LM1 - A/F ration Data interpretation
 

OK, I got the LM1 data and am told to go 12.5 on the Air/Fuel ratio. Here is what I get on the LM1:

at steady rpm, no acceleration

2000 rpm - 14.6
3000 rpm - 13.5
4000 rpm - 12.7

On full throttle hard acceleration at full boost of .8 bar at 4000 - 5000 rpm range LM1 reads 10.

So, my question is, when people say 12.5 is the goal, at what rpm and load are they referring to?

Thanks,

Rick

1986 911 turbo stock motor and turbo

I'd say on CIS you want to be richer than 12.5 at the red line, i'd aim for 12.0, to be honest i'd probably be happier with 11.8-9 flat out. When you're cruising off boost the you can be far leaner, high 14's even, but as boost comes in you want to rapidly drop into the low 12's and to keep things cool no more than 12 would be my aim. I was high 12's at WOT and put a hole in a piston, live and learn!
When you're running EFI and you can measure the AFR from cylinder to cylinder then 12.5 would be OK at 1.0bar I believe, but your measuring an average over all six with one sensor, I would not be happy taking the risk unless i could verify that i was getting identical flow from each injector and identical AFR on each cylinder

This is typical worn CIS behaviour. It runs pig rich then leans a bit on the top.

First, I suggest getting a AuxBox or RPM-converter so you can log both RPM, boost and lambda. Watching a display while driving is a great way to kill yourself.

Once you can interprete graphs offline, you can do something to fix rich condition you obviously have.

AFR of 10:1 at boost is way to rich. You are loosing power, using excessive amounts of fuel and dilution the oil. Checking control pressure is a good way to go, then maybe fitting adjustable WUR or RPM-switch to get rid of rich part.


Ideally, you would want something like 12.2-12.6 at WOT and full boost and around 14.6-14.7 at no load.

Goran,
I see various ranges of acceptable AFRs on boost with CIS. JBL likes 12.0 as the upper limit, you give a range of 12.2-12.6 while I shoot for 12.0-12.2 as the target.
What engine parameters are you basing your figures on? How do these figures change with increased boost pressure, say 0.7 to 1.0 bar on a typical 350WHP (@ 1bar) CIS 930 engine?
From dyno data you have done what is the difference in power when leaning from say 11.8 to 12.6 AFR? I have not done enough runs to see statistically significant results.

Rarely, i'd be happy with 12.2 also if it was confirmed as such. The problem i had with my LM1 was that the number after the decimal point was flickering quite badly at WOT making it almost impossible to read. In retrospect i would have liked to have seen high 11's so i knew i was safe. I've no doubt you can squeeze a few more horses out going closer to optimum AFR, but i think the gamble is too great with CIS, besides the mixture being richer helps temps, as long as it's not so rich it starts fouling plugs and washing out the oil. The main reason I advised Rick to stick to 12 or just under is for peace of mind, without doing a top end job on his engine and getting the injectors checked for perfect matching heading up to 12.6 like Beep says is to dangerous in my opinion, I guess it also depends what boost Rick is at, at 1.0bar i would think 12.6 is just too close to the bone

This is what my piston looked like after a long WOT run at high 12's

http://i139.photobucket.com/albums/q...ltedPiston.jpg

JBL930, do you track your car, or was this on the street?
Sorry to hear about your luck.. that really stinks.

Hi Mark, this was at a VMax event (Maximum Velocity), 2 mile runway and basically go flat out. My car was running medium mods, B&B style headers, Fabspeed duel out, 1.0bar spring in standard wastegate (getting around 0.9bar), K27HFS turbo, IA fuel head, IA airbox, Ported heads, Ported manifold, 964 cams, tapered injector blocks, 964t intercooler, the weak spot was a dodgy WUR, I had an adjustable WUR in hand on the day but blew the engine on the first run.
From my experience trying to run optimum 12.5 to 12.6afr is plain silly without doing major verification on each cylinder. Keep it around 12 to be safe.
I have a modified 993tt motor in the 930 now, just waiting on the second oil cooler to be fitted and some tuning and i'll be back out there going flat out SmileWavy

A pic of the engine being installed

http://i139.photobucket.com/albums/q...romtheback.jpg

Mark, I see you have a KX250, I raced motorcross from schoolboy through to my early 20's, it's a while ago now but my last season was on a KX250, only club racing but those bikes are in my blood! Porsches and motorcross, we have a lot in common :)

It's hard to generalize when it comes to what AFR gives most power. It varies from engine model to engine model. Also, the AFR that gives most power might not be the "safest" AFR.

