Cruise AFR?

[the poi]

So whats a good AFR to shoot for for cruise? Since I finally got my WB working, I wanna try to go for gas mileage as well as speed :)

[kyle242gt]

Hey Chris-

Shoot for as lean as you can get it. If it's too lean, it'll buck and surge like nobody's business.

I do my damndest to keep it above 14.7:1 unless I'm in it to win it.

From memory:
20Kpa - full lean, 45:1, unless it starts surging on decel
50Kpa - 18 *
70Kpa - 16
90Kpa - 14.7
110Kpa - 14.2
130Kpa - 13.7
150Kpa - 13.2 **
170Kpa - 12.7

* I think I may move my map points around a little when I get braver; I had to bring 50Kpa back to about 16, it was running too lean (surging).
** still only at about 120Kpa, give or take, so these are for the future

You can use the timing to bandaid an overlean mix, so you kinda have to go back and forth to get it dialed in.

[the poi]

Hey Chris-

Shoot for as lean as you can get it. If it's too lean, it'll buck and surge like nobody's business.

I do my damndest to keep it above 14.7:1 unless I'm in it to win it.

From memory:
20Kpa - full lean, 45:1, unless it starts surging on decel
50Kpa - 18 *
70Kpa - 16
90Kpa - 14.7
110Kpa - 14.2
130Kpa - 13.7
150Kpa - 13.2 **
170Kpa - 12.7

* I think I may move my map points around a little when I get braver; I had to bring 50Kpa back to about 16, it was running too lean (surging).
** still only at about 120Kpa, give or take, so these are for the future

You can use the timing to bandaid an overlean mix, so you kinda have to go back and forth to get it dialed in.
hmm, looks good to me. just came back from a drive with my first WB datalog, ill start comparing :)

[JohnLane]

I set mine up to cruise down the road at 1% CO out the pipe. I do not use a cat, but know this to be not too lean to keep a cat in it's happy range. This is also not so lean as to turn the NOx way up as happens when we ask them to run too lean.

Lean running is best done in engines with lots of turbulance in the chamber.

I'm curious to know just what 1% works out to in an AFR.

I set mine to run at 4-6% CO under boost. This made loads of power without clouds of black smoke on accel.

JL.

[Hank Scorpio]

hahaha I run 13.7:1AFR under cruise conditions and get 25mpg still.

my car hates running lean.

[Paul_VR6]

It'll have ALOT to do with ignition timing at the load point you're tuning. Leaner = more timing. I can get my 2L motor to do 17.6:1 without buck at light throttle, but only at 45deg total timing. :cool:

[the poi]

lean and advanced timing? intersting... doesnt that make the cc real hot?

[Hank Scorpio]

It'll have ALOT to do with ignition timing at the load point you're tuning. Leaner = more timing. I can get my 2L motor to do 17.6:1 without buck at light throttle, but only at 45deg total timing. :cool:


Defiently. Before I switched to MS'S I was getting good milage being fairly rich but I was also running **** for timing (maybe 10*). Now Im running MS'S lots of timing and the car drives loads better at leaner AFR's.

[Paul_VR6]

Isn't making the chamber hot a good thing though from an efficency point of view? It is thermal expansion that does make that piston go down. I haven't noticed any problems with running goosed timing at leaner AFRs. Just kept running better and better with the adv timing. Not sure about the theory, but it sure works. Gas mileage is ALOT better as well.

[The Aspirator]

I completely agree with what Kyle posted in his first post. That's about exactly where I tune my car to, and it drives great. Though right now it idles like crap (especially cold) and gets about 16mpg........ That's what happens when you throw a holset on and spend just a few minutes giving it loads of fuel :roll:. I've got some serious tuning to do, and now that I fixed that huge exhaust leak my WB is accurate again!

What are you guys running for timing? Especially in boost? I haven't spent that much time screwing around with the ignition side of things. How do you know weather to advance or retard it? (stoopid n00b question, I know). From what I've figured out, off boost you want it as advanced as you can before it starts to buck. And in boost you basically want it to ping then back the timing about 5*?? Right now my low boost timing is about 10, and it trails down to 2* at 15psi.

