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September 11, 2003
Stewart.....
If your engine is tuned for the high end
(and it certainly sounds this way.."useless road engine"...."lumpy
idle"), then going to
a 3.7 will make it more a useless road
engine in terms of the low end.
So...it you are using the car mostly at
highway speeds (say, 3k or higher) than
no problem. Town driving will become more of a hassle as you'll be at
lower
rpm more of the time at lower speeds,
unless you retain lower gears more of
the time then you are currently used to.
The more available 3.9 might make for
a more happy medium considering your
engine's apparent state of tune. A 3.9
might be a better choice for a happier
"medium".
Another route to consider might be matching your current diff. ratio
with a
Datsun 5 speed. It's first 3 gears are a
little bit lower than a Spridget ribcase, with a 1-1 ratio for fourth
(as in the
Spridget box) with a .82 5th for cruise.
In consideration of the foregoing lower
first 3 gears, a 3.9 would bring you back
a bit to current Spridget first 3 gear ratio's
with lower rpm at same speed in 4th and
5th.
Fr'instance, I utilize a 3.7 in my more
mildly tuned 1293 which utililizes the
old Cooper S grind (one step up from
stock...very mild cam) BUT, the cam is
timed in 4 degrees advanced which brings up the bottom end at slight
expense of the
top end, this "effect" being offset to some
extent by the use of higher ratio 1.5 rockers.
This combo makes for the best of all
worlds for town and highway driving,
more especially so since the foregoing
state of tune is teamed with the Datsun
5 speed. This makes for a very "torquey"
low and lower-midrange (for town or
"street" driving), while the car cruises
relatively quietly and comfortably at
70 (3.2k or so) on the highway,
with 4th being a very useable
suburban road cruise gear.
Cap'n. Bob
'60 :{)
PilotRob@... 25171
Posted on September 11, 2003 06:32 AM
Posted to category(s) Cylinder Head | Drive Train | Engine (external) | Engine (internal) | Exterior | Restoration | Transmission | Tuning
