NOS Waster, you're very welcome.
Glad to be able to, and also appreciate that you posted it as well.
BTW, re-reading my post, I meant it to say that the LS7 is basically the same (external) size and weight as the LS1, not the S14 engine. I see now how it could be interpreted either way, depending on how one reads it.
Civic, are you for real? OHV refers to cam in block, as compared to OHC, where cam is in the head. It does not mean that one has valves in a different location.
Seriously, don't try acting like a smart ass if you don't really know what you're talking about.
(and btw, Ford Flathead V8s do not have the valve over top of the cylinder)
On the subject of efficiency and part plurality, OHV struggles with high RPMs because it has more moving parts in the valvetrain. I keep telling you: we're not talking about black and white, here.
It seems to me that now the goal is to simply tell me I'm wrong. lol Well... I'm not, and I won't let it go uncontested.
So, onward......
High rpms are not a good thing in most applications. They are more costly to achieve, and reduce overal engine life. The only reason for them is when you are otherwise limited such as displacement restrictions in racing.
Case in point - can you think of a situation where power mattered absolutely, there were NO "rules" of any kind, and yet rpms were not sought out?
Air combat.
When designers needed to give an edge to their respective air forces, they did so with power. When doing so, they tweaked various areas of efficiency, or ultimately increased displacement. However, they never spun them fast.
You pretty much won't find any prop fighter spinning their engines more than 3000~3500rpm. Yet they make 3000+hp by wars end. This means monstrous amounts of torque. More horsepower could be had easily by spinning them faster. Particularly in the P-47 as it was built around a turbocharger (meaning that it wouldn't run out of breath at higher rpms). But they didn't do it.
The simple reason is reliability. As important as HP was to performance, engine life and maintenance and reliability were every bit as important. Literally life or death.
No other example brings that combination together - of power AND reliability both being literally life or death, and no rules body dictating displacement or rpm or induction limits, and yet... they still spun them slowly.
However, in regards to your notion that you can't spin OHV fast, both NASCAR and the LSx engines prove that notion false. There were even engines in the 60 spinning up to 7K -with flat tappets!
Point is, they don't need to. And, a smart engineer won't do it just to do it. There are better ways to achieve the power.
On the subject of weight, less of it is always good, but the engine isn't the whole car. To address that very argument ("OHV engines are better because they're lighter") I like a little thought experiment I've used before: Take a 3000lbs. car, equal in every way, but with two engine choices; a 5.0L OHV engine, and a 5.0L DOHC engine. The OHV engine weighs 200lbs. and makes 300hp. The DOHC engine has a significant weight disadvantage, weighing over twice as much -- 500lbs. -- but manages 100hp/L, making 500hp.
You've now got a 3200lbs. car with 300hp, and a 3500lbs. car with 500hp. Which is faster? We're dealing with hypotheticals here, so a simple power-to-weight ratio will do.
This demonstrates nothing but an ability to carefuly manufacture a hypothetical example to try to support your stance. There is no reason that one engine would be so lazy compared to the other. The valvetrain design certainly is NOT it.
Nor does your example get into issues of having all that weight high up, just under the hood, nor the amount of bulk required to do something like that in aluminum, and the associated design issues and compromises that go along with that.
On the subject of complicated timing arrangements, I've read variable valve timing with OHV is not easy (ie. complicated). Although it's been done over at GM, their system can't withstand hard driving, and is pretty much limited to SUVs and automatic transmissions (auto because engine RPM with a manual is too "unpredictable"). Another disadvantage-for-an-advantage. It should start becoming clear why cars aren't all OHV or all OHC.
Yes, you touched on it later in your post - tax on displacement. It's not quite FIA limitations, but it's close. Secondary to that is public perception. Look at this thread alone. People assume that big cube means heavy, old, low power, low tech, and gas guzzling. Absolutely NONE of which is true, but it's the perception. Unless your market wants big engines (Corvette, Viper, F-Body, etc), why would you try to use one? (remember, sales trumps engineering - always)
The whole "bulk of package" advantage makes LSx engines and other OHVs a convenient choice for engine swaps, but that's about it; an engine is always designed or carefully selected for its application. Hell, BMW still uses DOHC inline-6s in their smallest car. And for center of gravity concerns, I'd personally take a boxer engine over any V.
Even when you design a chassis around an engine, the smaller the engine, the more freedom the chassis designer has, and the fewer compromises they will be forced to make.
However, in most cases, the engine is NOT designed for the application, rather the other way around (as I said above). The LSA was not designed for the CTS. The LS1 was not designed for the 4th Gen F-Body, the LS3 was not designed for the Monaro/GTO, etc. And the series (both Gen III and IV) are present in various forms and materials (like iron) in many, many more applications. By virtue of it's small size and lightweight, it's incredibly useful across a wide range of applications, always with good power to weight for both efficiency and performance, as well as low CG for same.
Yes, a boxer is even better in that last regard. But that has other drawbacks as well. Everything is a compromise.
Actually, I6s are quite rare today;
"
today". My point was that when you start with something, you get a rep for it and you keep it. Even when going from DOHC I4, you keep DOHC with V6. It wouldn't be smart not to in those cases, however, it's all about marketing.