The thing I love about the fuel tuning is that you just watch the wideband and raise or lower the VE to what you want. Spark tuning seems to be more of a black art. Right now my settings work alright, but I'm sure I can find more power and smoothness out of it.

John

[the poi]

I completely agree with what Kyle posted in his first post. That's about exactly where I tune my car to, and it drives great. Though right now it idles like crap (especially cold) and gets about 16mpg........ That's what happens when you throw a holset on and spend just a few minutes giving it loads of fuel :roll:. I've got some serious tuning to do, and now that I fixed that huge exhaust leak my WB is accurate again!

What are you guys running for timing? Especially in boost? I haven't spent that much time screwing around with the ignition side of things. How do you know weather to advance or retard it? (stoopid n00b question, I know). From what I've figured out, off boost you want it as advanced as you can before it starts to buck. And in boost you basically want it to ping then back the timing about 5*?? Right now my low boost timing is about 10, and it trails down to 2* at 15psi.

The thing I love about the fuel tuning is that you just watch the wideband and raise or lower the VE to what you want. Spark tuning seems to be more of a black art. Right now my settings work alright, but I'm sure I can find more power and smoothness out of it.

John
thats the impression im under. im just concerned if i run too lean and too much timing itll start pinging whilst crusing... or is that virtually impossile?

[The Aspirator]

Never happened to me, it just starts to buck or be choppy if it goes too lean. Even if it did, don't you have that fancy knock retard setup?

John

[the poi]

Never happened to me, it just starts to buck or be choppy if it goes too lean. Even if it did, don't you have that fancy knock retard setup?

John
heh, you do have a point there. I forsee much tuning this weekend...

[linuxman51]

spark tuning is indeed a black art. remember, too much timing kills torque...

a good cruise afr is around stoich, i wouldn't try to go super lean and def. try and keep it out of the 13's

[Brick_Owner]

Command AFR should be 14.7:1 at idle and all steady state conditions. Depending on your other modifications, you should generally scale AFR to load. As the MS systems don't use a AMM, the only wat to calculate load is via the MAP and TPS and that's a guess at best w/o LOTS of datalogging with an AMM or similar.

The OEs don't add enrichment until load gets over 60%-80% (full throttle enrichmant), most are near 80%. You are safe using stoich for command until at least 75% load, then you NEED enrichment, typically to about 12.5:1 but at very high specific outputs, you may want something closer to 11.5-12:1. Generally enrichment is "switched", and not scaled, but I can see advantages in scaling for durability (lean knock is VERY bad).

If I were tuning a MS system, I'd run the h#ll outta it and after choosing decent "Average" spark tables, lean it out until it knocks, and add back 0.2:1 AFR or so to keep it safe.

[The Aspirator]

spark tuning is indeed a black art. remember, too much timing kills torque...Hey Kenny thanks! I didn't know that. Would that apply for off boost tuning also? I guess our high compression motors do make some torque off boost, at least mine feels kinda peppy.

I guess you just tune the spark until the car pulls the best. A few times I have noticed a big difference in power when messing around with the ignition in boost.

John

[kyle242gt]

For whatever it's worth, Here's my map, again, bear in mind that I'm still running about 120Kpa max... it was doing 140 for a while, but no longer... :???:

[SparkSettings]
RPMRange = 500 1000 1700 2700 3200 4300 5400 6500
MAPRange = 20 30 50 90 110 130 150 170
SparkTimeMAP0 = 10 10 15 20 20 20 20 20
SparkTimeMAP1 = 10 10 20 25 30 30 30 30
SparkTimeMAP2 = 12 12 25 30 33 35 35 35
SparkTimeMAP3 = 12 12 25 30 33 35 35 35
SparkTimeMAP4 = 15 15 25 30 33 33 33 33
SparkTimeMAP5 = 15 15 25 28 31 31 31 31
SparkTimeMAP6 = 15 15 22 25 27 27 27 27
SparkTimeMAP7 = 10 10 20 23 25 25 25 25

It's scary to "advance till it pings then back off" under much boost, so I'm basically planning to see what it likes at 90/110/130 and try to scale it from there to 150/170.

