Pushrods vs DOHC

[Todd15Fastback]

I've seen this drum being beaten ever since Ford popularized the DOHC design with the '03 Cobra and later the Shelby. 12 years later the OHV Vettes, Camaros, and Caddys are doing just fine.

You mean 1999 when the DOHC 32V motor appeared in the Cobra?

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[Daytona Coupe]

Lots of diesels use 4 valves and pushrods. Most of the Ford, Chevy and Dodge diesels are that way. There is nothing stopping the combination and it's used for some of the biggest torque/HP motors out there (the 6+ liter diesel monsters).

And they turn how many RPM?

Diesel is a whole different animal. There is a very good reason why you don't see 4 valve pushrod engines from the factory. It's basically Chevy and Dodge still doing pushrods because they are stuck in the past - partially due to financial problems. The rest of the auto world has gone OHC for good reason. It's only a matter of of time before Chevy and dodge quit using pushrods too.

Cam position has nothing to do with torque. The single cam engines being mentioned generally are larger, and are tuned to lower rpm. We could have more low end torque from the 5.0 if you were willing to trade some top end. It's a design choice, not a flaw in the architecture.

 

[Sinister]

You mean 1999 when the DOHC 32V motor appeared in the Cobra?

No because that engine was a turd. Pretty much all of them were in n/a form until the Coyote came out, aside from the '00 Cobra R but that was a very limited car that hardly anyone got to experience.

 

[Shanghai Dan]

And they turn how many RPM?

Diesel is a whole different animal. There is a very good reason why you don't see 4 valve pushrod engines from the factory. It's basically Chevy and Dodge still doing pushrods because they are stuck in the past - partially due to financial problems. The rest of the auto world has gone OHC for good reason. It's only a matter of of time before Chevy and dodge quit using pushrods too.

Cam position has nothing to do with torque. The single cam engines being mentioned generally are larger, and are tuned to lower rpm. We could have more low end torque from the 5.0 if you were willing to trade some top end. It's a design choice, not a flaw in the architecture.

The contention was that no 4V pushrod motors exist. That's flat out wrong. There are units in the GM stable, there are diesels.

As far as RPM - what does that have to do with it? Go get a Honda CX500 motorcycle and run it to its 10K redline. That's 4 valve pushrod engine running to 10K.

Diesels run low RPM not because of 4 valves - but because that's the way to maximize the energy in diesel.

There is no inherent limit to RPM with pushrods, and there are as many applications for pushrods as there are for OHC units. The reason you see more OHC units now is they tend to allow a shorter but wider engine. Shallower hoodlines, smaller cars can usually make the tradeoff. Older cars were more upright. It's why I could just about sit inside the engine compartment on my 1962 Ford Fairlane when I rebuilt the small block 221 V8 (289/302 block), but there is precious little daylight on either side of the new DOHC units. They are quite a bit shorter than the old beast, through...

So I hope we can put to rest the myth that pushrods are for 2 valves only, and only for low RPM. There are literally millions and millions of engines out there that say otherwise.

 

[Herr_Poopschitz]

Really? When Ford goes global with cars like the Mustang and Focus they compete with cars from Germany. And when they go racing they compete with cars from Germany, not to mention other foreign cars. "What wins on Sunday sells on Monday"

24 hours of Le Mans records "endurance racing"

Wins: 32 Germany / 4 USA (Shelby American)

Who would you benchmark when you develop a car like the Ford GT? You always BM against the best and other competitors for that matter.

Le Mans? Endurance racing? I guess you're unfamiliar w/ Corvette Racing and Pratt & Miller. I'm surprised someone so quick to 'quote' Le Mans stats would overlook their successes.

They seem to do just fine w/ their 'inferior' pushrod offerings.

So again, who gives a f what the Germans do? America makes the best powerplants I've ever dealt w/, regardless of cylinder head layout (and Aussies, but they're the same manufacturers). The argument that since the Germans don't do it, it must be inferior is ridiculous.

 

[Herr_Poopschitz]

You mean 1999 when the DOHC 32V motor appeared in the Cobra?

96?

...or 93 Mark VIII?

 

[Todd15Fastback]

96?

...or 93 Mark VIII?

Correct. 1993 I believe, called Intech. I only replied with 1999 as he said Ford as I consider them different

 

[Sinister]

Neither of them popularized anything however.

 

[Herr_Poopschitz]

Neither of them popularized anything however.

Your definition of 'popularize' seems a bit vague...

 

[Sinister]

Your definition of 'popularize' seems a bit vague...

Well then let me clarify. Did either of those cars make the DOHC platform popular? The '99 Cobra was a joke that had to recalled and led to Ford skipping an entire model year because of it. When it came back in '01 it was still a turd. It wasn't until the '03 Cobra came out that people stood up and took notice. A reasonably priced good performing car that could put down 500whp without major modifications? Yes please. But, it was supercharged as was the GT500. It wasn't until the Coyote came out that Ford's DOHC platform came into its own with n/a power.

