I have always used 15% for driveline loss then multiplied that number times the hp number and that gave me the hp loss/add either wheel to crank or crank to wheel. I was talking with someone yesterday and they said it didn't work that way. I said my car had 617 at the tire. I took 617x.15=92.55. 92.55+617=709.55 hp at the crank. Is this how this works? He was saying that they are 2 different numbers, but couldn't exactly tell me how. He is a Porsche 911 driver so maybe he just didn't like the comparison. For future reference and so I don't sound like an idiot, can you guesstimate crank HP by my math above?
Crank vs Wheel HP numbers
- Thread starter Davisenvy
- Start date
Short answer, yes. That's the math.
I'll be that guy... if you tried to talk about that to me at a meet I'd walk away. Unless it's been on a dyno no one cares. The only people that bring it up are the ones trying to seem cooler than they are. Don't be him.
Perceived horsepower is much more complicated.
I'll be that guy... if you tried to talk about that to me at a meet I'd walk away. Unless it's been on a dyno no one cares. The only people that bring it up are the ones trying to seem cooler than they are. Don't be him.
Perceived horsepower is much more complicated.
1) crank HP is like measuring your dick from behind your balls
2) if it makes 715 at the crank and loses 15% of that through the driveline the expected output would be 607.75
thats kind of how percentages work. If you take 15% off a 100 you get 85 but if you add 15% to 85 you get 97.75
2) if it makes 715 at the crank and loses 15% of that through the driveline the expected output would be 607.75
thats kind of how percentages work. If you take 15% off a 100 you get 85 but if you add 15% to 85 you get 97.75
Wheel is all that matters
People that say wheel or show a dyno graph and start talking a higher crank number...
A guy on another forum was talking about his dyno numbers and how it measures "engine hp" in the numbers it gives you....
People that say wheel or show a dyno graph and start talking a higher crank number...
A guy on another forum was talking about his dyno numbers and how it measures "engine hp" in the numbers it gives you....
when these cars were new, ford rated them at 390 crank hp but it quickly became obvious that they were underrated. bone stock cobras were dyno-ing in the 360-375 range which was more like 425 crank hp.
same thing with the 1999 (?iirc) cobras, they were not dyno-ing where they were supposed to be compared to what ford was rating them at. i think there was a class action lawsuit about it
same thing with the 1999 (?iirc) cobras, they were not dyno-ing where they were supposed to be compared to what ford was rating them at. i think there was a class action lawsuit about it
The general "rule of thumb" for horsepower ratings between crank HP and rear-wheel HP (RWHP) is ~18-20%. An automatic transmission will be closer to 20%, while a manual transmission around 18%. These are just a general guidelines.
He might be confused being a mid engine car thinking it has less drivetrain loss but he would be incorrect. If he is going to talk crank HP, he should be wearing a sign that says "I'm stupid" so you know not to waste your breath arguing with him.
For a little bit of humor.
He might be confused being a mid engine car thinking it has less drivetrain loss but he would be incorrect. If he is going to talk crank HP, he should be wearing a sign that says "I'm stupid" so you know not to waste your breath arguing with him.
For a little bit of humor.
I understand and I'm not asking so I can win the next argument. I just wanted to make sure I was thinking right and that it wasn't a brain fart moment. This guy is a family member and I don't think he wants to admit my car is faster than his.
Wheel / (1 - drivetrain loss %) = Flywheel
617 / (1-.15) = Flywheel
617 / .85 = 725
Flywheel * (1 - drivetrain loss %) = Wheel
725 * (1-.15) = Wheel
725 * .85 = 617
But yeah…who cares.
617 / (1-.15) = Flywheel
617 / .85 = 725
Flywheel * (1 - drivetrain loss %) = Wheel
725 * (1-.15) = Wheel
725 * .85 = 617
But yeah…who cares.
No, Fords are beneath him.
Different transmissions will have different driveline losses. Newer transmissions are most likely way more efficient. But I can be wrong. Also, if the transmission doesn’t have a 1:1 then the dyno numbers will be skewed.
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Sent from my iPhone using svtperformance.com
Factories always use Crank HP with no accessories attached for obvious reasons. an even comparison would be for us to use the same metric. More realistic would be for the factory to use wheel hp but that’s not going to ever happen
Newer trans offerings are pretty damn efficient.
18-20% drivetrain losss..... nope those days are over. Not unless its a giant DRW one ton truck.
18-20% drivetrain losss..... nope those days are over. Not unless its a giant DRW one ton truck.
They have been using different standards for the last 20 years that use all the accessories etc
SAE Adopts New Engine-Power Test
DETROIT - The Society of Automotive Engineers announces at its annual World Congress here significant new updates to improve the accuracy of the test standard auto makers have used for more than 30 years to rate the power and torque of light-vehicle engines in North America. Equally important...
1. Didn’t know 03-04 cobras are brand new technology. I’m not talking about a brand new car.
2. I always use 20% myself, because I would always rather be on the low side than self inflate my ego.
3. More HP doesn’t always mean faster. Traction is a big part of it. Same with “the driver mod”.
You could have made the same calculation in one step. You multiply 617 x 1.15 to get the same number. The 1.15 is 15%. Get it?
The other thing I'll say is no one cares about crank HP. The only thing that matters is what you're putting down to the ground.
@Davisenvy, as you can see from the comments above, the drivetrain loss varies, depending on the vehicle, transmission, etc. No harm in you using an approximate number like 15%, 17%, etc., but it will only be an approximation and you're, I know, good with that. Putting it on a dyno would be good if you're really wanting to see real world numbers to the wheels, but even then, dynos vary. Here's a clip from my Terminator FAQs. "All dynos differ slightly in reported output, due to differences in software revisions and calibration. For this reason it is recommended that you stick to one dyno shop when measuring performance differences between various motor mods installed. In general, Dynojet dyno numbers are a bit higher (typically 6-13%) than Mustang Dynos. And even Mustang Dynos can vary high and low due to operator setup."
FYI, if you were to use a dyno and have future engine mod plans, it is best to stick with the same dyno when you're wanting to accurately check the performance gains from those mods. For you, sounds like you simply wanted to know if the simple answer was to use an approximate drivetrain loss percentage applied to the advertised factory horsepower. Everything else we have all shared with you is just "gravy".
FYI, if you were to use a dyno and have future engine mod plans, it is best to stick with the same dyno when you're wanting to accurately check the performance gains from those mods. For you, sounds like you simply wanted to know if the simple answer was to use an approximate drivetrain loss percentage applied to the advertised factory horsepower. Everything else we have all shared with you is just "gravy".
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