Rob in Oz

A while back, I posted the timeslip for my 951 (14.335) at a fund raising drag day run by my club (Porsche Club Queensland) and since then I have decided to write a story on the event for the club magazine. I thought it might be interesting to give an interpretation of the times and speeds of a number of vehicles at the various points along the 1/4. I know what the reaction time means, and that the 60ft time represents the effectiveness of your launch, but what about the 330ft, 660ft and 1000ft times and speeds? Have a look at the table I've included for a Cayenne Turbo, HSV GTO (GM OZ exports these to the States as a Pontiac GTO, I believe), GM Commodore Ute (pickup) with some mods and running slicks - beat the 911 turbos (sob!), 964 Turbo with 2 drivers, 996 911TT, 951 (mine), 1968 911 with warm 2.7 installed, and a stock 3.0 911 SC. So...if you can give some comment on the info provided, I'd be most grateful.

TIA

Rob

Tomas L

Generaly the E.T values are influenced by many factors apart from power and weigth, for instance grip, gearing and driver skill. The difference in E.T because of driver skill for a car like the 951 that's a little difficult to get good starts with, can be substantial. The 1/4 mile trap speed is more strongly dependant of power and weigth. You can make a bad start and the trap speed will not be that much different.

Tomas

DanaT

Sorry it has taken so long but I will try and give a rundown with some examples and explain some of yours.

The first number is R/T (reaction time). A "perfect" reaction time is either 0.00, 0.400, or 0.500 depending upon the tree that is used and the manner that the R/T is displayed. MOST timeslips you see will be on a sportsmans tree (you will see each yellow light come on in sequence then the green) and the "traditional" timing method where a 0.500 is perfect. Anything above .500 you are sleeping at the line; anything below is an automatic loss becuase you left before the green light.

Next up is 60ft. This is basically how much traction and gearing you have to get off the line. In your examples you can see that slicks REALLY help. I doubt you will ever see 1.0g off the line on true street tires. That truck pulled 1.26 Gs off the line (average for teh 1st 60 ft). The 944T made about 0.65Gs over the same distance, the cayenne pulled 0.88Gs. This number is simply how good you can hook up.

330 ft is basically your low end power and gearing combination probably in 1st and maybe 2nd gear. This tells you how well you are transitioning through from getting off teh line into the power.

660 is mid track used to compare to 1/8 mile tracks.
1000ft is used to show if you are breaking up up top. You have to use this number in conjuction with the 1/4 mile time.

!/4 mile time and MPH are most of the time related but not always. Typically you 1/4 mile MPH (assuming a full throttle run) will change very little and tells you the power to weight (and some drag) of the vehicle. The 1/4 mile time is very dependant on your launch whereas the 1/4 mph isn't. But, you can gernerally tell some thing about a car. Let me go through my own time slips to explain.

Note that these time slips are at 6000ft so you wont see the same 1/4 mile speeds or E/Ts.

DDT 951 GSXR 1 GSXR 2 GSXR 3
Reaction
60ft 2.565 2.01 2.977 1.89
330ft 6.544 5.019 6.658 4.798
660ft 9.667 7.426 9.175 7.158
M.P.H 79.57 103.81 99.88 106.9
1000ft 12.299 9.567 11.257 9.156
E.T 14.503 11.855 13.018 10.88
M.P.H 102.13 89.86 128.18 135.22

If you look at the MPH on my 951 that shows a 102mph run. That run, if I could hook up, would be an E/T close to about a 13.2.

Now move on to the GSXR. The first run wasn't too bad off the line. But not the speed at the end of the 1/4 was 89.86 with a 11.855 E/T. To diagnose this run, you look at the 1000ft mph. It was 103.81. What this shows is that at the end of the track the run was aborted (or in bracket racing the brakes were applied to ensue that I didn't break out).

Going onto the second run of the GSXR, it had almost 3 second 60ft time. That was due (if I remember correctly) to a nice wheelie off teh line and having to back off. You will see that I lost lots of time off the line, but that the speed was high (128mph) for a crappy E/T (13.018). This run shows that basically the launch was screwed, but the power was there down the track (i.e. the "big end").

Going onto the last GSXR run, it shows a decent ET (10.88) with a 135 mph trap speed. A 1.89 60ft wasn't the greatest for a bike, but not too bad either. Typically decent laucnh would yield a 1.7-1.8 on street tires at full pressure. A 135mph trap however should put the bike around a 10.1-10.2. I could have been more agressive in the 330' area. However, this bike had problems down low with wheelies and teh first 330 feet was hard to ride.

I have included a few graphs of what is going on.



This graph shows the average acceleration between spots on the track for these run in Gs. What you can see is that the bike just pulls a lot harder than the 951. But looking at the bad run, the 951 pulled harder at first, then the bike got going at made more acceleration down track.

Looking at the next graph which shows distance vs time:



You see that the the good runs on the GSXR it pulls harder (as you would expect from the accleration graph) and just keeps running away from the 951 (it has a shallower slope to the curve). Now look at the 951 graph and the botched run off the line with the GSXR. What happens is that the 951 is ahead out to about 400ft or so. Then the GSXR catches up, and then pulls away from the car.

This is what is happening based upon those numbers. The numbers are mostly used by bracket racers to figure out how to dial in and how consistent the car is running in various parts of teh track.

I hope this gives a little bit of insight.

Just so youdon't feel bad, the commodore would have lost any race there becuase he left before the green light.

-Dana

Rob in Oz

Dana

Exactly what I wanted to find out! Thanks very much for your detailed reply. It'll be a great help in understanding the results.

Regards

Rob