You say that a speedo shop can't make it acurate at poth ends.
I beg to differ. I used to work on mass fuel flow transmitters for G.E
Aerospace which are used on ALL comercial aircraft. The fuel enter the
unit and is spun by a pawered little turbine, as the fuel passes through
it hit another turbine which is held in place by a calibrated spring.
The very same spiral design type spring that every magnetic drive speedo
uses. These spring s can be recalibrated. They do make certified
speedo's for the Cop cars. I used to have one, and it went up to 160
mph. Ihad been certified through the full range. It had a sticker on
the visor for the quarterly certifications. at 30 70 130 mph.
Rich
> ----------
> From: GDWF22A(at)prodigy.com[SMTP:GDWF22A(at)prodigy.com]
> Reply To: GDWF22A(at)prodigy.com
> Sent: Wednesday, September 17, 1997 5:00 PM
> To: alpines(at)autox.team.net
> Subject: Still on OD and tires.
>
> Bill Lewis; you are correct that the 4.0 six seems to handle 2000rpm
> in OD
> without complaint or "feelable" stress. Reason is, you have a
> relatively
> large engine size and not only that, your engine is cammed to develop
> full
> torque down low. Probably not max torque at 2000 (more like 2800) but
> none
> the less, it has ample torque at 2000 and if the road is level, wind
> is not
> from the front and load is not excessive...she rolls along nicely with
> partial throttle opening and only slightly less than max fuel economy.
> Due to lack of aerodynamics, you body will demand much higher hp
> production
> to increase from say 50 mph to say 65mph than would a slick sedan or
> coupe
> body. Example: a Porsche 911 body shape requires approx 30 hp to
> propell
> at 60 mph. Your Jeep likely needs about 45 hp at 60mph. And BTW, this
> difference gets disproportionately WORSE as speed goes up. I would
> guess
> the Porsche needs about 90 hp at 100mph and your Jeep needs about
> 170hp at
> 100mph.!!!Go figure.
> The Alpine size engines are SMALL and are cammed to produce peak
> torque at
> 3200 rpm. When they are lugged down to say 2000 and are in OD, they
> simply
> have nothing in the way of extra torque to give. Of course, the car
> still
> rolls along and the driver may not be aware he is causing internal
> strain
> in this engine...but thats whats happening.
> ------------------
> Dick S.; If you can drop by a major size tire dealer or distributor,
> he
> will have a spec book from the Tire and Wheel mfrs. assoc.
> This neat book (among other great data) gives the number or
> revolutions per
> mile for all tire sizes. The figure assumes normal wheel, inflation
> and car
> weight.
> Lets say you tire makes 700 rev per mile in the spec page.
> 700 X your 3.89:1 axle ration = 2723 engine revs per mile.
> Now we all know a mile per minute is 60 mph, so if you drive a
> measured
> mile at 2723 engine rpm you should cover that mile is exactly one
> minute !
> You say your tach has been checked as being OK. Was that done at both
> high
> and low readings? Was it done on a master tach which itself was known
> to
> be virtually perfect? I have doubts you could have done this yourself
> unless you had an expensive shop size Sun, Snap-ON or other multi
> thousand
> dollar digital tach to use.
> I'm not saying any of your data was wrong but since I don't know your
> personal situation I only suggest that there might be some degree of
> error
> and having things check out on master gages would worth it.
> ----------------
> Back in 1937, a supercharged Cord V8 set the USA speed record (AAA ran
> things in those years) at 107.5mph
> This was finally broken in 1953 by a Dodge red Ram coupe (V8 Hemi) at
> 110mph, again timed by the AAA.
> Reason I am relating this bit of history is....from 1937 to 1953 no US
> model could beat that Cord record but lots of owners thought they
> could. I
> met all kinds of men (no ladies) who bragged about their high speed
> runs in
> various cars. My boss at Buick had a 49 Roadmaster 320 cu in. and told
> of
> 120 on the speedo. Another friend told of his Kaiser Manhattan bumping
> the
> needle at 125 or some other silly number. I could recite endless
> tales of
> owners of everything from model A's to Cadillacs, which claimed speeds
> far
> higher than the car would ever see. I recall a new 53 buick special
> I
> owned which always was able to show 115mph. Once in the Buick
> engineering
> dept at Flint, I was shown some performance data on 1967 models and
> asked
> if they had it for my old 53 model. Sure they did and the proving
> ground
> figure showed my exact car capable of an honest 94mph !
> Magnetic speedos may be right ON at city speeds where cops give
> tickets for
> a 40 in a 30 zone. This same speedo gets wild at high speeds and lies
> like
> you wouldn't believe.
> There is NO fix. Speedo shops cannot make it right at both ranges.
> Electronic tachs are much more accurate and Rootes are about as good
> as any
> others of that era. Still errors happen for various reasons .
>
> Let us know if you ever check out your tire revs per mile and your
> tach
> accuracy. We will all enjoy the report.
> Dick T.
>
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