At 10:35 AM 8/7/2000 -0400, Edwin McCarroll wrote:
>.... a) If I decide to mount a front sway bar to the MGA, will I see a
major contrast to the present handling characteristics?
YES! And very much to the better. The factory (late) optional 5/8" bar is
okay for bias ply tires, but 3/4" is better for radial tires with the
better grip. For autocrossing on race tires you could use a 7/8" bar.
>Should I also mount a rear sway bar?
NO! And just as emphatically. Even with a 3/4" front bar and no rear bar
my MGA will still pick up a rear tire occasionally in a tight turn, and it
does it regularly on race tires.
>b) If all is in order, what should my tach. reading be at 60 mph?
3456 (for MGA 1500/1600 with 4.3 final drive) if your tires were exactly
the correct size and the instruments were working as planned (which they
seldom are). 3295 for the MGA 1600-MK-II (4.1 final drive). It is common
for the MGA tach to read 50 to 150 RPM on the high side at 60 MPH.
Variations in tire size will affect both the speedo and tach at the same
rate. My Dunlop SP20 165-(80SR)-15 tires register 100.40 miles on the
odometer in 100 miles of travel (with new tread and 25 PSI tire pressure).
This I check using a rally computer which is accurate to about 1 foot per
mile. As such, my tach should read 3469 at exactly 60 MPH true road speed,
but is most often reading more like 3550.
My speedometer also originally read a similarly a little on the high side,
about 2% too high through most of the normal driving range. I have
recalibrated this instrument by rotating the needle slightly on the
spindle, so now it reads dead on at 45 MPH, just a touch low at slower
speeds and just a touch high at highter speeds. My primary interest for
accuracy of the speedometer is in the mid-range speeds for road rallying.
>Mine is reading about 4300 rpm at 60mph. The TD which accompanied us has
had a rear end conversion (MGA). His tach. readings are lower than mine
at the same speed.
High ratio final drive gears maybe? Lift one rear wheel, turn wheel by
hand exactly two turns, and count rotations of propshaft to get the ring
and pinion gear ratio.
For a review of the workings of the MGA speedometer, go here:
http://www.ntsource.com/~barneymg/mgtech/speedo/st1.htm
The tachometer uses exactly the same parts as the speedometer except
without the odometer drive parts, and turns at the same speed in top gear
(MGA 1500/1600 models), 1440 turns per mile (given the correct tire diameter).
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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