Javelin wrote:mguar wrote: In reply to corytate: Pushrod engines in NASCAR make 950 horsepower out of 358 cubic inches.. that's 2.65hp per cubic inch Formula 1 make about the same out of 145 cubic inches that's 6.55 horsepower per cubic inch..And NHRA Top Fuel makes about 100HP per cubic inch. With pushrods. So, you were saying?
Yeah. They will. For about fifteen seconds. 
Javelin wrote: Seriously, look up the old Ford 427 motors. They started as OHV and Ford made some SOHC 2V versions (the "Cammer") and there really wasn't a power difference. Very interesting to research, anyway.
IIRC, though, the main reason for putting the cams on the head was to get the pushrods out of the way of the intake ports, a serious fault of the FE engines.
And then there's this workaround:
The 427 Tunnel Port - can't fit the intake port between the pushrods? Plow right through it!
Interesting: The 427 Cammer was closer to a true hemispherical chamber than the Boss 429. Or the 426 Hemi.
Also interesting: GM has a new Midget-specific pushrod 4-cylinder engine. (Rules always define racing engines, and there's a hefty displacement penalty for OHC) They finally are putting the camshaft on the exhaust side of the engine, so the intake ports don't have to snake through them!
mad_machine wrote: not necessarily true. Many OHC engines have the cams actuating directly on the lifters.. no rockers are involved at all. That does discard quite a few parts
Yes, but for packaging reasons, rockers are still frequently used. It's also the only way to do a single-cam 4v head.
Rockers also make variable lift a lot simpler since you can use an eccentric for the lost motion device.
mguar wrote: In reply to Javelin: NASCAR engines last 1000 miles and Dragster engines last 1/4 mile.(OK 5/8ths of a mile with burn out) Hmmm I'll leave that statement stand..
And the LSx's in the LeMans Corvettes last 24 hours of racing at a higher specific output. What's your point?
Ooh! Can I be the first person to scoff and say something like "Silly piston engines"?
Looks like I can.
Meh, it's all moot anyway. The big issue isn't pushrods (or chains or whatever), it's the actual camshafts. Right now to do variable lift/timing you have to have cam phasers, variable lifters, and all sorts of crazy engineering.
The future is all pneumatic valve engines. Infinitely variable valve events, even to individual cylinder. You can have different timing, lift, and duration as the engine warms up, or for power demands, etc. In fact, I'm pretty sure they wouldn't even need a throttle plate.
And despite what Mr. Mguar thinks, F1 engines are not OHC. They are Pneumatic Valve. 
The other cool thing was the Coates Rotary Valve. I really want to see one of these run in person:
And despite what Mr. Mguar thinks, F1 engines are not OHC. They are Pneumatic Valve.
I'm pretty sure that F1 engines still have cams(overhead cams that is). They just don't use valve SPRINGS. They use air pressure to avoid resonance among other things.
tpwalsh wrote:And despite what Mr. Mguar thinks, F1 engines are not OHC. They are Pneumatic Valve.I'm pretty sure that F1 engines still have cams(overhead cams that is). They just don't use valve SPRINGS. They use air pressure to avoid resonance among other things.
Every major engine supplier supposedly had completely camless versions of the V10's ready when the FIA pulled out and switched to this stupid rev-limited V8. 
Renault has some running around still testing.
Arrgh! My google-fu is failing me. I have an old Hot Rod laying around (maybe 2005-ish?) with an article on alternative tech engines, including the rotary valve. In it there's a picture of a Ford 2.5L Lima 4-cylinder with a custom camless head with pneumatic actuators. Used something crazy like 220V IIRC. I can't find that article or pic online though. Anybody?
In reply to Javelin:
They are not pneumatic, they are electromagnetic. The last engine i saw with that was a V8 in an Jag. huge energy to drive it.
I think the tech that Javelin meant to refer to was electronically controlled valves. Renualt did some reasearch into it (as most other mfrs I'm sure). The pros are (as mentioned) infinite variability to valve timing, very fast close to open time and no concerns about valve float/cam damage. The cons are high power consumption to operate the solenoids driving the valves open/closed and material issues at the valve seat due to high valve speed at closure. The pneumatic valves also pose problems when it comes to shipping. In the early days of pneumatic valves, several F1 engines were shipped to the track and failed immediately on spinning over due to the valves losing pneumatic pressure...
