Tuning For Maximum Economy, And Leanest Safe Afr

[GTRNUR]

Got a question for the professional tuners out there...

In light of our expected fuel price increase to a minumum of $1.40/litre for unleaded and probably up to $1.55-$1.60 for BP ultimate over the easter break i'm going to make sure my car has the best possible low speed economy tune in it.

So... this brings me to how lean can you go....

For when the car is cruising at speeds of 60-110k's under light load, as in not accelerating it should be possible to run the car considerably leaner than the 14.7:1 AFR that the catalytic converter functions best at. To be honest, emmissions be dammed! I want to maximize my fuel economy to the limit of what my RB20DET can do.

From research i've done in this area with other makes of car, Saab for example can run as high as 17:1 at 120km/h without any engine damage, and get 7lt/100km economy.

Does anyone have any real tuning experience as to how lean you can take an RB engine under light load conditions while it still being safe? I was thinking 15.5 should be possable at least...

Cheers,

Ian

[nfi]

I think you'll find that bad emissions come from the engine running too rich.

I personally would not run the engine to lean as partial throttle is typically the mostly likely time the car will ping as most tuners spend more time refining the flat out map rather than the partial throttle map.

Saying all this... when you say tune the car I presume you are putting a power fc in?

I would talk to someone you feel comfortable tuning your car and talk to them about running it very lean in partial throttle. I think you'll find they are hesitant to do it because if it blows its there creditability on the line.

Its also good to keep things in perspective when worrying about fuel consumption. Say that you run it lean and reduce fuel economy by 3litres/100km which I think is optimistic by the way. Say you do 300km a week. That is 9 litres more that you would have used with a tune that is perfect for the engine. That is no more than $15 a week. You can't surely tell me that is going to kill your bank account.

On another note, if you put a powerfc in, your fuel economy will improve anyway as the stock ecu runs the engine very rich.

Hope that helps.

Edited April 6, 2006 by nfi

[paulr33]

i have done it on my own car with powerfc + wideband and got some kick ass results. i leaned mine out quiet a lot, a bit past 15 on low load at 100km/h and fairly lean below 100 in low load / light areas.

i would suggest reading http://www.skylinesaustralia.com/forums/in...9377&hl=powerfc

most of the stuff you need to know is covered there (the last 3 or 4 pages)

[Busky2k]

You can get away with a slightly lean AFR on light load, like 15.5:1 but weather your engine will like it etc is really an individual thing..

[paulr33]

the main thing is exhaust heat

the leaner you go the higher the exhaust temps

[Busky2k]

Yeah so its gotta be kept under control with ignition timing. An EGT gauge would be the best..

[paulr33]

yeah a wideband and egt would be ideal

i shoulda got one when i was doing my tuning

ign timing increase is piss easy

up timing until it knocks

[MerlinTheHapyPig]

i thought the stock ecu leans it out automatically when cruising?

[GTRNUR]

Sorry I should have provided a little more info so here's it all....

The car runs a wolf 4 plus with MSD DIS4, 3 coil waste spark, 044 pump, 460cc injectors, stock plenum, front mount IC, high mount manifold, GT28 BB 400 with a 0.64 turbine an d 0.7 compressor. The car is a GTS4 with GTR manual gearbox. Diffs are stock i believe.

I do all my own tuning. Yes running rich makes for the worst emmissions as "NFI" said, but a catalytic convertor works most efficently at the afr of 14.7:1 and efficency decreases as you go leaner from there. As I understand it, although CO levels fall with a leaner burn AFR, other emmissions rise. I'm gussing SO2? Who knows...

I use a PLX devices wideband system to get my mixtures correct. Thus far i've tuned to 16lb boost and have 11.5:1 afr at that boost level. I'll be increasing that to about 20-22lb maximum when I get my new plenum. At 0 boost but full load i've leaned it back to 14.2:1. Peak power at this point is supposed to be made at 13.8:1, but this is my economy map... sort of. If I want power I rev it, make boost and its into 12:1-11.5:1 AFR territory.

At present its around the 14.7:1 at light loads at 100k's in 5th. Incidently thats about -10 in-hg on the boost gauge. As the Wolf ecu uses a MAP sensor not a MAF, I can easily identify that load point and tune that afr accordingly.

As suggested by paulr33 and Busky2k 15-15.5:1 is about what is considered fairly safe too. I don't have a EGT sensor though which is a shame because it would be extremely useful!

One other variable is that Paul's got an R33 which is a 9:1 CR engine if i'm not mistaken, and the RB20's are lower at 8.5:1 CR. The higher CR will allow a leaner burn due to better fuel/air squish, while maintaining a lower EGT in comparison to the same AFR on a lower compression RB20... in theory that is...

Thats my problem... lean tuning is mostly theory for me at the moment as i've read a fair bit but have yet to come accross a good tuner with real answers and RB experience.... I asked the question of one of the guys at Sub Zero today and he was going to ask a few other tuners and get a concensis for diferent RB engines. I'll let you know how that goes...

Fact is, 99% of tuning is all done for that top end power figure, which is a little odd becuase when you think about it, thats about where 1% of your actual driving is done.... So long as it drives in traffic, doesn't over heat and makes a shitload of top end HP, is aparenty all the average skyline owner wants. :S Or at least what the tuners tune for...

Everyone feel free to jump in and correct me here...

Cheers,

Ian.

[Busky2k]

Fact is, 99% of tuning is all done for that top end power figure, which is a little odd becuase when you think about it, thats about where 1% of your actual driving is done.... So long as it drives in traffic, doesn't over heat and makes a shitload of top end HP, is aparenty all the average skyline owner wants. :S Or at least what the tuners tune for...

