Silver c6 z-51

383vett

Someone here was working on one the last year or two. I don't think he posted his final results but he was gathering parts.

Silver c6 z-51

That is where I am at the moment, the device has to go between the master and the slave cylinders. So I plan on buying a used master off of ebay to see if there is a way to convert it to -4 line, then also if I can bleed the system properly without taking my exhaust down.

sr530

Most of the DIY hydraulic launch devices are simple hydraulic restrictions, most based on the same design used by the commercially available Magnus Launch Control Unit. The Magnus device features a bypass solenoid, which basically functions to achieve delay on launch only while bypassing for the shifts.

Every clutch/engine/chassis combination has a "sweet spot" in the clutch pedal's release, where the clutch slips just enough to launch the car efficiently without bogging the engine. A given clutch's "sweet spot" band typically starts when throwout bearing pressure drops to a point where a clutch's holding power roughly matches the torque output of the engine. The end point of that band is typically defined by throwout bearing pressure falling to a point where the clutch either begins to draw more torque than the chassis/tires can handle, or drags the engine too quick causing it to fall down/out of it's power range.

The below graph shows typical shapes of throwout bearing pressure curves you get when using increasing amounts of simple hydraulic restriction…



For this example, lets say that sweet spot zone is between 200Psi and 100Psi. Notice that from initial pedal release it takes a bit of time for the clutch to hit the 200-100Psi zone. The 3.5t curve above takes about 1.2 seconds to reach the 200Psi mark, which is the start of this application's "sweet spot" zone. Curves 4t, 4.5t, and 5t all take more than 3 seconds to reach 200Psi. Because drag racers typically want things to happen almost instantly, this graph shows that an actual usable release curve needs to drop almost vertical to minimize delay of the hit. This is why import racers that use simple hydraulic restriction also typically use hand brakes for staging- they release the clutch pedal to the point of clutch drag in an effort to minimize lag time, but then need the added hand brake to prevent that drag from rolling the car out of the beams. This allows using a higher amount of delay than would otherwise be practical.

Here's a graph showing how my ClutchTamer's separately adjustable "initial hit" feature allows throwout bearing pressure to instantly drop to a given "sweet spot" pressure band before the actual delay starts. The point where the lines go from vertical drop to horizontal is what we refer to as the "hit" point, notice that all the lines reach their "hit" point almost instantly. Simple hydraulic restriction devices like the Magnus unit do not have the ability to do this...



Basically the initial hit feature allows lines 5/6/7/8 to all almost instantly drop to within the 200-100Psi "sweet spot" zone, with each hitting the chassis/tires progressively harder. Line 9 falls too far initially, likely to either bog the engine or knock the tires loose. All the above lines were produced using a 4.5t delay setting. Switching to a 4t delay setting would result in the clutch passing thru the sweet spot more quickly, less clutch wear/tear but possibly causing excessive bog. A 5t delay setting would extend the time it takes the clutch to pass thru the sweet spot, allowing the car more time to gain speed before clutch lockup, which reduces bog.

If you want minimal slip after the shift, it's possible to do that with the ClutchTamer...adjust the pedal stop deeper, then just stab the pedal when shifting instead of bouncing it off the stop. But here's something to think about- if the clutch slipping after the shift improves recovery by 500rpm, on a typical 10.0 sec 3100lb car that can easily equal an additional 40hp or so for a few tenths of a second or more after each shift.

Here's a comparison of two nearly identical back-to-back runs with zero wheelspin during launch and "clutchless" shifts. The blue pass has less clutch delay and bogs to 4622 rpm at .728 sec into the run. The only difference with the yellow pass is an additional 1/2 turn of delay added to the ClutchTamer adjustment, which caused a decaying amount of slip to be added after each shift. The added slip time raised the bog rpm to 5202 which increased hp output, and it reached the top of 1st gear 0.089 sec quicker. The added slip time also slightly reduced the wheelspeed spikes after the shifts, which improved net power overall to the point where the yellow pass reached the same driveshaft rpm 0.502 seconds quicker at the top of high gear...Notice that the car gains rpm at exactly the same rates in each gear on both passes. The improvements come on the parts of the graph where the engine is losing rpm, which are basically controlled by the clutch...



Here's a graph with just the engine/driveshaft ratio displayed, so you can better see the differences in clutch slip time...



As you can see, it didn't take much of an increase in slip time to make a huge difference in ET.

If you do decide to DIY a Magnus style device, I suggest adding a second adjustable valve to the bypass circuit. That would give you the ability to experiment with adding a little slip after the shifts, or to dial it out if you wanted to.

Grant