Benefits of a gear driven head?

Speedhunters.com had an article who's author visited OS Giken in japan.

http://speedhunters.com/archive/2010/07/27/gallery-gt-gt-a-quick-stop-os-giken.aspx

They had this awesome picture of an S20 engine that had it's chain drive head replaced with gears.

The author states " This should totally change the feel of the KPGC10 Skyline 2000 GT-R the S20 is fitted to, giving it a smoother operation as well as a different sound. I can't even being to imagine what it will be like at 8,000 rpm!"

What other benefits would there be besides no cam belt changes?

Less drivetain lash I'd imagine. More direct response.

would this need oil? what happens if he strips a gear? seems like alot of failure points, though probably no more than a timing chain? I'm wondering if there's a measurable difference...

probably less failure points than a chain.. but will definetly have a noticeable whine. It might also have less rotating mass.. meaning it will rev up faster

Plus it looks friggin' badass.

Raze wrote: would this need oil? what happens if he strips a gear? seems like alot of failure points, though probably no more than a timing chain? I'm wondering if there's a measurable difference...

Subaru has released a handful of production motors with gear-driven cams before (early EA-series) and just released another (MY2011 EJ25), as well as Honda (VFR sportbikes).

I personally think they sound mean as hell, and my personal experience with the Subarus has shown me that there are certainly no reliability drawbacks. It's nice to not have to worry about a chain to fail or, worse, a belt.

They've used gear drives instead of timing chains on Chevys and Fords for years. Allows for more precise cam timing settings. Whether or not he will like the noise is another matter.

Isn't there more power loss thru the multiple gears than there is in a chain?

Looks like a Rube Goldberg device to me. Also seems to violate the rule of elegant engineering that believes that the simplest design with the fewest/lightest moving parts is the correct answer.

But yeah, it kinda cool.

It's a way to get the whine of a supercharger without all the pesky horsepower gain!

Seems like a lot of jiggery-pokery to achieve what worked very well in the first place.

Gear drive cams make sense in a pushrod application since the cam is so close to the crank, in anything else they seem like extra effort for little gain.

In reply to NOHOME:

The gear drive is fewer moving parts. A chain is not one moving part. Think of a 100 link chain as 200 side plates, 100 pins and 100 bushings; so that 100 link chain is really 400 moving parts. 400 places that a failure can occur.

That said, gears are expensive and noisier; chains are much quieter and cheaper to overbuild.

Long chains flop and flex and introduce timing issues.

I seem to recall that there was an aftermarket fix (for the SOHC L-six) in the form of replacing the chain guides with idler pulleys. Really expensive but supposed to be stable to 14k. (Too bad the crankshaft isn't)

The problem with gears is that they introduce harmonics, which do find their way to the valvesprings. (Not to mention all the crap they put in the oil) Notice that performance OHV engines nowadays use belts, not chains or gears.

Now, if you wanted to do a proper geardrive, use a jackshaft like the Ford military V8s from WWII did. Think like a (BEEFY) distributor shaft, except it has two gears, one on the cams and the other on the crank. Bevel gears and the torsional compliance of the shaft should help the harmonic problem nicely. Might be problematic to fit under the chain cover, though.

I don't think anybody uses gears anymore when they are actually serious about horsepower. Lotsa parasitic drag, lotsa backlash issues, lotsa little filings from the straight cut gears, lotsa noises, lotsa little needle bearings to fail, lotsa precise crap that can easily be replaced with a belt.

They do sound cool, though.

Porsche used them on the quad cam 4's in the 356 carreras and the race engines, it used to be the rule and not the exception...

I haven't seen a gear drive in years. Even in most pushrod engines now if the chain gets replaced it's with a belt drive.

I believe Ford made this design for an engine years ago. They stopped producing it because it was too efficient. They never died. cxhb would know more about this..

Right..

A company quit making an engine because it was TOO efficient.

Pull the other one, it's got bells on.

Shawn

maybe too efficent for what it cost to produce. It is cheaper to cast rocker arms and cut down pushrods to the correct length.. and they work 90% as good

I think my Honda rc51 engine has gear driven cams. I'm not sure it makes a difference since it never had a chain.

mad_machine wrote: maybe too efficent for what it cost to produce. It is cheaper to cast rocker arms and cut down pushrods to the correct length.. and they work 90% as good

Um.

There is never any such thing as "too efficient"!

Ford had two geardriven OHCs that I can think of. The DOHC tank engine I mentioned earlier, and the Foyt Indy engine, which was a race-only engine.

I had to edit this because I got my engines mixed up. http://www.bacomatic.org/~dw/engine/fordv8/foyt/foyt.htm Foyt engine.

My Cb-1 Honda had gear driven cams-shim and bucket valve adjustment was much simplifies. Ran hard for a 400, too.

Keith wrote: It's a way to get the whine of a supercharger without all the pesky horsepower gain!

LOL

mw wrote: I think my Honda rc51 engine has gear driven cams. I'm not sure it makes a difference since it never had a chain.

Indeed it does. If you hadn't mentioned that, I would have had no idea. Very interesting.

Bikes have long tried driving the overhead cams with bevel gears. It it were a winner, Honda would be selling it and every bike would have today.

Pete