OHC vs OHV

an OHV engine will make more power at a lower rpm

Not true. Lower RPM power has nothing to do how the valves are opened and closed.

No matter the truth, OHCs are so much cooler. They have been since the 60's when all the coolest British sports cars had them.

In reply to carguy123:

OHC..

Meh.

kreb wrote: I'm really sorry that GM hasn't made a 6 cylinder variant of the LSX motor. They got good numbers out of the final version of the 60 degree pushrod v6. Don't know why they never Made a shorty LSX.

NVH of a 90 V6 vs that of a 60?

Also the 90* would be a good bit wider.

GM already knows all about 90* V6 engines, they've learned their lesson.

I'm very fond of how simple ohv engines are, at least to me. easier disassembly, easier everything essentially.
And I've been saying for a while now how amazing the numbers GM is getting out of their "antique technology" are. Going to be ridiculous when/if they start running dohc, IF they succumb to the dohc disease like ford finally has.

alfadriver wrote: Oh, and not nearly as beefy as the valves. Way more effort goes into opening and closing the valves compared to the fuel pump.

The valves only open once per cam revolution. The DI pump lobe would open four times per cam revolution on a V8 engine, so the events are a lot quicker.

It's an interesting problem. No doubt they've figured it out, and I can't wait to see what they did.

mguar wrote: and now since they have removed zinc from modern oils because of the catalytic converter they have to add weight and complexity to a pushrod motor with roller lifters..

It's not the zinc, it's the phosphates. Zinc was just the first word in the chemical name...

But the revolution to rollers happened long before the oil reformulation happened. It was simple - roller engines get better fuel economy due to lower friction, even before you figure into the cam design capabilities of a roller. GM started phasing rollers in around 1986, complete around 1996. Chrysler was using rollers in OHC engines!

But don't worry... roller cams are showing wear problems now. I've heard rumors of the fuel lobes on DI engines wearing, as well.

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..

They are also within .1% in BMEP. HP is mainly a figure of how high you rev the engine, BMEP is how efficient the engine is.

Both series would make more power if not for rules limitations. IIRC, F1's main problems were the packaging rules, NASCAR's biggies are carb size, allowable gear ratios, and the use of flat tappet cams. One treatise on the R07 engine said that the oil system was "priority camshaft".

Trans_Maro wrote: In reply to carguy123: OHC.. Meh.

Wow. Check out the length of the rockers, also the valve spring placement. Sorta reminds me of a desmo Ducati if I lean my head and squint.

I figger the C/R was probably 4:1.

Riley twin cam (in block) engine. Donald Healey used these in his cars right up till the first Austin-Healey was built.

I have heard rumors they built a V8 before Dubya Dubya Twice but have not found any definite proof.

Knurled 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..

They are also within .1% in BMEP. HP is mainly a figure of how high you rev the engine, BMEP is how efficient the engine is. Both series would make more power if not for rules limitations. IIRC, F1's main problems were the packaging rules, NASCAR's biggies are carb size, allowable gear ratios, and the use of flat tappet cams. One treatise on the R07 engine said that the oil system was "priority camshaft".

Yep, the F1 engines are limited on RPM's by the rules, where conceivable they would make more power.

He's also high on their output by about 200hp.

Knurled wrote:

alfadriver wrote: Oh, and not nearly as beefy as the valves. Way more effort goes into opening and closing the valves compared to the fuel pump.

The valves only open once per cam revolution. The DI pump lobe would open four times per cam revolution on a V8 engine, so the events are a lot quicker. It's an interesting problem. No doubt they've figured it out, and I can't wait to see what they did.

Or 3- there are two flavors of DI pump cams. Just becuase the events happen faster does not mean the cam is that much different, or that the spring needs to be any stronger. If you look at the inside of a fuel pump, the actual pump is pretty small in diameter- so the load on the cam isn't what a valve is.

It's also a much shorter stroke....

The interesting thing is how they plan on making considerable power with DI- right now, the best pumps volume limit out just north of 400hp/400lb-ft of fuel flow. So you can run two pumps, OR use a DI/PFI set up- either of which has it's pros and cons.

Either way, putting the high pressure pump down into the valley makes the most sense, even with temperature problems.

mguar wrote: All pushrod motors I can think of are 2 valve heads.. Plus the rocker arms add considerably to friction ..

Didn't someone post a picture of a 4 valve pushrod head in this thread?

Rocker arms are not exclusive to OHV engines, there are plenty of OHC engines that have them. The rocker arms are just acted on directly by the cam instead of a pushrod so the friction is present in some OHC engines just like in OHV engines.

One of the packaging problems with OHV engines doesn't have to do with packaging the engine in the car, but packaging the pushrods in the engine. A lot of times the pushrods and the intake port want to occupy the same real estate (the pushrod will go right through the ideal intake port design). There's only so much leeway in placing the pushrods without going to an offset rocker arm so you end up with an intake port that gets pushed off to the side and takes an awkward 90 degree turn right before the valve, or you end up with a pinch point restriction in the port where the pushrod intrudes. The effects of this issue have been greatly reduced over the last several years because of the tremendous increase in availability of CFD for engineers. You used to have to send you design off to another group and wait for them to get time on the solver computer to run your design flow study, now it can be done on your desktop while you're working on another design, so manufacturers are getting much better designs to work around this problem.

