The Screaming Honda VTEC Engine
11-20-2000, 08:43 PM
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"The Screaming Honda VTEC Engine"
by Kevin Cameron,
Technical Editor - Cycle World Magazine
ROAD & TRACK MAGAZINE, September 1999, Page 79.
"Whether you see it as 120 horsepower per liter, or as 2 horsepower per cubic inch, the engine in Honda's new S2000 sports car makes a lot from a little. Consider the numbers: 240 bhp from two liters and four cylinders, with an astounding 9000-rpm redline.
Think about it--9000 rpm. It would be easy to suspect that Honda's motorcycle experience is at work here--motorcycle engines, after all, do employ high rpm. But a closer inspection reveals a distinctly automotive design.
For instance, motorcycle engines can reach high revs safely because they have very short strokes--a typical bore would be 72.0 x 46.0 mm, for a bore-stroke ratio of 1.5-1.6. Because of emissions considerations, production automobile engines cannot have such extreme ratios. The S2000 measures 87.0 x 84.0 mm, for a bore-stroke ratio of 1.04--pretty much modern automotive practice.
To achieve a high compression ratio with their short strokes, motorcycle engines must use a nearly flat combustion chamber. Because of this, their intake and exhaust valve stems are set at narrow angles of between 20 and 25 degrees. But with such a narrow valve angle, the S2000 (with its longer stroke) would give an excessive compression ratio. Therefore a wider 51-degree valve angle gives this 11.7:1 compression ratio engine a deeper automotive pent-roof combustion chamber shape. As with all current high-output engines on two or four wheels, individual intake runners are used, with steeply downdraft straight intake ports.
Now for the surprises. To reach its horsepower goal, the S2000 has to rev, but the combination of 8300 rpm at peak power and its long 84.0-mm stroke result in a very high piston speed. Piston speed is how far each piston travels in one minute--twice the stroke in feet, multiplied times the rpm. For many years, a piston speed of 4000 feet per minute (fpm) was considered to be some kind of limit. Although Formula 1 engine bore and stroke are no longer published, their current maximum piston speeds are likely in the range of 4500-5000 fpm. When we do the numbers for the S2000, we find its pistons stroking out a racy 4575 fpm at peak power (8300 rpm), and a whacking great 4960 fpm at the 9000-rpm redline. These F1-type numbers in a production engine show Honda isn't shy about pushing the envelope.
How can they do this? There is in fact no "limiting piston speed," as rpm capability has been steadily pushed upward by ever-improving materials and thorough development. Honda has used premium pieces to make the S2000's high piston speed practicable; heat-treated and surface-carburized forged
alloy steel crankshaft and connecting rods, with tough forged aluminum pistons. The great majority of production engines use cast cranks and either cast or sintered metal powder connecting rods, with cast pistons. Cast parts offer excellent value for moderate duty, but are unsuited to maximum stresses. To support the S2000's crankshaft loads, all five main bearing caps are incorporated into a single, rigid girdle casting. This kind of construction can be found in both motorcycle engines and automotive racing engines.
Although motorcycle engines led 4-stroke design through the Sixties, the leading edge today is defined by Grand Prix race-car engine technology. While 15,000 rpm is a usual redline for a 750-cc 4-cylinder Superbike race engine, F1 3-liter V-10s are redlined at 17,000-18,000--and Honda has plenty of experience in both disciplines. But while the S2000's high piston speed seems bold, realize that a production car engine--even driven hard--accumulates very little total time near peak rpm.
Another problem in making a lot of power from small engines is powerband width. The duration of time that the valves must be open for good power at peak revs is too long to also do so at the bottom and mid-rpm ranges, so acceleration suffers. Shorter timing improves acceleration, but wheezes out on top end. Honda's answer is its VTEC variable valve timing system, versions of which we've now seen for years in other Honda models. At lower rpm, each cylinder's four valves are operated by lower-lift, shorter-duration cam profiles, giving good cylinder filling and strong acceleration. When the engine approaches 6000 rpm, valve control is switched to longer-duration, high-lift cam profiles, providing the airflow required for peak power. The resulting torque curve is stair-stepped; the portion below 6000 is lower because valve lift is less in this under-6000 region. To compensate, a 6-speed gearbox is provided. And again, the transmission's design is decidedly automotive (that is, non-motorcycle) in nature; the light weight of a motorcycle allows its engine to pull a fairly tall 1st gear, while the S2000's 1st gear must be low to accelerate a car's substance.
