Hello

I am in the process of droipping a cummins 3.9 into a range rover and
for the moment have the chance to play around with the gearing. Would
appreciate advice on the best economy option.
Best guess, based on figures from friends is that 43hp is needed to go
at 65mph allowing for wind resistance, weight, drive train losses etc.
According to cummins torque curves 43hp should be produced at about
1000rpm. So is 1000rpm geared to 65mph correct or on the same engine
specs graphs, 1700 rpm is the most economical or should it be some
other rpm.
Any advice appreciated.
Thanks
Smokeyone

On 22 Jul 2005 22:02:26 -0700, mailstarclipper@btopenworld.com wrote:

>Hello
>
>I am in the process of droipping a cummins 3.9 into a range rover and
>for the moment have the chance to play around with the gearing. Would
>appreciate advice on the best economy option.
>Best guess, based on figures from friends is that 43hp is needed to go
>at 65mph allowing for wind resistance, weight, drive train losses etc.
>According to cummins torque curves 43hp should be produced at about
>1000rpm. So is 1000rpm geared to 65mph correct or on the same engine
>specs graphs, 1700 rpm is the most economical or should it be some
>other rpm.
>Any advice appreciated.
>Thanks
>Smokeyone

WHere this mine, I'd gear it so it was about 1700 at cruising speed
(say 65 MPH/ 100 KPH) but not much lower.

"mailstarclipper" wrote:
>Hello
>
>I am in the process of droipping a cummins 3.9 into a range rover and
>for the moment have the chance to play around with the gearing. Would
>appreciate advice on the best economy option.
>Best guess, based on figures from friends is that 43hp is needed to
go
>at 65mph allowing for wind resistance, weight, drive train losses
etc.
>According to cummins torque curves 43hp should be produced at about
>1000rpm. So is 1000rpm geared to 65mph correct or on the same engine
>specs graphs, 1700 rpm is the most economical or should it be some
>other rpm.
>Any advice appreciated.
>Thanks
>Smokeyone


I would gear it for best ecomony rpm at cruise of 65mph. (1700rpm) If
you geared it for 1000 RPM preformance would be terrible and so would
ecomomy because engien would be maxed out and lugging. I would be
curious to here how it works out overall. Jeep breifly used the 3.9 in
a few trucks in the 70’s.

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Thanks for the advice. I can go with 1700rpm but any further thoughts
or ideas.

Smokeyone

Check the engine's specs for max torque (not max HP) at
?,??? rpm -- that should be your target rpm for cruising.

Regards,
Franko

<mailstarclipper@btopenworld.com> wrote in message
news:1122181081.870521.303300@o13g2000cwo.googlegroups.com...
> Thanks for the advice. I can go with 1700rpm but any
further thoughts
> or ideas.
>
> Smokeyone
>