Getting Best MPG during Cruise
Aug 25, 2009, 02:10 PM
#1
Getting Best MPG during Cruise
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.
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.
Last edited by Hiboost; Sep 1, 2009 at 03:29 PM.
Aug 25, 2009, 02:26 PM
#2
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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:
You Evo cruises at only 40 or under load?
here is a log from my 8, lean cruise, 46*, etc:
Last edited by GST Motorsports; Aug 25, 2009 at 02:29 PM.
Aug 25, 2009, 03:49 PM
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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!
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!
Aug 25, 2009, 04:38 PM
#6
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:
You Evo cruises at only 40 or under load?
here is a log from my 8, lean cruise, 46*, etc:
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.
Aug 25, 2009, 04:48 PM
#7
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..
Also on my X, cruising at 3000rpm (100kmh) my load is about 50, so the 10-30 cols are pretty useless..
Edit: I posted a stock ecu map with the MPG optimized timing tables to make it easier to use.
Last edited by Hiboost; Sep 1, 2009 at 03:31 PM.
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Aug 25, 2009, 05:37 PM
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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.
Last edited by tipoytm; Aug 25, 2009 at 05:41 PM.
Aug 26, 2009, 07:30 AM
#12
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
Cheers C
Aug 26, 2009, 08:00 AM
#13
http://www.eng-tips.com/viewthread.c...=251159&page=1
In case anyone was unclear what MBT was:
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.
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.
Aug 26, 2009, 08:01 AM
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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
Cheers C