IDEA for better MPG
04-11-2012, 07:29 PM
#16
Yes, will produce more heat but at light cruise loads should not be an issue other than NOX can go way up. If it's running at lambda (14.7afr) leave well enough alone with fuel. The real trick is ignition.
04-11-2012, 10:47 PM
#17
yeah, it would seem that repairing warped heads would offset any cost savings from better fuel economy. Maybe once gas hits $10/gal though... 
This topic made me think about that old Cadillac V 8-6-4 engine though. IIRC it used a mechanical system to disable the valves on demand. But maybe with an injection system and a brain upgrade the concept could work on a 928. Might throw some odd vibrations though, running on 4 dead cylinders.
This topic made me think about that old Cadillac V 8-6-4 engine though. IIRC it used a mechanical system to disable the valves on demand. But maybe with an injection system and a brain upgrade the concept could work on a 928. Might throw some odd vibrations though, running on 4 dead cylinders.
04-11-2012, 10:57 PM
#18
Nordschleife Master
interesting responses. Yes lean cruise is fine (and done on newer cars with a special get system to bring the NOx back down.
I have run as low as 18:1afr but as a rule I stay around 17:1 or 16.5:1.
My boosted car has lean cruise and it works well at saving fuel, but you do need to adjust the ign map as well.
Additionally, this is not the best idea on a stock LH/MAF car unless you remain at a constant elevation. Massive elevation changes can make the car run exceptionally lean thus making it dangerous to drive.
I have put many many lean cruise miles on my cars over the years with no issues.
However for really saving fuel I want to try doing vapor burning instead of liquid burning, like a more exact method of the old fish carb......
04-12-2012, 12:56 AM
#20
You can probably get more benefit from airing up the tires, driving 10 mph slower and being very, very gentle with the gas pedal . Even cruise control accelerates too hard to be efficient.
04-12-2012, 04:49 PM
#21
Rennlist Member
Thread Starter
If you have a cat car (closed loop) all you need to do is unplug the lambda sensor from the car's harness and then start the engine. The LH defaults to a safe lean map, which would get you 25mpg at 130km/h. When you plug it back and restart the car, you go back to your default closed loop maps. Tried and tested on my racer.
if so this could be the idea!!
will it work on the US cars, like chebbies???
04-12-2012, 05:04 PM
#22
Rennlist Member
Thread Starter
Moving from 14.7:1 -> 17:1 you are leaning out the mixture by about 15%. My car gets 20mpg on the highway. 15% better is 23mpg. Leaning it out also decreases torque some so you'll need less throttling to make the same power. Your throttling losses will go down some. Best case I'd say that gets you to 25mpg. Running lean will also cause the catalyst to not work. And if you go so lean as to cause misfire you may melt the catalyst if done for more than a few seconds.
Might be able to do it with something like this.
http://www.jaycar.com.au/productView...T&SUBCATID=933
You would have to put the car in open loop, but by plugging it inline with your AFM I would think you could adjust the signal to shift your ratio any way you wanted.
http://www.jaycar.com.au/productView...T&SUBCATID=933
You would have to put the car in open loop, but by plugging it inline with your AFM I would think you could adjust the signal to shift your ratio any way you wanted.
There's not a lot you can do when running closed loop. If you tried to make temp too too high a resistance to go lean and get to the limit of loop control range the loop will just revert to mid range.
The best way is to put a switch on the code plug to select cat (normal) or non cat (open loop that you can mess with to your heart's content. When on non-cat you can certainlt vary temp 2 to a higher resistance to go leaner.
The best way is to put a switch on the code plug to select cat (normal) or non cat (open loop that you can mess with to your heart's content. When on non-cat you can certainlt vary temp 2 to a higher resistance to go leaner.
MK
I don't think this would work....since the LH is reading the O2 at cruise TPS......unless you can change cruise O2 reading to 17.0....it won't work
However it WILL work just fine on my SDS system.....well if I had an 02 sensor and it setup that way....but in theory I could do it quite easily.....
I don't think this would work....since the LH is reading the O2 at cruise TPS......unless you can change cruise O2 reading to 17.0....it won't work
However it WILL work just fine on my SDS system.....well if I had an 02 sensor and it setup that way....but in theory I could do it quite easily.....
