I just wanted to share an opinion I have developed while tuning and testing many n/a combos. This will pertain only to maf cars.

I have noticed quite a bit here that people seem to suggest adjusting pe vs rpm values to tune maf cars at wot. I have come to the conclusion that this is quite frankly the wrong way to go here. Does it work at wot, you bet it does. What about pe when the pedal isnt on the floor though.. woops now your wot is 12.7 and at 3/4 throttle its 11.5 when you go to pass somebody, gross. The problem here stems from trying to correct a problem with the maf calibration with a table that is only rpm dependant not airflow dependant. If the error is not the same your air fuel ratio goes out the window.

My suggestion is using the equation for commanded pe to set the air fuel ratio the same across the rpm range but at a safe level so it doesnt go lean. Take a log with a wideband of several different levels of throttle in pe mode including wot. Then average the error and adjust the maf tables accordingly. Try to keep everything linear and gradual. When it matches up to what you commanded adjust the pe enrichment values back to where you actually want your target wot air fuel ratio.

When you get everything right as soon as you hit pe even at half or 3/4 or full throttle air fuel will click right to whatever your commanded air fuel ratio because it will correctly read mass airflow not try to adjust around errors in it from things like transient response etc.

What I find from all this is throttle response and shift recovery are much improved and the cars tend to get faster down the racetrack. Tuning in one gear on the dyno using pe is ok and thats how alot of folks do it, but my car and others I was tuning in person got a bunch faster when I quit that and started adjusting it the way I described above. It even beats the speed density tune I had been using at the track.

I just thought I would throw this out there and see what others thought of it. Maybe others can share thier methods and tricks for getting wot to work better in other modes. I would even invite a bit of talk about timing and a/f preferences of the lt1 at peak tq compared to peak hp.

 

First thought - I never pass at less than WOT

Second thought - Makes sense to have your MAF calibrated at all operating conditions.

There is a similar idea in a couple of old threads that were titled "PE tuning without a wideband" or something like that - they turned off PE mode in order to tune the MAF in the PE range using the BLMS. Your method sounds safer.

 

Well pe comes in at 60 % throttle or so on a stock tune and mine comes in much sooner because I am pushing it with compression now. As for passing at wot people do not appreciate it when they can look through thier door glass and through my windshield at me while i'm passing them . Lets just say the new combo traps in the low 120's on motor. Theres also other times speeding up you will tip into pe mode.

I have read that old thread and its where the idea started to form. I dont trust the method in that old thread though. Narrow bands are a tricky thing, i have seen cars where the narrow bands report 980mv with air fuel ratios on the wideband being in the 14:1 range and read 900 in the 12.7 range. I think the wot temperatures on modded engines make a narrow band go a little nuts. Besides that there is a terrible lack of resolution with the blm cells unless you adjust them just for that. Besides that you have to remain in an airflow range long enough for the pcm to learn. If you have alot of stall and gear and hp its pretty hopeless. On the other hand logging wideband readings vs airflow you get the resolution of your datalogger and you can also spot trends by looking at the data for a few different load points. Even like this on a fast car you still only get a few datapoints but enough to work with.

If thats not enough I dont want to run a $1x,000 engine at 14.7 full tilt. Besides that alot of the mafs I have done this work on tend to show lean by as much as 6% in the low 400 g/sec range, sure hope the pcm learns fast enough to keep a hole out of the piston .

 

Yeah, as soon as I wrote that I thought "Corollary to #1 - I need more power."

Surprised nobody else has popped in here. This place is becoming even deader than advanced tech.

We now return you to your regularly scheduled "where should I buy an OBD cable" threads...

 

Yeah i'm suprised nobody else posted either. Perhaps somebody should start repeatedly posting that people need tuning (besides mail order) over in lt1 tech. I am not suprised the majority of them over there can't get out of the 12's with built 383's though. Sure some dude half across the country is going to nail your tune with no feedback at all , the same tuneup on the same type engine (parts wise) will run differently due to different brand injectors or a varience in the maf sensor etc. All they have to do for part throttle is get within 25% which they sometimes fail to do.

Another tip, once you're sure that your maf sensor is tuned correctly and what you get out air/fuel wise is what you put in in the pe tables. You can use the mass airflow grams/sec readings to determine a decent baseline setup for wot in ve mode as well. I can explain how to do this if anyone cares to see it.

 

I assume you mean the sticky from an old thread I created a few years back? a few things to keep in mind that I have learned since then: you only need a partial WOT run to get a good calibration of the MAF. You don't have to run it up to 6K RPM at 14.7 AFR to determine the MAF calibration. I have now found that WOT up to 3K RPM is just fine to calibrate the rest of the MAF tables up top. However, I stated in both posts, if you are uncomfortable doing WOT at 14.7, don't do it. I have no problem doing it and will continue to do it.

On another note, yes they do learn very fast at the upper MAF range because the resolution is reduced.

Further on another note, take my comment from my original post: I set my AFR for 12.5:1 and zeroed out my "%change to Fuel/Air ratio Vs. RPM at WOT" on TunerCat. From the beginning of the pull until shutoff, I averaged 12.6 AFR with a variance of +/- 0.25. I averaged less than 1% variance from the AFR I had tuned into the computer.

The final variance I have now discovered was because my crossover was set to 425 mv (stock) as compared to 450 mv. This would seem to account for the lean condition of 0.1 AFR from my calibrated.

