Date: Sat, 3 Nov 2001 12:55:42 EST
Reply-To: FrankGRUN@AOL.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Frank Grunthaner <FrankGRUN@AOL.COM>
Subject: Re: engine efficiency, I4s, subies, etc
Content-Type: text/plain; charset="US-ASCII"
In a message dated 11/2/01 3:17:02 PM, mdlind@rica.net writes:
<< Frank, I enjoy but barely understand your posts.
Myron, its a real problem. I often don't understand them myself! I like to
lay the fine points of causation on my monodigit typing limitation. Family
(particularly my 85 wpm 13 year old daughter) are talking about sending me to
summer typing camp. She just gave me a PAWS Typing Tutor program for my
birthday. Also closes the door to the study when I'm in here and she has
friends visiting. Too embarrassing!
If one was to put a TDI (150ft/lbs or so @ 1900 rpm) into the
vanagon, how does one, in your opinion, go about determining
proper gearing of the transmission. I am mainly interested in a
nice drivable, fuel efficient, Vanagon. The regular WB motors have
generally been "peppy" enough for me, I am not after particularly
fast acceleration or racing from stoplight to stoplight. What do I
miss in overall drivability as I consider mainly 65-70mph road
speed. I seems that to match the TDI motor to the vanagon and to
still go upwards of 70 mph I should consider a five speed. Why is
the diesel less tolerant of high revving than the similar built
gasoline engines? Or, why would I want to drive it over 3500-4000
rpm where both the torque and the hp drop rapidly? >>
As far as I'm concerned this engine is the unit of choice, but has been too
pricey for me to consider. Back when I did the first conversion, I was being
quoted $6,000 for the complete motor/computer package. I went out and put
some money in Platinum shares - then the cold fusion bubble burst and I went
back to sorting out the most cost effective gas engine.
I would also agree that the TDi should not be squandered on the 5.86 ring and
pinion of the regular N/A 1.6 diesel. Ideal case for a European or SA 5
speed. If I were to do it, I'd probably go for a Porsche 915 trans and have
top gear setup for 70 mph at 3000 rpm. Of course, if you are in about $3,000
for the TDi you will probably match that amount for the trans, rebuild of
trans and adapter hardware.
But in fact there is so much torque available with the TDi, the regular 4
speed transmissions will do just fine. The problem is the strength of the
Vanagon transmission. As I have often said, the weak link in this vehicle is
just forward of the flywheel! Now the Vanagon 4-spd transmissions have the
same 1st through 3rd gearsets (defining 1.26 to be equal to 1.23 for this
exercise). Variation is then in the top gear ratio and the ring and pinion.
The aftermarket gear sets are stronger than the factory stuff, and the R&P
can be beefed in a rebuild (4 spiders vs. 2). I would get a 4.57 or 4.83
trans, depending of what year you are starting with, add a set of 215/75x15
tires (with appropriate rims) and choose a 0.85 or 0.77 gear set for top. To
minimize expense, take the stock 0.85. This will give you around 3500 rpm at
70 mph., and a useful mountain gear in 3rd. But the question remains, can the
mainshaft and the 3/4 hub hold up to this. Sullivan either knows or will know
at least an anecdotal answer (single data point).
As to why the torque curves go to hell after 4000 on most automotive diesels,
I have always assumed that it was a fuel delivery problem. As the injector
transfer pressure go up, and injectors go electrical, and injection is
directly into the chamber, the torque curves keep going upward to higher
values. In addition, the exhaust circuits in most turbo diesels and flow
characteristics of the turbos are designed foe 1200 to 4400 rpm operation.
Variable vane technology would enhance this range. So its just money!
Frank Grunthaner
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