Food for thought
07-04-2010, 01:18 PM
#1
Drifting
Thread Starter
Member Since: Feb 2002
Location: Chapel Hill NC
Posts: 1,260
Likes: 0
Received 0 Likes
on
0 Posts
Food for thought
http://www.roadandtrack.com/auto_news/tech/rival-vees
Comparison of Ford 5lt and Chevy 6.2lt. Interesting to those who speculate on overhead cams in the new 5.5lt engine. It isn't going to happen!
"Both engines are all-aluminum 90-degree V-8s. Both use composite intake manifolds, coil-on-plug ignition and returnless, multiport fuel injection. Neither engine employs direct fuel injection—yet. Both engines boast roller rocker arms, both engines have rollers where the camshaft(s) meet the rest of the valvetrain, and both hydraulically adjust their valve lash. Variable cam timing is a feature on each, and neither cuts cylinders for fuel economy reasons.
Bowtie Bruiser
The more senior engine is Chevrolet’s LS3. Measuring a generous 6.2 liters or 376 cu. in., the LS3 is a direct descendant of the hallowed small-block Chevy V-8 introduced in 1955. While it shares only its fundamental 90-degree vee angle, 4.4-in. (112-mm) bore spacing and overhead valve layout with its predecessor, the LS3 benefits from 55 years of Chevrolet pushrod V-8 production and racing experience. We first saw this latest iteration of the small-block in the 2008 Corvette.
While it’s fashionable to decry the Chevy’s pushrod layout as antiquated, it has many inherent advantages. With only one camshaft nestled deep in the block, the engine is physically compact—the LS3 packs massive cubic displacement in considerably less volume than the sprawling Coyote with its large cylinder heads. Immediately, the LS3 is ahead where it counts most: power. Bigger engines generally make more power with less trouble and more durability than smaller engines, and that’s especially true when comparing the LS3’s 426 bhp at 5900 rpm to the Coyote’s 412 bhp at 6500. For the record, the LS3’s torque peak of 420 lb.-ft. is reached at 4600 rpm, whereas the Coyote’s 390 lb.-ft. arrives at a lower 4250 rpm, thanks in part to its dual variable valve timing. As a more physically compact powerplant than the Ford, the LS3 can be employed in a smaller car, while also allowing for more working room in an existing engine compartment.
With its cam in the block and pushrod/rocker-arm valves, Chevrolet’s LS3 V-8 is more compact than Ford’s dohc V-8. Almost as important, the 2-valve Chevy’s single-cam valvetrain has many fewer parts than the Ford’s jewelry store of valves, springs, rocker arms, lash adjusters, cams, phasers, pulse wheels, timing chains and tensioners. Fewer parts means less cost—always a good thing—and fewer parts can also translate into less weight. What weight the LS3 has is centered lower in the engine than in the taller Ford with its four steel cams, wider heads and four cam phasers sitting high and wide. There’s a definite handling advantage to having a lower center of gravity.
One benefit of the pushrod valvetrain, which the current LS3 does not take advantage of, is cylinder deactivation, or Active Fuel Management as Chevy calls it. The long travel inherent in a pushrod engine’s hydraulic lifters makes this easy, but Chevy has found the mechanical connection provided by the LS3’s manual transmission’s clutch telegraphs too many vibrations during transitions and 4-cylinder operation. The almost identical LS99 engine used in automatic-transmission Camaros does employ AFM, however.
Chevrolet’s compact LS3 V-8 has a cast-aluminum block, the valley of its vee filled with a hollow camshaft and valvetrain components. Pressed-in cast-iron liners are used in the cylinder bores. Negatives for the pushrod LS3? They also center on the valvetrain and its high reciprocating mass. With just two of them per cylinder, the LS3’s valves need to be large and the pushrods and sizable hydraulic roller lifters add to the top end’s weight. All together, this added mass asks much of the valve springs. Even with Chevy going to the expense of hollow intake-valve stems, the LS3 is limited to 6600 rpm, and to spin the engine any higher would require either prohibitively heavy valve spring pressures that usurp power and stress these components, or pricey titanium valves.
