MikeT 88IROC350

I got to run my car at the strip last sunday, and was able to take some data with my LM1 and/also TP RT. What should the WB AFR curve look like during a 1/4 mile run? IE should it be perfectly flat at the desired AFR, or ramp up lean as the rpm increases?

IE in 3rd gear i am at 12.30 right after it shifted from 2nd, then gradually ramps up to 13.30 right before I let off at the finish line. Also does the same thing in 1st and 2nd gears, just that I am in those gears for a shorter period. And there is a "rich spike" in AFR right when it shifts gears, and when i first nail the throttle, and let off. Is this normal?

My commanded AFR via the 2 tables is calculated at 12.407 from 1600rpm to 6400rpm, at normal coolant temps.

So either my tune is off, since the commanded AFR does not meet the WB, or the meter is not reading correctly. Another solution would be just to change the WOT commanded AFR to be a little richer at higher rpms.
I have a few degs of knock retard that I need to take out first.
TIA!

RednGold86Z

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This will probably reveal many opinions, both experienced and not.

I don't have track experience. But, in my opinion, the AFR that you're getting is close to desired (not flat, a little richer at peak torque, a little leaner at the top), perhaps a touch too lean on the top end, though. But, I would recommend getting it to match (within 0.3:1 of your commanded AFR, although it may not just be calibration (i.e. Perhaps your fuel pump is not flowing enough)).

When are you getting knock retard? If it's during the hard shifts, it seems to be a common issue, and might not be worth spending much time on.

MikeT 88IROC350

Ok Jeremy, thanks. I could bump the commanded AFR down from 4000rpm up so it is not so lean. Not sure how to get the actual AFR to match the commanded at WOT. It does equal it at the beginning of the run up in xx gear, then just slowly creeps up to 13.xx. I would think my FP is ok, i have a FP gage, and set it to 48psi. But it has never been changed, so who knows.

I am getting the knock retard throughout the entire WOT run, at full load. So I need to pull a few degrees and try a WOT run again.
I will look at part throttle BLMs again, since I think i am a little on the rich side.

Dominic Sorresso

Mike,

Are you doing these WOT runs in O/L or C/L? IOW, are the BLM/INT locked at 128, or temp setting for C/L high or does the WOT PW calc depends on the BLM when you enter PE? If your BLM isn't 128 or below when you enter PE, your AFR will be affected by that. I am also finding that ambient temps can make quite a difference in a WOT tune that seemed fine in cooler temps but richer in hot. think I'm going to be adding an IAT sensor to my EBL.

MikeT 88IROC350

Yea sure, Dom, I must be in O/L. In PE mode learn control goes off. And yes my BLM and INT are locked at 128. In part throttle cruising, they average around 122-128. I think I need to tweak them a little.

Not sure what you asking about the WOT pw calculation depending on BLM. This is on '88 MAF based 165 ECM, using an ARAP $6E derivative bin. The only tables I know of to calculate WOT AFR are temp based and rpm based, and they work togethor to get the AFR. I have it all calcuated out in a spreadsheet. I agree that the ambient temps can have a big effect on the tune, I not looking for perfect though!

Dominic Sorresso

Mike,

Well actually you answered my question. You are running in C/L. I meant were your BLM/INT locked at 128 during part throttle. Obviously not. The point being that if they are 128+, then the ECM modfies WOT AFR thinking that the motor is running lean. If BLM is 128 or below when you enter PE, the ECM doesn't modify the WOT PW. This is why you will see variability in WOT AFR depending on what the BLM was when you entered PE.

MikeT 88IROC350

Ok Dom, I think I understand. Yes the ECM is running in closed loop overall. My BLMs are allowed to vary 108-148. But when you go WOT, you invoke PE mode and learn control goes off. The recorded BLM in my TP scan was at 128 during entire WOT run. But on avg during part throttle engine operation, the BLMS are running below 128.

So what you are saying is that if my BLMs were running higher than 128, which is leaner, then the ECM would adjust the pulse width in WOT, aside from what I command in the tables? I think I can understand the logic there, but I AM NOT running on that side of 128.

In general terms, I can realize that if your part throttle "tune" is way off, that will affect your WOT (PE) tuning. But I dont think I am way off.

On another note, the recorded "Target AFR" in my scan is nowhere near what the actual is. They are running quite a bit more on the rich side.

Dominic Sorresso

Mike,

"So what you are saying is that if my BLMs were running higher than 128, which is leaner, then the ECM would adjust the pulse width in WOT, aside from what I command in the tables?"

Glad I could clarify it for you.

Grumpy

Look at your PE enrichment and see if there's a RPM % correction. You seem to be needing fuel at just the higher RPMs.

Might try moving the injector constant/ Battery voltage compensation to get the commanded and actual AFRs to line up closer.

Steve40th

Not to hijack the thread, but when does your ecm go into PE mode? Is it at 100% throttle only?
ANd if your tune is off on a dyno, and its reading lean then you hit it to wot, will the engine run rich during the dyno run since the ecm is still trying to add fuel right before PE mode?

Grumpy

There is a %TPS enable for PE. You can edit at what % TPS you go to PE.

Dyno tunes are great, for racing on dynos. They're also great for noting trends, after that, they're just *OK* for an intial starting point with a tune. A 5-6 sec dyno run is nothing like doing a burn out, and then making a pass as far as building under hood heat, and thermally loading an engine.

