Saw this on another race forum and did the calculations on my 3 cars and several others and found it to be very accurate. I don't believe it would be accurate for power adder cars. Divide 1320 by your ET = MPH Divide 1320 by your MPH = ET Example; NO WIND on this run, very important to consider! 1320 divided by 9.514 = 138.74 MPH (car ran 138.23 MPH) 1320 divided by 138.23 = 9.549 ( car ran 9.514 ET) On our Buicks I have found that if the chassis is optomized the car will always ET better than the MPH on the time slip shows. Usually .03-.05 . If your ET is slower than the MPH predicts, you have chassis, convertor, gear and tuning opportunities. All these changes need to happen in the first 330' .Or you have more of a street car. If you have less MPH than the ET predicts you have issues down track (after the 1/8th mile) to address. Fuel, convertor, gears? Again, this is more accurate for a race car but good food for thought as you approach tuning your combination. Tom
Street cars: 1320 / 15.38 = 85.82mph. Actual mph was 88. 1320 / 15.21 = 86.78mph. Acutal mph was 93.54, supercharged Riv.
Thanks Tom for the info. My car ran 11.33 @ 121mph. So according to the formula I should be around 10.90. Guess I've got some tuning to do in the first 330'.
Let's try this with my car. 1320/11.86=111.298 1320/111.5=11.84 I checked my timeslip and got the exact mph. Not bad.
I believe it works because mph on a track is a calculation based on the last 66' of track. It is not true mph ,but terminal mph.
How did you do that 70 GSCONVT? gears,tires,converter,springs.traction bars.jetting.timming. etc ????
Tom great math! Works very close for me, about .01 off. Actually when I have the car weighted down to run 10.50 it will run more mph than that, but if I take the weight out, it will figure the mph I run and vice-verser. I will remember this one. What you got going on for next year? JIm Netherland
I'm amazed that such a simple formula can be so accurate. I knew Tom and Jim would be dead on since they have worked very hard to get everything out of there racecars. Those machines are dialed in. I am very impressed that Phillip (70 gsconvt) got his street car optimized so well too. These formulas make me realize that I have not done so well at using the available power of my cars. My '67 conv ran 12.10 @ 111.39 (should be well into the 11's like Phillip). And my '72 Sedan ran 11.07 @ 123.64 so I should be deep in the 10s if I make the car work right in the 1st 330' and especially in the first 60'. I've got my work cut out for the winter....
I'm always interested in formulas like this. My last run of the year was a 13.30 @ 107.3. I have a street car, which is optimized for the street. But it shows that my combination has potential in a different car, since 1320 / 107 = 12.30. Therefore, being in a street combination costs me about a full second. On the other hand, if I'm on the highway and want to get "tangled up" with a hotshot dude in the next lane, I could keep up with a 12.30 car (even though my timeslip only shows a 13.30). -Bob C.
You do have to have the car hooked for the formula to work. Often when a car spins , it will mph better than normal. Old stocker racers wanting to set a mph record would air the tires up to get some spin and less drag on the big end to set a record. It is amazing it is so simple. Jim N.
Bob: If it spins some it lets the rpm come up faster, like having a higher stall convertor. It hurts et but getting the engine up will sometimes let it run more rpm on the big end and more mph. Not an always thing, but can happen. My buddy Bobb Makley was telling me that he was at a race this year that had a bunch of street cars runniing and the track was bad and he spun and only ran a 10.30 but went 153 mph. The car will normaly run in the 8s. Spinning didn't hurt the mph but killed the et. Jim.
Is there a mathematical equation for calculating horse power and torque needed to propel ie 4000 lb car at desired 12.50 et at 110 mph for example?
Yes it will take 410hp to run 110mph and 404.78 hp to run 12.5 You can find the math for these and many others at : http://www.hardcore50.com/members/calculators.htm I use this site all the time. Jim N.
My car put 376 hp and 475 tq to the rear wheels on a chassis dyno about 3 years ago. Of course, that was with 2nd gear wiped out on the tranny, if that matters.