Finally, you may reasonably ask, Why work so hard to get this power from only two liters? The answer is that a sports car should be small and light, and this requires an equally small, light engine. Extra fat in the engine requires extra fat everywhere else--transmission, wheels, tires, brakes and chassis. This is a spiral that has resulted in plenty of "sports cars" that weigh 3600 lb. or more. Only tight design discipline can avoid this, and that means, among other things, getting maximum power from minimum metal--exactly what Honda has done with the S2000's engine."
by Kevin Cameron,
Technical Editor - Cycle World Magazine
ROAD & TRACK MAGAZINE, September 1999, Page 79.
"Whether you see it as 120 horsepower per liter, or as 2 horsepower per cubic inch, the engine in Honda's new S2000 sports car makes a lot from a little. Consider the numbers: 240 bhp from two liters and four cylinders, with an astounding 9000-rpm redline.
Think about it--9000 rpm. It would be easy to suspect that Honda's motorcycle experience is at work here--motorcycle engines, after all, do employ high rpm. But a closer inspection reveals a distinctly automotive design.
For instance, motorcycle engines can reach high revs safely because they have very short strokes--a typical bore would be 72.0 x 46.0 mm, for a bore-stroke ratio of 1.5-1.6. Because of emissions considerations, production automobile engines cannot have such extreme ratios. The S2000 measures 87.0 x 84.0 mm, for a bore-stroke ratio of 1.04--pretty much modern automotive practice.
To achieve a high compression ratio with their short strokes, motorcycle engines must use a nearly flat combustion chamber. Because of this, their intake and exhaust valve stems are set at narrow angles of between 20 and 25 degrees. But with such a narrow valve angle, the S2000 (with its longer stroke) would give an excessive compression ratio. Therefore a wider 51-degree valve angle gives this 11.7:1 compression ratio engine a deeper automotive pent-roof combustion chamber shape. As with all current high-output engines on two or four wheels, individual intake runners are used, with steeply downdraft straight intake ports.
Now for the surprises. To reach its horsepower goal, the S2000 has to rev, but the combination of 8300 rpm at peak power and its long 84.0-mm stroke result in a very high piston speed. Piston speed is how far each piston travels in one minute--twice the stroke in feet, multiplied times the rpm. For many years, a piston speed of 4000 feet per minute (fpm) was considered to be some kind of limit. Although Formula 1 engine bore and stroke are no longer published, their current maximum piston speeds are likely in the range of 4500-5000 fpm. When we do the numbers for the S2000, we find its pistons stroking out a racy 4575 fpm at peak power (8300 rpm), and a whacking great 4960 fpm at the 9000-rpm redline. These F1-type numbers in a production engine show Honda isn't shy about pushing the envelope.
How can they do this? There is in fact no "limiting piston speed," as rpm capability has been steadily pushed upward by ever-improving materials and thorough development. Honda has used premium pieces to make the S2000's high piston speed practicable; heat-treated and surface-carburized forged
alloy steel crankshaft and connecting rods, with tough forged aluminum pistons. The great majority of production engines use cast cranks and either cast or sintered metal powder connecting rods, with cast pistons. Cast parts offer excellent value for moderate duty, but are unsuited to maximum stresses. To support the S2000's crankshaft loads, all five main bearing caps are incorporated into a single, rigid girdle casting. This kind of construction can be found in both motorcycle engines and automotive racing engines.
Although motorcycle engines led 4-stroke design through the Sixties, the leading edge today is defined by Grand Prix race-car engine technology. While 15,000 rpm is a usual redline for a 750-cc 4-cylinder Superbike race engine, F1 3-liter V-10s are redlined at 17,000-18,000--and Honda has plenty of experience in both disciplines. But while the S2000's high piston speed seems bold, realize that a production car engine--even driven hard--accumulates very little total time near peak rpm.
Another problem in making a lot of power from small engines is powerband width. The duration of time that the valves must be open for good power at peak revs is too long to also do so at the bottom and mid-rpm ranges, so acceleration suffers. Shorter timing improves acceleration, but wheezes out on top end. Honda's answer is its VTEC variable valve timing system, versions of which we've now seen for years in other Honda models. At lower rpm, each cylinder's four valves are operated by lower-lift, shorter-duration cam profiles, giving good cylinder filling and strong acceleration. When the engine approaches 6000 rpm, valve control is switched to longer-duration, high-lift cam profiles, providing the airflow required for peak power. The resulting torque curve is stair-stepped; the portion below 6000 is lower because valve lift is less in this under-6000 region. To compensate, a 6-speed gearbox is provided. And again, the transmission's design is decidedly automotive (that is, non-motorcycle) in nature; the light weight of a motorcycle allows its engine to pull a fairly tall 1st gear, while the S2000's 1st gear must be low to accelerate a car's substance.