CIS being mechanical and maybe flowing unevenly, it might be a good idea to run it richer than it should.

But most "real-world" engines give best power between 12.5-12.8. It all depends on plethora of details. Squish, ignition timing, position of ignition plug, cam timing etc.

Here is an interesting article, written by inventor of LM1:

http://www.innovatemotorsports.com/resources/rich.php

Also, most EFI systems don't measure lambda on per-cylinder basis. You just assume that every injector flows the same and tune for correct lambda.

As I said before, It might be a good idea on this particular case (930 almost stock) to go for 12.2 to gain some margin to protect from failing parts but IMHO, the biggest inherent 930 CIS problems is that it leans towards the end.

On older cars, it often runs like this: Pig-rich on the onset of boost (like 10-11:1), then gradually leaning towards the top...in some cases reaching 13.5:1 around 6000 RPM. I believe that engine would go better if this non-linear AFR behaviour could be corrected. With other words, less rich in the midle and more rich up top.

Thanks for the many view points on this subject. I did have the top end rebuilt 2000 miles ago. Noticed that my plugs exhaust ports were crusted with deposits when I installed the B&B headers. Pulled the plugs and found that all were crusted equally as well. From my spark plug observation I don't see a hot cylinder in the mix, although plug reading is hardly a scientific approach to quantifying the injector output!

From the conversation I'd say that:

1. possibly my CIS is not working as well as it should
2. I could go leaner on my mixture
3. Keep the WOT no more than 12 to be safe
4. acquire the additional measuring devices to further fine tune my results

What about the no load AFR? I suspect that if I lean out the WOT to 12 that my "no load" AFR will be higher than 14.7. Should I be concerned?


Thanks

Rick

You need the Brian Leask adjustable Warm up regulator and RPM solenoid, you can set all of the parameters with that, the WUR adjusts the control pressure to the fuel head by making it rich on cold start and then leaning it out as it warms up, then it also drops the control pressure to the fuel head on boost to fatten the mixture up again.
The adjustable unit allows you full control over all of the parameters, and the RPM controlled solenoid delays the boost signal to the WUR until the engine actually needs it, which gets rid of the pig rich mid range which will help with power and MPG. With fine tuning you can get a near flat AFR across the board, it also allows you to dial in more fuel if you go for more boost or other mods, it's the last modification i was planning on my car and it should have been the first!
Most of the modified 930's are running the Leask WUR, and i can imagine there are dozens of people on here with one, i'm sure they'll chime in and tell you what they think

Where can I get more info on Brian's adjustable WUR? I searched the name but did not find any contact info.

Thanks

Ahhh, that car sitting in Paul's work bay looks familar. Was sorry to hear about your motor. Give my regards to Paul, Ray & Mike.

You know the boys there then, good bunch of lads. Paul has done a great job with the install, i will pass on your regards! SmileWavy

JBL,
Were all the cylinders this bad or was it just this one. If so, which cylinder was it?

Just one i think, don't remember which one but i'll ask and let you know

Thanks. Not a big issue...just curious.

+1

Better to be safe than sorry.

As Goran said, get the data logging equipment.

What octane gas were you running? Was timing and boost good? Not excessive?

On a long run or at the track, I use 100 octane to prevent detonation/damage. Not that a higher octane is a cure all, but I think it helps prevent the problems among other things.

I am new to all of this and need some AFR help.

With a stock 1980 930 set up how do you adjust the AFR? Is it only the mixture screw adjustment near the top of the fuel distributor or is there another adjustment on the WUR?

Knock and pre-ignition are sometimes hard to detect.

Also, combustion-chamber geometry plays a significant role. With other words, if you swap out your nicely dished smooth pistons and install sharply recessed aftermarket pistons, squish area might change and you might get local lean areas while "total" AFR of cylinder still looks rich.