Any opinions on my map are welcomed :x:

[Brick_Owner]

I forgotto mention, that the HEGO sensor (O2) should have a LARGE part to play in AFR during "normal" driving (not during acceleration enrichment). But I don't know much about the MS aside from what I've picked up in the last few weeks here (and lnked). So I don't know if the CPU "sees" HEGO inputs and corrects or not.... it SHOULD.

[kyle242gt]

The problem as I see it with using stoich (and the EGO adjustment) in MS is that stoich is best for emissions, not for mileage or performance... the poi mentioned that MS-extra (or whatever) will have three target AFR's, that's a little more like it. Then you could say 20-50Kpa = 18:1, 50-70=16, 70-90=14.7, and no EGO correction above that.

If we were aiming for stoich up to 60 or 80% load (emissions), then I'd agree, otherwise, I say leave the EGO correction off, and use your WB to aim for your desired AFR. That's the beauty of MS and WB!

[Brick_Owner]

With a WB-HEGO, you could "tune" for driveability and economy 0-40%, then ramp up from 40%-80%, and use WOT enrichment above that. Something you cannot do with a NB-HEGO, or a conventional EEC.

[Paul_VR6]

The exact reason I was doing the low load, high AFR and high timing experiments was to try and get actual numbers so I can have a starting point for the target AFR code in MSnS extra. I think we're all on the same page there.

It's 100% true that stoich IS NOT the best AFR for cruise, idle, and MANY other load points. It's an excellent compromise and will get you 80-90% of a good tune without any thought. Add that to emissions regs and you can tell why OEMs use it for thier tuning point.

Anyway...

For timing, at most conditions you will generally lose torque past a certain timing point, even if it's not knocking. There's a timing point for max torque at every load and AFR, and it'll drop on both sides of that. Personally I've NEVER seen that point at the knock threshold, but then again I don't tune turbo Volvos :-P In any case, if you do tune to knock and back off, definitely back off more then a few deg. The 5deg mentioned above is probably a good number.. but I'd stay conservative if anything.

A good starting point for tuning the timing is to try and make maps without boost first. Figure out what "feels best" at part load, and for WOT you'll want between 30-45deg total timing depending on CR and gas. From there, you can start tuning for boost. A good baseline is use your WOT total timing up to about 2-4lbs and then start backing off 1deg per psi. If you have an efficent combustion chamber, high octane, or an efficent turbo/ic combo you can get away with less. I've seen some motors with multi valve and centered plugs with BIG ICs only take .25deg per psi. That's way pushing it with the Volvo 8v combustion chamber, imho.

For fueling, you'll want cruise as lean as you can stand, slowly richening up into the stoich range at medium loads. From there you'll want to tune to about 13:1 A/F at WOT with no boost. You'll want to get to the mid to low 12's by about 5-7psi and then to about 12:1 flat by 15psi. Anything above that, you should probably go richer just for the sake of chamber cooling, but it will make less power, but safer.

Tuning boost cars with the charge pipe disconnected is probably the best way to get an excellent baseline tune, then put it back for final tuning of your boosted areas. Especially with MS as all the silly math is right there for you.

Hope all this rambling helps. :cool:

[the poi]

it does indeed help. i've much to work on... but since we're on the subject, what is everyone shooting for on idle afr? my idle isnt perfect, lthough on kenny's suggestion, im willing to blame the heall sensor in the distro for less then perfect timing accuracy

[kyle242gt]

Thanks for the info, Paul. I've since built an MBC and headed to 150Kpa, where I found that 87 octane really isn't going to cut the mustard. Back to 140, and I've had to cut the timing from 35 max to about 22 at 130 and 18 at 150.

Which brings me to my barely-relevant question of the day - at what point are you cutting so much timing that it's senseless to run more boost?

And in a completely unrelated followup to that - what's the usual limiting factor in how much boost you can run? Pinging?

I like to see my idle at about 16:1, but a little richer helps smooth it out.

Right now I'm really wishing for a bigger fuel map.
*edit*
Forgot to respond to the richer AFR's at boost - I richened things up and cut the timing to get away from the pinging, down to about 12:1 at 7.5 PSI, and dagnabbit, my shiney new tailpipe is all sooty inside. Paul's suggestions seem a little richer than I've typcally read here...

[stylngle2003]

hey kyle...what rpm does your car idle at...i noticed that your lowest rpm point on your timing map is 500...does yours ever go that low, or is it a built in necessity, like you cant adjust the bottom most point?

thanks, and sorry for the ot ?

