Originally posted by nester@Apr 21 2006, 09:41 AM
Dyno Dynamics is an eddy-current dyno. It is not an inertia dyno.
Good point. My mistake.
If there is a change in hp, it's because parasitic losses are reduced - it's an underdrive pulley. OK, how about I disconnect my alternator, run total loss, give up my power steering, and disconnect the a/c compressor. Will you still say I gained hp? I didn't, I just removed the power those systems consume.
Fundamental to this: no power is gained if the engine doesn't move more air. I can play games with inertia, parasitic losses, even tire pressure, and change dyno numbers pretty easily, but they don't change the power the engine produces.
For example, way back in the 60's before most of you were conceived, Detroit published hp numbers that mathematically removed all the parasitic losses - alternator, water pump, oil pump, power steering pump, a/c - why? Because they wanted to publish the biggest number possible. Along come the Japanese in the 70's - they published BMEP - Brake Mean Effective Pressure - measured in the cylinder and integrated over time. It removes ALL losses from piston ring friction, crank and rod bearing friction, and only gives the theoretical maximum power the engine can produce. Again, the intent is to publish the biggest number.
Now we have all kinds of dynos available - inertial drum dynos, eddy current dynos, hydraulic dynos, water brakes - you name it, somebody has built a dyno around the technology.
From an engine development perspective, you want to measure at the crank. Why? Because it reduces the number of variables. Why don't we do this all the time? Because it's a bitch to get the engine out of the vehicle, mount it in a stand, hook up all the necessary control and measurement devices, and run it. It's a lot easier to hook up to a complete working car and run. Now you have a ton of variables to account for - all the accessory drives, all the interfaces between the car and the dyno (yes, if you measure on a drum type of dyno, you can get different readings just from the change in tire pressure), so you have to take the results with a grain of salt. So far, I've seen ony dyno that removes the tires from the equation - Dynapak. Everybody else is willing to accept the tire variables, but any dyno measuring with tires will show a difference based on the tire and wheel weight.
Some might say it's a better dyno, more representative of the real world, because lighter tires and wheels help you accelerate faster. Others will say, sure, that's all well and good, but it doesn't help me tune the engine if the tires are changing pressure (and they are because they are heating and cooling) while the engine is being tweaked. Which end of the telescope do you want to look down?
AFA underdrive, it may be OK, it may not. It depends on a lot of factors. It does free up horsepower. A lighter crank damper also frees up horsepower, and if it actually damps torsional vibration, then it's good. Fluidamper, ATI, and TCI ALL do this. I would recommend their products to anyone wanting more just by bolting on a part. None of these things "make" more power. Saying they make more power is the same as saying I disconnected my power steering and got 5 more hp. No, you didn't get 5 more hp, you gave up your power steering and recovered the 5 hp it takes to drive it.
I do NOT recommend solid pulleys because they do not dampen torsional vibration. Saying they do no harm is like saying, I've revved my engine to 10k rpm and nothing broke, so it must be OK. Wrong. You have no idea what parts have been compromised by this singular event, nor do you know the engine can sustain that rpm for any length of time greater than the one event you observed. Ask anyone who has done cylinder head work about valve spring failures, and you'll get the same story about natural frequency, oscillation, and catastrophic failure when you hit the "magic" rpm.
It's all simple physics.
