Bonneville America Forums Forums Off Topic Discussion Forums Lounge Horsepower formula anyone?

Ok, here’s one for all you engineers out there. I was talking to an acquaintance today about a new gadget he has. It’s a little box that goes on his dash of his car and tells him what the horsepower of his engine is. Apparently he had to put in the weight of the car and it’s occupants and it figures the power based on how long it takes to accelerate to a certain speed.

It seems to me that there must be a formula for figuring this out. Take the weight of our bike and ourselves and how long it takes to get to say 60 MPH, and figure what horse power and torque it takes to achieve that performance.

Anyone know where to find something like that? I’m WAY too cheap to spring for a dyno run but I’d still like to see what the Blue Streak is actually doing.

Um yeah it gets ugly...

http://en.wikipedia.org/wiki/Power_(physics)

from this it would be something like

Code:

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 1/2 * 700 / 32 * (5280 / 3600)^2 * (VSS^2 - VSSi^2) / T / 550 
 

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where the 700 is a guess at bike+rider weight, VSS and VSSi are final and initial speeds, and T is the time to go from VSSi to VSS.

Trying this for a rocket III using 900 lbs for weight and the reputed 3 second 0 to 60 time got me a scarily accurate 142 hp. Probably a coincidence but it shows it's in the ballpark and it's certainly sensitive to the right variables. At best though, it's going to give you some kind of average hp figure. Nothing like the precision of a dyno.

Anybody got an acceleration time for an america?

The short form is 1 HP = 3300 foot pounds per minute.

Chuck Hawks writes about the Triumph Bonneville motorcycle. ... They reported a
0-60 time of 4.9 seconds, and the bike's top speed was 105 mph sounds pretty close to me

HP = total weight * 200 / ET 3 (that would be cubed). For this formula to work, you need to get a drag strip ET.

For instance: a 2800 lb car with 200 lb driver, runs a 10.00 sec. ET. The horsepower at the rear wheels would be about 600. This assumes proper overall gearing, no wheel spin, a good racing type torque converter, and so forth.

NOTE: This very old formula does NOT work well with very light vehicles (such as motorcycles), nor with vehicles with great amounts of horspower, such as blown nitro drag cars (Top Fuel and Funny Car). But, it'll be dead-nuts on for your big block powered Camero bracket racer, or a Pro Stock Chevy or Dodge

I just ran the figures for a Pro Stocker and came up with a little over 3 hp per cube. Not bad for a 500 cubic inch push rod engine with carbs and burning gasoline.

Years ago some Chrysler engineers came up with a horse power calculating formula, which used trap speed and total vehicle weight. It worked well, too, but I can't remember what it was. Oh, they figured it out by dyno-ing their hemi drag engines and then putting that engine in a car an making time runs. In other words, they "back figured" the formula, using a company main frame computer (this was in the days before the PC was common.)

It doesn't matter these days, though, as NHRA shortened the speed trap at the finish line, by cutting off the back half of it! The traps used to be 66 ft. long both before and after the finish line, so as to get an average speed when one crossed that line. Because Top Fuel cars started going so darned fast, and because drivers would hold the throttle down 66 ft. past the finish line, NHRA just eliminated that back half of the speed traps so that fast cars wouldn't run off the end of the strip.

The shortened speed trap messed up the results of the formula.

Ow, I was a poli sci/ history major, this makes my head hurt Nothing easy?

Wow, looked at the wikipedia link.........telling ya, this is way over my head.

C a n S ome on e p llee aasee st o p t h e ro o oo oom f ro m s pp ii n in g ?

Welcome to my world

Plus it gives me an incentive to be honest about my weight

Twisted Throttle = GO!

Quote:

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I’m WAY too cheap to spring for a dyno run but I’d still like to see what the Blue Streak is actually doing.

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Take a long trip soon and head south. Our best dyno dood is in Muscle Shoals and does the HP only for $25.00. If you get the fuel ratio also, it's $40.00.
If you buy a DynoJet kit for $85.00, it's free.