So true. People get wrapped up in the top end number after a tune and forget about how the car actually *drives*. I've spend considerable amount of time in the first 10x8 cells on my PowerFC as thats where 95% of the driving occurs and I've tweaked the AFRs smack on 14.7 with readouts using my Innovate Motorsport LM-1 Wideband. This is because the PowerFC can then take care of any small variances as time goes by via its closed loop system and keep it at 14.7:1. I could go leaner again but any leaner than 15.5:1 and the car starts to misfire a bit. The fuel economy now is good enough for me anyway.

I have yet to tackle the low rpm/load low ignition map. I believe by relying on the stock knock sensor to find the MBT is the wrong way to go about it.

[paulr33]

the stock ecu (and powerfc) have closed loop which will make it aim for 14.7 on crusing for the ideal economy and emissions. i found with this style setup i was getting average ish economy usually 350ks on the street and 500 on highway. tuning with closed loop still on in the powerfc just meant the results were juggled a bit in real time. it was only when i turned off closed loop and tuned it myself that i got 400+ on street and 600+ on the highway.

so closed loop certainly isnt the be all and end all but certainly a good start. plus its a lot of work to tune all the fuel map cells as you need to make sure the afr's in the low cruise areas's are safe and not too lean.

turning off closed loop in the FC and driving around its a bit too lean in some spots

[dangerous_daveo]

....

Its also good to keep things in perspective when worrying about fuel consumption. Say that you run it lean and reduce fuel economy by 3litres/100km which I think is optimistic by the way. Say you do 300km a week. That is 9 litres more that you would have used with a tune that is perfect for the engine. That is no more than $15 a week. You can't surely tell me that is going to kill your bank account.

...

Not meaning to be a smart arse but... $15x52weeks = $780.00. But having said that I find most people use a tank a week. So with a good tune thats 500-600kms a tank (which is what I am getting) So thats closer to 18L (basing it on your estimation) which brings it out to $1560.00 a year saved. Sure as shit I could find a better way to spend that money than on fuel. Thats about 3 weeks wages for me, that would hurt. Just thought I would point that out. Also add this in to buying your fuel on the wrong day... then its even more.

[Cubes]

My understanding is that at 14.7:1 EGT's peak at their highest, below or above this the egt's drop.

Maximum economy really depends on the motor its self, lean it until drivability suffers.

As SK said to me... Lean it out under load, use the injector pump settings to gain throttle response.

Many of the RX7 blokes lean out their rotors (which are damaged by lean afr's easier than piston motors) to around 14:1 with a psi or 2 of boost. They then for example drop to 13.5:1 up to 5-6psi then 13 to maybe 9 then maybe 11-12:1 under 9-10+

It really depends on how the RB handles the lean conditions under 0 vacuum. If it bucks and is obviously not liking it richen it up until it no longer.. Maybe it can handle leaner.. who knows, no one really shares their information too much but I do plan to find out.

With the FCTune's auto tune function soon to be released I am hoping to get my hands on a wideband so I can do a little street tuning.

My current tune runs 14.7 during closed loop then drops to 13.5 (forget the vacuum) then 13:1 under 0 vacuum.

[Guilt-Toy]

I run my car lean as hell when i drive to work and back.

In the PFC setting ING/IGN i turn the number 1.000 down to 0.769 which is about 24% leaner then the standard map.

This figure is good when driving on the freeway and it does run a bit shitty around town but it is very driveable. I can save about 3 - 5 litres on my day trip to work and back which is 120km each day.

For $20 worth of fuel I get about 15 litres if i lean it right out and crooze at no more then 110 120 I have around 3 - 5 litres left over from my 120km trip. Not bad for a car with 740cc nismo injectors and 350 rwhp.

The downside to this method is that if come past a commodore on the freeway I cant hit it beside him and if you forget you have taken 25% fuel out of the map and you give it a good hit.. You can be walking very quickly so yeah its not that hard to go back in and put it back up to 1.000 if you got a good 20 seconds.

So yeah something I have wondered about is does an engine run better lean with more timing advance or with retarded timing ???

I used to put in a extra +5 deg timing in overall but stopped doing it and have not noticed any difference.

I believe the leaner on crooze the better. My turbo is top mounted to the extra heat would wash off pretty quickly and i do keep my eye out on knock levels heaps.

[Guilt-Toy]

I DO have a question on this topic actually.

IF I am running the PFC with 24% less fuel WITH Closed loop mode still on. Would the PFC still correct it back up to 14.7 or be trying to ??

If thats the case then I will try and turn closed loop off because my car can run at about 16:1 17:1 without whinging too much about it as I had my friends Autronic Wideband sensor in my car for a few months when I tuned my car myself and it was running fine.

So yeah. I might try this on the way home and see how it goes.

[2rismo]

As I understand it, although CO levels fall with a leaner burn AFR, other emmissions rise. I'm gussing SO2? Who knows...

Nitrogen rears it's EPA upsetting head here

Adrian

[MattSR]

Yes, NOx goes through the roof when you go lean

[paulr33]

yes with 02 feedback on it will always try and aim for default ideal afr. which can be set by datalogit also. if you drive around with 02 feedback off the afr's wont auto dial back to 14.7

[Guilt-Toy]

yes with 02 feedback on it will always try and aim for default ideal afr. which can be set by datalogit also. if you drive around with 02 feedback off the afr's wont auto dial back to 14.7

Hmmmmmm... I am going to turn off closed loop mode on the way home and see how it goes... its a 60km trip.

[paulr33]

if you do that make sure you have a wideband sensor to watch the AFR that comes out in case its too lean