I have done my research as far as strength, there’s plenty of guys out there running 9s that like them. The guy at silversport claimed that the 600ft lb. Rating of the tkx is underrated.
The .68 overdrive is probably nice for a lot of people. But with the cam I have in my car, I have to be going 75mph to even use overdrive.

Years ago when I dealt with Kiesler and thier Tko 600 tranny, it was rated at 600 ft lbs. my engine did not produce that much, but maybe within 40-50 of that. After I broke the tranny, i was told that launching on slicks at the track spiked the shockload above the 600. I got into a nasty brawl with them and they did end up sending me the broken 3rd gear and cluster gear for free. I installed it myself.

I then had the gears faceplated by liberty. I broke the 3rd gear again on the very first pass at the track as well as split the main case. I then went with a jerico.

Point is, i’m not sure what the torque ratings mean if we have no idea of what the shockloads are. A major factor is the clutch. The adjustable slipper type will reduce the shockloads on the shifts.

Just added this info for consideration no matter what trans is used. Good luck.

A stick car really shouldn't deadhook. I ran the same combo in 2 different car. One with 10.5" tires, and one with 14" tires. The old car never once had a problem with the trans. The new car will deadhook every where we went, and broke first gear in the Jerico. Yes I run a slipper clutch, and only 250lbs of base pressure. Will be interesting to see what the new Liberty does with an extra 140hp, and 90ft lbs of torque.

and we’re counting the days until your last shovel of snow is thrown and the mosquitoes hatch….

When you don't want a car to dead hook, you then have to hit the tires hard enough to knock them loose. Only 250lbs of base tune in a slipper may sound like a soft hitting clutch, but low base just means the balance of the clamp pressure required to get the wheelspeed you want has to come from centrifugal assist. The more traction you have, the harder you gotta hit the input shaft to get the wheelspeed. Then there's the fact that a clutch tune that relies heavily on centrifugal assist will hit the input shaft much harder than it needs to after a WOT shift.

I'm all for adjustable base, but for most applications the adjustable centrifugal assist feature leaves potential on the table. Torque x RPM, highest average number wins if you can get all that power to the track consistently. More launch rpm adds area under the engine's rpm trace, which means the engine will produce more power strokes in a given time frame. But what happens after the shifts can also add area under the engine's rpm trace.

With the typical diaphragm, B&B, or Long style pressure plate (spring pressure only, no added centrifugal assist), the drawdown part of the engine rpm trace after the shift will be pretty linear, basically a straight line like on this graph below...



With a SoftLok style "adjustable slipper clutch" that uses counterweights in addition to spring pressure to clamp the disc, the drawdown part of the engine rpm trace will form a gradual curve. Because the centrifugal counterweight component relaxes as the clutch pulls engine rpm down, overall clutch clamp pressure relaxes as well. Note that engine rpm initially drops very quickly after the gear change (trace falls almost straight down initially), but then the trace begins to curve as the clutch gradually loses it's ability to pull the engine down any further...



An advantage you get from the curved engine rpm drawdown shape is that it adds area under the engine's rpm trace (more engine power strokes in a given time frame). If the clutch had not slipped at all after the above 1/2 shift, the ratio change dictates it would have pulled the engine down to around 5245rpm (input shaft speed) after the tires hooked back up. But because the SoftLok style clutch has an additional centrifugal component, clamp pressure gradually relaxed as the engine lost rpm, which in-turn gradually slowed down the rpm loss. Because the car was also gaining speed while the clutch was slipping, the delayed lockup point raised the minimum rpm after the shift to 6302 instead of drawing the engine all the way down to 5245rpm as predicted by the ratio change. That added clutch slip time effectively tightens up the engine's operating range, which in-turn allows the engine to operate higher on the plateau of its HP curve.

Going back to the static-only (no added centrifugal assist) straight line clutch graph, it's important to know that you can adjust the angle of engine rpm drawdown after the shifts by adjusting the clutch's static clamp pressure. Note on the below graph that the angle of drawdown after both shifts are basically the same, while the drawdown after launch is still straight but the angle is different as launch rpm was drawn out over a longer time period...



The above difference between launch and after shift drawdown angles was made possible by externally controlling throwout bearing position during launch. Basically the throw-out bearing was not allowed to fully retract during launch, which prevented the full force of the clutch's spring pressure from clamping the disc. The throw-out bearing was then allowed to retract shortly after launch, which in-turn increased the clutch clamp pressure available for the shifts. The angle of drawdown during launch is adjusted via throw-out bearing position, while the angle of drawdown after the shifts is adjusted via static clamp pressure. In the end you end up with more clutch slip during launch, and less clutch slip after the shifts.

Here's the SoftLok style curved drawdown shape compared to what the "static only" straight drawdown could look like if static clamp pressure were optimized. Notice how the "static-only" (no centrifugal assist) straight-line drawdown angle can be optimized to add even more area under the engine's rpm trace than the traditional SoftLok style curved drawdown. Also note that the initial drawdown after the shift is not as steep. That flatter angle indicates energy is leaving the engine's rotating assy at a slower rate initially, which in-turn makes it easier to keep the tires stuck thru the shift. Because the engine is producing power at a quicker rate during the optimized "static only" straight-line drawdown, the clutch lockup point occurs sooner, which then allows the engine to get a head start on its climb to the next shift point...



When you add external throw-out bearing position control to the "static only" (no centrifugal assist) straight-line drawdown, it allows you to take advantage of much higher rpm launches without knocking the tires loose. That adds even more area under the engine rpm trace without pulling the engine down below its torque peak. The resulting high rpm dead hook launch really shines on a crappy track, it also reduces the need to adjust tire pressure and launch rpm for the purpose of controlling wheelspeed. Without the need to control wheelspeed, you will likely be able to make use of less first gear ratio, which will in-turn allow tightening up the gear splits if that is an option for you. Little gains here and there, but it all adds up.

In the end its much like a quick automatic transmission car. A less efficient coupling (converter) allows the engine launch higher and gain rpm faster, while also reducing rpm loss after the shifts. The increase in power production shows up as more area under the engine rpm trace, and that added power production more than offsets the loss of mechanical efficiency.

In my opinion, in most cases the traditional "adjustable slipper clutch" style centrifugal assist clutch tune is becoming outdated tech. First the centrifugal assist clutch tune limits your ability to take advantage of launch rpm, then it hits the tires harder than it needs to after the shifts. Knocking the tires loose after the shifts is usually what prevents guys from making the switch to radials. Even if you have a modern ECU that allows momentarily reducing power to absorb the spike after the shifts, those momentary power reductions still cost you ET vs a properly adjusted "static only" clutch that needs minimal or no power reduction after the shifts. When you combine a suitable static only clutch with the ability to raise launch rpm by controlling throw-out bearing position during launch, the adjustable centrifugal assist feature in most cases becomes obsolete.

Grant

I run a lot of counterweight. I also do not have as deep of a first gear as a "normal" stick car. Don't need it... and yes it helps with the splits. 2nd gear slider is the most abused part on a clutchless trans.