Page 6

Sept 9, 2015 - New England dragway

Went to New England Dragway Friday and it was another fun night.

It seems that the best tire pressure is 12.5psi (at least for Friday evenings track conditions with Hoosier QTP's). Starting at 14.5psi with 0.5 psi decreases(cold) the tires blew off on the launch (at 3700) and again when hitting 2nd gear until I got to 12.5. All "good runs" were between 11.2 and 11.3 seconds and 122.5 to 124 MPH.

Tried various launch RPM's and 3700 seemed to give the best 60' times of 1.6sec. If I went over 3900 60' increased to 1.7sec+ because the tires would spin.

I have a spreadsheet comparing a dozen of what I would consider decent to good runs where the operator, me, seemed to shift consistently:
-Best launch rpms = 3700-3900 (above 4000 and 60's jumped up)
-Best Tire pressure = 12 to 12.5psi
-Best rear shock setting = 9 (max)
-Caltracs 3/4 preload both sides (marginal improvement from 1/2 preload)-car always launches straight no matter what the preload is (0, 1/4, 1/2, 3/4)
-Fuel cell- Negligible difference between 5 gallons and 10 gallons of fuel (at 6 lbs/ gallon, approx. 30 lbs difference)
-Total weight with me in the car approx 3500lbs

Been reviewing the data logger to get a better understanding of what is going on. Here is a plot showing just a few of the channels and summary for a 11.2 sec 124MPH run.
- Launch at 3700rpms with the 2-step
- The 2-step comes off just as the clutch is engaging so a slight increase in rpms to 3900
- It hooks on the launch with a little spinning, the accelerometer hitting 1.63G's, and the engine RPM's being pulled down to 2800, which is just above the begining of the TQ power band.
- Then the tires break loose as evident by the drive shaft RPM's increasing and the accelerometer decreasing
- It then hooks again with 1.5G's and a slight pull down of RPM's, staying hooked with a decent rpm increase till shifting to 2nd.

Similar hook, break loose, and hook again in 2nd gear as well.

The plot shows the RPM pull down with each shift. The initial drop is me slightly letting up on the accelerator as I depress the clutch and shift.
2nd: 5600rpms gets pulled to 4400 (right in the peak power band)
3rd: 5700 gets pulled to 4200
4th: 6000 gets pulled to 4500

Looking at the time associate with breaking loose in 1st (.18 sec), and 2nd(.15 sec), that is increasing the ET by a good .35 sec, which means I should be able to break into the 10's, aligning with the Wallace Racing calculator results if everything worked.

I am using a Centerforce DFX clutch which is basically an ON/Off switch that locks when the clutch is dumped. It is not a clutch that can be easily slipped nor should be allowed to slip. It seems if I has a clutch that slipped (such as a slipper clutch) it would address the RPM's being pulled down and allow for a more linear increase.

This is a zoom in of the launch showing more detail.

9-25-2015- New England Dragway

Hit the strip again last night and things are getting better with the hooking up. Now the driver just needs to learn how to shift faster and better I am stuck in the 11.2sec range at around 124MPH, but it is consistent.

Still spinning slightly on the launch with a little bounce right after the front tires get air, so I need to smooth that out. The biggest improvement is now when I hit 2nd gear it hooks great and the tires get air time, where as before they spun and the front bounced a little. Even 3rd stays hooked all the time now.

Here is a vid of a launch from a 11.23sec 123.8Mph run last night.

I have narrowed down the tires and suspension settings as follows for repeatable results as long as I do not mess up with shifting:
-Best launch rpms = approx 4000
-Shift at 5900rpms (shift light is actually 5600 and by the time I react its about 5900)
-Best Tire pressure = 12.5psi
-Best rear shock setting (Calvert 9 way adjustable) = 9 (max)
-Caltracs 3/4 preload both sides

I am shifting as fast as the TKO600 transmission will let me, and according to the data logger each shift is taking about .3 seconds, so some wasted time. Looking at the accelerometer data, there is about .25sec (2nd gear) to .4sec (4th gear) of zero acceleration during the shifts. I am thinking about faceplating the TKO over the winter when I have the engine yanked out for that work.

The nose also drops a bit more between gears, so I may swap out the Calvert 90/10 drag shocks to something adjustable so I can control the compression more. I am thinking that that is also contributing to the spin in the first 10 feet of the launch, when the front tires lift, there is a slight hop, and when it drops down the weight comes off the rear tires.

Click here to go to Page 7