25psi

OHV engines have the camshaft below the cylinder head, and thus use lifters and pushrods to help actuate the valves that are in the cylinder head. Compared to OHC engines, they allow for better packaging, but are less efficient compared to OHC designs due to increased valvetrain mass. To open a valve, the camshaft pushes on a lifter, which pushes a pushrod, which pushes on a rocker am, which opens the valve. OHC engines don't have the weight of the pushrod to overcome. While the weight of a pushrod & lifter is seemingly insignificant, when you consider it can account for more than 15% of the valvetrain mass, and it has to open a valve up to 6000 times a minute (or more), it adds up to measurable difference. It's all about inertia - the less weight it has to move, the less energy is required to open the valve, and thus, there is more energy that can be transferred to the crankshaft - meaning more HP to the wheels.

What makes the OHV design look efficient on paper, has relatively nothing to do with the design of the motor, but moreso with the transmissions gearing. Given equal displacement DOHC will make more power 99% of the time over a wider rpm range.

Porsche 3.6 liter - 415hp n/a
M5 5.0 liter 500hp
Viper(range) 8-8.3 liter 500hp-600hp
350z 3.5-3.7 liter 332hp
ls1 5.7 liter 350hp

Secondly, DOHC allows you to utilize VVT on both intake and exhaust side of the cams.

The Manalishi

iTrader: (3)

OHC engines are also OHV engines. OHV means that the valves are over the piston, not next to it in the block, like a flathead. Most people, including manufacturers, use the same definition you did but in actuality its not accurate. But yea OHC engines are usually more efficient than conventional cam in block engines.

GMmexican

iTrader: (7)

I think the viper motor is a bad example since it is an 8.3 liter v-10 with no vvt....in terms of power to weight ratio

LS1LT1

iTrader: (16)

Ok, we covered the horsepower end of that spectrum.
Now let's talk about torque.

Irunelevens

I don't know why you feel compelled to turn everything into an attempted personal attack. I've driven (on a regular basis) mod motors, LT1s, LS1s, VQ30DEs, crappy pushrod Ford V6s, several Honda 4cyls, Honda V6s, etc. Not every car can have a V8, which is where most of the motors on that list come into play. You say you would "take an lsx over any of them," but with most of those cars it's not even an option. And I do know about long term performance/reliability and cost of ownership/maintenance, thank you very much. I know that I BOUGHT my first car ('94 Integra GS-R) with 134k miles on it with absolutely no qualms. Sold it @ 193k miles, and the only maintenance that had to be done on the car the whole time was a new clutch and a timing belt. And then I know about my mom's old LT1 Vette that had the transmission blow @ 114k miles (which the mechanic said was "about right"), and then the Optispark went south. And yes the transmission on my sister's '99 TL went bad @ 97k miles, but it was covered by Honda. So my experience with some of these "high-tech" motors is that they are VERY good. Just like the LSx is very good, for different reasons.

Edit: And I am in NO way a "Ford guy." I'm pretty sure we've been over this before.

texas94z

Totally true, Cadillac line represents the best of the best from GM and the competitors obviously figured out a way to beat GM/Cadillac. Cadillac a few years ago was a boring brand. Cadillac is becoming the standard of the world again if they keep up the good work.

LS1LT1

iTrader: (16)

The new CTS-V (even the entire CTS line in general) is an amazing performance/sports sedan.

texas94z

Of course, its a 4 door vette. The cts was a breakthrough for Cadillac.

25psi

The Viper does have VVT.

25psi

What about it? If we're comparing displacement in terms of power/torque then your argument is mute. Considering the examples that I gave you, I think the correlation should be hp to weight.

XxGarbSxX

If HP/L wasn't used as a basis for taxation in Europe, do you really think that the European automakers would have made the decisions they've made and gone down the path that they've gone down? HP/L is a nice number to look at on paper, but it's absolutely meaningless in the real world.

I'm sure the M5's 5.0L V10 is considerably larger and heavier than the LS7 in the Z06. Each has roughly the same output, but which engine has the advantage? The LS7. It's smaller, lighter, and slightly more powerful.

