Paul
By my formula (RPM * Tire Height) / (336 * Gear Ratio) it's more like 89 MPH
Tire Height = 21.3" (175x60x13)
Gear Ratio = 3.9
5000 * 21.3 = 106500
336 * 3.9 = 1310.4
106500 / 1310.4 = 81 MPH @ 5000 RPM in 4th (my Speedo sits right on 80 at
5000 RPM in 4th)
Tire Height = 21.3" (175x60x13)
Gear Ratio = 3.2 (3.9 * .82)
4500 * 21.3 = 95850
336 * 3.2 = 1075.2
95850 / 1075.2 = 89 MPH @ 4500 RPM in 5th
Electronic VDO Speedo initially calibrated over a measured mile and verified
against Sandi's 1995 Camry. It may be a MPH or so off but not much.
At the time I was paying more attention to the road then the gauges. I was
either turning less RPM's or going faster than I thought.
----- Original Message -----
From "Paul A Asgeirsson" <pasgeirsson at juno.com>
To: <millerls@ado13.com>
Cc: <grbyrns@ucdavis.edu>; <spridgets@autox.team.net>
Sent: Thursday, January 27, 2000 1:18 PM
Subject: Re: differentials
> Hi Larry,
>
> I think that something is amiss here. If the true road speed is 80 MPH,
> not necessarily what the speedo shows, then here are some examples of
> what the engine revs should be.
>
> Here is a small range of tire sizes for the example.
>
> Tire goes 70.75 inches per wheel revolution, 3.9:1 dif., 5th gear=.821
> reduction, times 1.33333 for the difference of 60 MPH up to 80 MPH
> Inches per mile=63360.
>
> 63360/70.75=895X3.9=3492X.821=2867X1.333=3823 Engine Rev per min.
>
> Tire goes 67.25 inches per wheel revolution, all same as above.
>
> 93360/67.25=942X3.9=3673X.821=3016X1.333=4021 Engine Rev per min.
>
> Could it be that you haven't regeared your speedo or adjusted it by the
> angle drive to compensate for the lower cable count from the Datsun
> engine to the Speedo? I'm pretty sure you don't have it in 3rd gear! <G>
>
> You may actually be going closer to a true speed of 92 miles an hour. No
> wonder it's buzzy! You may need a friend in the Highway Patrol or the
> Court Clerk!
>
> Paul
> PAsgeirsson@juno.com
>
> On Thu, 27 Jan 2000 11:23:21 -0800 "Larry Miller" <millerls@ado13.com>
> writes:
> >I have the 3.9 in my Bugeye with a modified 1275 and the Datsun
> >5-speed. 80
> >MPH is around 4500 RPM in 5th. It's still a little buzzy on the hiway.
> >I'm
> >contemplating a switch to the 3.7.
> >
> >Larry Miller
> >----- Original Message -----
> >From: "Glen Byrns" <grbyrns@ucdavis.edu>
> >To: <spridgets@autox.team.net>
> >Sent: Thursday, January 27, 2000 10:25 AM
> >Subject: differentials
> >
> >
> >> After examining the diff. on my Sprite I notice that it has quite a
> >lot of
> >> play in it. Checking the usual sources I see that replacement gears
> >are
> >not
> >> easily available. Assuming that I can eventually find a
> >servicealble
> >> differential assembly, what ratios are available and what would go
> >best
> >with
> >> the 1275cc.? The stock ribcase with the original diff. has too low
> >a low
> >> and not enough high. I expect to cruise the highways much more that
> >I
> >> expect to climb phone poles and don't really have the resources yet
> >to do
> >a
> >> 5-sp conversion.
> >>
> >> Thanks to the list as usual for the excellent advice. I've yet to
> >ask a
> >> question that wasn't answered with wit, wisdom, or both.
> >> Regards, Glen Byrns
> >>
> >>
> >
>
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