Furthermore, with one camshaft it is difficult to vary the intake and exhaust valve timing independently. The four camshafts in the 5.0-liter Ford make wildly varying cam timing easy, although the calibration engineers who must write the engine management software might disagree. Simple or not, this ability to customize the valve events for everything from idle to max power contributes greatly to the Ford’s efficiency.
Dearborn Howler
Ford’s aluminum block, also with pressed-in iron cylinder liners, promotes even cylinder temps via piston oil squirters and an optimized water jacket. When Ford’s engineers penned the 5.0-liter TiVCT V-8, their only constraints were to use the hugely expensive machine tools already on-hand in Ford’s engine plants. Management had also decreed that the new engine, known internally as the Coyote, would not, at least at first, use EcoBoost, Ford’s combination of turbocharging and direct fuel injection.
Practically speaking, this stunted the Coyote’s bore size because of the production machinery’s limitations of a 3.937-in. (100-mm) bore spacing. However, because the historically significant 5.0-liter (302 cu. in.) displacement was reachable with the tight 3.623-in. (92.2-mm) bore (and because the engineers had free reign to design for maximum efficiency), this was hardly a disqualifying limit.
Airflow is key to maximum efficiency, and the Coyote obliges with a take-no-prisoners 4-valve cylinder head that outflows any mainstream production car head. Matter of fact, the Coyote head shames many race cylinder heads. With its outstanding breathing, light reciprocating parts, excellent high-rpm oiling, intricate headers and other attributes, the Coyote easily hits 7000 rpm and 412 bhp. That’s 1.4 horsepower for each of its 302 cu. in. (The LS3 manages a still respectable 1.1 bhp per cu. in.)
Besides yielding such superior breathing, the Coyote’s overhead cam layout frees the engineers from accommodating pushrods. Thus, the all-important intake and exhaust ports can be more ideally shaped, and the water jacket optimized for even cooling across the heads. This lessens cylinder-to-cylinder temperature variation, supporting more aggressive tuning.
As noted, the Coyote’s 4-cam layout allows tremendous opportunities in variable valve timing. This let Ford engineers tune the Coyote for power—it has quite aggressive camming—then de-tune it on the fly for cruising economy whenever maximum power is not required.
Of course, the Coyote’s many but tiny valves pose little challenge to the valve springs, so the 5.0-liter is a carefree revver. Again, this means more power up high and less fuel burn at cruising rpm because there’s less displacement to feed. For at least partial proof, consider the Camaro SS’s EPA ratings are 16 mpg city/24 mpg highway, while the lighter, smaller-engine Mustang GT ekes out 17 mpg city/26 mpg highway. The reality here: The Mustang GT accelerates about as fast as the more powerful Camaro SS, but gets better fuel economy.
Dual independently variable valve timing allows the dohc Ford V-8 to tune for economy or power, whatever the driver demands. The price Ford paid for their more efficient V-8 was physical bulk—the Coyote looks more like a big block than a 5.0-liter when stuffed in the Mustang. It’s also more costly to build than the old sohc 4.6-liter V-8.
All this aside, determining which engine is superior depends on what you value. To many, “there ain’t no replacement for displacement,” as the old hot rodder’s creed goes. And true to form, the pushrod Chevy offers a welcome torque hit down low and some freedom from shifting. On the other hand, as fuel prices rise, the Ford’s inherent efficiency is compelling, and in this league any bump in fuel economy is a boon.
For further argument, consider Chevy’s Camaro V-6, which, like the Mustang’s, follows the many cams, many valves school. So when efficiency counts, Chevy also votes for mechanical sophistication. When cubic inches count, Ford discards some cams and valves. Just look at the new 2-valve 6.2-liter sohc V-8 found in the F-150 SVT Raptor, which is also the base engine in Ford’s F-250/350 pickups.
Of course, for perpetuating a V-8 rivalry, having two different engines in the pony car arena is a godsend. Each side has legitimate bragging rights, and each powerplant has the sophistication needed to ensure a V-8-powered pony car future. But when it comes to side-by-side contests between these two modern pony cars with their very different V-8s, it all boils down to this: personal preference and how much talent you have behind the wheel."
