Terry,
The 1592 engine makes peak torque at around 3800 RPM. This is
the point at which the power deminishes. When the power deminishes
at a greater rate over an RPM range than the increase in RPM ratio,
the engine begins to produce less horsepower. This occurs on an
alpine 1592 at around 5200 RPM.
The Laycock OD unit has a final drive ratio of ~.800 or a 25% ratio
increase.
Not the 20% increase that you specified. ( 1.25 = 1 / .800)
This will make the speed 25% higher in OD with a given engine RPM.
Look at the tag on your OD trans, if it starts with 25, the OD ratio is
.800
if it starts with 32, the ratio is about .757, which is a lot taller.
Assuming the tire circumference is about the same as it rolled out of
the factory (80 series 155 tires), the figures are as follows.
AND that the 83 MPH (at)4800RPM in non OD top is also correct.
Speed at 4800 in OD with 3.89 = 4.22 / 3.89 * 1.25 * 83
= 112.6 MPH.
A stock motor in a stock Alpine will not pull that kind of speed.
This is pretty tall, and I doubt that the motor will pull above 4500
with
this tall of a setup.
Your actual top speed would be about 100 MPH (at)5700 RPM, in
NON OD top.
Your acceleration will suffer, and believe it or not, the OD will not
gain
you any fuel milage increase.
The OD just saves wear and tear on your motor.
Jarrid gross
>I am driving a 1960 Series I with a 1592 engine, 3.89 rear end, and a
late
>series (25 spline) overdrive. The speedo and electrics for the
overdrive
>are not hooked up yet. I am running standard 13 inch tires.
>I can accellerate to 4800 r.p.m. in top gear (good accelleration up to
>then), at which point it will go no faster. I can maintain this speed
with
>only an inch or so of throttle depressed, and mashing the pedal to the
>floor makes no difference. I am assuming that 4800 r.p.m. is the
maximum
>the car is capable of in top gear, due to wind resistance, etc.
According
>to my owner's manual, 4800 r.p.m. is equivalent to about 83 m.p.h.
>I have the following questions:
>Assuming I can get the same 4800 r.p.m. in top overdrive, how fast will
I
>be going? The manual says 4800 r.p.m. in top overdrive is 95 m.p.h.
with a
>4.22 rear end. Since I have a 3.89 rear end, I should get 8% more
turns of
>the wheels (4.22/3.89) or 102.6 M.P.H. at the same revs.
>
>or:
>
>Since the overdrive will drop r.p.m. by about 20%, will the speed be 82
>m.p.h. X 1.20, or 98.4 m.p.h.
>
>Will I be able to get up to 4800 r.p.m. in o.d.?
>Which of my calculations are correct, if any?
>The answer is out there somewhere.
>
>Terry McKitrick
>1960 Series IB9006321LRX
>St. Albert, Alberta, Canada
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