Moved to The Car Lounge

[Old smart]

For "The “Car Lounge:�

“Just think about it, 290 bhp from a naturally aspirated 2500cc engine over 50 years ago. (W196) Guess what, not much progress since then. Most cars these days have to rely on turbos or s-chargers to crank out that much power/liter displacement.�

If that gets one’s attention, think about the Alfa Romeo Alfetta Tipo 158/159. By the end of its development at the beginning of the ‘50s, its 1500cc, straight-8 was producing over 400 BHP at over 9,000 RPM, though with a compound supercharger and super exotic fuel blended from methanol, castor oil, and water. I still remember hearing the screech of one (either a 158 or 159 – couldn’t tell from the blurry photo in my fathers album) as a little kid during the Korean War at one of the Royal Governor’s races at Waller Field, Trinidad, B.W.I. As I remember the story, it was then ex-works and owned by a South American mega-tycoon.

[Old smart]

“Horsepower” is over rated. But it is the number most commonly quoted – a number that is not directly measured unless you have a weight, a watch, and of course, a horse (or a herd of them). What can be measured is torque on a brake dynamometer (for us, in foot-pounds) and RPM (with a tachometer - the EU hasn't come up with a metric clock yet); horsepower is simply a derivative of those factors, times a constant.

Instantaneous (as in fleeting) British Brake Horsepower = Torque x RPM x 0.00019.

Often, manufacturer engineers test on an engine-stand dynamometer (giving power at the flywheel), and with no ancillaries attached to the engine. No driveline, no alternators, no hydraulic pumps, no A/C compressors, no belts, sometimes no water pumps. All that sapping resistance is removed for the benefit of Marketing & Sales. And if there is an opening to do so, they quote in PS or CV to get a higher number. Builders/tuners have other fish to fry.

What is more significant is torque; engine builders and tuners don’t care about BHP. What they strive for is gobs of torque with a rapid rise, then a long, high, relatively flat curve, and finally as little fall-off at high RPM as possible. That is all graphed on the dynamometer readout. But even that isn’t the whole, best answer. What is really important is the “area-under-the-curve,” the area bounded by the graph’s abscissa (x-axis), the torque curve, and on each end, ordinates (y-values) at about 1,000 RPM and “redline” RPM respectively. The value could be in square-millimeters or any other dimensional unit. (The area can be calculated with computer software, graphically with a “planimeter,” or in tabular form by Simpson’s Rule.) The greater the a-u-c, the greater the engine’s overall available power. The builder or tuner looks to do two things: increase the gross a-u-c, and form the desired profile of the torque curve. A “peaky” curve is usually not desirable unless you have a lot of transmission gear ratios available to keep the engine within a narrow range.

Torque (and BHP) can also be measured on a “chassis dynamometer.” That is with a complete vehicle with everything on it, including the driveline. It is power delivered to the driving wheels, and will always be less than flywheel power. When we were setting up the Caterham Seven on a chassis dyno (at Abacus Racing, Virginia Beach, VA), we had long, documented history that the De Dion driveline would account for 29 BHP at 5500 RPM (it varies by RPM). So our 122 at the wheels equated to 151 at the flywheel (out of a 1691cc, pushrod four). Stripped-down on a stand dyno, it would have given us a little more.

Rotary engines are difficult to directly compare. Among other things there are three power “events” in each revolution of each rotor vice one power stroke in four for a four-banger. Additional math involved for a smart three.

The reason that the Canadian CDIs are so successful in operation is big-time torque compared to their 40-or-so BHP.

[jonnysan]

Originally Posted by fishrdnc

For "The “Car Lounge:�

“Just think about it, 290 bhp from a naturally aspirated 2500cc engine over 50 years ago. (W196) Guess what, not much progress since then. Most cars these days have to rely on turbos or s-chargers to crank out that much power/liter displacement.�

If that gets one’s attention, think about the Alfa Romeo Alfetta Tipo 158/159. By the end of its development at the beginning of the ‘50s, its 1500cc, straight-8 was producing over 400 BHP at over 9,000 RPM, though with a compound supercharger and super exotic fuel blended from methanol, castor oil, and water. I still remember hearing the screech of one (either a 158 or 159 – couldn’t tell from the blurry photo in my fathers album) as a little kid during the Korean War at one of the Royal Governor’s races at Waller Field, Trinidad, B.W.I. As I remember the story, it was then ex-works and owned by a South American mega-tycoon.

Fish,
The Honda S-2000 produces 120bhp/litre of displacement with natural aspiration. Ofcourse, their tricky little V-tec has alot to do with that. Pretty slick idea, though...the V-tec.....at 4500rpm it goes off the low range cam lobes and onto the mid range cam lobes up to 6500....then off those cam lobes onto the high range cam lobes until red line of 8900-9000rpm. Very smooth, too, and to my surprise it doesn't even sound or act like it's going to come apart at red line. Electronically limited, too, so you can't overrev if you happen to miss a shift...(haven't done that yet but there is always a first time....
Fun little car to drive too. So soon I will have two fun cars to drive....

[Old smart]

Originally Posted by jonnysan

Fish,
The Honda S-2000 produces 120bhp/litre of displacement with natural aspiration.

I see the latest S2000 at 237BHP @ 7800RPM out of 2.2L. That is 108BHP/L, but still not bad. Actual road performance and tractability stems from the power-to-weight ratio (torque-to-curb weight ratio) - often overlooked. Torque, vice BHP, is the true measure as one does not drive at a engine's max RPM output, at least not if they expect the engine to last for very long.