FredR

Trying to get some thoughts here. The Sharktuner is a very powerful tool that gives one a powerful insight into what is going on in the 928's brains.

My perception is that the MAF load signal is an indirect measure of how much power [hence torque] the engine is likely developing at a given rpm modulated by how much fuel is burnt at that operating point. Less air=less power basically.

As someone who is not naturally happy with his motor [eternally seeking more/believing the motor is under performing] purchase of a ST2 was a must.

When one is pushing the motor along it is clear on the ST2 the the cells on the map that generate max power are limited to a narrow group that reflect the high load end of the MAF output for a given rpm. I have seen several outputs on Jim's sharkplotter programme for NA models and they typically show max power levels generated in the MAF load region of 260 and a bit higher. My motor typically maxes out in the 212 or 228 bands. Admittedly I can expect some reduced output due to our high ambient temps but in my mind that does not explain the numbers I read.

I have no reason to suspect the MAF is under reading [no lean condition] and I believe my motor is simply not pumping full measure of air for whatever reason. Cam timing is fine, compression pressures healthy, injectors functioning correctly etc. I do not want to push top end performance testing- too risky these days but I am pretty sure it is not what it should be, albeit the auto box struggles a bit with it's 2.54 gearing never mind the US spec higher ratio models.

Sad to say I am coming to the conclusion that something is less than it should be given all I have eliminated from the equation. With faster exhaust and improved inlet system I would expect more than I appear to be getting.

Any thoughts on this one [the MAF load signal] or am I being paranoid here?

I am going to do some more ST2 runs soon and will try a different MAF.

Regards

Fred

kurt_1

I went back through my data logs from 2011 and 2012 to check

I used to get the same figures, ending up in the 228 range until my MAF has been recalibrated by John Speake. Now I get MAF signal readings beyond 260, maxing out at around 265 typically at around 4500 rpms.

BTW: I also get (EZK-) load figures up to 100% while before the calibration I was maxing out at 93.

Maybe have your MAF checked out ? (mine was reading 3% lean)

Kurt

edit: those are S4 (90 MY) figures, shouldn't a GTS engine flow more air?!

FredR

I have a GTS chassis but my motor is a '90 from my wrecked S4 with a few tweaks.

I am going to try my reserve MAF that has been calibration checked by John. If the MAF fitted [relatively new] is under-reading air flow then I would surely have a weak mix unless I put positive corrections in the map. Most of my corrections at top end were negative values which I put down to using the rrfpr [that I had in there already] increasing fuel pressure therefore needing backing off with the pulse durations as it were. I have always found the RRFPR a bit quicker on the pick up than the stock fpr?

Regards

Fred

Hilton

Hey Fred - unrelated to the topic, but I got a couple of spam messages from your yahoo email account yesterday. Time to change your password there?

kurt_1

OK, that explains why you get S4 MAF-numbers

re correction: I have negative corrections across the board, around -100 in the idle range and -50 to -60 at high loads.
Actually, I didn't find a single positive correction in the tuned range of my cruise map. Don't know why that is, everything is perfectly stock and the mixture plots in SP look healthy.

regards
Kurt

FredR

Hilton,

Been there, done that- no idea what happened despite Norton being up to date. Apologies to anyone who got the spurious mail- quite a few servers rejected it. Must be another one of those stuxnet thingy's!

Just tried doing a ST2 session- damm thing did not work but now wondering if my net book is corrupted some how. Currently running diagnostics, Norton again, and updating whatever I can. Maybe the USB ports not working correctly albeit the ST2 software stated it was connected but not responding.

Regards

Fred

John Speake

Hi Fred, don't forget your air density is going to be low in your climate, this will affect airmass.

Have emailed you about "not responding".

killav

Fred,

It is my understanding (somebody correct me if I'm wrong) that a stock, properly functioning/calibrated MAF will accurately meter airflow to approx. 450 crank horsepower give or take a few ponies.

Side note: A car can easily go beyond this figure obviously, but your ability to meter it goes away at about that power level (with a stock MAF).


I have seen my car log somewhere around the 450 range in the summer time (100 degree days) with consevative timing, and I have seen it MAX out the MAF signal at 516 in the winter time with 7PSI of boost.......


How does the car pull?

Edit: I wish I could remember where I was at before forced induction. That would be more helpful to you. Hopefully somebody that is NA will post up where they are at in the load ranges. And what John says above makes sense on the MAF load you are seeing. The good thing is every other car around you is having to deal with it too!!

kurt_1

re: absolute MAF signal of 260: I checked again and that's what I get at steady state around 4600 rpms. That's basically as high as I went with my data logging when tuning ignition advance where I want a constant load for some time to go through the different cells of each "column". It's not so easy to do that beyond 5000 rpms :-)
So higher numbers should come with higher rpms.

FWIW
Kurt

FredR

Mike,

These readings have troubled me for some while- just been too lazy to do anything about it really. In the winter I like to drive and in the summer just too hot to do anything. I lost about 2kg in perspiration this afternoon fitting the Innovate kit.

I think the car generally pulls OK but to be honest I have not timed it recently. I do have the accelerometer kit that I should run on it. In the S4 the motor [as stock] pulled a 5.7 sec 0 to 60. I have a feeling it will not do that at the moment- not in summer at least.

As John says the hot air will not help but then my friend up in Dubai is pulling strong MAF readings in the 260 and if anything, Dubai tends to be warmer than Muscat. Jim Corenham's S4 pulled even more but to be fair probably at much lower temps given his locale.

I am convinced the motor is missing something mid to top end- just hope to find it and hopefully fix it. I have tried all the obvious things my knowlegable friends have advocated. Trouble is I have no benchmarks for comparison. Perhaps time to do another 0 to 60 on the RR kit.

Regards

Fred