[kyle242gt]

Hi Billy -

I haven't really pinned the idle down yet - it's about 1,000 now. I think the common reason for including the low RPM point is a bottom anchor for the map; though now that I think about it, if it just replicates the 1000 rpm map if below it, there's no real reason for it.

But I plan on getting the idle back to about 700 anyway.

I'm not to worried about RPM bins; what I'd like are more MAP bins. I'll probably wind up combining 130 & 150 at 140, and using the extra bin for 60 or 80... something :e-shrug: I guess I should also mention that 8x8 seems fine for spark, it's the fuel side of things I'm interested in.

[Paul_VR6]

Idle AFR just use O2 correction at stoich will work, but be sure to turn ego OFF for low coolant temp. Otherwise the car will not be happy. Most cars like to idle a touch rich, 14:1-13.5:1, but stoich is close enough.

My AFR recommendations for on boost AFR are a bit on the rich side, but rich is safe so always start there and tune to leaner, and SLOWLY. My experience is pretty much with smaller bore cars (81-83mm) so your chambers might be able to take less fuel and be happy with it. Depends on too many factors to speculate, however.

Limiting factor for boost limit should be engine destruction. Right? :-P Most of the time, it's knock threshold, but that depends on octane. More or less gas quality and octane, as well as your static and dynamic CR will be factors in how much boost you can run.

However more boost != more power all the time. There are times, and quite many, that you'll make more power with less boost and more ignition advance for a set quality of fuel and compression. The lower your compression the more 'forgiving' things get, as well as better fuel. These are the sorts of things that take a good bit of time finding out either on a dyno or on a track. One case that we saw this exact scenerio was a 9:1 comp turbo car on 93 octane and a junkyard T3. Car was quicker with 15psi and 20deg timing then 20psi and 15deg timing. Turbo was more efficent at the lower boost and the added timing at the lower boost made more hp. Strange but true. I wouldn't be suprised if you guys saw the same sort of thing with stock turbos. BIG turbos are a different story.

As for the timing "basement" I'd say about 15deg.. 20 though is a good number to be at, but from there to 15 it's diminishing returns and your margin of safety decreases quite a bit.

Kyle, why do you think you need more MAP bins? Where are your transitions from 0-100kpa? There a whole lot of them? You should only need a point or two past about 120kpa depending on how you tune.

[kyle242gt]

Kyle, why do you think you need more MAP bins? Where are your transitions from 0-100kpa? There a whole lot of them? You should only need a point or two past about 120kpa depending on how you tune.

30/50/70/90/110/130/150/170

30's decel, 50 is idle, 70 is light cruise, and 90-170 are just shots in the dark. I'm finding that I need another point, probably around 80, because as the boost ramps up, it richens the car more than I want/need. IE, on the freeway in OD, if I lean into it a little bit, AFR's drop to about 14:1 or so (which doesn't make sense since 90 should be 14.7? per my calcs).

Anyway, your info about allocation of >100 MAP bins is well taken. I'll have a look at it this afternoon. Maybe go to 30/50/60/70/80/90/110/170?

Thanks very much for your help! :cheers:

[Paul_VR6]

How are you calculating that you should be at 14.7:1 A/F when it's at 14:1? Remember if you're tipping the throttle in, unless you have accel enrichment turned off, it'll still add a little fuel. I wouldn't be suprised if that's whats happening.

If you tune the car with the boost tube disconnected for WOT at a specific A/F, you'll get some VERY good VE numbers at 100kpa-ish. Then all you have to do to figure out your VE numbers for boost is just do the math to get you to that A/F. So say you're VE number is 85 at 99kpa and 6k rpm and 13:1 A/F. If you want 12:1 at 6k under boost, you would just calculate ...

OldVE*(OldAFR/NewAFR)=NewVE : 85*(13/12) = 92.08

Because MS uses absolute pressure numbers, it's already adding the right fuel for boost. So, you don't need numbers that are linearly higher with MAP, like other systems.

You'll just have two boundaries, where you want your enrich to start, and where it will end. A good spot is just before the boost transition, about MAP=90kpa, and end it past where you think you might boost up to.