At 01:41 PM 1/19/98 -0500, you wrote:
>> I have just finished a basically stock restoration. The only thing I
>> changed was a 3.07 rear and 205 60 tires on 13in rims. My tack shows
>> 4K at 70mph. The engine sounds kind of busy but not overly.
>>
>> My questions are:
>> Is my engine really turning at 4K?
>> Can a 260 run at 4K all day without damage?
>> Is the information in Performance Tuning Sunbeam Tiger pg. 65-67
>> correct?
>>
>>
Brad,
No, your motor is turning slower than 4000 rpm. Let's have some fun with
numbers. To calculate the rpm, start with 1 mph = 88 ft/min, so 70 mph =
70x88 = 6160 ft/min. Now, you need to know the effective circumference of
your rear tires = 2 pi X effective radius ( a little less than the unloaded
radius because tire compresses, but also a little slip with the road which
errs the other way.) Anyway, the circumference of your rear wheels is
pretty close to six feet. So six feet is one revolution of the rear wheel
and at 70 mph = 6160 ft/min, the rear wheels are turning at 61610/6 = 1026
rpm. With a rear end gear ratio of 3.07, the engine is turning 3.07x1026 =
3152 rpm; a lot less than 4000. You can measure the diameter/circumference
of your particular tires/wheels and refine the answer, but this is pretty
close.
As to the information on pg. 65-67 of Chittendon's book, I don't have it in
front of me right now, so I may or may not have a comment. Generally, he
is pretty accurate; and you can't argue with success. I'll try and take a
look at it when I get a chance. Any questions in particular? In the
meantime it looks like you tach needs to be recalibrated.
Good luck with the car,
Bob Palmer
UCSD, AMES Dept.
rpalmer@ames.ucsd.edu
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