Date: Thu, 21 Jun 2001 01:48:00 EDT
Reply-To: FrankGRUN@AOL.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Frank Grunthaner <FrankGRUN@AOL.COM>
Subject: Re: Update on Waterboxer vs Transplant Power Options
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Mark,
Fighting over opinions is the furthermost thing from my expectations. If I am
writing these things with too much conviction I sincerely apologize. I
generally lurk on the list until something triggers and the series of posts
accepting the premise that high rpm is bad drove me over the edge. I just
wanted to get a discussion going on the relative merits of the issue. In the
rest of this, I try to address your points.
In a message dated 6/20/01 9:23:50 PM, kelphoto@islandnet.com writes:
<< I read your comments on the recent post involving bad things on the
list. I had written the article you referred too. I wrote a response,
see below, but didn't send it for a variety of reasons. Mainly I don't
want to fight over opinions and I felt that my comfort level with list
postings was limited to what I could do by helping others in a tangible
way. My comments about High Rpm power and such were just my own way of
looking at the topic. But here goes a few of my questions.
> C. Is it fuel economy or fuel efficiency? This is another severely distorted
> perception. Its a heavy foot that drains the tank of a properly maintained
> engine/vehicle package not rpm. I have been meaning to post a polemic on
fuel
> efficiency based on experiments I did over our latest 3000 mile adventure on
> the US Interstate system. But to summarize, the actual fuel economy was
> established by load, not simply velocity. Following load using my trusty VDO
> vacuum gauge, I tested long term constant vacuum running with constant RPM
> cruising. MPG varied from 12 to 24 mpg. The results are consistent with fuel
> consumption maps published by VW and these I have translated. These show
that
> the fuel consumed is related to the work required and not simply to the
> swept volume of air at a fixed Air/Fuel ratio.
>
I felt your post was impressive in the manner which you have applied
technical knowledge to a real world application. I was particularly
interested in the power/fuel consumption at high Rpm data you referred
to. I would very much like to see the evidence to that effect if you
could link or post it.
There are two lines of information one serious and one less so. The serious
one with extensive data comes from a technical paper published by VW (German)
in the late 80's in which they detail the development of their econo-cruise
meter. In the article they go through considerable data showing fuel
consumption vs. load, rpm and measured manifold vacuum. I discovered this
paper just after I did a set of experiments (wife called it a trip to Texas
to spend Xmas with her parents) in which I compared fuel consumption at
constant speed vs. consumption at constant manifold vacuum. Maintaining
constant vacuum became too difficult, but I was able to cruise at no less
than 10 inches, no less than 7, 5, 3 and full throttle. The fuel economy
correlated with vacuum, not speed. Clearly, less vacuum at higher speed
because of drag, load etc. So at 15 inches, 65 mph flat plains of New Mexico,
I got around 23.2 mpg. At three inches, I got 13 mpg. I have been working up
the data and comparing it with the VW paper with amazing agreement. I just
finished the translation and will try to post the material to a willing web
site (Tom, hint, hint). I was trying to put the whole thing in perspective by
solving for the load related terms in the power equations when I got
diverted. I had started to build an integrating fuel injector duty cycle
measurement system to map things with the Road Dyno board my son and I are
building so I could map these curves and the effect of tuning parameters on
them, but then I got the turbo Audi bug.
> A. Is it engine lifetime? This is a legitimate concern in the case of
> engines designed for sub 4000 rpm operation (as in most American Iron). But
> for machines designed (piston rings, cylinder wall metallurgy, valves and
> valve seats) for high speed operation (5000 to 6500 rpm) 250,000 mile
> longevity is built-in. Indeed, the peak connecting rod shock loads and
> bearing stress loads are often greatest for small displacement engines when
> the engine is operated at full load at low rpm. In the European market the
> inline 4 engine routinely sees continuous duty at 5500 to 6000 rpm.
>
Another item on high rpm that wasn't brought up is that piston ring
speeds in excess of 1000 ft per minute, around 4000 rpm on the
waterboxer, have higher wear due to harmonic resonance, if you could
comment further I'd appreciate it. This tidbit came from a mechanic that
works extensively on race motors and such, so I don't where the data
came from. I did correlate a green zone on the waterboxer tach up to
this piston speed so felt there was some merit to it.
The current ring technology is just amazing. The Europeans and Honda in
particular factor these issues into the rpm use zone design for a particular
application. A ring design that moves some of the resonances up to 1500 fps
and even 1850 fps, provide poor oil control and seal leak rates at lower
speeds. The resonance is effected by the material choice, the ring shape, the
wall composition and texture, etc, etc. I'll try to get together a few
references, unfortunately, most of VW's publications are in German. The
British don't have a clue, the Japanese don't publish and the US
manufacturers are still optimizing for good oil control at low piston speeds.
One key is the break-in time. High speed piston seal technology requires long
break-in times (30 to 50,000 miles is not uncommon).
The other comfort issue was would a new VW engine driven at RPM's you
advocate still have a "warranty"? I called VW, and got someone that
didn't have any inclination mechanical. My person sense is that the RPM
speeds do have an effect on engine life, and the manufacture's limit of
liability would not include high rpms.
The manufacturers warranty has no rpm limit. The ECU has a rev limiter to
keep the engine out of harm's way. Disable the rev limiter (add a high
performance chip) and they will have an excuse to disallow a broken rod as
warranty. Most high rpm damage that is warranty related is bearing seizure
and broken parts. Ring control and wear will be seen as oil consumption.
Current piston ring technology with synthetic oil will be hard pressed to
show consumption rates in excess of 1000 per quart even heavily worn (this
disallows scored cylinder walls and broken rings). VW would never replace an
engine for that kind of consumption. So, run it in competition as an SCCA
racer, and they will disallow the warranty. Run it continuously at 5 to 6000
rpm and they will hold you to the mileage limit! Seriously, if you want to
know what is happening to your engine follow the heavy metal analysis from a
reputable oil testing service. Cheap insurance. Remember, the sulfuric acid
generated in cold weather stop and go driving limits engine life far more
than an Italian tune-up.
Original unsent draft
Frank,
Thanks for your comments. I feel your last paragraph where you said:
I am currently preparing a
2.0 L Audi 3A bubble block which will run the 8V Digifant head, stock
compression, a SAAB T3 turbo charger operating at 4 to 6 psi (controlled
by
the SAAB APC system), SAAB fuel injectors, a G60 pressure controlled ECU
and
modified intake manifold with integral air-to-liquid intercooler.
Hopefully
this will have the torque of the 2.0 L engine with on demand modest
power
assist.
It is thi "on demand power" that I have been referring to. I define this
as the power reserve while cruising 65 mph and 3800. If I want to
either maintain this speed up hill, or carry more weight at this speed,
and up hills or pass someone, I would prefer to have the power available
without downshifting, or having to get a run at the obstacle or risk
bleeding off speed. I believe your
new motor address this issue well-- on demand power assist.
Yep, with these small engines, reasonable gearing and a turbo are the only
solutions (I think, possibly, perhaps, could be ... ). Clearly the issue is
torque. The best answer is the TDi, but in the gasoline engine world torque
is pressure and stroke. Porting, cam lift, gas flow dynamics all clearly
effect the problem, but the magnitude of their contribution is insignificant
to filling the cylinder with twice (or more) the charge density. With the
right turbo, a 2.0 L engine can become a 3 liter engine (122 lbs ft at 3000
vs 188 at 3000) on demand. Of course, you will pay for power used!
Frank Grunthaner
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