duke what do you think of this??

[Clem Z.]

http://www.mid-lift.com/intro-mid-lift.htm

[Duke W.]

Re: duke what do you think of this??

It's no secret that rocker arm motion is rotary, so the valve and pushrod ends travel in arcs, not straight lines. This is why rocker arm ratio varies and the "advertised" rocker arm ratio says nothing about what the actual ratio behavior is on the engine. It's further complicated by the fact that on some designs, like the OE ball and stud, the actual instant center of rotation moves as the rocker arm rotates. Shaft mounted rocker arms have a fixed center of rotation.

Some racers go to extremes using custom length pushrods to attain rocker geometry that yields the tangent of the valve end motion to be inline with the valve axis at the mid point of lift. This appears to be what this design is attempting to achieve, but it's not clear to me how it would not require a custom length pushrod to attain this objective like any other rocker arm.

And regardless of the design intent, it's not clear to me that going to these extremes will improve engine performance or even reduce wear, significantly, however, excess head or block milling can foul up rocker geometry and cause problems unless custom length pushrods are used to restore design geometry.

From a design standpoint, one can take into account variable rocker geometry in cam lobe design, but from my review and analysis of various lobe designs from both OHC and pushrod architectures, it's not clear to me if this is the case, however, from what I have read, Chevrolet put a lot of design and analysis effort into optimizing and stiffening the LS-X valvetrain, and it is much superior to vintage designs, which is why LS-X engines' specific power output and revs are comparable to modern OHC designs.

This harks back to taking a system engineering approach to valvetrain design. Picking a cam from column A, a rocker arm from column B, and a valve spring from column C will usually just yield a kludge.

As far as vintage Chevrolet road engines are concerned I prefer the OE rocker arm design because they are inexpensive and have proven reliability. The typical $150 spent on a set of aftermarket rocker arms is much better spent on cranktrain reliability and cylinder head work. Commonly used aftermarket "roller" rockers (typically just roller tip) are also heavier than OE so they will reduce valve train limiting speed, which may prevent exploitation of the entire power bandwidth "sweet spot" without increasing valve spring restoring force, which can cause more deflection and reduce valvetrain durability.

If this patent was issued in 1980, it expired circa 1997. IIRC patents are good for 17 years and cannot be renewed.

Most patents expire without ever earning the "inventor" anything in royalties, but it probably costs at least ten to twnety thousand dollars go through the process before a patent is awarded, assuming one is awarded.

Duke

[Joe C.]

Oh Yeah........How About This !!!!!!!

Wow! Clem, that was one helluva explanation of the perpetual motion theory! Can you believe it (whatever the hell they were trying to say, that is??)Anyway, if you think that's neat, how's about this for "trick".

http://www.hotrocker.com/what.html

Joe

[Duke W.]

Re: Oh Yeah........How About This !!!!!!!

Assuming this deal works as claimed, increasing rocker ratio with revs is going to take a very high force valve spring (and careful attention to coil bind) to allow the engine to achieve the very high rev range where the increased effective duration and lift is going to increase power, so, again, we end up back at valvetrain reliability and durability.

Given the type of torque bandwidth and power that tests of massaged vintage Corvette engines are yielding, there's absolutely no need for this kind of monkey motion rocker arm. Eighty percent torque bandwidth from about 2000 to over 6500 is nothing to sneeze at along with close to 300 SAE corrected RWHP and usable revs to a little over 7000 from a completely original appearance mechanical lifter 327. The KISS principal works!

The key is massaging the heads and assembling the engine with a relatively high CR that gets the most from current unleaded premium gasolines, some of which are only a couple of RON points behind leaded premiums from the sixties.

Duke

[Terry F.]

Re: Oh Yeah........How About This !!!!!!!

That should last a whole 5 minutes... Terry

[Terry F.]

Re: duke what do you think of this??

Duke, Regardless of whether a rocker arm is full roler or conventional I would think that the weight at each end of the rocker would influence valve train speed?? Thanks, Terry

[Duke W.]

Re: duke what do you think of this??

That's what I said. The heavier the rocker arm the greater the inertia and the the lower the limiting speed for a given spring. The rocker arm is essentially reciprocating inertia and adds to total valvetrain inertia. Heavy rocker arms are NOT a good deal.

Duke

[Terry F.]

Re: duke what do you think of this??

Just in my general search of rocker arms, I don't see a whole lot mentioned about this. Ultimately I would like to figure out or know the tip weight difference between a high quality full roller rocker and a standard rocker. If there is no difference that would be great. But, if it is heavier, should a person compensate for the difference by adding a little more spring strength to maintain valve train responce at the upper RPM range? Say for instance using 435hp valve springs in a 400/390hp 427? I am curious. There must be a formula for this. I have a feeling this is a total bullsh** question for you, sorry to keep you on the hook so to speak. I guess it sort of all boils down to weight and inertia. At what valve train weight and lift velocity will you over come the valve springs ability to maintain the lifter body against the lifter lobe. Goal being to use the absolute minimum to avoid premature wear of the lifter lobe?? Thanks for all your straight forward answers. Terry

[John H.]

And Then There's "Cam-In-Cam"

The new (2008) Viper V-10 (600hp, 560 ft-lbs.) is the first pushrod engine with variable valve timing; the intake lobes are fixed, and the exhaust lobes are separate, and can be re-phased with authority up to 40* at the crankshaft. Just patented jointly by Chrysler and Mahle.

