ignition timing at WOT question

[MadBill]

Clint, I love working with you at my "normal job."

If you could promise me 50 points at EMC I'd make the effort to purchase a system for my own use. I'm *that* interested in learning the side that I haven't gotten to use yet at BP.

Well the thing is it's just a tool, it will show up all kinds of shortcomings (providing direct guidance for some shortcomings), but in the end its the correction of those shortcomings that makes the difference. So the tool itself will be worth 0 points, but fixing up the shortcomings, which are made evident by the tool providing information that is not available by other means, will be worth X points.

I am going to discuss the lame burn of the last 30% or so of the A/F mixture, and maybe just lay out where % gains can be found in other areas as well. Rather than bury that info here, and be off topic as well, I should probably start a new thread. Being an OP always eats up some time though, so maybe I'll get to that towards the end of the week.

We'll be waiting with worms on our tongues*, Clint! (* bated breath)

[Warp Speed]

That is exactly what I and the rest of the readers here were expecting. Thanks for the morning chuckle.

Yep.............the truth!
Are you going to answer the question?

I guess not!?!

[Warp Speed]

WarpSpeed, about the only 264 engines you dynoed since June (and I don't know how you won another championship without the guidance of a real expert to ensure each F/A was 1λ, just blind luck I guess ), I have some questions that I think are pertinent to the subject of this thread, “Ignition Timing at WOT”.

At WOT, how much does the MBT vary with A/F from .85λ to 1λ? Does .85λ require less timing than 1λ ? If so, how much?

I guess it's all relative, but in the "narrow confines of my work" AFR has a significant effect on burn rate. How much is dependent fuel used, engine component temp and load/acceleration rate ect...
It can also be effected by ring seal and/or burn contamination.............but you knew all that! .

Do you tune the engines at all load conditions? Do you tune part-throttle, such as encountered in yellow flag conditions?

Yes, we tune the engine at most all operational loads and rpm ranges we would encounter. Being as the drivability in and out of the pit box is just as important as on track performance, this range is basically idle to 10,000 rpm, within the levels of the system of course.

Do you tune a lean cruise mode for yellows? Leaner than 1λ? What does leaner F/A require for spark advance?

We don't tune any part of the map to stoich, but we get fairly lean at the lower throttle and load positions to try and maximize fuel efficiency. A leaner mixture typically requires more timing to keep the same burn rate.

The reason I ask is I noticed several times this season that drivers would turn the engine off and coast, then clutch it back on and accelerate aggressively for a short burst, then turn it off and coast again, and do this repeatedly during the yellow as if they were avoiding running the engine in a steady state cruise mode. Some drivers did this even when there was no obvious reason, such as fuel conservation for mileage.

Haha, they are ALWAYS trying to save fuel.
A lap or two either way can make or break a race depending on circumstances that may arise. Staying out one more lap than the next guy could get you on a lap of your own if the caution comes out, maybe allows you to get on a different stop strategy ect. When getting close to the end, you may need to save for a couple green, white, checkered finishes, or so you only need a splash on a late race caution and can take two tires. It just keeps options open...
Even though we have tuned that area to maximize efficiency, there isn't a tune out there that uses less fuel than when not running! LOL

Some others, who did run in gear at the steady pace car speed, seemed to experience the same or similar surging and blubbering the engines did when carburetors were used. I say 'some' because some ran smooth and some blubbered and surged to the point the weight of the driver's leg would oscillate in a feedback loop and jack the throttle on and off until he would push in the clutch and wing the engine, rinse, repeat.

So, do you tune them for part-throttle or just concentrate on WOT? Why do some of them run so rough at PT?

It could be the differing tune strategies/levels of tune used by various organizations, or simply the rpm and load the engine was under at the time that causes the dreaded bucking. Hard to tune out some required valve events. Remember, these are just push rod v8s! LOL

(when I say "them" I mean the whole field, not just your engines)

[Rick Finsta]

I realize you were being partially flippant but AFR will always have a significant effect on burn rate - it's pretty basic chemistry (kinetics). The more molecules there are in closer proximity and the more energy present the more likely reactions are to occur... you know, mostly. I got the degree that didn't require p-chem...

So to what is attributed the bucking behavior, and how can it be mitigated? I've seen it in OEMs, but thought an engine freed from those constraints (namely, emissions) could avoid the behavior. Again, my understanding runs deep but my experience is narrow...

[Tuner]

I was not being flippant, I know lean needs more timing. I am curious how many degrees difference is required with these specific engines over a range of A/F, say 12.5 to 14.

The surging I see is either sloppy rich or too quick throttle linkage, usually a combination of the two. Mitigation is accomplished by correcting the tuneup and pedal travel to throttle opening ratio with bell cranks or modified cable quadrant shape.

