[sajo]

GM/Ford/Chrysler take a lot of flak from people all over the world because they continue to offer pushrod engines in their mainstream models. But are they really as bad as they are made out to be?
Cars like the new GM offerings in 2006 Chevrolet Impala, G6, a host of Buicks and many other trucks and SUVs continue to offer these engines. Infact, the Impala is said to have an "all new" 3.5L OHV V6 which produces 211hp.The "3800" V6 has been offered on almost all GM sedans (Even "premium" offerings like the Buick Park Avenue) and continues to be on some current and upcoming cars as well. Why do they so steadfastly stick to their OHV designs? Some supporters claim that they are better than most overhead cam engines.

Some major disadvantages of these "old tech" engines I have read about are :

- Huge displacement...Mediocre output.

- Low revving nature.

- Only 2 valves/cylinder layout.

- "Sounds" dated and low-tech!


Addition of things like variable valve timing and electronic fuel injection have boosted their output figures a bit.


Some advantages I have read about are (DOnt know for sure though, can someone please confirm?) :

- Compact dimensions

- Simpler design

- Better low end torque

- Less weight

- Lower lower reciprocating mass and fewer moving parts than comparable DOHC engines. (Hence better FE?)

eg : BMW 90 degree V10 4999cc
500hp at 7750rpm
383lbft at 6100rpm
528lb dry weigth

LS7 90 degree V8 7000cc
505hp at 6300rpm
470lb/ft at 4800rpm
458lb dry weight

Which one of the two types is better? From what I have been reading, the (D)OHC layout is more suited to high performance applications. So pushrods are better for towing/hauling applications?
Is their any crudeness/loss of refinement in OHV engines? I have not yet experienced any of them, hence asking. How does a modern LS2 "feel" compared to some high revving Jap/Euro engine?

Mods : Been searching for a thread like this, but cannot find it. Hence created a new thread.

[Mpower]

Well most of what you have posted is true. Just some points.

• Pushrod engines dont have to be necessarily coarse or harsh but they usually are because most of them havent changed in 10-15 years.
• OEMs have been selling them as base engines. Just yesterday I was driving the company minivan with a 3.3 Chrysler pushrod and it was fine till you mash the gas and rev it.
• Biggest problem is not being able to fit 4 valves although there are some with 3 valves per cylinder using a forked rocker.
• DOD (disp on demand) has given a new lease of life to pushrods. It much easier to deactivate a cylinder by collapsing the lifter in a pushrod.
• Now Ford which had given up on pushrods is going to design an all new V8 with pushrods.
• Pushrods really make sense in Vee type engines where you need 2 sets of timing drives and cams with OHC setup. With a pushrod, you can get away
• with one set. There arent any inline 4 pushrods anymore.
• For a super sports car, I wouldnt pick DOHC anyday. I really dont know what GM is trying to prove with the Corvette engine.

[islero]

Aren the Viper V10, Ford V8, and Chevy V8 beign used in so many cars today pushrod engines? Not to mention Nitrous' Ikon..........LOL

I only know they are considered outdated technology, I do not know technically in what way they are inferior.

[prabuddhadg]

There is no place for me on this thread, but I just have to say that we have some knowledgable people on this forum. All I knew was DOHC engines are supposed to be more high tech, and that was about all I knew. I get to learn a lot from all you guys. I am impressed.

[sajo]

@islero : The Viper's V10 was originally meant for use in trucks, and yes, it is a pushrod. GM also has kept the V8 going, with only one significant twin-overhead cam engine, the Northstar V8. The other engines like the LS (small block) (6.0L and 6.2L) and the Vortec series, continue to be OHV. Chrysler uses the famed 5.7L & 6.1L "Hemi" V8s in many cars and trucks.
Ford uses the 3 valve SOHC layout in its big displacement (5.4L) engine.
I kinda like the American strategy of if-you-need-more-power-just-enlarge-it.

[GTO]

Either have their own advantages, but Push rods engines are generally much simpler, and cheaper to make. Thats one of the main reasons why american car manufacturers still offer these on a mass scale albeit on lower speced versions. The main disadvantages of a pushrod are harshness, and being restricted in rpm range.

Buttttttttttttttttt what the Vette has achieved in terms of power output, gas mileage and the price its offered at....is pretty outstanding.

GTO

[headers]

Pushrod engines are also not as FE as the OHC engines..DOHC engines have the capability to rev higher..[read 10000 + RPM] easily than the push rod engines..

Also, push rod engines are difficult to maintain than an OHC engine..but for low speed applications where the need is torque..push rod engines make sense..