Also, I think you made an error with your valve openings per minute calculation. Each valve opens once for every 2 revolutions the engine makes. Not sure what pushrod engine you're spinning to 12k.

25psi

OF course the M5 would be larger and heavier considering it is a V10. The point I'm trying to advocate here is, the use of technology to overcome displacement. Given the same displacement, DOHC motors will make more power over a broader rpm range.

XxGarbSxX

The ONLY advantage OHC has over pushrods is that it's easier for the engine to rev higher due to a lighter valvetrain. For the same displacement, pushrod engines are smaller and lighter. With a good head and the right cam, you can make the same power as an OHC engine up to 6000-6500rpm before the valvetrain starts to become a considerable limitation. The way I see it, there's no reason to have, for a street application, an engine that revs to 9000rpm to make X hp when you can use a little bit more displacement and/or forced induction to make the same horsepower at a lower rpm. There is no bad aspect to having an engine that is physically smaller and lighter with the same power numbers.

And for all that technology that BMW used to get 500hp out of their 5.0L V10, it still gets 12/18 mpg. There's no official mileage figures out for the 6.2L supercharged CTS-V, but I'd be willing to bet that it gets a bit more than 12/18, and with 50 more horsepower to boot.

I'll reiterate. The only real reason that European auto manufacturers build small displacement high revving engines is to minimize taxes while not being unbearably slow.

25psi

The gas mileage has more to due with the trans being 1:1 in 4th and for allowing 5th and 6th gears to be over drives. This is what you sacrifice when doing this(BMW has 60 more hp, but 700lbs more weight):

http://www.youtube.com/watch?v=9_QpKNozKN0

The reason why its best to have torque in the higher rpms(more hp), instead of down low is to take advantage of gearing.

And if pushrod motor where so efficient, why hasn't GM or Dodge incorporated this into their 4cyl motors? Why does the new Caddy(6cyl) have DOHC?

JD_AMG

Pushrod engines are more efficient only on V-engines, I hope to god you have figured this out by now.
And GM themselves have stated they have OHC v-engines as marketing:
http://www.caranddriver.com/features...its_due_column

25psi

Its not the motor that makes the mpg efficient, its the gearing of the trans!

Are you forgetting that the LT5 was the motor of the day in the Vette.

1990-92 1993-1995

SAE Net Power 375 hp @ 6,000 rpm 405 hp @ 5,800 rpm
SAE Net Torque 370 ft lbs @ 4800 rpm 385 ft lbs @ 4800 rpm
Compression Ratio 11:1 11:1


Big numbers for 18 yrs ago

JD_AMG

Did I say anything about gas mileage?
LT5 - 405hp/385ft.lbs 630lbs
LS6 - 405hp/400ft.lbs 390lbs
Oops...
Do you want to talk about cost and physical size too? There is a reason they stuck with the pushrod engine...

25psi

Where are the weights for the motors? Link? What about cost? The Z06 is 70k new and the ZR1 is 120k new. I don't think cost is that much of an issue considering the cost of the cars. Again, given the same displacement DOHC will make more power, torque throughout a longer rpm range.

XxGarbSxX

I think that's more a result of the camming and, to a lesser extent, 4 valves per cylinder.

1 cam, 1 cam gear, 1 timing chain, 16 pushrods, and 16 valves are cheaper than 4 cams, 4 cam gears, 2 (much longer) timing chains, and 32 valves. How much more would the Z06 and ZR1 have been if they used OHC engines? Not sure, but it certainly would have been more. And how can you say cost was not much of a factor? Cost is always a factor, especially for the Corvette which is known for its bang per buck. You can only engineer what the accounting department will pay for.

25psi

The price can be negated if the production numbers are there. Supply and Demand can cut the cost down significantly.

Its deeper than just 4 valves per cylinder. Its the ability to change cam timing on both the intake and exhaust cams. Therefor a higher degree of tuning can be implimented. You also have a more efficient combustion since the spark plug is placed in the middle of the combustion chamber.