After installing the manual transmission from a 81 gsl into my 84 gs i found that my car likes to sit at nearly 3250 just doing highway speed. This seems a little high after someone told me that they get the best milage at 2200. Is this wierd to any of you or is it just the combo between the auto rear end and earlier style manual transmission.

Im not really complaining because i have never actually droven a car that kicks back in 5th gear at highway speed, and still accels prety quickly.

 

What is highway speed to you? They were designed for highway speed cruizing at 55mph.

 

100 km

 

I get 4k rpm @ 78 mph. Zoom zoom...

 

The gearing on these cars is such that the engine will be between 3K & 4K on most highways. You are not suffering from a lower geared rearend from an auto, as all 12a cars had a 3.90 rear gear, regardless of trans.
Reading thru a couple books titled "Rotary Engine" by Kenichi Yamamoto, one will discover that the most efficent RPM range of the Rotary engine, is around 3-4K. This is the RPM range in which it makes most effective use of the fuel/air mixture, resulting in the best MPG and lowest emmissions. One word of warning, these books I mentioned are very technical, and can easily overwhelm a person.
I suppose that Mazda used the research of Yamamoto, in deciding the gearing of these cars. After all, he was the head of engineering for the Rotary engine.

 

Thats really interesting, and good to know. I've been trying to drive much more conservatively lately due to the inflated gas prices so this helps.

 

k kewl, thanks, i was just wondering because it jumped nearly 400 rpm from my auto.

 

What is really interesting, is that the peak torque is also around 4K. This leads me to believe that cruise RPM in the 3500-4500 range is also desireable, so less throttle fluctuation is required to maintain speed.
I know that my '83 mostly stock 12a gets the best MPG when I am running 65-70MPH. This same speed also requires very little movement of the throttle pedal to maintain this speed, along with a reasonably low amount of static throttle opening.
Below 65, or above 70, my MPG will start to drop, at about the same rate.

 

so pedel position matters more then RPM on geting the highs mpg ?

I have thought this for about the last four months as I have been lugging the engine down at like 2-2.5 everytime I can trying to get better mpg's with no results. Going to try the shitf at 4k from now on see if that makes a diff

 

MPG depends on many variables. Driving style is part of the overall equation. The figures I am using, is refering to sustained highway cruising. Around town, I usually shift at 3-3.5K.
Combined city/highway, I usually average between 19 - 22MPG, highway averages between 24-27MPG. Both would likely be a little higher, if I refrained from the urge to open the secondaries a little more often.......

 

Haha I wish I saw those results...mine 12a is stock too, and I drive only about five miles every time I take it out with no highway, so thats where I might be loesing mpg's

Secondarys open at 3,600 ?

to the tread starter...sry for the jack

 

no problem, i already got my answer

 

You will not get any mileage when you are only driving that short of distance. The Rotaries need to up to full operating temp and that only occurs after sustained highway driving.
When i had my 83 12a with a mikuni on it and only drove 2-3 miles each way to work i only got 12-14mpg. But if i took it out on the highway for a trip i got between 22-26mpg.

 

Quite true doc. The Rotary, like any engine, will achieve optimum combustion when operated within the normal temperature range. When the engine is below the normal operating temp, the combustion is not as complete, therefore it will use more fuel.

 

This past winter, making short trips to the store and back, 6-8 miles round trip, my fuel mileage dropped as low as 8.5 miles to the gallon with the Mikuni and 1/2 bp. Over Christmas, I made a 1300 mile road trip and highway mileage was 24, if I drove the speed limit. It would have been higher, but I was running a non-oem thermostat and had trouble keeping the engine temp above 153* on the Autometer temp gauge.

Had I been running the correct thermostat, I estimate my mileage would have been 2-3 mpg more. I consider the mileage to be very good when taking into account the extra drag the widebody kit and larger tires have on the car. Short trips, with a cold engine kill fuel mileage and waiting for the engine to fully warm up before moving doesn't help much either.

Running a 180* thermostat gives the best mileage, don't recommend a 160* unless pushing the engine for racing.