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In my web travels I trust the technical knowledge of the people on this forum more than anywhere else, so I'll pop the following questions concerning dynos.

1.) Assuming you're running in direct gear, how does the dyno compensate for your rear end ratio and tire diameter? Is the number plugged in to the computer, or is it somehow measured and factored in?

2.) What's the difference between SAE and STD corrections?

3.) Can the way the car is strapped on the dyno affect the numbers?

4.) Is there a lot more loss through soft and flexible drag tires, as opposed to stiff street tires? Will you get less loss with more inflation?

5.)How much does warming up the trans and rear lower losses? I recently ran my Cobra, fully warmed up, and got great numbers compared to guys who really ran their cars cold to lower effective intake temps. Also, doesn't the stock computer limit fuel flow until a certain coolant temperature is reached?


Thanks in advance for the expected insightful info!
 

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Snake Charmer
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PhillyCobra said:
In my web travels I trust the technical knowledge of the people on this forum more than anywhere else, so I'll pop the following questions concerning dynos.

1.) Assuming you're running in direct gear, how does the dyno compensate for your rear end ratio and tire diameter? Is the number plugged in to the computer, or is it somehow measured and factored in?
Horsepower = (Torque*RPM)/5250, so your gear ration/tire size doesnt really matter to the dyno.

PhillyCobra said:
2.) What's the difference between SAE and STD corrections?
SAE uses a correction factor for altitude, temp etc, its not very accurate though outside of a very narrow range, a hot day will still give you lower numbers than a cool day, even when corrected.

PhillyCobra said:
3.) Can the way the car is strapped on the dyno affect the numbers?
Yes it can, see more comments below.

PhillyCobra said:
4.) Is there a lot more loss through soft and flexible drag tires, as opposed to stiff street tires? Will you get less loss with more inflation?
Generally better gripping tires will have less slip on the dyno and give a truer number but slippage isnt really an issue unless car has boatloads of tq.

PhillyCobra said:
5.)How much does warming up the trans and rear lower losses? I recently ran my Cobra, fully warmed up, and got great numbers compared to guys who really ran their cars cold to lower effective intake temps. Also, doesn't the stock computer limit fuel flow until a certain coolant temperature is reached?

Thanks in advance for the expected insightful info!
The car will do certain things when it deems collant is not up to operating temp. The dyno is a tool and not a very good way of comparing your car to another car on another dynp, but its really all we have. Dyno calibrations vary as well as different styles and models of dyno's. Use it as a tool and try and do things in a consistant fashin like making runs at same coolant temps etc. Cold lubricants may cause more friction, being too hot causes increased fuel temps and intake air temps, there are a ton of variables and many make such small differences that its not really worth worrying about. You best bet when monitoring a cars performance or response to mods is to try and use the same dyno, pull at the same coolant temp and ideally on days or times when atmospheric conditions are as close to previous pulls as possible.
 
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