Engine Output comparisons(splinter thread)

[tpepmeie]

Originally Posted by Paul Workman

Yeah, I feel your pain, Steve!

IMO, the only cure is the "Keep it simple, stupid" law.

For me, that comes down to the power/torque (at the wheels) under the curve. Everything else just further confuses the issue (and the conversation goes down 'the rabbit hole', but QUICK!).

The ONLY people engine dyno numbers are important to are (automotive) engineers and salesmen (bragging rights).

Case in point: When the Japanese got into the outboard motor competition, the domestic motors couldn't keep up with the Japanese outboards. The reason came down to the fact the Japanese rated their motors at the prop shaft, whereas domestic companies went for the crankshaft value.

Same with our cars: measurements at the wheels is what is really important. It doesn't matter how (power) got there, 'it is what it is and that's all that matters (or should matter).

Paul,
ya know I love ya, man. But I have to respond to this one.

-- I can't recall ever seeing a comparison, or a even a calculation of, the area under the curve for any engine, ever. Requires integration of tq over time. And then, over what speed range? Peak Tq to Peak HP? I dunno, this isn't defined anywhere by SAE. If you have an example of such integration, please share Also, optimal gear selection can/and should be used to maximize the torque available for acceleration at the rear wheels. Dynojets pull in a constant gear, usually 1:1 (4th in our case). That's not how most people drive....

-- measuring power at the rear wheels is a valid form of comparison. But it requires so many variables to be held constant. Day-to-day, and car-to-car. Very hard to control. For instance, higher tire pressure can "cheat" the chassis dyno results by reducing friction between the tire and roller. Lower viscosity gear lube, transmission & diff. temp., even roller lubrication You get the picture. Not to mention that chassis dyno cells are often nothing more than an open bay in a workshop. They are not always (rarely?) designed to exchange the room air adequately to make sure the intake air is not contaminated.

-- 99% of chassis dynos, such as most dynojets, are inertia only. You can't expect to hold a constant speed/load point and optimize the tuning. the engine is always accelerating the roller mass (and at varying rates, at that). If that happens to match the acceleration rate for your car down the drag strip then great. Otherwise not sure it is a sound correlation to performance.

-- Most reputable race engine shops, from professional race teams to high end consumer shops, have an engine dyno to break in and calibrate their engine. And especially to do detailed development work on cams, manifolds, etc. Not to mention that OEM's also certify their engines' performance on a controlled engine dynamometer program.

Look, I like chassis dyno's as well for convenience, availability and ease of use. You can tune WOT fueling pretty well, as many do. My own testing confirmed that if configured and calibrated correctly, Dynojets can be very consistent between locations, in my case within 5 hp. But you can't deny the wisdom of using a controlled engine dyno to accurately measure the performance of a race or high performance engine.

To each his own, my friend Buy you a beer in BG if I attend.