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Manshifting an ACT2900...

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bastarddsm

20+ Year Contributor
5,620
1,458
Aug 26, 2003
Mendota, Illinois
In my never ending quest to make my car quicker and more street-able I've spent a ton of time and effort trying various combinations of parts, and other things to make them work. Lately I've been working with an ACT2900/street disc setup, as it really works nice for DD. The problem is they typically don't shift well. I've done a lot of work to figure that out and fix the problem - the stock system doesn't move the TOB far enough to full disengage the clutch. So anyway here's a look at a datalog from a 9200RPM 1-2 shift I got the other day.
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This is just the raw data, but take a look at it. The green trace represents the upper clutch switch state, the purple like represents the 'nlts' limiter acting and turning the injectors off and then back on. Finally look at the Red RPM trace, notice the peak and where the slope changes. Now I'll add in cursors at the clutch switch transitions.
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Clutch up, down, and back up in .357s, average stuff is in the .5-1s, and some really really good guys get it done in .25s. Now here's a neat one - I'll move the cursors to the points where the clutch actually releases, and then grabs.
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.280s! That's the clutch disc going from 9200 down to 5600 in .28s. That's crazy!

What's even better about this is the trans is all old beat up junk. It's a used 1/2 slider and synchros that I bought in 2008, and have been using since! For comparison, last fall I was experimenting with a Tilton Twin Carbon, and I was getting shifts (clutch up/down/up) in the .32s range. I was also running a face-plated gear set last summer - even clutch-less shifting only using a blip of the throttle to shift it, these averaged about .30s throttle up-down-up. To give you an idea how quick a .30s shift is:
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The secret to getting shifts this quick is simple, get the clutch to release. Look for a new tech thread on this soon!
 
That is some lightning quick shifts. Appreciate all the info you shed light on for us. Some people may not like answers you give but you speak from expiernece and honest whether they like to hear it or not. So thank you for that.

My favorite part of the video is probably the fact that it was at gateway. (So it looks identical to)

Are you gonna be at IFO this Sunday?

Thanks seth
 
I'm gonna try and be at ifo. Probably not racing though. Can't get a trailer lined up, so I don't want to put the 'send it' tune in it. The block in it right now is cracked in a few spots and eventually it's gonna break the front corner off by the water pump. So I'm just having fun with it on a 20psi tune and trying to work some kinks out of it. New motor is being machined right now.
 
I'm gonna try and be at ifo. Probably not racing though. Can't get a trailer lined up, so I don't want to put the 'send it' tune in it. The block in it right now is cracked in a few spots and eventually it's gonna break the front corner off by the water pump. So I'm just having fun with it on a 20psi tune and trying to work some kinks out of it. New motor is being machined right now.
Well that Is unfortunate, would love to have seen your car go down the track. Hopefully Aaron @Slow95gsx will make the trip again and get to see his car make some passes this year unlike his unfortunate problem last year.
 
I’m using a 2900 with an unsprung 4-puck. It works great with my hydraulic, and pedal mods.
What mods did you do to get it to work flawlessly?
 
Basically redesign the clutch actuation system. I'm working on a new set of pedals that should decrease pedal pressure and still allow complete disengagement. It needs more TOB travel to get it to release. Several ways to accomplish that. Smaller slave, bigger master, longer master ect. But theres a lot more to it than that. I'm trying to get my thoughts collected and do some more testing to show whats really happening.

My end goal is I want this car to run 8's and not have a terrible clutch that's grabby and chattery and heavy. Well see what happens.
 
Well thanks for all the updates and information. I have a 2900 or a QM Twin and am not sure which I would rather run, but the SBC 2300 is not near enough so it has to come out and get in another car but not the Red Talon, to much car for it.
 
In terms of they are a giant car ruining turd. They don't have any inertia to damp the power pulses, they are on/off, they hold too much torque, and they don't shift that much better.

They only have 2 true benefits, they hold up pretty good, and they work with stock clutch actuation system.
 
Don't get me wrong they have their place. A road race car I would have one for sure, or even some big power drag car. But street car no way. I actually want to try one with the organic discs, and a 20lb flywheel. I bet that would be pretty decent.
 
The basket style clutches work much better.


For my car I run a smaller diameter slave, and I moved the fulcrum point on my pedal assembly for more travel. It made for more pedal effort but that’s not an issue for me.
 
I feel like unless you're on a track or have enough tire and turbo to come off the line on Anti-lag you really don't need a twin disk. I loved the fact that it could hold any power I threw at it but hated everything else about it. I'm really debating going back to a heavy flywheel for a while. The only thing keeping me on the fence about it is my machine shop asked for my flywheel for balance and I don't know if they were balanced separate.
 
A twin disc only has one real down fall and it is the nasty vibration noise you hear from the rear diff area which you eluded too from the poor engine dampening, but at the end of the day my car made more power than my 2900 could handle and it had to go, such is life.

I had the fidanza flywheel, OEM 2g disc and act 2900 and it was decent but the benefits of the twin are so much better, one of which is taking a bunch of load of the thrust bearing. The noise is something I attribute to being something cool like a BOV or a Turbo/supercharge whine.

As for driving it all the time I can handle the twin no problem and I don't even run an accumulator.

Look to each their own, I ran a singe for all it was worth, heck I think they made some 3200lb single disc, but the twin is soooo much better, not to mention pedal effort is almost stockish.

The best of both worlds would be a real heavy flywheel with a twin disc setup.
 
A twin disc only has one real down fall and it is the nasty vibration noise you hear from the rear diff area which you eluded too from the poor engine dampening, but at the end of the day my car made more power than my 2900 could handle and it had to go, such is life.

I had the fidanza flywheel, OEM 2g disc and act 2900 and it was decent but the benefits of the twin are so much better, one of which is taking a bunch of load of the thrust bearing. The noise is something I attribute to being something cool like a BOV or a Turbo/supercharge whine.

As for driving it all the time I can handle the twin no problem and I don't even run an accumulator.

Look to each their own, I ran a singe for all it was worth, heck I think they made some 3200lb single disc, but the twin is soooo much better, not to mention pedal effort is almost stockish.

The best of both worlds would be a real heavy flywheel with a twin disc setup.
I think you missed the point of my post. A stock type single is a better clutch for 95% of all dsm's, the only reason the twins gained traction in this world is no one could get them to shift. The point was to show that it's not only possible to get them to shift, they can shift better than a twin.
 
I'm interested in seeing the extent of the modifications required to make a single disc outshift a twin. There would certainly be some benefits, but probably not worth it for for most people if it requires reengineering the entire system from the pedal box down.

My twin shifts awesome, but pretty much sucks for everything else. I'd go back to a single disc if I found one that would shift without requiring extensive modification.
 
I think you missed the point of my post. A stock type single is a better clutch for 95% of all dsm's, the only reason the twins gained traction in this world is no one could get them to shift. The point was to show that it's not only possible to get them to shift, they can shift better than a twin.

I didn't miss any point. Singles are good for up to a certain point then they must be changed for something that can hold more torque and you're right that is 99% of the DSMs out there. I am not aware of people complaining that quick shifting a single disc is a problem, but neither a twin nor a single can shift faster than the other, that is a push. I figured out long ago about getting the disengagement correct resulted in accurate fast shifts, heck Jacks put up a bunch of videos a Looooong time ago about this issue and clutch drag which are related. Carry on.
 
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