Bimmer32

A good ET value tells how well (skillful) you launch your car. A good trap speed value shows how well you shift in the latter half of the 1/4 mile track. Given that you have a perfect run (e.g., 4 runs, take out the highest and lowest and average the remaining), input those values and you should get a pretty accurate number. Does your car actually weighs 4100 lbs?

The different calculators have their advantages . . . as noted, the Fox calculations are good for cars with more than 550 HP. LRT (Lucious Road and Track) calculations usually turn out more HP for fast cars (like the 545i and 550i). Hale's calculations are conservative if you calculate HP based on your ET values it but it's trap speed is fairly accurate.

I don't have access to atitude density . . . I would like to incorporate in my calculators for sea level correction. But this is just for fun and not a job, and I don't want to re-invent a wheel when someone's already done it.

I obtained the formulas from various Internet sites related to phyiscs and auto math; I couldn't find an Internet calculator that told me "how" it got the numbers. Eventually, I want to get that book, "Auto Math" and create an Excel spreadsheet to put on my PDA. That way, when I do decide to go to the tracks (4 miles from my house), I'll have it handy.

In my opinion, dynos and G-Meters are great, but I think it's more accurate to figure HP trap speeds at the drag. But to figure out ET and trap speed, I'll start with the math, compare it with mags' test, and if still not satisfied, I'll go to the track. For $15 bucks a run, I could do four for $60 and have some fun at the same time. Then I'll be better able to gauge my competitors.

Bimmer32

How much is the subscription to the service and for how long?

znod

Your calculator is pretty good given that you created it yourself. Check out posts 446 and 447 on this thread. I created the "calculator" and instructions for use by those here before I found the site I mention next. But, quess what, I can get you to a great site on DA, etc., with free calculators. Go here and have fun. I have excelled all the important formulas and some of my related derivations from this site for computational use.

Based partly on the site, here is some of what my spreadsheet calculates (inputs in red):

F = Temperature Fahrenheit (Tf)
C = Temperature Centigrade (Tc)
Tk = Temperature in Kelvin (k) = Temperature Centigrade (Tc) + 273.15
AS = Altimeter setting in inches of mercury (Hg)
AS = Altimeter setting in in Pascals (P) (mb X 100)
DP = Dew Point in F
DP = Dew Point in C
Pa = Station pressure = Actual pressure in Pascals (P) (mb X 100)
Pv = Water vapor pressure in P
Pd = Dry air pressure in P
Sv = Saturation vapor pressure in P
RH = Pv / Sv (mb)
D = (Pd / (Rd*Tk)) + (Pv / (Rv*Tk)) = Density in kilograms / meters cubed (kg / m3)
DA = Density Altitude in kilometers (km)
DA in Feet (100' = 0.03048 km) =
CF = 1.18[(990 / Pd)(Tk/298).5] - .18 (Pd in mb) (CF = Correction Factor)

Pro RR All-Loss RWHP:
Estimate engine-dyno FWHP reading by eliminating the effects of parasitic inefficiencies
and aerodynamic drag:
Calculate adjusted-for-engine-mechanical-inefficiencies J1349 FWHP"
Calculate the constant HP values needed to overcome the engine mechanical inefficiencies
Using the above value, calculate adjusted-for-engine-mechanical-efficiency HP value:
Apply CF to the adjusted-for-engine-mechanical-efficiency HP value:
Subtract the constant HP valuefrom the above results to obtain the adjusted for altitude and
weather J1349 FWHP value:
Calculate the J1349 1962' DA-related FWHP correction

znod

As a recall, the basic calculators from SMOKEmUP are about $5 per mo. Go to SMOKEmUP; the rates are easy to find.

znod

Bimmer32

Awesome link. Thanks. When I get some time, I want to create a simple (relative) Excel interface with all or most of the partinent variables for users to input their track and environment data to essentially "race virtually." To have fun, most people just want to race, have safe fun, and see the results. This should please those "anti-street racing" opponents - me included. They don't really care about the calculations (except for a few of us ). So that's my goal. Now I just have to fine time and that auto math book.

When I get the Excel calc complete, I'll run by you for error checking, cool? No promise on time table.

znod

I'm glad you liked the site. You are very welcome. And, yes, I would check anything you want. Cool to what your goal is. Good luck.