What Are The Advantages of Pushrod Engines Over OHC?

[Truckedup]

Are there any V or opposing pushrod engines that DON'T have interchangeable heads?

I believe some Fords and Mopar?

[PackardV8]

better low end torq

Very minor point, but the choice of an OHV versus OHC does not result in an inherent difference in low end torque.

Because the OHC can be more durable at high revs, Honda, et al, built some less torque/more horsepower production engines. Toyota, et al, chose to use an OHC but maintain low end torque at the tradeoff of less high RPM horsepower. It works either way.

Now that variable valve timing and lift production problems are solved, there's no reason a DOHC can't have both low RPM torque and high RPM horsepower.

In fact, the Viper OHV10 has variable cam timing on the exhaust and it's theoretically possible to have it on the intake also.

[Brian P]

push rod engines are cheaper and easier to mod and that is why the LS is so popular with hot rodders

Really?

Why would this be the case?

There is nothing inherent to the layout that makes a pushrod design easier to mod.

It's easier to swap camshafts in a DOHC engine ... you don't need to screw around with the lifters and pushrods and you don't need the length of the engine of clearance in front of the engine to get the camshaft out and in. You have to mess around with the timing chain/belt to do it ... but you have to do that with a single-cam pushrod engine as well.

With DOHC it's a trivial exercise to set the intake and exhaust cam degreeing separately. With the traditional pushrod single cam layout, you are stuck with the relative timing between them that is ground into the camshaft. Can't adjust them separately.

Chevrolet LS engines are popular with hot rodders largely because there are a bazillion of them out there. The number of performance parts available for a given engine is not a function of whether it uses a pushrod or OHC valvetrain layout. It IS a function of how many of them are out there, how good the basic design is (and I don't question the LS engine for this), and how much demand there is.

[hoffman900]

OHC engines are easier to modify for the sole reason that with the majority of them, you can change camshafts without pulling the front end of the car off or pulling the engine. Plus what was stated above.

[Ratu]

Setting up four cams (including the timing) in the heads of a V engine is definitely not as easy as doing it for just one. I don't mind doing it, but it does take more time. Certainly I get charged more to set up four cams as opposed to one when I ask the local shop to do it for me.

[MadBill]

Suppliers also tend to charge per cam rather than per lobe...

[hoffman900]

Suppliers also tend to charge per cam rather than per lobe...

How many builders get the centerlines correct the first time?

[pamotorman]

push rod engines are cheaper and easier to mod and that is why the LS is so popular with hot rodders

Really?

Why would this be the case?

There is nothing inherent to the layout that makes a pushrod design easier to mod.

It's easier to swap camshafts in a DOHC engine ... you don't need to screw around with the lifters and pushrods and you don't need the length of the engine of clearance in front of the engine to get the camshaft out and in. You have to mess around with the timing chain/belt to do it ... but you have to do that with a single-cam pushrod engine as well.

With DOHC it's a trivial exercise to set the intake and exhaust cam degreeing separately. With the traditional pushrod single cam layout, you are stuck with the relative timing between them that is ground into the camshaft. Can't adjust them separately.

Chevrolet LS engines are popular with hot rodders largely because there are a bazillion of them out there. The number of performance parts available for a given engine is not a function of whether it uses a pushrod or OHC valvetrain layout. It IS a function of how many of them are out there, how good the basic design is (and I don't question the LS engine for this), and how much demand there is.

i am not a ford guy but i believe the ford OHC engines came out years before the LS engins so why did they not catch on like the LS ??

[Keith Morganstein]

push rod engines are cheaper and easier to mod and that is why the LS is so popular with hot rodders

Really?

Why would this be the case?

There is nothing inherent to the layout that makes a pushrod design easier to mod.

It's easier to swap camshafts in a DOHC engine ... you don't need to screw around with the lifters and pushrods and you don't need the length of the engine of clearance in front of the engine to get the camshaft out and in. You have to mess around with the timing chain/belt to do it ... but you have to do that with a single-cam pushrod engine as well.

With DOHC it's a trivial exercise to set the intake and exhaust cam degreeing separately. With the traditional pushrod single cam layout, you are stuck with the relative timing between them that is ground into the camshaft. Can't adjust them separately.

Chevrolet LS engines are popular with hot rodders largely because there are a bazillion of them out there. The number of performance parts available for a given engine is not a function of whether it uses a pushrod or OHC valvetrain layout. It IS a function of how many of them are out there, how good the basic design is (and I don't question the LS engine for this), and how much demand there is.

i am not a ford guy but i believe the ford OHC engines came out years before the LS engins so why did they not catch on like the LS ??

Big physical package, small displacement and bore. Most are 2V. They are good power added engines, but not an easy swap.

[Brian P]

i am not a ford guy but i believe the ford OHC engines came out years before the LS engins so why did they not catch on like the LS ??

There are too many other factors to simply blame it on one being OHC and the other being pushrod. Lots of them are out there in trucks and taxis and police cars, and are simply never going to be high performance engines.

[pamotorman]

was not the LS engine developed for the chevy pickup because there are not enought corvettes sold to justify a engine development program

[roc]

High RPM is were most OHC engine have the advantage but didnt make much sense as from the factory in the US 6000 RPM was about the limit.

You may want to check out the new Cummins Diesel 4V OHC V8 engine in the Nissan Titan XL.
Most of the new engines coming out of Cummins are OHC engines, and diesels aren't what I'd call "High RPM".

Right on... the X15 and the new X12 are OHC. The B6.7 and L8.9 remain OHV. The 5.0L V8 is actually DOHC.

PS.: The ISX15 was born as DOHC, but one cam was for the fuel injectors and the other cam was for int/exh valves. The 'fuel cam' was ditched with the adoption of High Pressure Common Rail fuel system in 2010.

[Brian P]

The LS engine has the benefit that the same layout is used in the truck engines and in the high-performance car engines. The truck engines are iron block and the higher-performance versions are aluminum block, but the layout is the same, and stuff is generally interchangeable between them. You would know this better than I. (I don't do automotive V8 engines.)

But a Ford 4.6 SOHC 2-valve in a Crown Victoria, is a lump, and always will be. The DOHC 4-valve versions were rare (only in Lincolns and "special" versions of the Mustang) until pretty recently (2011-ish). The 5.0 in the F150 nowadays is DOHC 4-valve - but that's only since 2011.

And then there's Ford's infuriating habit of making the same-displacement engine in two different assembly plants with significant design differences between them so that stuff doesn't interchange. (I know GM is not innocent of this, either!)

LS engines that you can make into a monster are plentiful. "Mod motors" in the desirable DOHC 4-valve configuration ... not so much.

None of this has anything to do with pushrod versus OHC.

[modok]

Everybody seems to be well aware of the advantages of OHC,
A few of the responses make me think, they never considered the advantages of pushrods.
You can design all kinds of things.... but what do they cost to make? How easy are they to work with? What happens when this or that fails?
50 years ago I can image many smart alec remarks about how putting camshafts in an aluminum head.... is a fools errand.....and in many ways it is, but just because it's hard doesn't mean you can't do it. You can do lots of things the hard way and make it work, especially with a good reason.
Half the stuff on the street is doing it it must be easy......well, actually it's pretty amazing.

I assume the reason the LS engine is a pushrod V8 because the designers were classic gearheads, who liked pushrod v8s

[user-23911]

If you've got a pushrod engine and want to do a serious upgrade,21st century style, you'll dump it and replace it with a 4V DOHC engine and spend time modifying that instead.