The only adjustments I want to make as far as Fuel savings go, is to lean up my a/fs when cruising @80mph. It seems anytime I go over 75mph my a/fs go to **** (Low 13's, high 12's), I want to get better control over this, since 80mph is my normal cruising speed on long trips. But, I do not want to cause any damage to my engine at the same time, I'm more than willing to sacrifice some mpgs for better longevity of my motor.

I "think" this will require adjusting the "Air/Fuel Gear 5-6" map, in the rpm range of 3500, 4000, and 4500. And in the Calculated Eng Load ranges my car has at those speeds. But how do I know what's too lean? Exhaust temps? My only source of data is from the PCM (which includes EGT's from the rear O2), no aftermarket gauges.

 

Not worth it. EGT's would tell you a story, but at the cost of sensors. And if you get too lean you should have lean misfires.

 

You mean not worth trying at all or using EGTs to figure it out?

I tried a map out about 2 weeks ago and had the AFs adjusted to low 14's between 75 and 80mph and mpgs were better. Everything seemed okay, but iI was nervous about it being too lean so I changed back maps. I thought the only reason we ran so rich was for the cat, which I don't have.

 

I too am running low 14s at 3500 cruise ...

 

Closed loop exit is 6000 rpm stock, but why does it leave closed loop at around 3800-4k rpm?

I enjoyed closed loop up until about 89 mph, how?
closed loop tables exit load C, factory is 0.28 calc load at 4k, and 0.00 at 4500 and higher
my tables says 4k= 1.00, 4500=.75, 5k= .66, 5500=0.47 so unless i exceed .47 load, i stay in closed loop until 5.5-6k. the trick then is to aim for 13.8 or so afr. 14.4 at 3500 is ok, but you'll need a little more as the rpm goes up.
i'm pretty sure I only had to change the closed loop exit load c, as i only cruise in 6th, and i assume c=5th/6th. , i also edited the omp map for more oil over 4k and in cruise.

This was on my blue car that i sold, but i've recently serviced it for the new owner with some new coils. most people agree it's faster then my yellow one.

 

Thanks for that info, I'll check that out as soon as I get home.

 

Did you adjust the map before 4k, or did you just leave that part alone?

 

You got it right dude, pic 3 is exactly what mine is, but that just means you'll need to exceed 100 calc load to go into open loop, but under 4k, it don't think it matters?

 

Great info I really want to learn to tune my car correctly. I am a little worried about screwing it all up. Anyone got a link to a beginners guide to engine tuning or learning the basics with the Cobb AP. I have raised the Rev limit and lowered the fan temps but that is about it. I Autocross so efficient power would be nice and also exactly what is in this thread.

I drove through the keys last weekend 45-60mph and averaged over 22mpg for 100 miles then as soon as I hit the highway 70-80 it dropped to about 17mpg.

 

There is no guide unfortunately. surround yourself with people smarter than you and listen... thats been my approach. but it is very slow coming.... Been at this for a couple years now.

 

Shouldn't, I know how to downshift when I wanna go.

Here are some threads that helped me learn.
https://www.rx8club.com/engine-tunin...ssport-178635/
https://www.rx8club.com/major-horsep...-120276/page6/
https://www.rx8club.com/engine-tunin...eed-ap-215661/
https://www.rx8club.com/engine-tunin...w-tune-234580/


I'm trying to do that.



I've also been dipping into adjusting A/F Gears 1-2 3-4 maps for power. I know this is dangerous since I'm new to tuning but I figured I might as well learn on this engine since it's compression is on the low side of life (105psi).

 

Thanks you rock. Time to get some reading done.

 

Wish I had seen this thread earlier. I've already tried all this. Increased my CL exit load, advanced my timing, and even tricked my o2 sensors. Increasing the CL exit is slightly beneficial, but not as much as you might hope. Advancing timing is also slightly beneficial. in the end you can get that 17mpg up to 18-19 ish, but it will have much less of an effect than how you drive.

Oh and as a sidenote. If you trick your sensors you can push the engine really lean, at least with a lower compression engine, right up until you start losing power (not lean misfires), but EGTs will never turn and come back down. Your indicated fuel economy won't increase by that much (did not do it long enough to get solid numbers) and you will run the risk of cooking your side seals. I plan on trying this again after I rebuild, but the conclusion I made was that nothing that slows down the fuel burn in the engine will improve the fuel economy.

Also, look at the A/F maps if you bring all the 10s and 11s up to 12.5 it will give you a noticeable increase in power. Again this was on a low compression engine. YMMV.

 

0_0

 

it wasn't worth the effort or the risk IMO

in the end it's a rotary, gas mileage will never be great, you can get some but IMO a lot of past reports from people who claimed they suddenly got miraculous mileage after being tuned were erroneous; I tried it all too and have perfect compression, no matter what changes I made the only way to get any decent mileage was to keep speed and revs down. It takes so much power to overcome the inherent friction forces. It takes so much fuel to accomplish that equilibrium power point.

or go downhill/down wind

 

This might be a feature of a low compression engine. If during the combustion process, unburned fuel is getting blown forward past a weak apex seal enough to burn in the exhaust stroke, the EGT will be higher in a way not easily influenced by the raw a/f reading.

 

Super mpg through just tuning - probably not.

But, there may be something odd to take advantage of. If one looks at the distrubution of rotary engine heat losses, it absolutely takes off at high rpm. Watch your oil temps shoot up and mpg's shoot down if you set the cruise at ~40 mph and 5000 rpm. Papers attribute this 'difference' between piston and rotary engines to friction of the apex seals against the housing increasing greatly with rpm.

The same experiment in the other direction however, seems to yield a smooth increase in mpg's as the rpms drop (shifting to keep a more or less constant speed) until the range from 3500 to 2500 rpm where there's a big increase in the Cobb calculated mpgs. If real, it's a bit surprising. Sure, pumping losses are less because of the more open throttle plate, but at first look, it doesnt really explain the sudden difference.

 

 

I don't think it's the unburnt fuel moving forward, but more the lower compression causing a slower burn rate. As the fuel burn slows it starts moving further and further back in the cycle until it's burning in the exhaust pipe. In an ideal engine with no hot spots and ideal fuel you should be able to advance timing and lean out the mixture until all the fuel is burnt in the chamber and throttling losses are minimized. But we don't have ideal engines with ideal fuel. This is also why e85 can give as good a fuel economy as it does with as low a specific energy as it has.

 

I threw the tune on my car, and haven't really noticed a difference yet. But majority of my driving is city traffic, I was only looking to improve on long road trips that involved +90% Cruise @80mph.

Once the car is out the shop I plan on going on a decent gambling binge in Biloxi and see will see if it gets better.

Normally I average, 14-16 City, 17-20 Hwy, and 23 is my all time best.

 

EGT's are the easy way. the cat's limit is 650c, and its actually probably the reason the car is rich beyond 3500rpm.

without the cat your limit is somewhere around 850c.

going from 13 to 14 AFR isn't going to be a huge change in mileage, so team is kind of right, and of course you want to err on the slightly rich side.

the other place for improvement, is the cold start/warm up phase, its super rich to try and light the cat off faster, so that could be leaned out somewhat.

just remember to go slow, and try a little at a time

 

No Kitties here.

And I already have the a/f leaned a little for warming up.