Pet peeve, OHC engines ARE OHV engines. OHV is compared to L head or Valve in block designs whre the valves are NOT Overhead.

And there was mention of NASCAR VS F1 HP/Liter. Can we not use HP/liter for anything either? It's meaningless, as it's simply easier to get more hp/liter from a smaller engine. I mean, a Cox .049 model airplane engine makes over 500hp/liter, but you wouldn't want to power your car with it...

As was mentioned, pushrod engines are not any more ancient than OHC engines. There were DOHC engines as early as 1912, and even US manufacturers had DOHC, 4 valve per cyl, aluminum engines in production by 1932. The '50s thinwall pushrod V8 was in fact a high tech alternative to the overly complex European DOHC engines, in order to provide similar or greater levels of power in a smaller, more reliable, cheaper package. And isn't that what advancing tech always does? Makes things perform better in a more compact, simpler, cheaper form? These days advanced tech is in metallurgy and engine controls, not in how the valves are actuated.

wow arao makes 32v heads for the lsx too......

32v ls7 powered miata mmmmmmmmm yummy.....

Zomby Woof wrote:

And to be honest, it is a more reliable and rebust design.

I disagree. With less moving parts, the OHC setup will be more reliable, and most OHC top ends that I know of are far more robust than OHV.

And I disagree with you. OHC setups really only lose 1 part (the pushrod). They still have to have a rocker, lifter, spring, retainer, etc. And you're adding in an extra cam (or 3), higher pressures, and can't have the advantageous ratios. Not to mention a much larger timing train (look at Ford Mod and Audi V8 chain failures). In a V-engine, OHV is about the best setup you can do from an engineering standpoint.

novaderrik wrote: yeah, an OHC engine will rev faster and higher, but an OHV engine will make more power at a lower rpm- even if it puts out less power per unit of displacement.

I don't think either of those statements are true. If you took identical engines except for the layout of the cams (so same cam specs, same # of valves, bore x stroke, etc, etc) it should be a wash. The OHC might have better valvetrain stability, but again that all depends on design/engineering.

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.

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?

So to add to the discussion. The Ford Cologne V6: Could be had in multiple displacements but lets look at the 4.0 liter variety. It could be had in a cam in block (OHV) and an over head cam (OHC) configuration. Why did Ford do this? I dunno...

Chris_V wrote: Pet peeve, OHC engines ARE OHV engines. OHV is compared to L head or Valve in block designs whre the valves are NOT Overhead. And there was mention of NASCAR VS F1 HP/Liter. Can we not use HP/liter for anything either? It's meaningless, as it's simply easier to get more hp/liter from a smaller engine. I mean, a Cox .049 model airplane engine makes over 500hp/liter, but you wouldn't want to power your car with it... As was mentioned, pushrod engines are not any more ancient than OHC engines. There were DOHC engines as early as 1912, and even US manufacturers had DOHC, 4 valve per cyl, aluminum engines in production by 1932. The '50s thinwall pushrod V8 was in fact a high tech alternative to the overly complex European DOHC engines, in order to provide similar or greater levels of power in a smaller, more reliable, cheaper package. And isn't that what advancing tech always does? Makes things perform better in a more compact, simpler, cheaper form? These days advanced tech is in metallurgy and engine controls, not in how the valves are actuated.

This entire thread could be discarded as this post summarizes everything quite nicely.

tuna55 wrote: This entire thread could be discarded as this post summarizes everything quite nicely.

But FWD ROCKS.

Chris_V wrote: And there was mention of NASCAR VS F1 HP/Liter. Can we not use HP/liter for anything either? It's meaningless, as it's simply easier to get more hp/liter from a smaller engine. I mean, a Cox .049 model airplane engine makes over 500hp/liter, but you wouldn't want to power your car with it...

I like to call it ricer math. On dyno day last year at school, the kia won the ricer math showdown, with 70 hp/litre for a 2.0, vs a c6, an '11 Ram, and a mid 70s nova with a 350. This does not make the kia faster than the c6, which got something like 60 hp/litre to the wheels. =]
hp/ton is a little better but it still leaves out some important stuff like, ummmmmmm..... gearing?

Javelin wrote:

Zomby Woof wrote:

And to be honest, it is a more reliable and rebust design.

I disagree. With less moving parts, the OHC setup will be more reliable, and most OHC top ends that I know of are far more robust than OHV.

And I disagree with you. OHC setups really only lose 1 part (the pushrod). They still have to have a rocker, lifter, spring, retainer, etc. And you're adding in an extra cam (or 3), higher pressures, and can't have the advantageous ratios. Not to mention a much larger timing train (look at Ford Mod and Audi V8 chain failures). In a V-engine, OHV is about the best setup you can do from an engineering standpoint.

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