Pushrod engines rock on
Further refinement and development of the pushrod engine may seem odd in
today's
market dominated by overhead-cam power plants. German and
Japanese manufacturers have already dropped pushrod engines with Ford Motor using just a couple for their
vehicles.
But Chrysler and General Motors have bucked the trend, using refined versions for a plethora of their vehicles,
including the Corvette. While cost is usually touted as the main reason for sticking with the venerable design, others,
such as fewer moving parts and better integration with Displacement on Demand technology, play a factor as well.
For the regular consumer, the distinction between the two is probably as meaningless as whether the CPU in their computer is from AMD or Intel. As long as it does the job.
Reader Comments (Page 1 of 2)
Mike O. 12:28AM (12/19/2005)
For the people who do not want to register, http://www.bugmenot.com
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V?or Rubiera 12:28AM (12/19/2005)
In my point of view it was the HEMI engine that in modern times really wake up the use the pushrod engine. GO HEMI GO!!!!!!!!!
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naggs 12:28AM (12/19/2005)
years before the hemi the ls1 really brought hi tech hi output and the inheriently superior pushrod design together.
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Mal Fuller 12:28AM (12/19/2005)
For a reduction in moving parts and fewer wear points, the flathead rules! Nonetheless, I don't think you'll see them make a comeback anytime soon.
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Ophrey 12:28AM (12/19/2005)
Here we go let the flames soar, I prefer OHC myself, by both being equal in displacement the OHC will always produce more HP and more peak torque.
Most people and most car enthusiasts will also admit to how a OHC is also smoother as it accelerates and not as "Thrashy"
"For the regular consumer, the distinction between the two is probably as meaningless as whether the CPU in their computer is from AMD or Intel. As long as it does the job"
What fun is that? As long as it does the job.
I thought you were an enthusiast. As for the Intel, AMD analogy you may be correct except the AMDS now are raping intel chips in raw power for gaming, and intels better for applications.
The only advantage I feel for the pushrod setup is
1. Cost.
2. smaller more compact design.
3. lower end torque.
The fuel economy advantage is more allocated to gearing, i feel anyways.
If pushrods were better dont you think they would be using them more in high performance cars, does anyone really think GM and Chrysler know somthing the rest of the automotive world doesnt? and why in racing when they race OHV VS DOHC are OHV allowed more displacement to narrow the gap in power.
An for you old school motorheads Torque does not mean a car will be faster it only means itll feel faster, hence why my 03 protege auto, feels slower then my 98 Lumina auto, however the mazda has higher trap speeds and at better E/T.
In conclusion I feel OHV are for the clearance rack at walmart hence why the general loves em so.
Imagine if the vette was a DOHC at the same displacement, yes it would cost more, and be bigger but it would probably have around 600hp and around the 600/lbs/ft marker.
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Ophrey 12:28AM (12/19/2005)
"Pushrod engines are more reliable, more fuel-efficent"
Ill give you easier to work on and lighter thats about it. More reliable and fuel efficient, what type of grass are you smoking??? Displacement for displacement more of the time DOHC will get better fuel economy, however gearing is an important factor most people choose to leave out otherwise honda/toyota wouldnt be known for fuel efficiency and GM/Ford/DCX would be, oh wait a minute that also works for reliability aswell,or maybe in your world the OHV GM/Ford/DCX make a more known to have fewer problems then Honda and Toyotas DOHC.
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Joel A 12:28AM (12/19/2005)
"I thought you were an enthusiast."
I am, Ophrey. (Kewl handle, by the way.)
Give me ROTARY, baby! :-)-
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md 12:28AM (12/19/2005)
Ophrey, you are right on many points, but OHC engines are more economic than OHV engines. There is less mass in an OHV engine, allowing it to run more efficiently.
OHV engines will actualy make more torque, especially in the lower RPMs, while an OHC engine will make more horsepower.
Most consumers can not tell the difference, nor do they care, but each design has its merrits and drawbacks. For city driving, the better low end torque and better fuel mileage of an OHV is desirable. For the highway, however, an OHC engine will run smoother and have more available passing power.
In truck and SUV applications a pushrod engine is really the desirable setup mostly due to its durability and low end torque.