[Patrick H.]

Re: And Then There's "Cam-In-Cam"

Why patent jointly? Won't they be the same company soon enough?



Patrick

[Clem Z.]

Re: duke what do you think of this??

the new LS engines only have a needle bearing on the pivot and the valve tip end of the rocker is still non roller to save weight on the tip to prevent valve float. the new ZO-6 uses the same setup and revs to 7000 RPM. you only need a roller tip when you are into very very stiff spring rates. all the friction in the chevy stamped rocker arm is in the ball pivot point not the tip as i have never seen a tip turn blue from heat like the ball pivot. the 435 and the 390/400 use the same valve spring.

[John H.]

Re: And Then There's "Cam-In-Cam"

Patrick -

Who knows? As long as my retirement checks keep coming, it works for me; Kerkorian will be 90 next month, and he hasn't slowed down yet either.

[Duke W.]

Re: duke what do you think of this??

You can probably imagine that aftermarket vendors don't want to discuss how much heavier their rockers are, or how much they might reduce valve train limiting speed, or that you need a gorilla valvespring if you want to rev a "high ratio roller tip" rocker arms to even rev to a measly 6000, all of which will likely reduce valetrain service life to considerably less than OE. The same applies to cam vendors who hawk "aggressive profile" cams.

I have some SB valvetrain component weights - actually the correct term is "mass". I don't have comparative masses for aftermarket roller tip rockers, but I think anyone can tell from inspection that adding a roller and pin to the end of even a stamped rocker will increase mass. Right now 327 valvetrains make a little over 7000 on OE springs, valves, and the LT-1 cam, and I believe some judicious spring reshimming will increase this to a solid 7200. More revs mean more average power through the gears because the power rolls off very little beyond the 6500 peak. It's nearly flat until the valvetrain gets into a little false motion, and the tipoff is the point on the dyno sheet power curve where the power suddently begins to rolloff ever more quickly.

I can make some simple pencil and paper calculations on inertia loading, but it basically comes down to system engineering, careful assembly with great attention to details that most amateurs and "professional engine builders" ignore, and testing engines in co-operation with vintage Corvette owners who have a rebuild project and want to maximize engine performance without altering visual appearace or overall opearating characteristics, which is an ongoing process. But it's tedious and most owners probably don't have the experience or mental attitude to restore an engine at this level of mechanical detail. But the aftermarket offers no magic bullets!

The answer to your question is to use OE components because they flat work. But how can just one guy like me convince everyone of this when I am up against millions in advertising dollars by aftermarket vendors hawking their wares. The secret to "more power" is pushing compression ratio to the limit of what modern pump premium will handle without detonation, which is higher than most guys think and massaging the heads, the details of which have been widely available in various books for over 35 years.

As far as BB valvesprings are concerned, the mechanical lifter SHP engines use the same spring as the milder hydraulic lifter versions - just like on SBs, and the additional revs are due to "softer action" lobes - somewhat milder acceleration and jerk than the lower revving hydraulic lifter cams. This philosophy worked for Ed Winfield 70 years ago. It worked for Duntov 50 years ago (and, indeed, Duntov may have gotten the idea from Winfield - at least that's what Ed Iskendarian once told me in so many words), and it can continue to work for anyone today.

It never ceases to amaze me how many 350s I see with low compression, high overlap hydraulic lifter camshafts, "high ratio roller rockers", and gorilla valvesprings that make poor torque bandwidth, unimpressive top end power, and run out of breathe at 6000 revs. It's just comical, but these guys spend huge sums of money for all this stuff to get barely more than mediocre performance.

Since the OE SHP BB redline is 6500, they will have no problem making this level of revs on the OE parts, and I'm sure careful attention to valve spring setup will extend this, but it may come down to head flow being the limiting factor. I have no where near the experience or test data on BBs that I have on SBs, but I have no doubt that they are near equally responsive to "tuning" and assembly detail that will increase torque bandwidth, power, and maximum usable revs without altering appearance or overall operating characteristics including idle characteristics and without using aftermarket valvetrain parts or camshafts.

Aftermarket rockers for a road engine are an absolute and complete waste of money! I absolutely recommend only using OE or OE equivalent valvetrain components and cam lobes, and this includes mixing cam lobes from different OE camshafts and indexing them to my owned engineered requirements and then having this "custom camshaft" ground by any vendor who has the lobe masters, which several do.

It's all in the details!

Duke

[Duke W.]

Re: And Then There's "Cam-In-Cam"

John - can you give a verbal description of how it works. I know GM has a "twin cam" development LS with two cams in the block - one for the inlet valves and one for the exhaust valves, and the only reason to do this would be to have variable phasing for each set of valves.

Variable phasing of exhaust cams is now used for NOX control. At idle phasing reduces overlap to a minimum for good idle quality and stability.

At cruise the exhaust cam is retarded to increase overlap, which increases exhaust gas residual and eliminates the need for a separate and less reliable EGR system to meet NOx standards.

Then at WOT the exhaust phasing can be varied as required to create the flatest possible torque curve.

IIRC the GM 4.2L DOHC inline six has variable exhaust cam phasing, and I think a version of the Ecotec does too, or will in the future.

Duke

[Terry F.]

Re: duke what do you think of this??

The parts list I was looking at showed a slightly stiffer spring for the 68 435hp?? Terry