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October 10, 2007
tire grip
I've made a spreadsheet to try a few different "what if" scenarios (adjusting corner weights, Center of gravity, downforce, and power), and it all hinges on getting a good ballpark coefficient of friction for the tire. I know it's impossible for me to get an accurate model due to all the variables that can change (i.e. I don't have $20k to have Calspan model my Kumhos!) but I'd like to get a ballpark curve so I can at least see what a change will do.
So far from Herb Adams book, he's got a table on page 2 with traction vs weight:
0:0
500:275 (coef of friction is 1.81)
700:500 (1.4)
1000:1000 (1)
1280:1500 (.85)
1500:1900(.79)
The polynomial I got from an excel trendline is:
-.00028*X^2+1.261*X+73
Milliken has a few charts on p78 and 79 of slip angle vs lateral force that has several curves based on vertical load for the 275 goodyear eagle ZR, a 27x14.5 Champ car rear tire, and a 25x9-13 F1 front tire. I'll get the numbers from that in a few nights when I have a chance.
The goal of all this is to figure out that 300 lbs of downforce will give me an extra 200 lbs of grip, which will let me corner at .2 more g's, which gives 4 mph faster exit speed, and saves 3 seconds per lap (purely made up numbers, but should be ballpark). Or see that ditching the 150 lbs of turbo gear on the nose and losing 250 hp will not slow me down.
Posted by Z28tt at 10:31 AM | Comments (0)
October 5, 2007
Accel 300+ ignition box issues
A while back, the Camaro wouldn't start, and I traced it down to no spark. The fuse for the 300+ was blown. I replaced the fuse, and it blew again as soon as the car cranked. There were no shorts in the wires going to the coil, and the Camaro ran with the 300+ bypassed on the factory HEI ignition. I then tested out the 300+ by replacing the fuse, and grounding the white trigger which usually causes it to fire the coil, and as soon as the trigger wire grounded, the fuse blew. I called MrGasket/Accel (216.688.8300), who suggested I send the box back to get repaired at their Jacobs Testing Facility in Carson City, NV. Not having heard back in a month, I've got to call them (775.882.6600, press 0 for operator). We'll see!
Posted by Z28tt at 9:07 AM | Comments (0)
October 4, 2007
Watkins Glen line update
Just got back from a 2 day track event at Watkins Glen with the Schattenbaum region PCA. The Z28tt broke the spare T56 on the 2nd lap (locked in reverse after I came into the pits, with gears 1-6 binding the transmission). I couldn't feel the synchro engage in R, but it did in 1 through 6, so we decided the reverse gear clutch fork or roll pin had broken. Since there were 2 track days, Mark Frouhar helped remove the tailshaft housing to get at the reverse gear cluster, and hopefully disengage the synchro and get the forward gears back. As soon as I got the tailshaft housing off, bits of bearing fell out, and ended my chances. Instead, I now had 2 days to instruct and get ride alongs with other folks. After a track walk (3.5 miles!), you could really feel how the concrete patches don't have nearly the same grip as asphalt. Another interesting thing was that all the corners are banked more towards the inside and banking tapers off (3 lines) towards the outside of the track. This makes for some interesting lines, staying more inside than usual.
Turn 1 - turn in earlier than expected to bring car down to the apex, and track out onto the rumble strips.
Turn 5 (sweeper after bus stup) - enter 1/2-2/3's over to the left, bring is steadily down, and get on the throttle as soon as you know you'll make the apex.
Turn 6 (going into laces) - Don't be fooled by the painted line moving left - the pavement stays straight. Some folks were turning in very early and leaving a good 5-8 feet on the right side of the car. The banking is steeper on the inside line, and lets you get a faster exit speed.
Turn 7 (toe of the boot) - Enter normally, and bring it down immediately below the concrete. Get on throttle, and cross concrete on the way out and out.
Turn 9 (off camber left) - Turn in right after crest of hill.
Turn 10 - Slight brake/lift depending on HP. Not much need to slow down at all.
Posted by Z28tt at 11:49 AM | Comments (0)