Derived HP and torque numbers?

[Mark Rinker]

If a GPS observed top speed of 123mph is recorded for a 2006 K3500, Allison 6spd, 3.73 gear ratio, running 285/75/16 rubber, what are the estimated horsepower and torque numbers? Weight with gear and driver = 7500#.

[DmaxMaverick]

HP/TQ can only be calculated by speed if time is also in the equation. If you were to make a full throttle run up to 123 MPH, on a purely level surface, with the vehicle weight known, the HP/TQ could be known. Otherwise, no. HP = work performed over time. This is how the G-Tech and inertial dyno's calculate power levels.

If you could, then your HP/TQ #'s would be right up there with the Prius. They can go 123 MPH.

[Mark Rinker]

http://vlsicad.ucsd.edu/~sharma/Potpourri/perf_est_intro.html Time is not an input with this calculator, it only asks for torque. However, I couldn't get it to read any higher than 117mph...regardless of the torque #s input...?


>>> If you were to make a full throttle run up to 123 MPH, on a purely level surface, with the vehicle weight known, the HP/TQ could be known. >>> This is basically what I did.

As for the Prius... http://www.youtube.com/watch?v=mzFK56epaHI Elsewhere a 112mph top speed is sited.



So, without time numbers...what is estimated TORQUE produced to attain 123mph, with specs listed above?

[DmaxMaverick]

I left out the time factor in the quote (although I stated it earlier). Without time, you can't calculate HP or TQ, with just speed as an input. If you were to use your top speed to calculate, you would have to be at maximum power usage, with all other factors known (weight, grade, wind drag, etc.), and not just against the governor, which is where you were unless your governor has been adjusted. If you know your torque at a specific RPM, then you could know your your HP, as well. HP = (Tq x RPM) / 5252. At 5252 RPM, HP and TQ are the same. Under no circumstances can HP be calculated without the time factor. It can be measured by other means, but guaranteed, time is part of that equation. HP is a representative figure of work performed over time. Nothing else. Tire size, weight, gear ratio, etc. have nothing to do with engine output power. They add to the drivetrain parasitic loss factors. They are, however, factors with how much power is available where the rubber meets the road (RWHP).

The Prius speed is limited electronically. Yours was too.

[Mark Rinker]

JK - was I up against a speed limiter on your tune of 123? There was alot of wind noise, and I did feel a 'surge' but lifted rather than see if it repeated.

[Mark Rinker]

I left out the time factor in the quote (although I stated it earlier). Without time, you can't calculate HP or TQ, with just speed as an input. If you were to use your top speed to calculate, you would have to be at maximum power usage, with all other factors known (weight, grade, wind drag, etc.), and not just against the governor, which is where you were unless your governor has been adjusted. If you know your torque at a specific RPM, then you could know your your HP, as well. HP = (Tq x RPM) / 5252. At 5252 RPM, HP and TQ are the same. Under no circumstances can HP be calculated without the time factor. It can be measured by other means, but guaranteed, time is part of that equation. HP is a representative figure of work performed over time. Nothing else. Tire size, weight, gear ratio, etc. have nothing to do with engine output power. They add to the drivetrain parasitic loss factors. They are, however, factors with how much power is available where the rubber meets the road (RWHP).

The Prius speed is limited electronically. Yours was too.


Sheeez Einstein :rolleyes: my assumption was that I had arrived at 123mph as my max speed, not rev OR mph limited, but wind drag limited.

From the calculator previously posted, I had tried to estimate torque by inputing various values, until receiving an output speed of 123. However, 117 was the highest output the calculator would give, regardless of torque figure input.

Again...anyone have a reasonable estimate of torque - based on the following assumptions:

123 is the drag limited top speed;
all other specs are accurate as listed above;
level surface, no wind, one earth atmosphere, at sea level, etc. etc. etc.AN ESTIMATE AS REQUESTED IS OKAY!!!



(On edit: I routinely pick Prius' out of my grille while refueling.)

[Kennedy]

JK - was I up against a speed limiter on your tune of 123? There was alot of wind noise, and I did feel a 'surge' but lifted rather than see if it repeated.

Yes you got me there. It's set at 118 so factor in a bit of speedo/tire error and 123 makes sense.

Economy tunes aren't supposed to go that fast:eek:

[Mark Rinker]

Yes you got me there. It's set at 118 so factor in a bit of speedo/tire error and 123 makes sense.

Economy tunes aren't supposed to go that fast:eek:


Can I send it (ECM) back to you and have it programmatically removed? The speed was taken by GPS, so no error there.

[Kennedy]

Sure

The accuracy would be in the speedo vs tire size (rollout) at the given speed which I'm sure will be different than the tire size at normal speeds.