Reactionary

I'm working on something that has not been mentioned in here before. But I'd like to first get exact figures from the experts. Specifically, I'm wondering if the rotary squirts more fuel during engine startup than a piston engine. I suspect that it does and possibly 2 to 2.5 to 3 times more per each startup.

Can anyone tell me how much more fuel the rotary uses on startup than a piston engine? Relative figures (eg. 2.5 times more fuel) would be fine, but it would be more ideal if I could get exact figures (eg. rotary uses 1/20 gallon per startup and piston engine uses 1/40 gallon).

Reactionary

Ok, no one has responded. I thought there are people on this forum who knew. But I will start my experiment anyway on my 2 cars, one an RX8. I want to stress that I am not doing another gas mileage thread. What I want to do is determine the effect of different number of startups during a tank or half tank of gas on the overall mileage. My hunch is that the rotary uses an excessive amount of gas to start the car (as well as during idling, as one can tell from the heavy exhaust smell; but I am not examining differences in idling time, however). I believe I can do this over the next month or two because my work schedule will be consistent on a weekly basis for this period of time. I am not interested in fwy cruising mileage or city driving mileage, per se. All I want to do is keep my weekly driving schedule about the same (which means fwy cruises of 17 miles one-way 3 times a week and 27 miles 1 time a week; the rest of the miles will be mostly on city streets shopping and doing errands). I will do each measurement condition for 150 miles (ie., refuel and calculate mileage every 150 miles), traveling with basically the same driving schedule to basically the same places and trying to drive in basically the same manner. Assuming each driving schedule (over each 150 miles) is kept the same, then each condition should vary only in the number of startups. Based on initial hypothetical calculations, I am thinking about doing 3 startup conditions: eg., 20, 30, and 40 startups. The 3 startup conditions will be examined for my RX8 and for my other car. Thus differences in mileage should be attributed only to differences in number of startups. In this manner, I can then deduce the amount of gas used per startup!

Note that whether I go for fwy cruising or mostly city driving doesn't matter because I am not trying to calculate those. What matters is that my driving schedule, whatever it is like, needs to be as similar as possible for each measurement condition. As the number of startups increases, overall mileage for that particular 150-mile schedule should decrease. If the rotary does indeed use significantly more gas than a piston engine for startups, then as the number of startups increases, I should expect the drop in overall mileage to be greater for the RX8 than for my piston engine car. Initial hypothetical calculations indicate this drop may be quite a lot for my RX8, as much as 2 MPG over 14 gallons of gas when the number of startups goes from almost none (which would be a continuous trip/driving schedule with no stops) to 30 or 40 startups.

beachdog

Reactionary, have fun with your experiment.

On a much less scientific basis, I have posted previously in the mpg threads that start-up/warmup/shutdown cycles impact mileage much more than anything else. I have driven in bumper to bumper gridlock for 100+ miles and gotten almost 23 mpg - full tank to start/ 1 start/ drove /filled up. I have driven at 75 mph and gotten 22 mpg - again full tank /1 start /drive and then fill up. I have driven 150 miles over 5 days with about 10 engine starts and gotten <17 mpg. No official testing, just observations.

Pretty well reinforces what we were told during the gas shortages in the 70's. Plan your trips so that you minimize the number of times that you have to use the car in any given day.

Reactionary

Hey, we're thinking the same thing. The case where you were in traffic but didn't stop is exactly the kind of contrasting observation that we're looking for.