Ok I'm ready to hold my feet to the fire and probably the rest of my body Stainless
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I took a few minutes and ran the numbers you gave me through the spreadsheets on my site (
http://purplesagetradingpost.com/sumner/bvillecar/bville-spreadsheet-index.html ). Let's remember here there are numerous areas for error in doing the following, but it is a good exercise.
What I started with:
Body approximately 24" X 28" for 4.7 square ft. of frontal area.
I used only the back wheels tire as they are the bigger ones at 5" x 20" if I remember right. 2 of them gave me 1.40 sq. ft. of frontal area.
Total frontal area 6.1 sq. ft.
I worked with the 204 mph run with 167 HP as I felt you knew the HP better there. I subtracted 15% for drive-line losses (a guess - chains are good, but you still have the primary and gear box losses). This resulted in 142 HP at the rear wheels. I did use my "HP Needed" spread sheet to see the HP needed to run 228 if you knew it took 167 HP to run 204 mph and came up with 233 HP a little less than the 247 you thought you had with the shot of nitrous. Did you run the nitrous the whole run??
Then I went to the "Drag Force-HP-Thrust-Weight" spread sheet and figured the Cd backwards by plugging in the 204 mph and the 6.1 sq. ft. of frontal area and kept changing the Cd until I came up with 142 hp to run 204 with a set Cd and frontal area.
The Cd I came up with was .4. Now remember this is the combined Cd of the body and the tires. The body surely is less and the tires are probably more. If the tires where further away from the body like what I'm doing and what Seth did I would try and do this with two calculations.
I went another step to see what the weight should be on the rear tires to get the traction to run the 204 and 228 and came up with the following. This is the total weight needed at the rear of the car.
Speed ------------------- .6 traction coefficient --- .5 TC -----------.4 TC
204 mph -------------- 432 lb. ------------------- 518 lb. ----------- 648 lb.
228 mph -------------- 543 lb. ------------------- 651 lb. ----------- 814 lb.
.6 is the traction coefficient of good salt and . 4 is for bad (slippery salt). Weights over these are good. What is the rear weight of the car??
Now remember there are variables here (actual rear wheel HP, accurate frontal area) that could throw all of this off. More drive-line loss would mean your Cd is actually lower. For instance if we went with a 25% drive-line loss the rear wheel HP would have been 125 HP and the Cd would be .35 overall for the complete car (body and wheels/tires). This actually might be more realistic. Also with the lower Cd the weight needed on the rear wheels for traction would also go down. I'll let you go to the spreadsheet and figure the new weights. I'm not going to do it all
Give you something to think about also. I didn't figure in the part of the car that isn't there and sees no air
.
c ya,
Sum
