Getting Best MPG during Cruise

[Hiboost]

So once you can run 11 second quarter miles and belt out 500 HP, what is there left to play with? Being able to get decent gas mileage on a daily driver or saving some gas to and from the race track is never a bad thing as long as you don't have to sacrifice performance!

After researching a bit I found that there are a couple methods to improve MPG.

Lean Cruise is one way but I found that it was somewhat tricky to get right and the Cruise LTFT's really start to get out of wack if you place all RPM ranges you typically cruise at from 2500-4000 in open loop. There are some gains to be had if you are at 14.7 AFR, but since mine tend to average 15.0 AFR already there wouldn't be as much benefit changing it to 15.4-15.6 AFR. So for now I'm placing that on the back burner.

Increased Timing is another way to basically boost power when out of boost so that you can run with lower throttle settings for the same speed. There are limits of course and after seeing what HBSpeed suggested and a few articles about tuning EMS systems, it seems that around 44* timing will net some gains. That will vary from engine to engine but for now that is what I'm testing with. I also increased some areas of the map from 50-80% load cells as a test but if there is any knock or surges of power I may have to back those out again. This has also seemed to counter the unstable airflow I was getting at ~3800 rpm in 5th with my Garrett turbo where going up hills on the expressway would send the car into 80-100% load cells and flutter the BOV which was annoying.

So far I've managed 29 MPG over a 4.5 hr trip to the Buschur Racing Shootout this year. Resetting the MPG gauge on a flat highway at 70 MPH seems to yield around 30-32 MPG which is about 2 MPG higher than I can usually get. I've also gotten 30 MPG on my 15 minute commute to work averaging about 70 MPH which seems fine to me.

Feel free to test this out yourself AT YOUR OWN RISK, there are no guarantees it will help your setup as my car has all the bolt-ons plus a free flowing Garrett GT3076r turbo. The blue shaded areas are the most important for light cruise although not all cars will run under 40% load when at speed so adjusting at least the 50% load area can make a huge difference in your results. Those wanting to stay on the more conservative side can stay with just adjusting the blue shaded areas from 0-40% load and you can try 42*-43* for peak values instead.

All cars will have a different optimal value for power/efficiency and until you verify where you get the highest vacuum (negative boost), making timing adjustments too high will actually start to reduce power and have the opposite effect we are trying to achieve. This happens because at some point the timing is so far advanced that it is fighting the compression stroke slightly instead of optimizing it. Since it's hard to get knock at light loads to indicate you have gone too far it might only give you a slight surging/bucking feeling and datalogging average load, timing, boost, AFR, and IPW might be the best way to see a trend of where you are maxxed out for gains and starting to lose power again.

Let me know if these help anyone get some more MPG or if you have had any success adding in Lean Cruise to the mix.

[GST Motorsports]

Yup this will increase mileage a bit. I've been doing the same on my personal 8 on E85 for over the last year with good gains. I've also found the same that open loop doesn't help a ton in mileage.

You Evo cruises at only 40 or under load?

here is a log from my 8, lean cruise, 46*, etc:

[Q15H]

Add EGR flow and appropriate timing advance. You might need to go back closer to stoich on the mix though.

[flagg77]

Thanks for the thread Chris.

Quesion for you / folks on this change. Would this impact EGT's in anyway? I guess i'm asking, what else does this impact if anything? Are we simply reducing our cat's efficiency with this change or anything else?


Thanks!

[tephra]

I find that leaning out the mix for cruise REQUIRES more timing, so I am not sure if the benifit is there...

Also on my X, cruising at 3000rpm (100kmh) my load is about 50, so the 10-30 cols are pretty useless..

[Hiboost]

Originally Posted by GST Motorsports

Yup this will increase mileage a bit. I've been doing the same on my personal 8 on E85 for over the last year with good gains. I've also found the same that open loop doesn't help a ton in mileage.

You Evo cruises at only 40 or under load?

here is a log from my 8, lean cruise, 46*, etc:

Yeah according to my logs the car is happy with around 35-40% load at 65-70 MPH. Going up and down hills will swing that between 20-60% load but for the most part it averages out to 35-40% load at those speeds. I'll have to test 45*-46* at some point to see if it will offer gains over 44* but I didn't want to get greedy right off the bat.

This is one case where being able to change settings "on the fly" and nudge the car 1* advance while cruising at a constant speed would be helpfull so you could see where the gains of torque and lower load % were topped out and begin to require more throttle again. I'll have to settle for same stretch of road over same time period at the same speed and compare load and TPS averages.

