still quite unfamiliar with dyno, plz help out here

1. I noticed that there's a noticeable difference of performance (HP/TQ) between auto tran. and manual tran. cars if they are tested by a dyno-jet, and why is that!? and does that mean the same thing for the regular situation (on-road)?

2. what do we call the dyno result...wheel horse power?!
The result we got from dyno is not the same as "engine HP" (200 for TSX case, is that what it called, engine HP?), and is there a particular way to convert between these 2 kinds of horse power?

thx so much, guys!

 

I'll try to answer both questions in one go.

A dynamometer measures the power put to the ground so you will see losses from driveline inefficiencies when you compare a wheel dyno with shaft dyno (one that requires the engine to be removed and mounted to what is essentially a big brake). There are bigger driveline losses with AT cars then there are with MT. Typically an automatic transmission loses around 20% of engine power before it reaches the ground whereas a manual transmission will only lose around 15%. These are real world differences which is why a wheel dyno is a better test of performance. If you want to get a rough idea of engine horsepower you would just multiply wheel horsepower by 1.2 for AT and 1.15 for MT but those are just rough estimates.

 

1) fancy AT causes more power to be lost before they get to the wheels, and yes you will see it in real life. That's why AT 0-60 are always slower than MT.

2) Like Dan said, the amount lost in a MT is around 15%, while an AT is aroun 20%.

However do NOT multiply WHP by 1.15 and 1.20. This is bad math I found. If you can follow check this out.

Equation relating WHP and HP
WHP = HP * (1- % lost from transmission)

This is the wrong equation!
WHP * 1.15 = HP
=
WHP = HP * 1/(1.15)
=
WHP = HP * (.87)
=
WHP = HP * (1 - .13)

That is saying WHP is 13% of the engine HP.

The proper equation would be
WHP = HP (1 - .15)
=
WHP = HP (.85)
=
1/(.85) WHP = HP
=
1.18 * WHP = HP

So for a MT, multiply the WHP by 1.18 to get the HP. For an AT, multiply by 1.25.

 

Just to add some fuel to the fire, I've noticed that on the dynos that I've seen, the vertical title says "SAE horsepower." Is there some difference amongst the SAE horsepower, and other horsepower numbers (Like the 200 hp that's listed in the brochure).

 

Dan and Zixor...
thx for the great info^^

one more question, how about the TQ, do i multiply it by the same number used for HP?

 

Horsepower = torque x rpm / 5252

So you can sub the right side of that equation in anywhere there is HP, same for WHP. In essence, yes multiply by the same factor.

As for SAE HP and Torque, I believe they are "SAE Corrected" HP and Torque. A dyno can vary based on the sea level, air conditions, etc. I think the software takes that into effect using a formula and puts out SAE Corrected numbers.