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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
Comments: To: kelphoto@islandnet.com
Content-Type: text/plain; charset="US-ASCII"

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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