Martyn,
I did this a while back on my Bugeye, On my car the speedo is
actually more accurate with the 3.9 than it was with the 4.22. By my
calculation the change resulted in a 7 percent reduction in speedo
reading, amd an equivalent drop in RPM's for the same speed in top gear.
I did not notice much of an improvement in Highway speed maybe three or
four MPH. Nor did I notice much difference in acceleration but then
again I did not have much to begin with. I am still running a 948 engine
in my car. Top speed is around 85-90 depending on tail winds. It does
make a nice drop in the RPM's though. The change in diff ratio is almost
equivalent to the difference between running 145/80R13 tires and
165/80R13 tires. When I had both the 3.9 diff and the 165/80 tires the
car felt a bit sluggish until I changed to 165/70 tires which are
roughly equivalent in diameter to the 145/80R13.
Regards,
Peter S.
>Date: Thu, 31 Dec 1998 09:03:03 -0500
>To: spridgets@Autox.Team.Net
>From: Martyn Ridley <ridleymj@bis.on.ca>
>Subject: Changing from 4.22 to 3.909 diff
>Reply-To: Martyn Ridley <ridleymj@bis.on.ca>
>
>I would like to change the frog diff from 4.22 to 3.9 to get a little
extra
>highway speed. The car has a ribcase gearbox but or what vintage I
can't
>say. Have any of you done this? What all must I change since I have
this
>desire to keep the speedo accurate (not that Sprites are likely to
exceed
>the 100km/h max by sufficient amount to attract the constabulary!!).
>
>PS: Has anybody seen the 'continental' speedo for a frog. I was
thinking
>of 'metrifing' the olde girl while making the diff conversion.
>
>Cheers, Happy new year, Hog Monet (kilted lurkers, please correct
spelling!!)
>Martyn
>The Journey, not the destination, becomes a source of wonder.
> (Loreena McKennitt - liner notes - 'The Book of Secrets')
>
>
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