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rwhp covert to motor HP


Hunter
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I think the new Shelbys lose less through the drivetrain...

 

Using that math above:

 

Mine dynoed at 610 RWHP x .15% = 91.5 HP. That is 701.5 HP to the motor. I have been told that these new Shelbys have been severely underated (this was told to me buy a reputable Shelby dealer/owner). Now I believe it.

 

Excuse me if the math is wrong, I never claimed to be a math-major. :)

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I think the new Shelbys lose less through the drivetrain...

Using that math above:

Mine dynoed at 610 RWHP x .15% = 91.5 HP. That is 701.5 HP to the motor. I have been told that these new Shelbys have been severely underated (this was told to me buy a reputable Shelby dealer/owner). Now I believe it.

Excuse me if the math is wrong, I never claimed to be a math-major. :)

 

I've heard the same thing.

 

I see 10% reported for the later models. I'm sure the advent of the electric power steering assist plays a big part in that. No hydraulic pump to add to the parasitic loss.

 

If that's the case, you're about 30HP too high and that would be right in line with Fords advertised HP rating for a '13.

 

 

Phill

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Remember that dyno tests are a snapshot of the exact conditions present at that moment. A Mustang Eddy-current dyno will report lower (many say more TRUE) numbers, whereas Dynojets (inertia method) are generous. I won't get into THAT debate, but they do report very different results. Ambient air temp, water grains in the air, altitude, tuning, everything adds to the mix. Heck, even the shop can influence things. One major magazine had fun with this a few years back, they brought a Mustang to 3 or 4 different dyno shops in their immediate area, all on the same day, and the numbers were ALL OVER THE PLACE. Almost a 150 HP swing, if I remember correctly. Also keep in mind, lots of shops win customers that way. If I could bench press 250 at Gold's Gym and only 225 at Average Joe's, I might conclude that Gold's is better somehow! There is a shop on Long Island that is known to put up huge numbers, and they also sell customers things they don't need, etc... smart folks avoid that guy, but not everyone is smart, right? Jer

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The math geek in me says you are doing the calculations "backwards" :). If there is 15% "loss" going from flywheel hp to rear wheel hp, then take RWHP and divide by 0.85 (1 - 0.15). For 10% loss, divide by 0.90 (1 - 0.10).

 

So 610/0.85 = 717 hp at the flywheel.

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Agree, you take the 15 percent from the flywheel to get rwhp, not rwhp and then add 15 percent. I have 502 rwhp so I have to have approximately 590 hp at the flywheel then take 15 percent from that to get my 502 rwhp. Give or take a few percentages. If you add the 15 percent to the smaller number which is the rwhp then your flywheel h.p would be less.

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Agree, you take the 15 percent from the flywheel to get rwhp, not rwhp and then add 15 percent. I have 502 rwhp so I have to have approximately 590 hp at the flywheel then take 15 percent from that to get my 502 rwhp. Give or take a few percentages. If you add the 15 percent to the smaller number which is the rwhp then your flywheel h.p would be less.

 

 

Your numbers are right but the statement if the math isn't.

 

Lets say there is a 15% loss and you start with 1000 hp at the crank (nice if you can get it but makes seeing the math easier)

 

The model says you would have 1000 x .85 = 850 RWhp

 

Going backwards from rwhp to crank hp you don't add 15% (which is multiply by 1.15) but instead divide by .85

 

850 / .85 = 1000

850 * 1.15 = 977.5

 

This why a price that is discounted by 5% is not the same as the discounted price marked up by 5%

 

 

 

 

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Your numbers are right but the statement of the math isn't.

 

Lets say there is a 15% loss and you start with 1000 hp at the crank (nice if you can get it but makes seeing the math easier)

 

The model says you would have 1000 x .85 = 850 RWhp

 

Going backwards from rwhp to crank hp you don't add 15% (which is multiply by 1.15) but instead divide by .85

 

850 / .85 = 1000

850 * 1.15 = 977.5

 

This why a price that is discounted by 5% is not the same as the discounted price marked up by 5%

 

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when the 5.8 was being wrung out before production, one of the guys working the dynos , on the preproduction engines told me that on the dyno stand the 5.8's were making 715-735+ bhp.. B)

Edited by frydguy79
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Jer's analysis makes the most sense. Numbers can lie, based on the liar's numbers. That's why I don't really get caught up in the what a dyno says unless I'm using it to improve a certain engine problem. Way too many variables to deal with, none of which can be duplicated like in a manufacturing diagnostic plant.

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Jer's analysis makes the most sense. Numbers can lie, based on the liar's numbers. That's why I don't really get caught up in the what a dyno says unless I'm using it to improve a certain engine problem. Way too many variables to deal with, none of which can be duplicated like in a manufacturing diagnostic plant.

 

Comparing two separate dyno's is very problematic. A single dyno should be repeatable to within a mergin of error and also accounting for temp and humidity etc. absolute hp numbers from a dyno are difficult since they are not calibrated. My guy in ft Collins said he'd had a visit from the Colorado weights and measures but I could never find they officially do so

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The math geek in me says you are doing the calculations "backwards" :). If there is 15% "loss" going from flywheel hp to rear wheel hp, then take RWHP and divide by 0.85 (1 - 0.15). For 10% loss, divide by 0.90 (1 - 0.10).

 

So 610/0.85 = 717 hp at the flywheel.

:drop: Math Hurts.

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