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I Still Like Pushrods, They're Still Viable

Engine tech, for those engines, products, and technologies of yesteryear.

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PackardV8
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Re: I Still Like Pushrods, They're Still Viable

Post by PackardV8 »

JCR wrote: Wed Apr 21, 2021 4:02 pm
David Redszus wrote: Wed Apr 21, 2021 10:46 am What improvements have been applied to aircraft engines since then?
As for aircraft piston engines, none. While technically feasible, it not regulatory feasible. So there will be not improvements made due to them being "certified".
It's also a liability issue. A significant percentage of homeowner lawnmower retail cost is lawyer-related. That's why no manufacturers are stepping up with 21st century aircraft engine designs.
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Re: I Still Like Pushrods, They're Still Viable

Post by Truckedup »

I was doing electrical construction at a large local auto dismantler. There were several buildings with hundreds of late model engines arranged by make...All the larger displacement DOHC V6's and V8's appeared huge, high and wide....The Hemi's less so...Then came the LS Chevy section, they appeared small and compact , you could see spark plugs and the starter motor.... :D
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire
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Re: I Still Like Pushrods, They're Still Viable

Post by Ken_Parkman »

The point of the Porsche article was in support of pushrods as in some cases a superior technology. Obviously in aircraft weight and packaging are ultra critical so this is an extreme example, but the point is relevant. The "high tech" OHC engine could not make up for the pushrod advantages. The OHC 193 cu in 6 cylinder was larger and heavier than the 320 cu in 4 cylinder, and as installed was lower performance, payload and efficiency and also more expensive.

So which is the higher tech?
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Re: I Still Like Pushrods, They're Still Viable

Post by Ron E »

Nice to see an adult discussion on this. All types have strong and weak points. Matching the best compromise of these with requirements of a specific application is why they're all still relevant.
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Re: I Still Like Pushrods, They're Still Viable

Post by PackardV8 »

I know of a work boat in which many years ago, a Detroit Diesel was essentially walled in as the boat was modified; the rationalization was it was a special-use boat which would be obsolete before the engine had to be replaced. It would require cutting the boat apart to replace it. Doing an "in-frame" with sleeves, pistons and head requires the mechanic to lie in a dirty bilge and work on his back. Every ten years, they call him, he doubles his price, but that boat is still working. Pushrods rule!
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Re: I Still Like Pushrods, They're Still Viable

Post by MichaelThompson »

Hang on a second guys. Diesel engines and gasoline engines are different animals. In order to certify a Diesel engine for road use you need to add thousands of dollars worth of emissions control systems. This has put diesels in light vehicles in the almost impractical category.

Also are we actually saying that variable intake and exhaust timing are not huge benefits of OHC’s no matter the number of cylinders and their arrangement?

The only mechanical drawback to OHC’s is the cam drive system maybe. Yes they can be bulkier but they also clear the valley area for important things like low profile long runner intake manifolds or even positive displacement superchargers.
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Re: I Still Like Pushrods, They're Still Viable

Post by PackardV8 »

MichaelThompson wrote: Fri Apr 23, 2021 8:23 am Hang on a second guys. Diesel engines and gasoline engines are different animals. In order to certify a Diesel engine for road use you need to add thousands of dollars worth of emissions control systems. This has put diesels in light vehicles in the almost impractical category.
Yes, and the same forty-year learning curve was necessary to get gas-burners where we are today. Those of us who were there in the '70s remember how very bad those first-generation emissions controls were and how they hobbled the engines. It's possible the diesel can get past the band-aids, but they may not have forty years to do it. The electrics will be here before that.
MichaelThompson wrote: Fri Apr 23, 2021 8:23 amAlso are we actually saying that variable intake and exhaust timing are not huge benefits of OHC’s no matter the number of cylinders and their arrangement?
The GM Atlas-series DOHC 4, 5 and 6-cylinders were GMs first use of VVT technology. It was hailed as the future, but only lasted 2002-2007.
MichaelThompson wrote: Fri Apr 23, 2021 8:23 amThe only mechanical drawback to OHC’s is the cam drive system maybe. Yes they can be bulkier but they also clear the valley area for important things like low profile long runner intake manifolds or even positive displacement superchargers.
Ken Duttweiler was asked why all his engines for Speed Demon were pushrods. "DOHC V8s are just too wide to fit inside our envelope. We can make all the horsepower the car can use with a pushrod engine and they fit, barely."
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Re: I Still Like Pushrods, They're Still Viable