Javelin wrote: OHV is about the best setup you can do from an engineering standpoint.
If you've spent any time as an engine builder, you would disagree with that 100%. The pushrod, and the timing chain are the big problems, and the small lifters, and little cam lobes aren't helping, either. Roller lifters helped that a lot, though.
Zomby Woof wrote:Javelin wrote: OHV is about the best setup you can do from an engineering standpoint.If you've spent any time as an engine builder, you would disagree with that 100%. The pushrod, and the timing chain are the big problems, and the small lifters, and little cam lobes aren't helping, either. Roller lifters helped that a lot, though.
I have (I was a Certified Engine Rebuilder in the military), and the issues you describe are just poor engineering from back in the day, which applied to nearly every engine. Look at the drivetrain in a new pushrod motor (LSx, Hemi, etc) and you'd be amazed. Full roller cam, "captured" lifters with tie-bars, beefy pushrods with good geometry, aluminum roller rockers, beehive springs, etc. And hell, the double-roller timing chain has been around for what, 60 years?
If you really want to see bleeding-edge engine tech, look at the NHRA or IHRA Pro Stock engines. The cams are raised by a ton in the blocks which really makes things nice from a valvetrain layout.
That's just a lot of work to overcome a bad design.
Put the cam over the lifters, run it by belt, and call it a day. It's about as stout, reliable, and hands off as a system gets.
Just remember, it's a system. And the point is to move air in a specified manner to make power and torque in a specified way, most of the time at a certain price point.
don't get too deep into which is best. It depends. And rules matter.
In reply to Zomby Woof:
Are there any belt-drive OHC engines anymore? I know I sure as heck don't want to change any Audi chain tensioners!
Even the Ford 4.6 SOHC was pretty work intensive:
I know a lot of Japanese V6's used them in the 90's though, they weren't too bad.
In reply to alfadriver:
What do you think about the electromagnetics? (Thanks BTW, though I still can't find that damn article or picture).
I was always (and still am) a fan of belt driven OHC. Quiet, inexpensive compared to chain drive and pretty damn reliable. I have seen lots of belts with a recommended 105k interval still in place at 175k or even higher. It's also cheaper to repair or replace (unless it's an interference engine and it busts).
People freak about timing belts all the time but they're usually a 90k+ maintenance item. On most cars it takes a weekend to replace and costs a couple hundred bucks with the water pump and everything. Per mile that's basically nothing, time or money wise.
What are cams, pushrods, and rockers?
Puts down "The Wankel Rotary Engine".......oh wait, I remember now....
The same debate waged here is also the source of the same debate as to what is the displacement of the rotary.
Javelin wrote: In reply to alfadriver: What do you think about the electromagnetics? (Thanks BTW, though I still can't find that damn article or picture).
Jury is still out. Right now, I'm not optimistic about them at all, but with improvements in magnets, it's possible that these massive poppet valves will work.
They DO work, it's a matter of a whole bunch of stuff to be ready for prime time, if ever.
I would imagine pneumatic valves would vary in speed quite a bit depending on engine load, especially when you start adding tarbos and moar boost. Might get tough to close those valves. But I'm speculating.
Hey, why don't we all switch to intake valves that are opened by the vacuum in the cylinder as the piston descends? No valvetrain losses.
I seem to recall that the engine in the Wright Bros.' airplane used this design so it could be as light as possible. I could be totally wrong.
Curmudgeon wrote: I was always (and still am) a fan of belt driven OHC. Quiet, inexpensive compared to chain drive and pretty damn reliable. I have seen lots of belts with a recommended 105k interval still in place at 175k or even higher. It's also cheaper to repair or replace (unless it's an interference engine and it busts).
Honestly, you COULD hold your breath on that one.
Recent developments have produced wet belts (oil bath), which are durable. The minuses of belts are being fixed pretty quickly so that their pluses will put them back ahead of chains.
And that does go for both under head cams and over head cams for drive.
Curmudgeon wrote: I was always (and still am) a fan of belt driven OHC. Quiet, inexpensive compared to chain drive and pretty damn reliable. I have seen lots of belts with a recommended 105k interval still in place at 175k or even higher. It's also cheaper to repair or replace (unless it's an interference engine and it busts).
You don't need OHC to enjoy all of the positives of a belt drive!
They make timing belt kits for a ton of V8's. Pretty slick.
that is pretty slick.... are SBC interference engines?
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