I attached pics of problems that a gentleman with race-prepped opel c20xe engine encountered. He run C/R of 12.1:1 and had good (=rich) AFR's. We discussed damage on another forum and everyone is scratching their heads.
I personally believe that new fancy recessed pisons messed up geometry inside the chamber and he was getting lean areas around exhaust valves.

It's a tough call to mate hot cams and smooth-dished pisons w/o doing piston recesses.

I also believe that the reason turbocharged engines survive much higher C/R ratio (altough dynamic) is that their pistons have smooth domes, thus making good combustion chamber geometry possible. It's the turbo that is doing the C/R raising. When you try high C/R with N/A engine, there is just not enough meat inside to do this...so you end up using tall pistons and then start cutting into them so that valves don't smack on them. All this cutting introduces lot's of sharp enges ino combustion chamber and it goes boom.


http://forums.pelicanparts.com/uploa...1209408040.jpg
http://forums.pelicanparts.com/uploa...1209407353.jpg
http://forums.pelicanparts.com/uploa...1209407539.jpg

I have personally done back to back dyno comparisons and there is no measurable HP difference going from an AFR of 11.5 to a 12.0. This may not be true for every vehicle out there, but this was true on my particular setup (11.3:1 C/R 993 single turbo with 6 psi making 412rwhp), and on several other platforms that I have tuned.

If it were me, I would never run a leaner AFR then 12.0 at WOT on an air cooled CIS turbo motor, too much risk with near zero gain. You have no knock feedback control features on that engine, and it only has to lean out a bit before you start to knock and damage parts very easily. Running mid-high 11's AFR is not rich enough to wash down the cylinder walls or dilute the oil, and it is worth the extra margin of safety, especially on an air cooled engine where head and piston temps can be a problem that leads to failures.

Interesting perspectives from you both Goran & Buckeye.

Goran, why is it that the melting of the piston always occurs near the rings? I would have thought looking at that piston you would get a hot spot on that very thin edge on the left hand side between the two valves cut outs? Do you think that thin edge caused pre ignition of the fuel?

There could be other factors at play here. A/F contamination, carbon build up could be at play. A/F contamination can come from oil getting into the mixture. This will lower the octane of the incoming mixture. Valve guides, PCV and turbo bearings are the most common causes.
Carbon build up comes from over rich conditions or oil contamination. Carbon will raise the compression ratio bringing on pre-ignition or detonation.
Geez, even an improperly adjusted valve can give you headaches. If the valve has little time against the seat or is prevented from seating on seat due to carbon buildup, that valve will start glowing like a glow-plug. :eek:

Not to mention deck height, after-market pistons with Mahle cylinders, type of plug, and on and on.

On hard accel, I have mine set to 11.7 and it settles at 12.2 within 15 cycles. At no load, it's at 14.2 - 14.4. At cruise (2800 rpm), it's at 13.6 - 13.8.

As for the Innovate LC-1 and XD-16, make sure you re-calibrate often. Mine wanders after about 4 - 6 months. Before I open the laptop to tweak the tuning, I re-calibrate and usually find that solves the problem.

I would guess that extensive amount of squish around edges and somewhat complicated tumble of fuel mass leads to lean conditions around edges of the piston wich promotes knock. Also, exchaust valves are hotter than intake so in 4v engines, you will mostly see erosion around piston edges near exhaust valves. While center of piston in this case is covered with ridges, it's also postioned directly under the plug (thus ignited first) and probably exposed to good air/fuel mixture as well.

Remember, flame front has finite speed and in this case plug is positioned in centre. The plug is ignited before TDC, and while flame front propagates, piston is moving upwards. The piston edge under exhaust valves is hottest place, in this case with lot's of squish and reached by flame front last (and thus compressed by piston). That's the probable reason of why it got damaged in that position.

If you look at 930 piston damage further up, I would guess that hole appeared furthest away from a plug as well.

Both of my burnt motors had opposite problems - the hot spot was the intake side of the piston. When the last problem occurred, it burned (or frosted) the piston between the top and the first ring. The top of the piston shows no problem.