Date: Mon, 11 Oct 2004 13:42:14 -0400
Reply-To: ROBERT DONALDS <donalds1@VERIZON.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: ROBERT DONALDS <donalds1@VERIZON.NET>
Subject: Re: Safe 2.1/1.9 Rpm: survey/query
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I my early days of engine building I spent many hours building and testing
40 HP VW engines for a Formula Vee SCCA race car
The point of ring resonance hits home But I called it ring flutter. I built
one engine and used what I called a mint low mileage set or pistons and
cylinders. This engine on the dyno typically made 55 HP at 6000 RPM but with
this used set of mint pistons and cylinders the power got to 40 HP AT 4000
RPM and leveled off right there at 40 HP all the way to 6000 RPM.
when I swapped out the piston and cylinders to a new set the power came back
to 55 HP a 6000 RPM
I have never used a set of used piston because of that experience
The piston size of the 40 HP VW engine is 77mm that's works out to 3.030 and
the stroke was 64 MM
The piston top ring land is as much responacable for oil control as it is
for compression
I think ring and piston life are determined by oil quality ( age )
combustion chamber temps and the amount of unburned fuel that washes down
the cylinder walls on cold start up and in extreme rich conditions
going faster miles an hour
I remain
Bob Donalds
all rights reserved
----- Original Message -----
From: "Mark Keller" <kelphoto@SHAW.CA>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Monday, October 11, 2004 12:03 PM
Subject: Re: Safe 2.1/1.9 Rpm: survey/query
>I throw in my bit here too.
>
> I brought up the issue engine durability and high rpm's vs piston ring
> harmonic resonance a while back. Apparently when piston rings slide up
> and down the cylinder walls beyond a certain speed i.e. feet per min, I
> believe the criteria worked out that our 3" stroke engines reach this at
> just over 4000 RPM, conditions begin to be conducive for ring resonance.
> The Green arc on our tachs stop here, with a hashed green area up to
> 4400 Rpm., as "temporary operation" range.
>
> When Bob Donalds speaks of not re-using old pistons when
> reconditioning the engine, becasue the rings lands are always worn,
> this is where damage from harmonic resonance shows up. One listee
> wrote the list with a testimonal that he suffered engine problems,
> right after a 4600 something Rpm Test Run and that tear down revealed
> damaged ring lands. Abeit the last run was probably the "last straw
> which broke the camel's back."
>
> Piston rings do resonate at some velocity. Personally the RPM onset of
> ring resonace is probably dependent: on milage, wear on the engine,
> which piston and ring combo, cyclinder wall condition and etc. . My
> feeling is that operation above the 4000 - 4400 range and up for
> continued operation is incompatible with engine longivity. How long is
> too long? Well condition and quality of your engine are the main
> variables, The more miles on the motor, the less I'd be tempted to push
> past the 4400 RPM limit for very long, remembering our camel example
> above, and not knowing the PO's driving habits!
>
> Another listee Frank Grunthaur(sp) wrote back on this topic, that
> manufactures had devised a way to control piston ring resonance, with
> some trade offs. If you were build an engine to rev high, I guess
> 4000-6000 rpm, lower tension rings could be used, but cylinder sealing
> at lower RPM suffered-- something to that effect.
>
> Piston Ring resonace damage is a real issue of a cumulative nature.
> Testimonials from owners of VWs inline engines suggest that they run at
> RPM above our limits for a lifetime of use without issue. Perhaps, and
> not a reason for me consider a swap, but if you have a inline engine,
> then go with the high rpm rating VW gives for inlines. For my peace of
> mind, comments like Bob Mcdonalds, piston ring land wear, VW's "Green
> Zone" on the tachometer, and the knowledge that piston ring resonance is
> lurking in the high rpm range, lead me to believe my engine's durability
> in enhanced by venturing above the limits only when needed.
>
>
> Mark Keller
> 91 Carat
>
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