If OHC is so great then why.....

JHZR2 · May 11, 2006

quote:

Originally posted by got boost?:

industrial engines are built to maximize fuel efficiency.

[/QB][/QUOTE]

And as I mentioned before... HONDA GX, i.e. industrial grade, professional grade small engines are OHV! This is coming from HONDA! Ditto for Robin Subaru's high end professional lines!

(and dont be mislead by the honda site.. the GC engines being OHV is a typo... read the tech sheets and specs).

Granted these are small engines, none larger than 24hp, but even Honda must realize the need for OHV in HD applications!

Though at the same time, Ford uses OHC engines in some of its HD pickup trucks...

JMH

Junior · May 12, 2006

Fuel mileage is CERTAINLY a valid way to gauge overall mechanical/thermodynamic/chemical efficiency of an engine.

------------------

I'll have to disagree with you there. Mileage is not a good way to gauage efficiency of an engine. It does not take into account the HP output of the engine. Fuel per HP hour is a more accurate way.

JHZR2 · May 12, 2006

LHV fuel in to electric power out is how we are quantifying our new advanced power systems...

This of course backs out to kg/hr fuel in compared to kWe*hr power out.

JMH

CBDFrontier06 · May 12, 2006

So which is more efficient? My roommate's Ford Sport Trac 4.0 SOHC 12 valve putting out 210 hp and getting 17 / 21 mpg, or my Nissan Frontier 4.0 DOHC 24 valve putting out 265 HP and getting 17 / 20 mpg?

Huhwhye · May 12, 2006

There are other vairables. Which is really more efficient. Can't say for sure

MPG can be affected by

Weight of vehicle
Aerodynamics
Driveline losses
Driving Style

Maybe one engine is more efficient. But then maybe one vehicle is more efficient in it's use of that engine.

robbobster · May 12, 2006

quote:

Originally posted by got boost?:

It is also not correct to equate OHC with multivalve heads, as valve actuation is totally independent of the number of valves, for example, there are many "pushrod" 4 valve per cylinder engines currently in production.

I'm not familiar with these...
Are they non-automotive applications?

G-MAN · May 12, 2006

quote:

Originally posted by robbobster:

quote:

Originally posted by got boost?:

It is also not correct to equate OHC with multivalve heads, as valve actuation is totally independent of the number of valves, for example, there are many "pushrod" 4 valve per cylinder engines currently in production.

Click to expand...

I'm not familiar with these...
Are they non-automotive applications?

I've never seen or heard of any multi-valve pushrod engines, either.

got boost? · May 12, 2006

I think you are confusing "volumetric efficiency" (the efficiency with which the engine can move the charge into and out of the cylinders)with "thermodynamic efficiency" & "mechanical efficiency" & maybe even "chemical efficiency". the volumetric efficiency is dependent on many factors, total valve area is one of them, and --all other factors being equal--, a 4 valve head will have a higher volumetric efficiency than a 2 valve head - ON THE SAME ENGINE. Ford's modular engine can not be compared to the LSx series of engines, and in fact the LSx engines likely do have higher volumetric efficiency than a normal aspiration 4 valve modular. there are several reasons for this, chief among them is the small bore of the modular engine which serves to shroud the valves. the LS7 for example has a high volumetric efficiency.

It is also not correct to equate OHC with multivalve heads, as valve actuation is totally independent of the number of valves, for example, there are many "pushrod" 4 valve per cylinder engines currently in production. the only valid point of contention between OHC and "pushrod" is mechanical efficeincy, i.e. - which one loses the most through friction - I don't know the answer to that. Most industrial/truck engines I know of are "pushrod", (even the multivalve diesels). whether this demonstrates that "pushrod" is the more mechanically efficient form of valve actuation I don't know, however, industrial engines are built to maximize fuel efficiency.