 

[Cascadia_302]

Le Mans? Endurance racing? I guess you're unfamiliar w/ Corvette Racing and Pratt & Miller. I'm surprised someone so quick to 'quote' Le Mans stats would overlook their successes.

They seem to do just fine w/ their 'inferior' pushrod offerings.

So again, who gives a f what the Germans do? America makes the best powerplants I've ever dealt w/, regardless of cylinder head layout (and Aussies, but they're the same manufacturers). The argument that since the Germans don't do it, it must be inferior is ridiculous.

Whatever, it's a big world out there and for any company the takes your attitude and says f-it we don't need to benchmark say the Germans or the Japanese is soon out of business.
For gods sake the Japanese came here and BM Henry Fords production line and turned it into a world class production system that is being BM by industries from around the world.

No doubt about the success of the Vett's, in fact the're the sweetest sounding power plant out there imop.

 

[Hack]

Why are you making German companies some kind of benchmark? Who cares what they do?

I didn't intend to benchmark against German companies. I just wrote a list of companies that make really high quality and high performance cars that spare no expense. I could have put Ferrari on the list. Or Lambo - oops German engineering there too.

I realize our Asian friends can make good stuff too. Recently especially some stuff is quite decent. But I still don't think of them as the tops. The European cars are the ones I would lust after if price were no object. Those are the bedroom wall poster cars.

You would have to be goofy to say that corvette is better than the best offered in Europe. Any comparison favorable to the chevy has to start with "at that price". Price no object the best cars don't have pushrod V8s in them. Period.

 

[Norm Peterson]

The cost of gasoline in Great Britain and Europe is considerably higher than it is here, which pushes the notion of smaller displacement engines being used at relatively higher percentages of maximum load (reduced pumping losses because the throttle is further open).

Actually, Mercedes did develop a pushrod engine of sorts a while ago for Indy-car racing. Apparently there was a big enough gap in the rules to permit a rather unique single cam solution to be competitive. IIRC, the pushrods were extremely short, which probably forced the cam to be located unusually high up in the block. It's a little sad that nothing consumer-oriented ever came out of it.


Norm

 

[Norm Peterson]

The contention was that no 4V pushrod motors exist. That's flat out wrong. There are units in the GM stable, there are diesels.

As far as RPM - what does that have to do with it? Go get a Honda CX500 motorcycle and run it to its 10K redline. That's 4 valve pushrod engine running to 10K.

Diesels run low RPM not because of 4 valves - but because that's the way to maximize the energy in diesel.

There is no inherent limit to RPM with pushrods, and there are as many applications for pushrods as there are for OHC units. The reason you see more OHC units now is they tend to allow a shorter but wider engine. Shallower hoodlines, smaller cars can usually make the tradeoff. Older cars were more upright. It's why I could just about sit inside the engine compartment on my 1962 Ford Fairlane when I rebuilt the small block 221 V8 (289/302 block), but there is precious little daylight on either side of the new DOHC units. They are quite a bit shorter than the old beast, through...

So I hope we can put to rest the myth that pushrods are for 2 valves only, and only for low RPM. There are literally millions and millions of engines out there that say otherwise.

Considering long term durability, I don't think rpm can be ignored. There are trade-offs between valvetrain stability and its mass and the need for heavy valve springs (read: greater parasitic losses, not a good thing these days). As you stiffen the pushrods to push their buckled modeshape off to still higher rpms, they get heavier. As you make the valves larger to permit effective cylinder filling at such rpms without running into problems with excessive overlap, they get heavier. Ultimately everything in the valvetrain gets heavier.

A single cam four valve pushrod design is going to be one huge kludge.
http://www.bing.com/images/search?q...0518247&thid=HN.608012067910518247&ajaxhist=0

Although NASCAR's 9000 rpm engines easily meet the rpm measure here, they can't count, as they are not expected to run more than a few hundred miles before needing at least a refresh. Never mind that they cost as much or more than a whole Mustang as it is. So as good as they are as high rpm large displacement engines, this isn't a street-driver solution. Not even in the absence of emissions requirements.

It's misleading to use a 2-cylinder engine with (twisted, for lack of a better word) 250cc cylinders having barely a 3" bore and a 2" stroke as a point for comparison with V8 engines having inline 750cc cylinders, 4"-ish bores, and 3.6" or greater strokes. The only way you're going to fit four valves into a 3" bore is if they're downright tiny, meaning very light and easily controlled at that sort of engine speed.


Norm

 

[dirty-max]

My duramax put down 645/1226 with its 4v pushrods motor I don't see why everyone says GM needs to go to DOHC when they are doing just fine perfecting the pushrod motor for years why fix something that isn't broke lol every pushrod motor out there gives ford a run for their money while complying with emissions and they still have room to improve I'm sure so many people in here dogging on pushrod motors just because they own a ford it's sad they are all badass I love them all

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