Getting Best MPG during Cruise

[Hiboost]

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

Seems like we are in the right ballpark for timing then. There may be some gains bumping timing earlier from 2000-2500 as well as testing 45-46* from 3000-4000 RPM's. Also depending on where your car sits for load during cruise adjusting 50% load area slightly higher yet might work as well.

[zTargeTz]

what about mivec changes? or is that pretty much been worked over already (are the current JDM maps the most efficent for MPG?)

[LIGHTSPD]

Originally Posted by tipoytm

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...

I have not checked MPG all I was looking for was MBT at certain loads. By knowing MBT I know the timing value that will work best there. The idea is to improve the efficiency of the engine if I go to far in my timing the engine will actually be working against itself resluting in lower MPG. If I don't give it enough I will not be building the most possible cylinder pressure that I can build. An engine is basically a glorified air pump. The more eficiently you pump the air the efficiently the engine runs. SO lets talk about MPG we want the engine to produce the most amount of cylinder pressure possible using the least amount of fuel to do that. So we command a leaner mixture say 15:1. Now this leaner mixture is doing a couple of things it is using less fuel which is good but is also starting to produce hotter cylinder temps moving us closer to preignition. I could get into a long winded speach about detonation and preignition but in this case preignition. Now on our cars I was able to go 2 degrees over MBT at cruise before I even saw any knock counts so that tells me the combustion chamber on this car is very efficient. What we want to do is max out the torque measured on the dyno at cruise speeds and cruise load. This is referred to as MBT it is different for each fuel as well so there is no set rule. As well adjusting the MIVEC is also going to effect this. BY adjusting the cam overlap we are able to change the cylinder pressure. As well by adjusting the exhaust cam we are able to simulate an EGR effect as well. This is where it gets more complicated you could add exhaust to the mixture which is going to dilute the mixture mildly depending on how much EGR you run. This is going to make the mixture less volatile in doing this you will be able to add more timing. The only purpose of this is would be to increase the cylinder pressure. Sometimes you can get so close to MBT that this does not help. Thats why they call it R&D lol. I hope this helps some of the new guys who are just trying to learn.

Cheers C

[tipoytm]

^ thanks for the info... I'd love to hear if anyone else has tried this with results

[xhomm02]

I also increased the timing by 12% in 0-50 load (up to 45 degrees) and by approx 5% in 60-100 load and I got 7% better mileage during cruising. Have to say I am running on liquid petroleum gas, which is approx AKI95.

[Hiboost]

Originally Posted by 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?

I was just smoothing out idle a bit since my car was wandering a bit lean making it sound like I had cams. After bumping timing 2* that seemed to have gone away now, plus it should be a good setting for Cosworth Cams when I get those installed.

[coevolve]

I logged a modified version of the map you posted Chris. Everything looks good though I haven't had time to really calc mpg yet....I can post data from the log (10-15 minutes at 60-70 mph ~90 degree ambient) upon request...

I have a question thought that is semi-off-topic.
What load cells do you hit when you are down shifting coming into a corner? I assume the load would be rather lowish...40,50,60 and the RPMs initially higher 4k+. Chris, are you maps close to stock in these cells? If they aren't would the increased timing for gas mileage result in spiked egts on the track?

[Hiboost]

Originally Posted by coevolve

I logged a modified version of the map you posted Chris. Everything looks good though I haven't had time to really calc mpg yet....I can post data from the log (10-15 minutes at 60-70 mph ~90 degree ambient) upon request...

I have a question thought that is semi-off-topic.
What load cells do you hit when you are down shifting coming into a corner? I assume the load would be rather lowish...40,50,60 and the RPMs initially higher 4k+. Chris, are you maps close to stock in these cells? If they aren't would the increased timing for gas mileage result in spiked egts on the track?

From 4500+ they are pretty much stock, maybe 1* increase in a few places that I noticed there was a dip in timing compared to surrounding cells. EGT's shouldn't be an issue except under boost and 100%+ load cells either way though. Since at 5000+ you will be in open loop you could slightly richen up the fuel tables to compensate, although to much fuel in the 10-20% load cells will give you qutiea bit more fireballs.

Generally the car goes full lean and turns off the injectors after about a second of letting off the throttle during engine braking and that is cooling things down quite a bit until you get into boost again.

[coevolve]

Just in case make sure you are looking at the X and Y axis right since mine are altered from stock and that can cause some confusion.

Yeah, I modified accordingly....speaking of that...I imagine you modified the base xml file scaling to change the X and Y axis?

...EGT's shouldn't be an issue except under boost and 100%+ load cells either way though

I knew this but my thinking was if the EGTs would already be higher than normal (cruising) due to the previous, straight-away, chicane, whatever, spent at 100%+, wouldn't increasing timing in the lower % cells increase EGTs as well?
Obviously this is moot when talking about 1* here and there...

Thanks Chris!

[tipoytm]

Originally Posted by Hiboost

I was just smoothing out idle a bit since my car was wandering a bit lean making it sound like I had cams. After bumping timing 2* that seemed to have gone away now, plus it should be a good setting for Cosworth Cams when I get those installed.

Cool, thanks! Are you on the 80020 ROM? I've read somewhere that it smoothens out the idle compared to previous versions, and it seems to do so when I shifted from 80018 to the newest one... Just wondering if I should try out advancing the idle timing a little bit too, although my idle is fine as it is.

[Hiboost]

Originally Posted by tipoytm

Cool, thanks! Are you on the 80020 ROM? I've read somewhere that it smoothens out the idle compared to previous versions, and it seems to do so when I shifted from 80018 to the newest one... Just wondering if I should try out advancing the idle timing a little bit too, although my idle is fine as it is.

Hmmm not sure what they would have changed, unless it was something in a table we can't access. Currently my ROM is based off 52680017 (Inherits: 52680015).

[LIGHTSPD]

Wow an allnight dyno session and my head is still ringing kind of like drinking all night. Anyways I am on the 0017 ROM at this time as well. I will call you later today or this weekend Chris. Sounds liek we got alot to talk about.

Cheers Cam

[Talon_66]

Better gas mileage?! Im interested

[LaXGSR]

Thanks for sharing these ideas! I am now running 43 degrees of timing at cruise. One word of caution (at least on my car), I had issues with advancing timing more than 1 degree in the 50 load column, and ended up keeping stock timing mostly in the 50/60/70 load columns. My car would knock on normal driving, especially at low rpm's. For instance, if I jabbed the gas pedal at about 2000 rpm's, it would cause repeatable knock. I ended up doing more smoothing so that my most aggressive timing is around 3000-3750 rpm's at 0-40 load, and it gets less aggressive at both lower/higher rpm. Also note that at higher speeds (above 70), my car tends to cruise between 50-60 load. Since I couldn't easily get a smooth knock-free map when adjusting the higher load cells, I just left them stock. Thanks again! I'll report back in a week or so with any noticeable mpg changes.

[Hiboost]

Hmmm that is interesting. It could be that all the mods I have for cooling and extra flow are giving me more headroom for timing increases. It's also interesting that at 70 mph I'm still running around 35-40% load versus 50-60% load. I haven't seen an ounce of knock since increasing the timing to where it is now. Let us know what kind of mileage you are seeing from the changes you made though, and good job with datalogging to verify that your setup will work with the extra timing!