Comparison of Ford 5lt and Chevy 6.2lt. Interesting to those who speculate on overhead cams in the new 5.5lt engine. It isn't going to happen!
"Both engines are all-aluminum 90-degree V-8s. Both use composite intake manifolds, coil-on-plug ignition and returnless, multiport fuel injection. Neither engine employs direct fuel injection—yet. Both engines boast roller rocker arms, both engines have rollers where the camshaft(s) meet the rest of the valvetrain, and both hydraulically adjust their valve lash. Variable cam timing is a feature on each, and neither cuts cylinders for fuel economy reasons.
Bowtie Bruiser
The more senior engine is Chevrolet’s LS3. Measuring a generous 6.2 liters or 376 cu. in., the LS3 is a direct descendant of the hallowed small-block Chevy V-8 introduced in 1955. While it shares only its fundamental 90-degree vee angle, 4.4-in. (112-mm) bore spacing and overhead valve layout with its predecessor, the LS3 benefits from 55 years of Chevrolet pushrod V-8 production and racing experience. We first saw this latest iteration of the small-block in the 2008 Corvette.
While it’s fashionable to decry the Chevy’s pushrod layout as antiquated, it has many inherent advantages. With only one camshaft nestled deep in the block, the engine is physically compact—the LS3 packs massive cubic displacement in considerably less volume than the sprawling Coyote with its large cylinder heads. Immediately, the LS3 is ahead where it counts most: power. Bigger engines generally make more power with less trouble and more durability than smaller engines, and that’s especially true when comparing the LS3’s 426 bhp at 5900 rpm to the Coyote’s 412 bhp at 6500. For the record, the LS3’s torque peak of 420 lb.-ft. is reached at 4600 rpm, whereas the Coyote’s 390 lb.-ft. arrives at a lower 4250 rpm, thanks in part to its dual variable valve timing. As a more physically compact powerplant than the Ford, the LS3 can be employed in a smaller car, while also allowing for more working room in an existing engine compartment.
With its cam in the block and pushrod/rocker-arm valves, Chevrolet’s LS3 V-8 is more compact than Ford’s dohc V-8. Almost as important, the 2-valve Chevy’s single-cam valvetrain has many fewer parts than the Ford’s jewelry store of valves, springs, rocker arms, lash adjusters, cams, phasers, pulse wheels, timing chains and tensioners. Fewer parts means less cost—always a good thing—and fewer parts can also translate into less weight. What weight the LS3 has is centered lower in the engine than in the taller Ford with its four steel cams, wider heads and four cam phasers sitting high and wide. There’s a definite handling advantage to having a lower center of gravity.
One benefit of the pushrod valvetrain, which the current LS3 does not take advantage of, is cylinder deactivation, or Active Fuel Management as Chevy calls it. The long travel inherent in a pushrod engine’s hydraulic lifters makes this easy, but Chevy has found the mechanical connection provided by the LS3’s manual transmission’s clutch telegraphs too many vibrations during transitions and 4-cylinder operation. The almost identical LS99 engine used in automatic-transmission Camaros does employ AFM, however.
Chevrolet’s compact LS3 V-8 has a cast-aluminum block, the valley of its vee filled with a hollow camshaft and valvetrain components. Pressed-in cast-iron liners are used in the cylinder bores. Negatives for the pushrod LS3? They also center on the valvetrain and its high reciprocating mass. With just two of them per cylinder, the LS3’s valves need to be large and the pushrods and sizable hydraulic roller lifters add to the top end’s weight. All together, this added mass asks much of the valve springs. Even with Chevy going to the expense of hollow intake-valve stems, the LS3 is limited to 6600 rpm, and to spin the engine any higher would require either prohibitively heavy valve spring pressures that usurp power and stress these components, or pricey titanium valves.
Furthermore, with one camshaft it is difficult to vary the intake and exhaust valve timing independently. The four camshafts in the 5.0-liter Ford make wildly varying cam timing easy, although the calibration engineers who must write the engine management software might disagree. Simple or not, this ability to customize the valve events for everything from idle to max power contributes greatly to the Ford’s efficiency.
