Hey Guys!
Could someone please explain the pros and cons of a close ratio
gearbox vs a standard shaved gear gearbox with relation to
practability, value, reliability, usability and general
application. Thanks–
Bill Swaim 1960 XK150 FHC S836944DN
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from Swaim sent Sun 21 Feb 2010:
Bill,
What is is, is explained here.
Basically a CR box will more closely match the power band of the engine - usually if you change gear at max BHP then the next gear up will drop the revs to the rpm at which you
get peak torque and so on up through the gears. A non CR box may have a few compromises
based on achieving a reasonable engine speed for economy and noise/comfort at commonly
driven speeds, such as speed limits, and the ability to get away from a standing start
easily on a steep hill.
The caveat for all
Practicability. If it fits it fits!
Value - depends what the price/condition is for one versus another.
The caveat here is what are the ratios and how much different are they. The XK engine has
a fairly wide power band - 2000 rpm to 5000 (5500) rpm and and a good amount of torque so
a CR box is less important than some 4 cylinder engine which relies on a very narrow rev
range to develop enough power to get up a hill. In the this case to maintain speed you
change down to a gear where you can operate above the peak torque rpm. in the Jag it just powers on up there.
Usability - there are calculators around that allow you to plug in the gearbox ratio, the
diff ratio, tire specs, size, profile or diameter/radius to give you road speed and rpm.
So based on the difference between option A and Option B ratios in the gearbox, work out
if the higher or lower RPM at the speeds normally driven is better or worse in
relationship to staying in the power band, and preferably in the highest gear possible.
The overall ratio in first will determine the ease of getting off the mark, and the
possibility of having to slip the clutch if the first gear is much taller.
Regards
Keith–
The original message included these comments:
Could someone please explain the pros and cons of a close ratio
gearbox vs a standard shaved gear gearbox with relation to
practability, value, reliability, usability and general
application. Thanks
–
Keith Bertenshaw
Rockaway, NJ, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –
I probably should know the answer to this what would be the gearbox number be on an XK120 gearbox with close ratio gears?
terry