I know saving fuel is important, but why do they do the goose-and-cut when there is clearly no reason, ½ tank of fuel or more and only 10 laps remaining?

[dieselgeek]

That is exactly what I and the rest of the readers here were expecting. Thanks for the morning chuckle.

Yep.............the truth!
Are you going to answer the question?

I guess not!?!

Sorry, been in Vegas all week working on those "easy 4000hp turbo deals" only went 270mph last night in testing.

Will resume the discussion when I get home, Jay. Please dont wear out your keyboard in the meantime!

[nitro2]

Clint, I love working with you at my "normal job."

If you could promise me 50 points at EMC I'd make the effort to purchase a system for my own use. I'm *that* interested in learning the side that I haven't gotten to use yet at BP.

Well the thing is it's just a tool, it will show up all kinds of shortcomings (providing direct guidance for some shortcomings), but in the end its the correction of those shortcomings that makes the difference. So the tool itself will be worth 0 points, but fixing up the shortcomings, which are made evident by the tool providing information that is not available by other means, will be worth X points.

I am going to discuss the lame burn of the last 30% or so of the A/F mixture, and maybe just lay out where % gains can be found in other areas as well. Rather than bury that info here, and be off topic as well, I should probably start a new thread. Being an OP always eats up some time though, so maybe I'll get to that towards the end of the week.

We'll be waiting with worms on our tongues*, Clint! (* bated breath)

Looks like you'll have to wait a little longer, probably towards the end of next week. Pedaling pretty fast at the moment.

[Rick Finsta]

Sorry, Tuner I was talking to Warp Speed - his comment was clearly sarcastic and I just wanted to reinforce that it is a widely accepted phenomenon as you point out. One thing you could do to observe the relationship is use a scatter plot and ignition sweep testing to see the relationship between AFR, Timing, and Torque over engine speed. Plot timing advance on the X axis, torque on the Y axis, and use something like [TorquexRPM/1000] on the Z axis and you could likely visualize the relationship. Switch the variables around until you see something that looks meaningful and allows you to derive a relationship. When I get to the chassis dyno here I'll try to remember to do just that.

It is interesting that you mention the throttle angle for surge; I have a factory Honda (Acura motor) that is DBW that exhibits this behavior during WUE on cold days but I always attributed it to emissions consideration tuning on the fueling side and never thought about the air side of things. I wonder why they didn't fix it using a quick correction of throttle angle using the DBW and then a return to the steady state to prevent the surging loop. I suppose it is entirely possible that they never saw the behavior under testing conditions but that seems unlikely which is why I attributed the behavior to the emissions considerations.

Lastly; is it possible that the drivers simply perform this as an administrative consideration? That is, they do it all the time so they are consistent and don't forget? I think it means they aren't running a wall-wetting acceleration enrichment scheme as every time they kill the ECU they would lose the puddle mass for the calculation. It seems odd that with the level of testing they perform that they wouldn't be using x-tau/EAE, though. Perhaps Warp Speed has comments on that he can share?

[Belgian1979]

Maybe it's just done to avoid a rich mixture from sooting up the plugs.

Hm, maybe I'm just guessing.

[Rick Finsta]

You could use a decel fuel cut to address that, though, or the aforementioned wall-wetting strategy. I had been so used to giving blips of the throttle during deceleration in my street/strip car running carbureted that it has been hard to break the habit with EFI, even though the system doesn't suffer from a rich condition upon throttle closing.

Another question now that you made me think of it - are they triggering after start enrichment every time they fire back up?

[Belgian1979]

You could use a decel fuel cut to address that, though, or the aforementioned wall-wetting strategy. I had been so used to giving blips of the throttle during deceleration in my street/strip car running carbureted that it has been hard to break the habit with EFI, even though the system doesn't suffer from a rich condition upon throttle closing.

Another question now that you made me think of it - are they triggering after start enrichment every time they fire back up?

I don't see any use for afterstart enrichtment in that situation. Could just as well be handled with AE.

[Rick Finsta]

Apologies, I didn't mean to imply I did, either. I'd assume they have the AE values at 100% (+0%) under working conditions (warmed up engine) but there are so many variables that go into fueling economy that I think we need a lot more information before we can figure out why these guys are doing what they're doing.

[Belgian1979]

no need to apologize

[Belgian1979]

I worked on my efi system some more. I made a longer advance curve in the sense that before I was having my maximum ignition advance of 36° at around 2800. I not wet it a little further so that it reached its maximum at around 3200-3300 rpm. This had the effect that my VE values increased overall (and a lot in the higher kPa areas - engine needing more fuel)
Discussed this with Scott and the opinion here is that before this curve I was probably ahead of MBT and now closer to it.

So this gives me the impression that based on the VE values, you can estimate approximatly what timing would be right.

Any input to this ?