Dearborn Howler
Ford’s aluminum block, also with pressed-in iron cylinder liners, promotes even cylinder temps via piston oil squirters and an optimized water jacket. When Ford’s engineers penned the 5.0-liter TiVCT V-8, their only constraints were to use the hugely expensive machine tools already on-hand in Ford’s engine plants. Management had also decreed that the new engine, known internally as the Coyote, would not, at least at first, use EcoBoost, Ford’s combination of turbocharging and direct fuel injection.
Practically speaking, this stunted the Coyote’s bore size because of the production machinery’s limitations of a 3.937-in. (100-mm) bore spacing. However, because the historically significant 5.0-liter (302 cu. in.) displacement was reachable with the tight 3.623-in. (92.2-mm) bore (and because the engineers had free reign to design for maximum efficiency), this was hardly a disqualifying limit.
Airflow is key to maximum efficiency, and the Coyote obliges with a take-no-prisoners 4-valve cylinder head that outflows any mainstream production car head. Matter of fact, the Coyote head shames many race cylinder heads. With its outstanding breathing, light reciprocating parts, excellent high-rpm oiling, intricate headers and other attributes, the Coyote easily hits 7000 rpm and 412 bhp. That’s 1.4 horsepower for each of its 302 cu. in. (The LS3 manages a still respectable 1.1 bhp per cu. in.)
Besides yielding such superior breathing, the Coyote’s overhead cam layout frees the engineers from accommodating pushrods. Thus, the all-important intake and exhaust ports can be more ideally shaped, and the water jacket optimized for even cooling across the heads. This lessens cylinder-to-cylinder temperature variation, supporting more aggressive tuning.
As noted, the Coyote’s 4-cam layout allows tremendous opportunities in variable valve timing. This let Ford engineers tune the Coyote for power—it has quite aggressive camming—then de-tune it on the fly for cruising economy whenever maximum power is not required.
Of course, the Coyote’s many but tiny valves pose little challenge to the valve springs, so the 5.0-liter is a carefree revver. Again, this means more power up high and less fuel burn at cruising rpm because there’s less displacement to feed. For at least partial proof, consider the Camaro SS’s EPA ratings are 16 mpg city/24 mpg highway, while the lighter, smaller-engine Mustang GT ekes out 17 mpg city/26 mpg highway. The reality here: The Mustang GT accelerates about as fast as the more powerful Camaro SS, but gets better fuel economy.
Dual independently variable valve timing allows the dohc Ford V-8 to tune for economy or power, whatever the driver demands. The price Ford paid for their more efficient V-8 was physical bulk—the Coyote looks more like a big block than a 5.0-liter when stuffed in the Mustang. It’s also more costly to build than the old sohc 4.6-liter V-8.
All this aside, determining which engine is superior depends on what you value. To many, “there ain’t no replacement for displacement,” as the old hot rodder’s creed goes. And true to form, the pushrod Chevy offers a welcome torque hit down low and some freedom from shifting. On the other hand, as fuel prices rise, the Ford’s inherent efficiency is compelling, and in this league any bump in fuel economy is a boon.
For further argument, consider Chevy’s Camaro V-6, which, like the Mustang’s, follows the many cams, many valves school. So when efficiency counts, Chevy also votes for mechanical sophistication. When cubic inches count, Ford discards some cams and valves. Just look at the new 2-valve 6.2-liter sohc V-8 found in the F-150 SVT Raptor, which is also the base engine in Ford’s F-250/350 pickups.
Of course, for perpetuating a V-8 rivalry, having two different engines in the pony car arena is a godsend. Each side has legitimate bragging rights, and each powerplant has the sophistication needed to ensure a V-8-powered pony car future. But when it comes to side-by-side contests between these two modern pony cars with their very different V-8s, it all boils down to this: personal preference and how much talent you have behind the wheel."
07-06-2010, 05:23 AM
#3
2nd Gear
Member Since: Jul 2010
Posts: 2
Likes: 0
Received 0 Likes
on
0 Posts
