Date: Mon, 14 May 2001 19:17:51 +0100 From: Johannes H Andersen <johsnopsamsafish.com> Subject: Re: RMP to MPH ratio?
Kyle Kontney wrote: > > Hello all, > > I have two SAAB 900S cars. They have a slight difference and was wondering > if anyone could tell me if this is adjustable, or if this is normal. Please > note: these are Automatic, not manual shift, 4-door non-turbo. > > The 88 900s gets better gas mileage, and the RPM to MPH is about half > numerically. For example, if I am traveling at 70 MPH, my RPM is 3500. > > My 89 900s has a different ratio. For example, 70 MPH, my RPM is 3800. > > So I am wondering if there is something wrong? > > What is the acceptable RPM for the speed ratio? > > -Kyle > themoz(at)wi.rr.com Hi, the MPH/RPM ratio is fixed, it is determined by top gear ratio, final drive ratio and wheel size. A higher RPM for a given speed is used in the automatics to achieve sufficient engine flexibility and driveability, not necessarily for optimal gas mileage. Hopefully, your auto box is engaging correctly in top gear for the automatic without slippage or kickdown? Johannes
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