In high performance applications, however, an OHC engine is a much better choice.
In middle of the raod applications, such as mid size sedans, they have both been effectively used.
There are of course exceptions to these trends. The corvette and Viper are good examples of high performance vehicles that succesfully utilize pushrods, and the Ford 4.6L and 5.4l V8s are OHC designs that make great low end torque and are doing just fine in terms of durability in their truck applications.
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whofan 12:28AM (12/19/2005)
I don`t mind a over head cam in an inline block such as a 4 cylinder engine. With a V6 or V8 engine you have to have two separate cam shafts with two timing chains.
I like one timing chain and the shorter the better, for less chance of streching.
With four valves per cylinder I see where the OHC is better but push rod engines have served me well. As a licensed ( non praticing) mechcanic I like OHV better.
Ford has OHC in their trucks, spark plug changes are a nightmare. 10 feet of chain to turn the cams doesn`t set well with me, but it works. On a high mileage engine I question the accuracy of valve timing (Due to chain strech) on a OHC vs OHV.
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Alonzo 12:28AM (12/19/2005)
Nope, I can't agree with this. Not for performance cars. Low end torque is fine, but it's nothing you can't make up for by revving the engine. And the germans have found other ways to boost the torque output in their engines.
No, the biggest problem with pushrods in cars is their weight. That weight affects handling, milage, braking, acceleration, and top speed. It just makes for a worst car overall. About the only vehicle that you would want to put a pushrod in is a truck. All of those traits are already screwed up in it anyway.
And I know why GM and DCX kept using them. It's because they had a choice between increasing an engine's power output the hard way through technological innovation, or they could just build a bigger engine. And what did it matter? Everyone was buying SUV's then anyway.
But it takes Chrysler 8.3 liters to produce 500 horses? and BMW can do the same with 5 liters? Come on.
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paulkastner 12:28AM (12/19/2005)
What is amazing to me is the total lack of knowledge on GMs engines. Cobalt,Aveo,Trailblazer,colorado,all ohc enignes. So please stop with the lack of ohc in gms engine progam. When pushrods do better they use them when they don't they use ohc. GM has 4cyl 5 cyl 6cly 8cyl enignes with ohc.
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Geotpf 12:28AM (12/19/2005)
Aveo is not exactly a good example of GM's engine technology. More like Daewoo's. Oh, and considering how small it is, it's fuel economy is pathetic.
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B as in B, S as in S 12:28AM (12/19/2005)
The engine doesn't give a darn where the cam is, as long as it's tuned right. Heck look at GM's 4.8L pushrod V8 in the Silverado 1500, vs. the F-150's SOHC 4.6L -- the OHC engine comes up 50 HP short! Same for the non-HO Mopar OHC 4.7L. (Yeah the GM's bigger, but not THAT much bigger.) And it took adding 3V heads and VVT for Ford's 5.4L to match GM's 5.3L in power.
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JWhite 12:28AM (12/19/2005)
actually, the fuel savings the article is talking about is the ease of adding Displacement on Demand. It was MUCH easier and cheaper to add to the OHV design for DCX (and GM) then OHC. Both designs have merit. It depends on the application and the desired properties and packaging and cost per unit.
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HC_Earwicker 12:28AM (12/19/2005)
I found the article rather disappointing - particularly given that it is from the New York Times. For a much better article on the subject, take a look at
http://www.thecarconnection.com/Auto_News/Techno_Beat/In_Defense_of_Pushrods.S198.A7178.html
- HCE
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JGN 12:28AM (12/19/2005)
It's a real shame, GM devotees will defend the General right up until the day it dies.
What is going to save GM is real change. Making the most out of the best they can, not just constantly taking the cheapest route. It is leaving them further and further behind.
GM is just the master of the quick fix and the shortcut.
I can't understand they think that 'staying the course' is going to work for them. Are they out of ideas?
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Brian 12:28AM (12/19/2005)
#9
"As a licensed ( non praticing) mechcanic I like OHV better."
Uh huh. What exactly is a "mechanic license" and where do you get one?
To the claims that one sort of engine will produce more torque and one will produce more horsepower blah blah blah... BULLSHIT!
