When are Pushrods a good idea?

[Trifler]

I'm wondering about Pushrods. There's never a time when you can only use Pushrods, they're more expensive, less fuel efficient, produce less power, and weigh more than OHC. So, in what situation(s) would you actually want to use Pushrods over OHC?

In concept, it seems like Pushrods should cost less than OHC on a V-8 since only one camshaft is needed instead of two, but that hasn't been the case when I've tried it.

[Unreal2004]

I would use pushrods if I was reproducing an older engine, or one that didnt need to rev high. Pushrod engines DO have benefits over OHC engine, namely reliability when neglected and not maintained as well as should be. In the game pushrods SHOULD be cheaper than dirt to build but as I just tested myself the Direct Acting OHC head is always cheaper then the pushrod head at any year of development and build year...........this isnt right.............at least I dont think it is.....

[Killrob]

There is another thing about them which is a significant advantage: size... for a given capacity they are super-compact compared to all SOHC and DOHC systems. While this isn't that big of an advantage while only having the engine designer, the car designer will give a completely different perspective: you need to actually have it fit into the engine bay.

[Unreal2004]

Didnt think of that, cant wait to see how small the flatties will be when they come out If you have ever seen the difference between a CJ-3A with the L-Head (flathead)134 and a CJ-3B with the F-Head (Intake in head, exhaust in block) its tremendous! The hood is sooooooo tall on the 3B to accommodate the valves up top and thats with pushrods.

[Daffyflyer]

To be honest, a major advantage of them was that it was easy to convert a flathead to OHV, just replace the valves with pushrods, bung some new heads on top and away you go. This would have been a big advantage when changing over from Flathead to OHV engines, and then from there I think they stayed around as a lot of car makers spend 20 - 40 years making iterative improvments to older designs rather than doing new clean sheet designs.


They are quite a bit smaller in head size too.

I wouldn't say they'd be much more reliable than a direct acting OHC setup, given that the ONLY moving parts in that is the cam pressing directly on lifters/springs onto the valves.

[Pontz]

In my opinion, pushrods are a bit underrated ingame. There are and were a lot of applications where pushrod valvetrain is premier choice for
various reasons. Working for a caterpillar dealer I can say that especially construction machines are using them in combination with solid lifters, so there is
not even hydraulic valve lash correction, which is standard for automotive engines for a long time.
A construction machine engine must be capable of running up to 24 hours a day, 6-7 days a week, sometimes under severe load. Sure, they are large displacement,
low rpm diesels, but there must be some advantages in terms of costs and reliability, otherwise it makes no sense.
And telling that pushrods can't achieve high rpm is also not entirely true, as nascar engines rev up to 10k rpm iirc.
The size advantage can be neglectable in some cases, as american cars for example can have a lot of free space in their engine bays around
the engine, where some OHC or DOHC heads would fit too.
I don't want compare apples to pears, but I think that pushrods need some balacing, because as Trifler and Unreal2004 said in their posts, there is
hardly a situation where you would use pushrods at the moment.

[Daffyflyer]

NASCAR V8s only hit such high revs thanks to exceedingly high valve spring pressures mind you.

Big changes are coming with the next update too.

Also, in your opinion would you say that an OHV valvetrain is more reliable than an equivalent bucket OHC setup? I'm willing to believe it might be, but I'd be interested to know why (bearing in mind we assume hydraulic lifters for all engines)

Are there any other advantages that OHV is currently lacking do you reckon?

[Unreal2004]

OHV is much more reliable that OHC in a neglected engine for one, if you dont change the timing belt it will break much much much earlier than a chain driven OHV, if the OHV is gear driven then it can for all intents run forever (unless you use a plastic gear drive then you will have issues). An OHV engine will also have a much simpler casting setup for the head, there doesnt have to be any special oil galleries drilled in the block & head or special hollow bolts to hold the cam since the oil will go up through the lifters and pushrods to the rockers at the top, there are no bearing bores that need to be machined into the head or objects (cam) sticking outside the head that need to be sealed so they dont leak. They also give a VERY convenient place to run fuel and oil pumps off of, my truck's diesel injection pump is run off of the cam gear, makes for an easy mounting right in the intake valley.

In the end I believe that an OHV will have greater reliability and cheaper service costs than the equivalent OHC setup just for the fact you don't need to worry about changing a timing belt, if you ever do break a chain the car itself is usually falling apart as well and its time to replace the car. Also alot of OHC engines drive the water pump off of the timing belt, this means if the water pump fails you tend to get coolant in your oil and its a much more involved repair than a typical OHV water pump replacement.

Pontz has a very good point about engine size, you look at a typical American engine bay and it is HUGE (think 80's chevy pickup) but we still ran pushrods because they were cheap to build, maintain and were very reliable. Look at the Ford 300, that engine is damn near bullet proof and uses pushrods, if it was an OHC I dont think it would have earned that reputation.

I am not bashing the OHC in anyway though, this post is just meant to highlight the pluses of the OHV that can be missed these days, OHCs have their place just like OHVs do. In the end if I wanted low cost, simplicity and reliability I would go with an OHV, if I want the utmost in power, quietness and more electrical goodies (VVT e.t.c) I would go with OHC.

ON EDIT: A word I left out I added in RED

[Daffyflyer]

Excellent post! We shall consider that info when tweaking reliability

[Pontz]

Let me introduce a different approach:
Instead of boosting pushrod reliability, a small penalty to "early" OHC setups could be more historic or realistic. As far as I could read myself into it, the major advantage of OHV
setup was it's easy upgrade from existing flathead/sidevalve engines, as Daffyflyer mentioned a few posts earlier. But there was also a disadvantage to early OHC setups, namely the
lacking of proper guidance methods for the timing belt or (longer than OHV-) timing chain. You also need a pulley to tighten the belt.