The real reason you don't see OHV on imports is because other countries tax cars based on displacement. And SOHC/DOHC will perform better (in terms of horsepower) given a certain displacement. This is one place where hp/L truly matters.
Old vs new vs public perception. Same thing, differnt look. You don't NEED DOHC for power in small sizes. There are many other ways to achieve that goal without increasing displacement.
However, taxing on displacement is case in point for my argument above. The perceptions run so strong and so deep, that gov't will tax people for it, which in turn, cycles back around and furthers these false assumptions.
You know, my WS6 gets 27mpg on the highway, yet puts down 300hp/330ftlbs at the rear wheels, bone stock. Clarkson got 45 in a Prius - a car that's sole reason for existance and claim to fame is about ultimate fuel economy. So much for the theory that more displacement inhernetly means more fuel consumption (see next paragraph for more). (we have a gas guzzler tax too, and the Z06 got away without having to pay it too)
And, the greatest thing is, my car was made to be a performance car, not a fuel miser. It has huge 275/40ZR17s on all 4 corners, it's packed with amenities, and while aerodynamically clean, not to the extent that a prius is. It also weighs 3500lbs thanks to never ending stupid safety regulations and a desire for chassis strength. YET.... it was also meant to be cheap too. So not much effort was put into it from a design standpoint, not like a Corvette or Ferrari anyway. A different PCM tune, more power with steeper gears, weight reduction, DoD, DI, lower ride height, flat underside.... the list goes on of stuff that could be added to make my sports car quite fuel efficient, despite it's "big V8".
I understand you're not a fan of NASCAR (neither am I), but the engines they use are smaller than the LS7. And obviously designed for a very different set of conditions.
Only difference is bore x stroke. And it's still a 5.7 in NASCAR. Remember, the LS1 had it's block tweaked into the LS6, and from there, a slight redesign lead to the LS3, which was 6.2L, but for all practical intents and purposes, still basically an LS6 (which is basically an LS1). The 7, in simply a bored and stoked LS3. This is why these engines all take up the same space and weigh the same, dispite the displacement ranging from 346ci to 427ci.
The real difference between NASCAR and LSx's is money. Just like F1 engines cost $$$$$$ and don't last very long, the same is true for NASCAR. LSx's are street engines that have to fit a bottom line and be reliable for at least 100,000 miles, under most driving condtions an owner would put it through.
People also love to point out when DOHC engines make the same power as larger OHV engines. Why not put DOHC on the larger engine too? We've all seen DOHC on a 2.0, throw DOHC on a 5.0 and see what you get.
Spoiler: Europe has known the answer for years (in expensive cars, yes, but expensive for a variety of reasons
beyond engine tech), but
Ford is now finding out for themselves.
It's not DOHC that does that.
Also, do not equate peak power output with real world usability and livability. As well, you simply can not ignore everything else (design/manufacture cost, bulk, weight, reliability, CG, etc). But that is what you are doing in the name of placing DOHC at the top.
Bear this in mind. I'm not saying that DOHC is worthless. I AM saying that we aren't running F1 cars at their peak all the time, and in the real world, on road cars, there IS a better way to go about it. But mostly, I'm showing people that large engines with OHV valvetrains actually DO have advantages and good points. Which is why I'm forced to reply to every single one of your posts, because you are trying to undo this (and are also trying to suggest I'm wrong when I'm not). It's this very mentality (which I'm attempting to address) that lead to the comments that set me off in the first place.
Fair enough. But if you're going to complain about assumptions like those, it's not fair for you to turn around and assume OHC = inefficient, too much weight, needless complexity, and too bulky.
Yes it is. For the street in a street car. Absolutely. (in the absence of special parematers and restrictions, like taxes, mistaken public mindset, etc - speaking purely from an engineering and peformance standpoint, bearing in mind the total street car life/usage)
I understand how Ecchi-BANZAII!! (c'mon, if you're going to be rudely obvious, we have names here) could have irked you with his post. But your comments have been just as needlessly dismissive as his was. Each form of valve control has its advantages, disadvantages, and appropriate applications. One happens to favor high-RPM power, another happens to favor low-RPM torque and response, and the other (SOHC) sits somewhere in the middle. That's all.
'cept I have not been assumptive or dismissive at all. If anything, I could say that you have been in this attempt to place DOHC back at the top at any cost. You're ignoring or dismissing most real world factors in the name of this struggle. Which is why I'm forced to slog it out in such a lengthy way that people often hate to read.
As for your final comments, we'll have to agree to disagree. But I hope you can see how hp/L might matter to someone who lives where displacement is taxed.
Again, you don't seek HP/l, you seek HP. getting 200 hp/l out of a 1L is NOT better than getting 100 hp/l out of a 3L engine. I'm using numbers that are easy to see purely for the sake of example. There will be a range of disp sizes under the tax threshold, and going smaller and trying to wind it up more is not advantageous at all. But it makes for better ricer math. And thus, in the end, that's all it is. Nobody really uses it for anything other than trying to brag, and it's almost always the guys with the little engines that do it (compensation syndrome on their part maybe? lol!
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(<- that's a joke and rhetorical btw, not a question that needs an answer))
