Pushrod vs OHC - Honda Motorcycles - FireBlades.org
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post #1 of 62 Old 07-20-2005, 10:12 PM Thread Starter
 
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Pushrod vs OHC

A couple of interesting points for people on this subject, and yes, I bring it up because I like debate.

Wholly unscientific, just observations of various cars, HP, and milage.

2006 Vette (pushrod) 6.0l V8 400 Flywheel HP, 18-28 MPG
2005 Mustang GT 4.6l OHC V8 300 FHP, 17-25 MPG
2005 Honda S2000 2.2l DOHC I4 240 FHP, 20-25 MPG

I find it interesting GM has made a pushrod motor the least thirsty and most powerful engine of the group.



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post #2 of 62 Old 07-20-2005, 10:26 PM
 
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Re: Pushrod vs OHC

I think there are wayyyy to many other factors to figure in than just the valvetrain config. Particulary the horsepower per liter, gearing, and rpm range. The cars posted, I think its comparing apples to oranges
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post #3 of 62 Old 07-20-2005, 11:02 PM
 
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Re: Pushrod vs OHC

One could easily say that the Honda S2000 engine is more efficient then the vettes as it is making over 1/3 of the HP while only using a little more than 1/4 or the displacement...while attaining similar MPG#'s Lots of different ways to look at this one, very interesting topic...

back to the old addage no replacement for displacment are we?
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post #4 of 62 Old 07-20-2005, 11:19 PM
 
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Re: Pushrod vs OHC

The 6 liter vette produces 33% more hp than the mustang which has 33% smaller displacement. I don't see the difference.

"another beautiful theory beaten to death by a gang of ruthless facts..."
- Tom Hanna (Master Metalshaper/Nitrogeezer)
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post #5 of 62 Old 07-21-2005, 1:54 AM
 
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Re: Pushrod vs OHC

All good points so far.

Also of note, the vette turns almost NO rpms at speed on the highway. Not sure about the torquey C6, but my old man's C5 will turn 1600 or so at 73-75... Thats nothing, its barely idling...

Of course, it can get away with gearing like that because the engine is such a stonking stump puller!
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post #6 of 62 Old 07-21-2005, 1:59 AM
 
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Re: Pushrod vs OHC

Thinking about it, I don't think OHC makes much of a difference compared to pushrod, it does the same thing in a different way, I guess the tiny difference between them would have to do with which has the least drag and the weight of the reciprocating parts
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post #7 of 62 Old 07-21-2005, 11:33 AM
 
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Re: Pushrod vs OHC

Quote:
Originally Posted by Mattress
Thinking about it, I don't think OHC makes much of a difference compared to pushrod, it does the same thing in a different way, I guess the tiny difference between them would have to do with which has the least drag and the weight of the reciprocating parts

Except for one big difference: THe OHV motor in the 'Vette has only 2 valves per cylinder.

Lots of other things to consider here, and ccwilli3 touched on a major one: RPM's. But more specifically, the way that the EPA (or in EnerGuide in Canada) conducts mileage testing. Cruising at 60Mph the Corvette motor is barely above idle, and the first to fourth skipshift is also used in the cycle. This is the same reason the EPA reports 60mpg for the Prius while owners typically get around 40. THe testing favors cars with lots of low-end torque.

In real-world driving I suspect the S2000 owner would see quite a bit better mileage compared to the corvette owner.

Technically, the corvette motor is a lower performance engine compared to an S2000, with half the horsepower per litre of displacement. It is debatable as to which method is better to obtain more power; more cc's or more RPM's.

This isn't very scientific, but would a 2.0 litre motor cruising at 5400RPM use basically as much fuel as a 6.0l motor cruising at 1800RPM?

It's a good debate.

And then there's this asshole...
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post #8 of 62 Old 07-21-2005, 11:38 AM
 
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Re: Pushrod vs OHC

Wich motor has more potential for modding? The vette or the S2000? Not to add fuel to the fire or anything, but it seems like the stock s2000 is closer to its "ceiling" than the vetter motor is.

HD
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post #9 of 62 Old 07-21-2005, 11:46 AM
 
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Re: Pushrod vs OHC

Something I forgot:

I don't think GM is clinging on to the pushrod design for all-out performance. The design has a major advangage in its size; pushrods allow for compact cylinder heads and valve covers, allowing them to stuff the motor in a very small space ie under the low-profile hood of a corvette.