The engine doesn't care how the valves are opened. It only cares how far they are opened and for how long. The mechanism that accomplishes the opening is irrelevant.
Less torque from a OHC? The big semi truck engines are going to OHC and they are all about torque. Is 1800 ft lbs enough?
Less HP from a OHV? Nascar engines are about 5.7 liters and make 700+ hp. Drag race engines can produce 6000+ hp.
Other issues such as servicability, reliability, weight etc may be valid. Power output is determined by many features of an engine design, the location of the cam is not one of them.
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Ophrey 12:28AM (12/19/2005)
"Nascar engines are about 5.7 liters and make 700+ hp".
Nascars are very "low tech" and slow,
How about a 3 liter from Honda that pushes out around 900+hp "F1" Now thats an engineering marvel.
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x23 12:28AM (12/19/2005)
"Imagine if the vette was a DOHC at the same displacement, yes it would cost more, and be bigger but it would probably have around 600hp and around the 600/lbs/ft marker."
early '90s ZR-1. by most accounts the latter (ie. current) non-cammed engines are better.
"Nope, I can't agree with this. Not for performance cars. Low end torque is fine, but it's nothing you can't make up for by revving the engine."
GM has made high-revving OHV engines for some time. DZ302 from the late '60s was a 7000 RPM factory consumer engine. the current LS7 is a 7100 RPM engine. i've driven plenty of fun and fast OHC engines that revved no where near that high. i honestly am not a real big fan of revving much past 5500 or so. anything more than that is basically just annoying to drive. especially in stop and go. and how "high-revving" became synonymous with "fancy high technology" is beyond me.
"And I know why GM and DCX kept using them. It's because they had a choice between increasing an engine's power output the hard way through technological innovation, or they could just build a bigger engine."
seems like most the engines *anyone* was making produced lower output in 1980 than in 2000. at the same displacements. technology increased power output across the board. comparing a weezy late '70s 350 to the recent LS1 tells me *some* sort of technological innovation was occuring. i mean we're talking like 4-5 times the power out of the same exact displacement. and that's without resorting to gimmicks/cheating of slapping cams on it. which Honda or Toyota block from the early '80s is still being used and creating 4 times the power output?
"No, the biggest problem with pushrods in cars is their weight. That weight affects handling, milage, braking, acceleration, and top speed. It just makes for a worst car overall."
what? i get the impression you have no clue what you are talking about. taking 2 similar displacement engines... an OHC engine is nearly twice the size of an OHV engine. there is a picture floating around showing a 4.6L OHC next to a 302 OHV... the cammed engine is nearly twice as big and is actually a smaller displacement engine. so if anything the high-tech cammed engine is "a worst car overall".
#2 Kenny already pointed out the last point i always feel obliged to making in inane OHV vs. OHC debates... so i won't have to again. personally i like them both... whatever gets the job done. there isn't a "winner" in this debate anymore than in the PS3 vs. Xbox debate or the PC vs. Mac debate or the 9mm vs. .45 debate or the Republican vs. Democrat debate. there is however a lot of nonsense and misconceptions floating around.
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Richard Warren 12:28AM (12/19/2005)
Saying that OHC engine will give more horsepower just because it's an OHC is just plain silly.
Valves don't care and neither do most drivers care how the valves get opened, OHC, OHV, flat head.
There is simply more to it than that, overall displacement, valve timing, size of the valves, how well the intake manifold is designed for air flow, how smooth the finish is inside the intake manifold, how the area around the valves is shaped, how clean that area is, valve spring tension and lifter design to ease valve float, spark plug position, piston design, injection timing, injector spray pattern. Not just the position of the valves. And more.
Each has it advantages and disadvantages, I have no real preference for either design.
But there is a lot of hyperbole and misinformation out there, many times it comes from folks who have never twisted a wrench or actually worked on a car at all.
OHC, OHV, Flat Head, Rotary all have advantages and disadvantages.
Want some real advantage? How about no valves? how about getting rid of two strokes? Yep, lets talk 2 stoke power, less moving parts, lighter overall weight, higher revs. It's downside emissions, yet with computers, changes in fuel mix and lubricants, might just be a winner
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