[sajo]

Originally Posted by prabuddhadg

All I knew was DOHC engines are supposed to be more high tech, and that was about all I knew.

Same here. Used to think there must be something wrong with the Americans, since the world has long since moved on..Now I am not so sure. Especially since I have been hearing that pushrods return similar FE figures for engines with similar power output with significantly larger displacement than DOHC engines.

[turbo_v12]

I think the main reason for FE on American cars is because they have massive engines with teensy weensy power outputs.

You yourself posted of an LS engine which produces 500 bhp with a 7 litre engine. Obviously that would give a better FE since it reduces the stress on the engine.

Also, supercars outside the US have better figures with smaller engines. (Imagine Ferraris and Lambos with 7+ litre engines)...

Hope you guys get what I am trying to say here...

[nitrous]

Push-rod engines are old-tech and have no advantage compared to today's camshafts.

My push-rod engined ikon is
1. PowerLESS - 58bhp from a 1.3L(the esteem's 1.3L puts out 85)
2. Gas Guzzler -8.5-9kpl (for a 58bhp car) :(

[DRC]

Well, looks like all the comments here are good info..

Ever wonder why they have such a restricions...
Major reason is that the pushrods have wieght, and like pistons have to be moved. So does DOHC, what big deal you may ask!

Answer here is they move like pistons, unlike cam shafs, which spin in one direction, these reciprocate like pistons, and being lage metal part they have sizable inertia. which result in going out of sync during hi-rpms, which simply means the cam follower to which the push rod and the valves are attached are no longer following the cam. This result in harshness in the engine and rpm gets limited. They also waste a lot of energy.

One other interesting thing, the then engineers tried is this. Rotary valves. Which completely eleminates the inertia problem, rather uses it to its advantage. The technology did not progress because of the lack of material which can perform well inside a combustion chamber and yet providing sealing charecteristics. Present valves have self sealing properties against the pressure.

Read this some time back, can't remember the source.

[2fast4u]

simple eg is that of RE 350cc 18hp and a pulsar 180cc with 15 or 16hp. But u will find there is a huge difference in torque.

One thing for sure is that pushrods are not capable to revv high and mostly will get out their peak in 3to 4k rpms.

Ive seen the Saudis and Bahrainis feel so much humiliation after their big capriceSS, 5.7ltrs and 6ltrs + engines get smoked by my 2ltr engine. these engines are best to lug and tow boats, caravans and portacabins.

at todays oil prices these American Engines are just guzzling fuel without actually going any further. high time they shelved them.

[sajo]

IMHO, the OHV do have some (limited) scope for improvement. Like in the Z06. The engine is anything but low revving (7100rpm redline) and delivers good fuel efficiency too. Its only the second 400+bhp car in the US to avoid the gas guzzler tax there. (the first one being the Corvette C6, another pushrod). Besides, it produces most its (substantial) torque from as low as 1600rpm.

[TCX]

Originally Posted by sajo

IMHO, the OHV do have some (limited) scope for improvement. Like in the Z06. The engine is anything but low revving (7100rpm redline) and delivers good fuel efficiency too. Its only the second 400+bhp car in the US to avoid the gas guzzler tax there. (the first one being the Corvette C6, another pushrod). Besides, it produces most its (substantial) torque from as low as 1600rpm.

Totally agree with you.

[ECM]

Trying to make this threa easier for the general benifits of those who love car's heart(Engine).Now why I am posting this bcoz I felt somehow few members are in dilema between OHV and OHC engines!!
*A pushrod engine or overhead valve (OHV) engine is a type of piston engine that places the camshaft below the pistons (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine) and uses pushrods or rods to actuate rocker arms above the cylinder head to actuate the valves. Lifters or tappets reside in the engine block between the camshaft and pushrods.
This contrasts with an overhead cam (OHC) design which places the camshafts above the cylinder head and drives the valves directly or through short rocker arms. In an OHC engine, the camshafts are normally part of the cylinder head assembly, while in an OHV engine the camshaft (rarely more than one) is part of the main engine block assembly.
---------------
This is OHV engine technically in snap,look at it

++++++++++++++++++++++++++++
And this is OHC or SOHC engine

4-cylinder 8 valves SOHC engine
++++++++++++++++++++++++++++

One more type is there and which is known as DOHC or twin cam engine which has 2 cam shafts inside it,see it here
4-cylinder 16 valves DOHC engine
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Now expert can carry on this subject,I have made this topic/poll little bit easier perhaps.