Leaning out fuel can improve MPG but the real trick is to properly tune ignition in the Part Throttle Ignition tables of the DME. The idea is to get the car on a load dyno and fine tune the cells that are used for cruise speeds, tune for max torque with AFR=14.7 and you'll have your very best MPG. Just leaning out fuel does not cut it because it can reduce torque. The bottom line is to generate the most torque possible with the least amount of air for the given unit of work. Where the unit of work can be defined as pushing the car along at say 60MPH. You simply want to achieve the given unit of work with the least amount of intake air which also coincides with peak torque with that unit of air. That's the science if your really serious about MPG.
I think i posted it on the list about 10 years ago.mark
04-12-2012, 05:17 PM
#23
Rennlist Member
Thread Starter
yeah, it would seem that repairing warped heads would offset any cost savings from better fuel economy. Maybe once gas hits $10/gal though...
This topic made me think about that old Cadillac V 8-6-4 engine though. IIRC it used a mechanical system to disable the valves on demand. But maybe with an injection system and a brain upgrade the concept could work on a 928. Might throw some odd vibrations though, running on 4 dead cylinders.
This topic made me think about that old Cadillac V 8-6-4 engine though. IIRC it used a mechanical system to disable the valves on demand. But maybe with an injection system and a brain upgrade the concept could work on a 928. Might throw some odd vibrations though, running on 4 dead cylinders.
interesting responses. Yes lean cruise is fine (and done on newer cars with a special get system to bring the NOx back down.
I have run as low as 18:1afr but as a rule I stay around 17:1 or 16.5:1.
My boosted car has lean cruise and it works well at saving fuel, but you do need to adjust the ign map as well.
Additionally, this is not the best idea on a stock LH/MAF car unless you remain at a constant elevation. Massive elevation changes can make the car run exceptionally lean thus making it dangerous to drive.
I have put many many lean cruise miles on my cars over the years with no issues.
However for really saving fuel I want to try doing vapor burning instead of liquid burning, like a more exact method of the old fish carb......
Ive tried it all and still no matter what i do, its always around 20mph. the most important thing is goinig easy on the throttle. thats hard todo with a 928, because it is so easy and fun to accelerate!
04-12-2012, 06:23 PM
#25
Rennlist Member
Not really.... Alex's car has had several map tuning sessions. So his result will probably not be the same on another car.
The only way to reliably persue your goal is to switch to the non-cat map and Sharktune accurately.
The only way to reliably persue your goal is to switch to the non-cat map and Sharktune accurately.
04-12-2012, 07:20 PM
#26
Rennlist Member
John, we discovered this phenomenon when you realized that Promax have not plugged in my newly installed WB O2 sensor. My car is German, so it was coded to run closed loop. When we mapped for power with you, we elected to go open loop, but left the original closed loop factory map for economy when commuting between races. I certainly would not try it on a higher compression engine, but it worked well on the GT motor I had I initially.
04-13-2012, 02:07 AM
#27
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Cut the body off and turn it around.
I put 10 gal in each time i gas up...i drive until the red light come on...repeat...my odometer sits at about 120-130ish each time when it happens
Heck, i get may be 12-15 on the hwy with mine? 8-10 if i were constanly putting my foot into it. Just part of ownership.
I put 10 gal in each time i gas up...i drive until the red light come on...repeat...my odometer sits at about 120-130ish each time when it happens
Heck, i get may be 12-15 on the hwy with mine? 8-10 if i were constanly putting my foot into it. Just part of ownership.
04-13-2012, 05:11 AM
#28
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the other way of doing it would be to cut the spark and only run one bank or certain cylinders at cruise, this seems to be the way most manufacturers are going these days to improve mpg. If you work out what you cruise at and how much torque you need to produce you could look at shutting down certain cylinders to give you the power required.
04-13-2012, 05:26 AM
#29
yeah, but you need to kill the injectors first and foremost, as i mentioned in my half joking 4-6-8 comment. intentional unburned fuel flowing doesn't really solve the original challenge and of course creates many more...
And Mark, is this the thread you refer to regarding the myth of lean overheating?
https://rennlist.com/forums/928-foru...oich-is-4.html
I went through much of it.. a very informative yet complex read. I need to go through it again tomorrow before changing my mind on this. thanks.
d
PS - i feel kinda dirty discussing fuel economy and 928's together.
And Mark, is this the thread you refer to regarding the myth of lean overheating?
https://rennlist.com/forums/928-foru...oich-is-4.html
I went through much of it.. a very informative yet complex read. I need to go through it again tomorrow before changing my mind on this. thanks.
d
PS - i feel kinda dirty discussing fuel economy and 928's together.
04-13-2012, 09:56 AM
#30
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