Finally, you may reasonably ask, Why work so hard to get this power from only two liters? The answer is that a sports car should be small and light, and this requires an equally small, light engine. Extra fat in the engine requires extra fat everywhere else--transmission, wheels, tires, brakes and chassis. This is a spiral that has resulted in plenty of "sports cars" that weigh 3600 lb. or more. Only tight design discipline can avoid this, and that means, among other things, getting maximum power from minimum metal--exactly what Honda has done with the S2000's engine."
11-20-2000, 09:03 PM
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Thanks S2000 Driver -
This is a great read. Pretty cool. 2 monthes ago, when I was in Waterford Raceway (little 1.4mile track outside Detroit, MI). We were talking about car weight. It was with Shelby club event. So, you can imaging big Mustang GT and Mustang Cobra weight around 3400lb stock. They told me with racing tires in Waterford, the tire only last about 2 track days worth of 6 hours of seat time.
Now, the other guy with a Caterham 7 with Vauxhal(speeling?) engin. He is using Kumho Vector tires, 6 events later, he is still on the same set of tires.
Buttom line, weight counts. The more weight you save, the easier it is on your wallet.
Having fun tracking the S2K if you have a chance. In the mean time, I will see all of you guys on the track next year. Look out for my S2K next year.
This is a great read. Pretty cool. 2 monthes ago, when I was in Waterford Raceway (little 1.4mile track outside Detroit, MI). We were talking about car weight. It was with Shelby club event. So, you can imaging big Mustang GT and Mustang Cobra weight around 3400lb stock. They told me with racing tires in Waterford, the tire only last about 2 track days worth of 6 hours of seat time.
Now, the other guy with a Caterham 7 with Vauxhal(speeling?) engin. He is using Kumho Vector tires, 6 events later, he is still on the same set of tires.
Buttom line, weight counts. The more weight you save, the easier it is on your wallet.
Having fun tracking the S2K if you have a chance. In the mean time, I will see all of you guys on the track next year. Look out for my S2K next year.
11-20-2000, 11:12 PM
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What a great article! I love reading the incredible engineering details behind our marvelous engine!
It's the engine that is truly the soul of this fine car! Even with it's stunning styling, it's razor sharp handling and it's practically purpose-built design, with a 3.0 liter, six cylinder engine it might have ended up being "just another sports car".
It's the engine that is truly the soul of this fine car! Even with it's stunning styling, it's razor sharp handling and it's practically purpose-built design, with a 3.0 liter, six cylinder engine it might have ended up being "just another sports car".
11-20-2000, 11:19 PM
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Stealthy_S2K, Waterford Hill is where I first developed my appreciation for sports cars.
I grew up in Detroit and naturally was weaned on muscle cars, going to my first drag race at Detroit Dragway (long defunct) when I was in grade school in the early 60's.
When I was in high school, a friend's brother-in-law owned a Porsche 356 and he took us out to Waterford Hills to watch the sports car races. I was hooked. I immediately gave up my interest in drag racing and I've been interested in sports cars ever since!
I grew up in Detroit and naturally was weaned on muscle cars, going to my first drag race at Detroit Dragway (long defunct) when I was in grade school in the early 60's.
When I was in high school, a friend's brother-in-law owned a Porsche 356 and he took us out to Waterford Hills to watch the sports car races. I was hooked. I immediately gave up my interest in drag racing and I've been interested in sports cars ever since!
11-21-2000, 06:07 AM
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Please contact the Society for Automotive Engineers (SAE) at (724) 776-4841 and ask them for Paper Number 2000-01-0670 "Development of the High-Power, Low Emission Engine for the 'Honda S2000'" by Honda R&D Co., Ltd. It's a VERY interesting read...
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11-21-2000, 09:53 AM
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You can also go to the SAE Web site, www.sae.org and order it. It is available by mail, fax or downloadable as a PDF document.
I'd post the direct link to the order page, but they use a Java servlet and there is no direct link. You can search for it, just type in "S2000" in the search box, or use the document number "2000-01-0670".
I'd post the direct link to the order page, but they use a Java servlet and there is no direct link. You can search for it, just type in "S2000" in the search box, or use the document number "2000-01-0670".
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