I read an article several months back which had a good argument about engine efficiency. Rather than simply measuring horsepower per displacement, what about horsepower per total external volume and weight of the engine. WHen you look at it this way, the motor in the corvette is far more efficient than your average HO cammer.

And then there's this asshole...
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post #10 of 62 Old 07-21-2005, 11:51 AM
 
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Re: Pushrod vs OHC

Here it is.

http://www.caranddriver.com/article....&page_number=1

And then there's this asshole...
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post #11 of 62 Old 07-21-2005, 12:43 PM
 
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Re: Pushrod vs OHC

Minor tangent....

As the manufacturing guys will tell you, one of the major advantages to OHC lies in the engine assembly flow...with an OHC, the head comes into the stream with the valves already set. Time the cams...done...

Meanwhile a pushrod motor assembly line has a bottleneck at the machine where the valves are set...

Aside from the differing performance aspects, one of the major drivers for OHC adoption is a manufacturing related one...much in the same way that FWD was foisted onto us...

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post #12 of 62 Old 07-21-2005, 12:53 PM Thread Starter
 
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Re: Pushrod vs OHC

Quote:
Originally Posted by phobiaphobe
In real-world driving I suspect the S2000 owner would see quite a bit better mileage compared to the corvette owner.
While it's still new, we've got about 800 mi on ours now, most of it from a long highway roadtrip last weekend. We see 23-25 MPG. It is turning around 4000 RPM at 70. I'd guess Vette owners would've seen similar numbers in similar conditions.

Quote:
Technically, the corvette motor is a lower performance engine compared to an S2000, with half the horsepower per litre of displacement. It is debatable as to which method is better to obtain more power; more cc's or more RPM's.
Yes, I've been looking at this motor from a fairly scientific standpoint (piston speeds, hp/l, which is about 110 for the S2000, 67 for the Vette) and am still mazed at what Honda did with the motor. It achieves literal race car performance, and it's first scheduled tune up is at 105,000 miles. It is truly a statement by Honda, the "Performance First" company. But, who cares. I don't buy cars to brag about my hp per liter to people.

As a consumer I don't care what makes the car go. I want to know my average milage, and feel my car take off when I press the gas. If the General gives me a car with more CI's, but it still gets good milage, and turns less RPM, I don't care.

G-Force, I actually think it's a pretty good comparison. The Vette and the Stang are about the same weight. The S2000 is much lighter, which should of course help it in the milage game.

Quote:
I read an article several months back which had a good argument about engine efficiency. Rather than simply measuring horsepower per displacement, what about horsepower per total external volume and weight of the engine. WHen you look at it this way, the motor in the corvette is far more efficient than your average HO cammer.
YES! The S2000 motor is HUGE for a four cylinder. I can only guess at the reasons (needed room for the VTEC cam wizardry, tall deck block for long rods, etc etc) but it is very obvious.

Quote:
It's a good debate.
I think so.



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post #13 of 62 Old 07-21-2005, 12:58 PM Thread Starter
 
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Re: Pushrod vs OHC

Quote:
Originally Posted by EDDIE110171
The 6 liter vette produces 33% more hp than the mustang which has 33% smaller displacement. I don't see the difference.

The Mustang makes 100 less hp, and it gets WORSE milage. Ford! (BTW, it's 25% less)




Last edited by luvtolean; 07-21-2005 at 12:58 PM.
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post #14 of 62 Old 07-21-2005, 12:59 PM
 
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Re: Pushrod vs OHC

Quote:
Originally Posted by luvtolean
... The S2000 motor is HUGE for a four cylinder. I can only guess at the reasons (needed room for the VTEC cam wizardry, tall deck block for long rods, etc etc) but it is very obvious.



I think so.

One of the disadvantages of Hondas DOHC VTEC is its bulk; they actually use rocker arms and shafts, which makes for a very tall and wide cylinder head.

And then there's this asshole...
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post #15 of 62 Old 07-21-2005, 1:02 PM Thread Starter
 
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Re: Pushrod vs OHC

Yeah. It's a pretty sophisticated car. If I was a betting man, I'd bet Honda makes VERY little money on each car sold.

Over on S2KI they do have links to statements by Honda officials that the car does make money. Creative accounting or fact?




Last edited by luvtolean; 07-21-2005 at 1:02 PM.
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