[Hiboost]

Originally Posted by flagg77

Thanks for the thread Chris.

Quesion for you / folks on this change. Would this impact EGT's in anyway? I guess i'm asking, what else does this impact if anything? Are we simply reducing our cat's efficiency with this change or anything else?


Thanks!

That's a good question, I'm not sure what it will impact at cruise and low loads besides saving some fuel. Without an EGT gauge/probe I have no idea if it was changed or if the cat efficiency (assuming one was there) would be impacted.

I find that leaning out the mix for cruise REQUIRES more timing, so I am not sure if the benifit is there...

Also on my X, cruising at 3000rpm (100kmh) my load is about 50, so the 10-30 cols are pretty useless..

That's one of the reasons I scrapped the 1250 and 1750 RPM ranges in exchange for 4250 and 4750 and the 10, 30, an 30% load for 230, 250, and 270% load cells. Most of the cells in that area were just a big repeat or were easily interpolated for almost identical values if removed. The only tricky part was checking what other tables were impacted by the change in X and Y axis, turns out Low Octane Timing Map, Ignition Warmup Retard, and Evap Map #1 and #2 had to be adjusted.

Edit: I posted a stock ecu map with the MPG optimized timing tables to make it easier to use.

[tipoytm]

Nice, I really want to try this, perhaps increasing timing to 41-43 on my cruise load cells that I can log and find out.... my X is fully stock, but I don't have a WB... so you could say I'm very cautious. Do you think it would be safe to try this out and just watching out for knocks? I constantly log with my carputer setup.

[tephra]

yeah you are in closed loop so your AFR's will be 14.7:1

basically you should be ok looking for knock, but really we need a proper way to calculate MBT...

[tipoytm]

Thanks... I'll try it out soon :-) At this point, I'm more interested in getting the best possible fuel economy & efficiency rather than cranking out more HP.

[Bob_tm]

My best fuel economy settings are:
AFR 15.2 - 15.4
Intake mivec 10
Exhaust Mivec -20
Ignition stock.

For 3000-4000 rpm and 40-70 load

[LIGHTSPD]

For what it is worth I had the shop car on the dyno last week. MBT for cruise area running a stable 14.7 AFR in closed loop. AT 40-50% Load was where I was playing at 2000-2500rpm 43 degrees and at 3000-3500 was at 45 degrees. Keep in mind I was running stock Mivec at these RPM. I am also running a fuel that is 10 percent ethanol. Not sure if this helps anyone but it is what it is.

Cheers C

[Hiboost]

http://www.eng-tips.com/viewthread.c...=251159&page=1

In case anyone was unclear what MBT was:

MBT timing = Maximum Brake Torque timing. Knock limit aside, at a given speed and flow rate, it is the spark timing that gives maximum torque, (and minimum bSFC). It doesn't mean maximum (or minimum) spark advance. The word "maximum" refers to torque - not spark.

Basically, if combustion starts too soon, the gas pushes back on the piston as it is coming up in the compression stroke, creating negative work which reduces torque. If the spark is too late, peak cylinder pressure is reduced, and hence, so is expansion work. So there is an optimum spark for maximum torque. If one were to draw out a curve of torque vs advance, (starting out below MBT), as spark is advanced torque will increase until MBT timing is reached, after which point further advance will cause torque to go back down. The top of the curve is somewhat flat, so the percentage increase in tq drops off as spark advance approaches MBT.

In the ideal Otto cycle, MBT timing would be at TDC, as mentioned above. But due to the non-zero burn duration of a real engine, MBT timing is not at TDC.

[tipoytm]

Originally Posted by LIGHTSPD

For what it is worth I had the shop car on the dyno last week. MBT for cruise area running a stable 14.7 AFR in closed loop. AT 40-50% Load was where I was playing at 2000-2500rpm 43 degrees and at 3000-3500 was at 45 degrees. Keep in mind I was running stock Mivec at these RPM. I am also running a fuel that is 10 percent ethanol. Not sure if this helps anyone but it is what it is.

Cheers C

91 or 93 oct? How much improvement on MPG? I got the timing map updated on my current ROM, but have yet to flash yet...

[tipoytm]

Hiboost, I'm curious as to the slight increase in timing @ 500-1000+ RPM; low load (40-60?), what is the benefit of this?