I got rid of the syms replica and installed RDCR's duckbill trunk.
What is this duckbill you speak of? I searched trunk and duckbill with RDRCR's name and nada.
 

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Just got my driveshaft installed today and its very nice. Shifts are smoother now and rpm goes up quicker. Didnt notice any vibration up to 120 (but wasnt going that fast for long). Hopefully tomorrow the roads will be dry so I can give a better review and make sure there arent any vibrations at any speed.
 
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