Too often people think the VE is going to increase as the revs go up, hence the tune gets rich at higher RPM. While at light loads, and tuning for 14.7 the opposite might be true, that doesn't mean the engine is going to behave the same way at WOT, as it does at lighter loads.

You have to experiment to find what ARF makes your combo run best, and that includes, richening it up, or leaning it down as the RPM increase. **Generally**, you have to add fuel, and reduce timing, to keep it out of detonation, which is your first concern, but lean is mean, and makes more HP, trick is getting the motor to enjoy being *lean*. That's why you need to watch both AFRs, and EGTs. You can wind up with good EGTs and be on the wrong side of Stoich, as well as have an *ideal* AFRs, and have too high of EGT.

vernw

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Grumpy, I imagine you'll probably just tell me to do a search, but how does one tune for exhaust gas temps? Coolest vs hottest, temp range to shoot for, etc....

JP86SS

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I have a neat little chart I found I can send you Vern that indicates the relationships.
Edit: Article is here, link still works.
https://www.thirdgen.org/forums/diy-...cle-above.html


Grumpy,
Can measuring the surface temp of the header provide acurate enough results for EGT or do you really need to be in the stream?

87_TA

I would like to touch on this a little being its one of my methods..

Surface temp will and can vary alot due to wall thickness, coatings, Fan on/off.. But I have a do use it.. especially when tuning blind IE: cam with lots of overlap - causing lots of unburned fuel to make o2 read false lean condition, therefor over richening car no matter what your tune is.
So you are forced to run Openloop, when the o2 swing table will not fix it.

Its abviously only good at idle, Unless you ride under hood of car - But at wot it probably would not transfer heat fast enough anyway.

But in a cam with lots of overlap your exhasut temps should be low due to the overlap pulling intake charge into header.. alot of times you end up way hot because of the o2 thing..

So yes its a valuable tool for tuning Open and even closed loop idle to me, along with plugs and feel of car. Really hot headers will cause you lots of problems..
Lots of wire failures.. And the over rich condition causing the heat will cause lots of cross grounding.
Also it can be a valuable tool to find problems, bad injector,valve, bad valve adjustment, ect. Anything to not make a cylinder fire right.


Possibly the best line I have ever heard, and true..

Have so many times seen cars make gains on dyno, that have never transfered to the track. Some have, but I have seen lots not.

vernw

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WOW - I'm still reading it, but it sounds bit like the author is oretty knowledgeable - Thanks for the link, John!!!

Grumpy

EGT = Exhaust Gas Temperature.
Not radiated heat temp of exhaust.

EGT, tells you how close you are to the thermal limits of the engine you are. There is a correlation to timing, and AFRs, ie peak EGT occur at Stoich. With a WB you can tell which side of Stoich your on, so you can tune your engine with less likelyhood of melting down. Rich of Stoich, and EGTs drop, as well as lean of Stoich, the temps drop.

Grumpy

In conventional auto use, at 2,000dF you'll generally see the exhaust valves leaving the engine, in the form of lil *sparks*. At ~1,800dF, you'll find the dome of the pistons, have started to erode, BTW, it's often mistaken as detonation/ pre-igniton. The difference is one has *rounded* traces of damage (excessive temp), where as pre-ignition/ detonation leaves *crisp* edges to the points of erosion.

EGT, is one way of infering weither you're rich or lean of Stoich., by what happens when you make an AFR change. If leaning the mix down, drops EGT, you're lean of Stoich. Experimenting with out knowing which side of Stoich you are, can instantly be very damaging.

**Generally** running EGTs of ~1,600 dF is *safe*. This is ASSUMING the timing is close, and isn't pushing the engine into detonation.

*Just as a point of reference*, and not for the *new guys* (or those that *think* they're well clued in) [<G>] to try to duplicate, at ~26 PSI of boost, I'm running EGTs of ~1,600dF, and an AFR of ~12.4:1. Now there's alot going on behind the scenes to do that, but, while folks talk of in-cylinder cooling, and using fuel to do it, timing, and MATs have a huge effect on what all you can do. Oh, and this is with an extremely small amount of alky injection, on 87 Octane.

On one ocassion, with the pulling tractor, we *hit* 2,200dF, and wound up having the turbo turn into a hand grenade.... The turbine wheel exploded, in a very, very, violent manner, ie we lost a lot of sheet metal from flying sharpnel, not to mention a very expensive turbo.

If you have ANY DOUBT about where you're at, or doing, I'd say stick to the 1,300dF area, and do your learning down there, so you not *typically* going to trash an engine if you goof. Miss the tune timing wise, and you can do alot of damage!, even with reasonable EGTs, and AFRs.

JP86SS

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Sorry to take this so far off track Mike,
I think I see the light in that comment much clearer now.
All the numbers are just numbers unless you really know where you are.
reported values from WB's arn't necessarily accurate but trending can show you where you need to be.
After re-reading that article again it became clearer.
Leaning out when on the low side of stoich will drop EGTs and also some power. richening from there will give you gains at the cost of rising temps.
Leaning out on the rich side will raise temps and maybe show a gain in power that you should have been working towards from the other side.
I see how things can go bad in a hurry in that regard.

Grumpy

Bingo.
Maybe an absolute would be a better word..
Yep.
Yep, while an engine can sustain a fair amount of light detonation, heavy detonation, can lead to pre-ignition, and instant engine damage. ie heavy detonation can cause serious damage in the long term, but pre-ignition is an extremely violent condition.