Engine Output comparisons(splinter thread)

[efnfast]

Glad you admitted your head hurt, 'cause so does mine.

[Paul Workman]

Originally Posted by efnfast

Glad you admitted your head hurt, 'cause so does mine.

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).

[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.

[jss06c6]

Originally Posted by tpepmeie

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.

Todd,

Just to add a slight twist on your notes... there are indeed chassis dyno's that, when properly equipped, are capable of holding virtually any load at any RPM for tuning. We labored hard between three platforms for tuning our engines and powertrains at my new shop; Engine Dyno, Hub Dyno and Chassis Dyno. For a performance shop, after a lot of discussion, we opted for a properly equipped Chassis Dyno. The Engine Dyno is great for engine development work but requires a dedicated dyno cell with controlled air supply, exhaust and engine cooling. Obviously, it requires the engine to be pulled from the vehicle. When trying to optimize the engine performance itself, it provides the most repeatable environment for engine builds, hands down.

Hub dyno's have the ability to hold a load at very high HP/TQ ranges (in the thousands), making them great for powertrain tuning for race day. BUT, and this is a big BUT, they can be damned hard on limited slip differentials as each hub is independent, making it very hard to keep the load presented to each axle consistent, which is very risky at high HP/TQ numbers. This can lead to severe loads presented to the clutches in your diff, unless you're running spools versus differentials (NHRA class).

Properly equipped chassis dynos (large eddy brake setups) allow ease of tuning across the entire RPM/MAP table just like an engine dyno or hub dyno. This setup will hold virtually any load at any rpm for enough time to grenade the engine (not your objective!). We opted to go this route. The setup we came up with will hold up to 3,500 hp and uses drums large enough to limit slipping of the tires. We have the option of adding a second large eddy brake should we need this.

Our desire for our Dyno is for TUNING, not simply putting out a WOT number (useless in my mind).

Great dialog in this thread.. Admire your work Todd!!

Steve