Converting HP/TQ from Wheels to Crank

[Dan2013]

I have a 2013 Camaro SS L99 that I added Kooks headers, Kooks 3" X pipe, K&N CAI, ported throttle body and tuned by a SLP authorized tuner. We tested it on the dyno at 371 HP and 389 lb/ft of TQ to the wheels. I have read varying opinions about how much HP/TQ you lose in an automatic from the crank to the wheels. If I use the 20% rule I have approx. 465 HP and 486 LB/TQ at the crank. Anyone have other ideas on calculating HP/TQ to the crank?

[jake2212]

Just divide your rwhp by .8 an you get approximately how much crank hp you have

[Dan2013]

Originally Posted by jake2212

Just divide your rwhp by .8 an you get approximately how much crank hp you have

That's what I did. I was just curious if anyone had more accurate calculations on our Camaros.

[62nalide]

Pretty much no one anymore goes by crank HP anyways

[VR Baron]

Even .85 on a "optomistic" dynojet. Depends on the dyno type you used and alot off other factors but .85-.80 is close range

[Dan2013]

Originally Posted by 62nalide

Pretty much no one anymore goes by crank HP anyways

I agree amongst "car people" but to most others all they understand is raw horsepower. That's what they hear in commercials. The average Joe doesn't know how much their mini van puts to the ground. LOL

[axis]

Since the only way to truly test crank HP is to put it on a engine dyno, all you can do is guess. The problem is, anyone that knows anything about cars is going to laugh at you when you say you have 460hp. If all you're after is the biggest number you can get, might as well find the conversion that gives you the most and call it good.

[Dan2013]

Originally Posted by axis

Since the only way to truly test crank HP is to put it on a engine dyno, all you can do is guess. The problem is, anyone that knows anything about cars is going to laugh at you when you say you have 460hp. If all you're after is the biggest number you can get, might as well find the conversion that gives you the most and call it good.

Don't disagree at all. It just seems from all my research that people have agreed that 20% loss to the wheels for automatics and 15% for manuals. Seems to be a long standing belief. That's why I was curious if they has been any progress in estimating more accurately.

[axis]

Originally Posted by Dan2013

Don't disagree at all. It just seems from all my research that people have agreed that 20% loss to the wheels for automatics and 15% for manuals. Seems to be a long standing belief. That's why I was curious if they has been any progress in estimating more accurately.

I haven't heard of any new developments in converting from whp to chp. The problem is, no one that knows cars cares enough to go through the expense and trouble to narrow it down.

[Dan2013]

Now that I am thinking about it, the L99s typically dyno around 330 at the wheels. If I am at 371 that is a gain of 41 HP. With the L99 being 400 HP stock at the crank, it's logical it's AT LEAST 441 HP at the crank with my modes. I gained 41 HP to the wheels so again it's logical that I had some loss from the crank to the wheels so maybe the 20% rule isn't too far off. I'm just talking out loud. Don't mind my babbling.......

[TinyToasta]

The only thing you can technically measure is torque, everything else is done mathematically...

In Europe we usually measure torque at the wheel which is converted to rwhp. By releasing the throttle and letting the car run out drivetrain drag is measured. The drag number is then added to the measured torque (or calculated rwhp). The result is hp at the flywheel. If done correctly on a good (accurate) dyno this gives very reliable results as far as hp is concerned. SAE corrections would need to be applied as well.

This measure takes away the fact that the very same drivetrain eats up 200hp on a 1000rwhp car or only 70hp on a 350rwhp car - if you'd apply the x 0.8 formula.