I think you were originally trying to say that DOHC engines get more work out of a gallon of gasoline than "pushrod" engines (this is also known as fuel efficiency). The answer is determined solely by the question posed in the last paragraph (which has the higher frictional losses). to say all OHC engines are more efficient than all "pushrod" engines is certainly untrue if we again compare any of the LSx engines with any of the DOHC modular engines. Fuel mileage is CERTAINLY a valid way to gauge overall mechanical/thermodynamic/chemical efficiency of an engine.

As to the nissan V6 thing, the VQ is one of the best engines on the market (might be THE best V6). But as a nissan fan (300zx turbo owner) I prefer the old iron block VG series, as those engines are capable of supporting much more power (>1000hp reliably under full power RACE conditions).

quote:

Originally posted by windnsea00:
Just saying, "My LS2 6-spd gets 28mpg on the freeway" doesn't mean it is a more efficent motor in making power which I think a lot of people tend to confuse. Note, I don't own a LS2.

[ May 12, 2006, 12:47 PM: Message edited by: got boost? ]

Scimmia · May 12, 2006

I believe the Cummins desiel engine is a multi-valve pushrod design, but I can't think of any others off the top of my head. There were rumors about the LS2 being multi-valve before it came out, but that didn't make it to production.

There are a aftermarket solutions I've seen for making a pushrod engines multi-valve.

got boost? · May 12, 2006

as examples, powerstroke 6.0/cummins/duramax are all "pushrod" 4valve per cylinder engines. I don't know of any OHC medium duty engine, there is a reason pushrods are favored for industrial engines, also, I don't think honda makes industrial engines.

I did a quick search on Google and everything I read indicates "pushrod" valve actuation is more efficient than OHC due to inherent mechanical losses.

It takes a given amount of torque to maintain a vehicle at a given speed. highway fuel mileage is an especially good estimate of an engine's "efficiency" at producing the needed power to maintain highway velocity.

I don't understand why people insist OHC is more "modern" (actually OHC was developed first) or somehow better. The truth is, for mass market vehicles, where fuel mileage, packaging, weight, servicability, reliability are the main concerns, I can only conclude "pushrod" engines are superior. I simply can't think of any reason to conclude OHC is better. FWIW, I've never owned a vehicle with pushrod valve actuation.

this page gives a bit of info as to the possible future direction of GM pushrod engine technology:

http://www.carcraft.com/techarticles/0303_GM/index3.html

a dual cam in block pushrod design would remove the true advantage of DOHC valve actuation which is independent intake/exhaust cam phasing (variable valve timing).

As to the packaging advantages "pushrod" affords:

Ford’s DOHC 4.6L V8 vs the older 5.0 (4.9) V8
http://www.vorshlag.com/pictures/motor-4.6-4V-004.jpg

And a 1.8L Miata motor next to an LS1
http://www.vorshlag.com/pictures/BothRight.jpg

[ May 13, 2006, 12:07 PM: Message edited by: got boost? ]

got boost? · May 13, 2006

quote:

Originally posted by JHZR2:
Ford uses OHC engines in some of its HD pickup trucks...

I don't think this is true can you provide an example. the "super duty" trucks are considered "light" trucks. some heavier F450 and F550 models might be considered medium trucks, but I think they only come with a choice of diesel engines (cat, navi, cummins).

JHZR2 · May 13, 2006

quote:

Originally posted by got boost?:

quote:

Originally posted by JHZR2:
Ford uses OHC engines in some of its HD pickup trucks...

Click to expand...

I don't think this is true can you provide an example. the "super duty" trucks are considered "light" trucks. some heavier F450 and F550 models might be considered medium trucks, but I think they only come with a choice of diesel engines (cat, navi, cummins).

Youre right.. I phrased it wrong... I meant HD versions of their LD trucks, i.e. super duty trucks. It would be incorrect to say that these trucks have lives of leisure though... maybe not as HD as a medium size or larger truck, but all the same, up for some hard work.

But I am on the pushrod bandwagon too... unless Im talking small efficient engines.

JMH

If OHC is so great then why.....

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