Post by MichaelThompson »

PackardV8 wrote: Fri Apr 23, 2021 1:08 pm
MichaelThompson wrote: Fri Apr 23, 2021 8:23 am Hang on a second guys. Diesel engines and gasoline engines are different animals. In order to certify a Diesel engine for road use you need to add thousands of dollars worth of emissions control systems. This has put diesels in light vehicles in the almost impractical category.
Yes, and the same forty-year learning curve was necessary to get gas-burners where we are today. Those of us who were there in the '70s remember how very bad those first-generation emissions controls were and how they hobbled the engines. It's possible the diesel can get past the band-aids, but they may not have forty years to do it. The electrics will be here before that.
MichaelThompson wrote: Fri Apr 23, 2021 8:23 amAlso are we actually saying that variable intake and exhaust timing are not huge benefits of OHC’s no matter the number of cylinders and their arrangement?
The GM Atlas-series DOHC 4, 5 and 6-cylinders were GMs first use of VVT technology. It was hailed as the future, but only lasted 2002-2007.
MichaelThompson wrote: Fri Apr 23, 2021 8:23 amThe only mechanical drawback to OHC’s is the cam drive system maybe. Yes they can be bulkier but they also clear the valley area for important things like low profile long runner intake manifolds or even positive displacement superchargers.
Ken Duttweiler was asked why all his engines for Speed Demon were pushrods. "DOHC V8s are just too wide to fit inside our envelope. We can make all the horsepower the car can use with a pushrod engine and they fit, barely."
Your points are all well taken and of course the debate rages on.
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Re: I Still Like Pushrods, They're Still Viable

Post by Ken_Parkman »

My 2011 Ram is pushrod and has VVT, variable inlet runner length, and cylinder deactivation. In 200k of serious abuse the only problems have been a rad hose clamp broke and exhaust manifold stud breakage, one each side. In general it has been terrific and I am quite happy with it. But it is a serious pain to change the plugs.

On a V configuration engine pushrods help packaging in all 3 dimensions and that is a big deal. It does lots of good things for the installation, and the reduced specific output can easily be made up with increased displacement with a minimum trade off. The aircraft example is an extreme example as the much larger displacement pushrod engine is able to produce it's power in the rpm band appropriate for the propeller, and you do not need a reduction gearbox - massive advantage. And the frontal area of the 320 inch pushrod was less then the 193 inch OHC so the aircraft aerodynamics are much better. The OHC experiment became absolutely idiotic even though many thought it would be a big improvement - but those people did not understand engine design also includes the complete installation.

With an inline engine the math changes as the OHC typically only hurts you in height. As long as it fits under the hood it's not so bad. Add to that inline engines are usually smaller displacement and have reduced low rpm power capability. So you want the 4 valve DOHC to get the cam duration down and broaden the power band - and add more gears.

As stated a huge factor is the rules you are designing to. If you have a displacement limit or factor as opposed to a good design factor all the above goes out the window. Marketing is also a huge factor as it has been drilled into us you must have these "hi tech" things, even when it is bad design.

Today the technology has come so far that larger displacement engines are not necessary for everyday use and this is what is killing the pushrod.

I've often thought a cool design for an engine for a modern car would be a small displacement pushrod v8, say 3 or 3.5 litres instead of a 2 litre 4 cylinder. But make it really compact and light - scale a ls way down. Put all the modern tech in the design. So it would be a 1.5 l 4 cyl in cruise so you would have a large throttle opening with good cylinder pressure and low pumping losses, yet still have good power and an inherently good low rpm power that displacement gives you. Bet you that would make a great engine with fantastic packaging and installation advantages, and not suffer with 4 cylinder secondary shaking force and moment problems. The pushrod V8 really is natures perfect engine. But I'm not in automotive design and they don't ask me.
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Re: I Still Like Pushrods, They're Still Viable

Post by MichaelThompson »

Once again that packaging issue is a give and take question. The open valley not only clears room for an optimum intake manifold but also how about a starter or oil cooler etc.

I don’t know but I like them both for different reasons and I admit I lean heavily as a Ford guy so maybe my opinion is prejudiced but I can’t think of a neater power plant than the 3.5 Powerboost in the 2021 F150.

