UnknownJinX

I know boosted people use the 5-speed because the R15M is indestructible.

As for the hole, I, too, wonder if that will be harmful. The S2 did add an extra oil injector per housing and I also premix. Hmm...

Loki

iTrader: (1)

All of my testing, over years, repeatedly and consistently gave better fuel economy at 130kph and 4200ish rpm than 110kph and 3600 (the rpm may be off because the tach lies and because I don't remember exact figures.. it's a stock s1 6speed).

I never really tried <3k rpm cruise because that's too slow and it feels awful. Assuming we're testing highway cruise there may be a whole other dimension of rolling and wind resistance that doesn't degrage much between 110 and 130. In other words, maybe the power required to cruise at 130 is not so much higher than the power required to do 110 that 130 is a more efficient cruise speed.

Also maybe the BSFC peak of a rotary climbs higher in rpm for the same load as it loses compression. Mine is still the original 2004 engine, it's definitely not running factory compression.

As for the hole.. Mazda must have their reasons.. these things get tested backwards and forwards. Maybe it's a weird oil saving strategy. At low load/rpm you're not generating high EGTs or apex seal speed/pressure. Maybe it's not necessary/wise to add oil to that.

I know that's a lot of maybes and handwaving, without a bench test I can't fully explain my observations.
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Brettus

iTrader: (2)

I think wind resistance goes up by the square of speed ...(something like that ... it's not a straight line) . So definitely you should use more gas the faster you go . Your tests show something else has come into play .... IE efficiency of the engine IMO.

Brettus

iTrader: (2)

As an aside .... i did a lot of experimenting to see if fuel economy could be improved by running leaner . I found it made very little difference . Logs indicated that throttle had to be open further and let more air through (needing more fuel) . Indicating that power was lost by running lean and had to be made up with more airflow.

UnknownJinX

Your case is definitely an oddball IMO. I personally cannot test 130 km/h on local highways unless everyone here can come up with a grand total in case I get caught by the cops and have my car towed. I had a friend who had that happen to him, and that's about how much it cost for him.

As for the fact that the rotary is powerless under 3k RPM, I do agree, but it's definitely enough to keep you going at the same speed on flat ground. I personally find my car to be able to climb hills at 3k RPM, so cruising on flat ground should take less than that RPM. If you need power, just downshift.

Of course, there are no set rules and one beauty of driving a stick is that you are in control. When I had my old Corolla, I left it in 4th(1800 RPM) at 64 km/h if the traffic is kinda busy so I don't have to shift constantly as the speed can fluctuate. If the road's empty at night, however, I dump it into 5th(1200 RPM) because I will be sticking to that speed.

A good analogy would be like riding a bicycle with multiple gears. At a set speed, there is usually a gear you are comfortable with. Too high of a gear and you will tire yourself out as you have to stomp real hard on the pedal, and too low of a gear and you will also tire yourself out as your legs try to stomp the pedals as fast as possible to maintain that speed. Same idea as an engine.

As for the hole, I wonder if this is done to pass the emission tests since the car runs at that RPM range during the emission test. This theory is a bit getting close to wearing a tin foil hat, though. Mazda isn't VW, after all.

All that said, I am merely curious about cruising RPM. If the light turns green in front of you and the cars don't move until like 30 seconds later, you know I am not in front of you. I will still drive spiritedly. My thought has always been that I am willing to pay for fun, but if I am not having fun(waiting for someone, cruising, etc.), then I save my gas money. I shut my car off when I am waiting for someone.

Too bad there is not an AT owner here. Could have just asked them about it since the AT usually keep the cruising RPM in the 2.5k range.

Running lean isn't feasible on a stock car anyway. The exhaust temperature is hot as it is. Running even hotter will not only destroy the cat, but will also damage the sensors. Also, leaner = more NOx emission so that's another reason Mazda couldn't consider it.

Loki

iTrader: (1)

Just so happens I'm on a 6 hour drive today on a road I did at 130 4 days ago, so I'm taking it easy at 110 and taking readings.

Too early to judge mileage but I have at least one result so far: at 110 the car is permanently in closed loop, at 130 it bounces between open loop and closed loop. In open loop it runs richer, around 13.9-14. In closed loop it runs 14.7 on the dot.

​Stay tooned..

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Loki

iTrader: (1)

Well f*ck me. 110km/h cruise control 95% of the way. 23.06mpg or 10.2L/100km. Better than EPA.

I kept track of calculated load and MAF rate at different cruise speeds, will post back later.

I'll have to look back but this may be my best mpg ever.

A couple of early thoughts: all of my testing was on flat land, while this drive was through Vermont where there is very little flat land (but very little net altitude change from start to end, I verified). Perhaps the mountains set up a natural pulse and glide.

Motakai

Holy hell, 10.2L? I gotta try this... MPG has been absolutely killer for me lately...

UnknownJinX

Yeah I will have to do some testing on my part as well for city cruising, 50~65 km/h(30~40 mph) range.

Tried to do it last night but the traffic was not empty enough for me to get reliable readings. Might have to sneak out past 12 at midnight to try it.

Brettus

iTrader: (2)

When I was doing mileage testing ..... I got a shock when I realised just how economical a stock rx8 could be if you drive like the beige brigade . 24mpg was easy.

UnknownJinX

Really? Wow.

That said, I am not aiming for that kind of gas mileage at all. When accelerating, I still rev the car to about 4~5k RPM. Again, the only thing I am changing here is trying to stay at a lower RPM during cruising in the city, keeping the engine at about 2.5~3k RPM instead of 3k~4k RPM(which might trigger an open loop as well).

I mean, my old Accord V6 automatic was rated at 19 MPG city and I think I averaged about 18 MPG when I sold the car with about 20% of highway driving. I do not drive easy.