Ben

 

I think some of the people that really need to get deep into the LT1 PCM are also running boost therefore dump the MAF and simply use SD VE tables. Any boosted app should immediately dump the MAF anyway since it maxes out so early.

There should be a Boosted PCM section seperate from the NA section in my opinion.

 

Well that kind of backs up what I found as well, usually the error i've seen holds true from about 150-175 grams/sec on up and generally comes down just a bit if your motor breathes hard enough to cross 400grams/sec.

The reason I said I hope it learns fast enough to keep from burning it up is, from the few cars I have worked on like this they have generally shown about 5-6% lean from what was commanded, worse on tip in. 12.7 gets you 13.4ish, the same error shooting for 14.7 gets you into the 15's. Also depending on how much hp you are making you can be putting quite alot of heat into the piston and rings. From the oem testing I have seen engines at 12.5 or a bit richer will last a long time running at peak hp, 13.5 lasted about 8-10 minutes and 15.0 lasted about 10 seconds.

Your comment about just going to 3000rpm is probably a good way to control the temp of the narrow bands at higher rpm and airflow they tend to go a little crazy from over temp. However that is not an option to me, I have a stall that goes just over 4000rpm and some pretty deep gears. That would be maybe 3 frames at 10 frames a second.

Not slamming your way at all its just not for me, just offering a way to do something similar with the maf and a wideband. I completely agree with that method of tuning a maf car, I feel its the only correct way. I have the tools to do it the way I described so why not.

 

Care to form a write up on tuning the boosted stuff rather than have people sort through a few massive threads. Basic principles what needs adjusted and why etc.

 

Pretty cool information. Can you share it? Always wanted exactly this kind of data to see what can really happen at high rpm/loads.

 

I dont have the hard data on it. Just happened to be there a couple of days when they were doing the testing (externship). If I did have the actual data I dont think they'd want me sharing it. But the fact that lean air fuel ratios make engines go bang is common knowledge so I can share that.

Also just as another tid bit, oem maf meters at the point of manufacture have an accuracy tolorence of around +-5%. I can only assume that is why the oem tunes seem rich on so many cars. I also assume that is why some cars seem to be 'freaks' and have just that little extra bit of performance. While others really pick up a bunch from a tune even when stock.

 

I've got one post that covers everything (basically a write up) in the beginning of the post, everything after that is comments from people, Q&A, etc, other learnings but the first post is updated with learnings. It's a 2 bar discussion without a MAF though. Everyone that's tried it says it works great just as good as the 1 bar, usually the 2 bar guys are also running huge injectors which seems to create a lean tip-in which is also resolved.

https://www.camaroz28.com/forums/sho...d.php?t=560089

 

I still use the MAF on a FI application. (97ss 383ci ATI-D1(about 14psi) M6-trans AFR heads/ 72# Low Z injectors/ Large Spearco and Meth-H20 injection, OBD-2 PCM) I do not use PE vs. Temp. Only PE vs. rpm to tune WOT. I also did alot of work to tune non-WOT closed loop control. Alot of road testing. Re-cal of the MAF was required to do this, but, was still trial and error method. I still run the 1-bar MAP sensor. I use LT1-edit version 2.2 for flash. The software allowed me to raise the MAF threshold freq. and mod the BLM updates for low speed non-WOT mode.

It has been running very good now, but, it sure took an effort to cal the PCM. I was forced to buy a WB O2 (Dynojet) sensor to do this tuning. I had to tune for both WOT and closed loop MAF mode. I had trouble with my MAF which really affected run with a FI application.

I have also had combustion trouble with Meth/H2O injection @ low air temperatures. When there is low intake air heat, the Meth/ H2O will not flash to a vapor state, and, interfears with combustion. I rigged a switch to turn off the Meth/H20.

The 2-bar and speed density tune really do temp me to try. I have a mail-order OBD-1 PCM that did not work for me. Possibly I could try speed density flash by just swapping the PCM and 2-bar MAP.

I wonder if it would be usefull to swap flash programs?
B.

 

not quite sure who your talking to, but are you saying you can get the MAF to read above the ~450 g/sec (or whatever) limit? I was reaching the limit of the MAF with my stock motor at 6psi around 5500rpm, since going 383 with AI heads and cam it's much lower than that. If I remember correctly I searched for a way around it sounded like there wasnt one.

 

My experience has been that the top limit on OBD2 PCM MAF is about 512gm/sec. I do have a problem with exceeding mass air flow limit, and, the MAF output frequency threshold limit. I had no answer for the loss in performance (due to low fuel flow) as the OBD2 PCM tends to cut the injector pulse width by 1/2 then this MAF limit is exceeded by large air flows. I was lucky that LT1_edit had a new upgrade to version 2.2. This allowed me to max the MAF hi_freq limit cal from 10700 to 70k+. This prevented injector pulse width 1/2 modulation @ WOT, and, I tuned for an AFR of 12.5:1 for boost conditions, and, 14.7:1 in closed loop mode.

I almost went to an FAST system due to this problem.

Sorry, I have no experience with tuner_cat.

I agree that speed density mode would possibly be your only option to get around this OBD2 PCM design limitation for FI applications.

I have read posts by LJ and C. Millard that OBD1 PCM's do not operate with the IPW trim of 1/2 when the MAF high freq is in excess of the cal limit. Probably something GM wrote in the OBD2 PCM code, but, I have never got verification of this.