The 3.5 is DOHC 4 valve with twin independent valve control coupled with a 10 speed that contains a 45 horsepower electric motor in the bell housing.

I don’t think the same level of efficiency can be achieved if this was a 2 valve pushrod engine.

The Barra inline six from Australia or the 2JZ six are incredible in their efficiency and ability to produce horsepower AND torque.

Meanwhile the LS/LT the Gen III hemi and now the 7.3 Godzilla Ford are downright awesome as well but literally all three of these really cannot make the EPA and CAFE standards as they are today. The GM and Mopar engines are equipped with band aids and the Ford gets around all this by only being available in a 3/4 ton and up truck.

Dutweiller and many other racers really are free from the aforementioned emission and fuel economy standards.
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Re: I Still Like Pushrods, They're Still Viable

Post by Nikolas Ojala »

Suppose we used different fuels, because the modern very tight EPA and CAFE standards practically force us either using different fuels or electrochemical batteries.

Imagine an RCCI engine. It requires two different fuels. The first fuel has very low reactivity, much like high-octane gasoline or alcohol (methanol or ethanol) and the second fuel has very high reactivity, such as modern Diesel fuels.

Let's say that the low reactivity fuel was ammonia and the high reactivity fuel was dimethyl ether. They both burn very cleanly, and there is no carbon in ammonia.

That kind of RCCI engine could be very clean also with two valves per cylinder and without variable valve timing. The engine control works by fuel injection, NOT by butterfly valve that regulates flow. Variable valve timing is not necessary exactly because the fuels are already clean.

Much simpler example would be a Diesel engine that burns only dimethyl ether. At least Volvo has been experimenting with DME Diesel trucks. The engine is essentially a Diesel engine with a different fuel system.

If variable valve timing or number of valves were no more necessary, because emission standards were met by other means, then industry could again concentrate producing compact, inexpensive and reliable engines.
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Re: I Still Like Pushrods, They're Still Viable

Post by ClassicRob »

I’m on my cell so I can’t be long winded here but I just want to say that I VERY much agree with the spirit animal of the OP.

I too, find myself going backwards today and happily settling for less (but more fun) levels of HP. I miss the simpler days and I am happier messing with 375hp 350’s than the 500+hp rides that are also at my disposal. Could it be a sign that the times are too fast or are they just missing something completely?
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Re: I Still Like Pushrods, They're Still Viable

Post by hoffman900 »

I think the the packaging thing is overstated. F1 has been using V engines for decades and those guys live and die by packaging ( (for aero and weight) and they are still DOHC designs. Just very compact.

Same goes for MotoGP bikes which are mostly V4s now.

A finger follower valvetrain can be very compact.

It’s a shame that Ford and Toyota have the only really large-ish OHC engines. Both are really intended for trucks so they aren’r slimmed down like they should / could.

For a mass produced, cheap engine, pushrods do work pretty well. I still like pushrod engines... the aircooled VW/Porsche engines are especially cool. The last NASCAR redesign engines are absolutely awesome, even if they are approaching 15 years old now. I would love to see OEM’s throw NASCAR money at redesigning from scratch, without the NASCAR limitations (other than displacement).
-Bob
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Re: I Still Like Pushrods, They're Still Viable

Post by Ken_Parkman »

Almost always racing has a displacement limit, so there pushrods are bad; certainly F1, so it is a no brainer there.

It is cool how to see advanced design and technology addressing the packaging disadvantage of OHC/DOHC, and conversely addressing the rpm range limitations of pushrods in Nascar/PS until the rev limits were added.
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Re: I Still Like Pushrods, They're Still Viable

Post by MichaelThompson »

The Allison 1710, the Rolls Royce Merlin and Griffon and the Ford GAA V8 are all WWII era aircraft power plants and all three are OHC designs. (The Ford started life as a V12 but when FoMoCo didn’t get a contract from the government they were shortened to V8’s and used very successfully in tanks)

All of these were gear driven OHC’s. The Allison and the RR were SOHC’s with roller followers while the Ford was DOHC with “cam on bucket” style valve gear.

Certainly airplanes have packaging concerns but in my humble opinion pushrod valve actuation on these engines would actually be more complicated than an OHC affair that could approach the VE’s that these engines were seeing.
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