Horsepower - is GTECH RR showing horsepower to the flywheel?

[SRosch]

Hello. I just bought a new GTECH PRO RR for my son. He has a 2004 Mazda 6 5-door with a 6 cylinder engine. Over the past 18 months we've made some changes to the car, adding an AEM short ram air intake, new brakes, shocks, springs, new custom exhaust, E3 plugs, and a UNICHIP. The car was rated by the manufacturer at 224 horsepower. We eagerly awaited the delivery of the GTECH PRO RR. When it came we calibrated it as best as possible - the rpm calibrations are off slightly, and took it to a 'desolate' area to check out the drag racing setup. The runs show horsepower peaking at 175hp, with a 0-60 time of 7.0 seconds at 5000 rpm. We ran the same setup 3 times and the numbers were consistent. Of course, my son was devastated as he thought he was making more power. Since we have never put the car on a dyno and we're newbies to this, is it safe to assume that we are making less horsepower than the manufacturer claims? Is there something that we missed on the setup ( pages 21-23 quick startup in the manual ). How does GTECH measure horsepower if it isn't hooked up to the ECU?

Thanks for any help.

[SRosch]

OK. We found the answer on the GTECH support site.
http://www.gtechprosupport.com/support/HP1.htm[url][/url]

[GTechAdmin]

Seeing 175 on the Gtech for a modified car that had 225 stock sounds about right. Remember these number include all the losses. Engine peripheral losses (pumps etc.), drivetrain losses (gears, differential), rolling resistance losses (tires) and finally aerodynamic losses are all included. This is the power that's left to accelerate the car. Read the message below for more info. Hope this helps. Thanks.

The key is to have very smooth shifts and to concentrate only on one gear. This is the same driving technique as on the dyno. Doing a flat-out acceleration run like in a 1/4 mile stint is not the right way to do a horsepower run because some of the shift jerks can get into the measurement. G-TECH has a mathematical filter that takes care of the jerks but it's best to avoid them because it may filter out some of the true acceleration. Also, you need to spend enough time in the second gear for all the boost to develop in a turbo-charged car. Sometimes 3rd is a better choice for turbos.
Lastly, 224 HP is a marketing figure, include up to 10% industry-accepted engine variations, water/oil pump losses, all the drivetrain losses, aerodynamic losses and you get to 175 HP in a hurry. Absolute HP measurement is a very evasive number, ask any dyno operator and they will tell you about all the corrections (fudge factors) that they have to deal with. At best these are only approximations.

It's best to use the numbers that G-TECH gives you as a reference before and after modifications. That's the most accurate way to do tuning.