Imagine you want to introduce a brand new engine series, featuring a modern, perhaps newly researched OHC setup to render your dusty flathead/OHV obsolete, then you should suffer
from the same curses or risks like real car companys did. Ask yourself: Expensive new design from scratch...? Shaky timing belts...? Maybe stick with proven technology....until
we cand handle the new?
Now to the penalty I mentioned, but it depends on your approch how to model research of engine parts in the finished game: Brand fresh born technology with sudden failures, high costs
and distrust from customers after those failures rise. Polish your tech inhouse by assigning hordes af engineers to build test rigs, study the math, improve the iron cast...or watch how your
new car featuring (insert new tech here) stutters, but perhaps gain painful real life experience from it. People knowing the old school "Transport Tycoon" game may remember that every time
a new plane, train or truck is introduced ingame, it suffers from regular breakdowns due to low reliability % until time (and invisible imaginated research) cures it's childhood diseases. Because
of this, it's sometimes better to stick with the old steam locomotive until its time is really over and the new diesel outruns it clearly (and hey, the steamer is paid! ).
Sure, not every milestone in automotive history was doomed to die at the beginning, but some were. And some needed a small touch by fortune and coincidence...the experiences of the oil
crisis brought eco boxes on their way, for example. I don't know if the idea of developing your tech to reduce it's (historic) flaws fits into your current imagination of how automation should
work, but it may be a way to bring each technologies (initial) pros and cons into the game. It would reward the brave researching player with the benefit of superior technology once he mastered
it by coin and labour.
It would also allow to distinguish the engines of different ingame companies: Company A's brand new 2.0 litre I4 DOHC thrown on the market to compete with company B's top dog, but it's A's
first step with DOHC technology, while B is producing and fine tuning them for years. In theory, they are the same. But in reality, they are not. So how to simulate this realistic? (technology year?)
A good real life example would be BMW's inline six or the Honda DOHC I4. My thoughts so far

[thereddaikon]

OHV is much more reliable that OHC in a neglected engine for one, if you dont change the timing belt it will break much much much earlier than a chain driven OHV, if the OHV is gear driven then it can for all intents run forever (unless you use a plastic gear drive then you will have issues).

That is assuming you are comparing to belt timed OHC engines. My daily is DOHC and chain timed. It has the same advantage there. Also Belt/chain/gear is not a choice in game so it a bit of a wash. All automation engines are belt driven I think anyways.

An OHV engine will also have a much simpler casting setup for the head, there doesnt have to be any special oil galleries drilled in the block & head or special hollow bolts to hold the cam since the oil will go up through the lifters and pushrods to the rockers at the top, there are no bearing bores that need to be machined into the head or objects (cam) sticking outside the head that need to be sealed so they dont leak. They also give a VERY convenient place to run fuel and oil pumps off of, my truck's diesel injection pump is run off of the cam gear, makes for an easy mounting right in the intake valley.

Unless you are dealing with an engine like the early Northstar that was notorious for leaking oil, even from places that oil shouldn't be, that really isn't an issue.

In the end I believe that an OHV will have greater reliability and cheaper service costs than the equivalent OHC setup just for the fact you don't need to worry about changing a timing belt, if you ever do break a chain the car itself is usually falling apart as well and its time to replace the car. Also alot of OHC engines drive the water pump off of the timing belt, this means if the water pump fails you tend to get coolant in your oil and its a much more involved repair than a typical OHV water pump replacement.

See above, many OHC engines are Chain timed, some also gear timed, but that tends to be a race thing. You tend to see this especially in german engines. I don't know of a mercedes engine that isn't Chain timed. BMW engines to my knowledge are the same way. Why Ferraris aren't chain timed I will never know.

Pontz has a very good point about engine size, you look at a typical American engine bay and it is HUGE (think 80's chevy pickup) but we still ran pushrods because they were cheap to build, maintain and were very reliable. Look at the Ford 300, that engine is damn near bullet proof and uses pushrods, if it was an OHC I dont think it would have earned that reputation.

Size is IMO the biggest advantage of pushrods.I think the reliabilty of american V8s has far more to do do with their stout nature and relatively low stressed state of tune relative to other engines. Even the very powerful Z/28 camaro made only 70hp per liter, not that it needed more than 350bhp. I have heard of people damaging the valve trains on OHV engines through running too many revs and the pushrods failing, but the only times I have heard of OHC valvetrains failing is normally when either a timing belt fails due to neglect or if something goes wrong on the bottom end. Again, belt's weakness isn't an inherent issue in OHC. In theory you could have a belt driven OHV motor. And remember simple doesn't necessarily mean reliable, besides any non-VVT/VVL engine has a pretty simple valvetrain, OHC or not. There really isn't all that much to it. One could argue greater friction and drag due to the more complicated valvetrain but that's canceled out by the low VE and low rev nature of OHV anyways

I am not bashing the OHC in anyway though, this post is just meant to highlight the pluses of the OHV that can be missed these days, OHCs have their place just like OHVs do. In the end if I wanted low cost, simplicity and reliability I would go with an OHV, if I want the utmost in power, quietness and more electrical goodies (VVT e.t.c) I would go with OHC.

I really do think that valvetrain config has little to do with engine life. Much much more important is engine stress level, how it is treated, maintained and how good the components that make it up are. You will see that many domestic "bulletproof" V8s have other characteristics present that probably have a bigger impact on this. heavy iron blocks, low revving nature, relatively low compression and in low stress setups. An engine like that will certainly live longer than a high strung, high specific output motor no matter what its made of.