I was 307 bone stock
True hp rating
Race Director
Joined: Jan 2007
Posts: 18,643
Likes: 14
From: Norman Oklahoma - The Only State in the Union with no Blue Counties!
The rule of thumb is 15% loss from the flywheel to the wheels but all cars are somewhat variable. My car, when it was stock was rated at 345 at the FW, a mustang or weight loaded dyno revealed 293 HP at the wheels
Le Mans Master
Joined: Sep 2007
Posts: 7,604
Likes: 8
From: Belleville Il
It can also vary with transmission,,an auto will have less RWHP than a MN6. If you have a stock (untuned ECM) repeated runs will result in small gains (for a while) as it adjusts air/fuel for wide open throttle (WOT) running.Mine was used in a dyno display at the mid west Nationals,where they did 3 pulls the first time and every hour there after did 2 more pulls for a total of 13 pulls.first pull read out was323.51hp/324.76tq the last read out 338.9/345.91. Early on the top end A/F was rich and each pull showed a very small A/F adjustment and power torque increase. Basically this is what the tuners do,,they know what the upper end ratios should be and "tell" the computer to run there. 
Administrator
Joined: Mar 2001
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From: In a parallel universe. Currently own 2014 Stingray Coupe.
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It's about 15% loss with a manual tranny, 18% or so for an auto.
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