Date: Fri, 31 Jul 1998 20:14:36 -0700
Reply-To: Lawrence Dongilli <buspilot@WORLDNET.ATT.NET>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: Lawrence Dongilli <buspilot@WORLDNET.ATT.NET>
Subject: ECU/Ratio Rocker Info
Content-Type: text/plain; charset=ISO-8859-1
Derek Drew wrote:
>We need to have some additional discussion of these points of Dennis
Haynes:
>The down side of this is increased valve guide wear
>from the increased valve travel and the increase operating angle of the
>rocker working against the valve.
I'll talk about the Berg rockers here because they are the only ratio
rockers I
personally own (1.4:1):
In a nutshell, the big advantage to a ratio rocker is you get a larger
movement out of the valve with a minimum amount of movement from the rest
of the valve train. The increased rocker ratio gives you a greater travel
at the valve for a given lift at the lobe. This means that reciprocating
mass is greatly reduced because the only part that is being
accelerated/decelerated at a higher rate is the valve and it's _directly_
related components (spring, retainer, keeper and valve end of the rocker
arm). When the extra lift is gained by using a high lift cam with stock
rockers, the _entire_ valve train must now respond (all the above _plus_
the pushrod and the lifter itself). All this adds up to a lot of extra
inertia.....which takes more valve spring pressure to control. This is one
reason to move the adjustment screw to the other (slower) side of the arm
(as is typical)....the effective inertia is further reduced, helping to
keep valve float under control. I think this may be the primary argument
against roller tip rockers......the roller and bearings add a lot of extra
mass/inertia to the valve end of the rocker.
From a power perspective, the mere addition of ratio rockers will increase
the valve lift without increasing the basic duration. This will tend to
broaden the overall power band without the sacrifice of bottom end power.
A lot of the effectiveness of the ratio rocker depends upon the
intake/exhaust flow capability. Eventually, one can reach a point of
diminishing return....where adding yet more lift yields a smaller gain in
airflow (the same thing can happen with big carbs, big cams or big valves
when added by themselves). This is where porting and polishing/larger size
pipes/etc. come into play. I think it is quite evident from looking at the
curves from Vintage Vee Dub on Kyle's webpage that the Wasserboxer seems to
respond _quite_ well to the extra airflow. I _believe_ the rockers used
are the Berg 1.4:1, the smallest ratio in their lineup. The Type 1 engines
also responded well to the addition of the ratio rockers on an otherwise
stock engine. Can anyone tell me off the top of their heads what the stock
rocker ratio is for the Vanagons?
If the ratio rocker is properly designed, there will actually be a_reduced_
side load on the valve stem. When you move the rocker fulcrum point closer
to the pushrod you are, in other words, increasing the radius of travel of
the part of the rocker acting on the valve. Essentially, the larger you
make the radius, the closer the arc comes to being a straight line...the
theoretical perfect (yet physically unobtainable) rocker. It is one of
those things you can approach forever but never reach. The flatter the arc
of the valve end of the rocker, the less lateral movement
(sideload/scrubbing) acting on the stem. If, instead, you run a high lift
cam with a stock ratio (1.1:1 for example in the air cooled Type 1 and
1.3:1, I believe, in the Type 4) there will be _at least_ stock and likely
higher side loads since the original smaller arc radius is retained.....and
now, with the higher lift cam, you are asking it to rotate further than it
did before. As long as you are sane with cam selection, this won't be a
really big problem. When you run a really aggressive profile with a stock
rocker, wear and tear can be significantly accelerated.
Another benefit can come from the proper machining of the valve contact
face of the ratio rocker. If the valve contact face on the rocker arm is
machined to the proper radius, the face will effectively _roll_ across the
face of the valve stem. This is one reason it is a good idea to make sure
the faces on your stock valve adjust screws are in good shape. Did you
ever notice the radius on their faces (at least when they were new)? If
you have worn adjusting screws that have flats on the faces, the screw is
being _scrubbed_ back and forth across the valve stem face....rather than
rolling across it. I know some folks like to use the so called swivel
foot/bigfoot adjuster screws (a stock item on the 911)....and I have used
them myself. I have often wondered about their effect on valve stem/guide
wear since there is _zero_ rolling action.....sliding only...on the stem
face. I am presuming (hoping) that, because of its larger contact area,
the face of the swivel foot is actually riding on an oil cushion on the
valve stem face....because they seem to work well enough. I suppose their
biggest benefit is that they should help prevent the rocker tip from
'mushrooming'....but that is another topic. The Berg ratio rockers put the
adjusting screw on the opposite (pushrod) end of the rocker. A special
cupped screw that mates with the pushrod is used. The end acting on the
valve face is oversize and ground to a specific radius that lets it roll
across the valve face. Very nice....much more contact area with the valve
stem face than a standard adjusting screw too. I've got an air-cooled Berg
engine at home that was in two different Busses (lower gear ratios/higher
revving) over the years with over 50k miles on it with very happy valve
stems being actuated by 1.4:1 rockers. It is sitting on an engine stand
simply because I don't have anything to put it in at the moment. I suppose
a roller tip rocker may do pretty well in this regard, likely reducing side
loads to virtually zero....you would just have the mass/inertia issue to
deal with. Perhaps it is not as much of an issue on a slower revving
engine, though. I believe there are a couple of production car
manufacturers that are now using roller tip rockers.....perhaps in the
luxury domain?
The only real issue here (at least mechanically) is that of increased
pressure between the cam lobes and lifter faces. When the rocker ratio is
increased (shorter lever on the input and longer lever on the output),
basic leverage physics dictates that it takes more force acting on the
lifter to move the assembly. Everything is multiplied....linear movement
of the valve _and_ linear force need to overcome spring pressure. Gene
Berg said that as long as metallurgy between the lobe and lifter is correct
and proper break-in procedures are followed, there should be no problem
with wear here. I asked Richard Holzl at Vintage Vee Dubs about cam/lifter
wear in the Vanagon and he stated he has not had any problems in this area.
>Dennis also worries about having a richer mixture damaging the catalyst.
Sure, a rich mixture will cause problems......but again, if you run the
chip by itself _or_ the chip and the ratio rockers _together_....the
mixture is supposed to be proper. There will _only_ be a problem if you
run the ratio rockers _by themselves_ without the necessary chip change.
Richard made this point very clear to me.....stressing it several times.
He has even mentioned re-releasing the dyno plots with the particular
curves _deleted_ showing _rocker change only_ because it seems to be
causing a fair bit of confusion. It is not even supposed to be a
discussion issue.
Lawrence Dongilli
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