"PS9" (PS9)
02/09/2014 at 12:24 • Filed to: None
2
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"PS9" (PS9)
02/09/2014 at 12:24 • Filed to: None | 2
| 16 |
1. GM. 2. Chrysler. 3....
...Bentley!
Ravey Mayvey Slurpee Surprise
> PS9
02/09/2014 at 12:28 |
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Bentley's V8 is pretty old school. Which is awesome.
Brian Silvestro
> PS9
02/09/2014 at 12:36 |
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Those engines last forever. They're built so meticulously.
Joe_Limon
> PS9
02/09/2014 at 12:39 |
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Catepillar!
Arch Duke Maxyenko, Shit Talk Extraordinaire
> PS9
02/09/2014 at 12:55 |
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Shouldn't a pushrod V8 be more efficient than a DOHC as there is less parasitic power loss from rotating mass? Cam shafts are not the lightest things in the world.
Somethingwittyer likes noisy
> PS9
02/09/2014 at 13:13 |
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Huh. The more you know.
JR1
> Arch Duke Maxyenko, Shit Talk Extraordinaire
02/09/2014 at 13:19 |
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Pushrods do allow for a lower center of gravity and a lower hood. Better center of gravity.
1337HPMustang
> Arch Duke Maxyenko, Shit Talk Extraordinaire
02/09/2014 at 13:20 |
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I can't imagine driving a camshaft takes much power at all. Also OHC engines have less mass to move (no rockers or rods) per cam so the differences would be minimal I'd imagine. I've got a sohc v8 in my stang so I'm just being a ford engine aficionado.
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Arch Duke Maxyenko, Shit Talk Extraordinaire
> 1337HPMustang
02/09/2014 at 13:29 |
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Rods and rockers weigh less than a cam and then there is the timing chain, those aren't moved for free.
Danimalk - Drives a Slow Car Fast
> PS9
02/09/2014 at 13:50 |
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Pushrod all the things!!
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1337HPMustang
> Arch Duke Maxyenko, Shit Talk Extraordinaire
02/09/2014 at 14:22 |
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Yeah I guess so. Still they can't be more efficient since they're pretty much limited to 2 valves per cylinder, right? It'd be interesting to have two engines, all things being equal except one is a 2V ohv and the other a 3V SOHC
The WB
> PS9
02/09/2014 at 14:52 |
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I don't know people think pushrods are bad. OHC tech is not any "newer" than the pushrod V8, and in a fit-for-purpose scenario (big displacement, low revving engine) there is no reason not to make a valid design choice like a pushrod operated valvetrain. It is cheaper, more robust, and less complex.
jdrgoat - Ponticrack?
> The WB
02/09/2014 at 15:24 |
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In fact, OHC is an older technology than OHV. And, depending on your definition of high revving, pushrods aren't lacking too far in production cars these days.
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The WB
> jdrgoat - Ponticrack?
02/09/2014 at 15:26 |
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Agreed. Ford sent themselves back a decade in the 90's when they started playing with OHV, and lost a lot of ground to Chevy who kept with the pushrods. They've only just caught up in terms of performance, and they still cost more.
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jdrgoat - Ponticrack?
> 1337HPMustang
02/09/2014 at 16:10 |
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No reason that a pushrod engine would be limited to 2V. There are plenty of examples of multivalve pushrod engines. The example that springs to mind has a single lobe for the pair of valves (either intake or exhaust), and a rocker that's v-shaped to open the pair of valves with one pushrod.
Another thing I've seen is a SOHC 1 cylinder engine, that had but two lobes on the camshaft, and the same v-shaped rockers to open the 4 valves.
I can't think of an example in a passenger car, however.
Jedidiah
> 1337HPMustang
02/09/2014 at 17:07 |
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Oldsmobile experimented with multiple valves and OHC in the early 70s. They found out that multiple valves did no better than 2 large valves at maximum lift, but a greater number of smaller valves improved flow while approaching max lift.
They made a pushrod big block called the W-43 with four valves per cylinder and a pentroof combustion chamber and then they made a DOHC big block called the OW-43.
Here's an article about the engines. There is another article that talks about a silver 442 blowin the doors off people late at night and they never opened the hood.
LSXforYourSuperCar
> PS9
02/09/2014 at 20:36 |
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It boggles my mind why DOHC engines are considered to be automatically the most efficient engine type.
After heat loss, pumping loss is the greatest barrier to good BSFC (search it on wiki, i don't care to explain it again).
Pumping loss is the energy required to move the air from the atmosphere into the engine, and then of course a four stroke engine needs to pump-out the exhaust at the same or greater speed. It's like how aerodynamics requires double the horsepower to go from 190 mph to 201, it takes exponentially more energy to try to move fast moving air, slightly faster.
You see, a small engine producing 500hp will suffer more parasitic pumping loss than a large engine producing 500hp, because the larger engine does not need to move the air from the intake to exhaust so quickly. Haste makes waste