maf transfer curve - dual mafs - question

[subwoofer]

Is the max MAF output voltage at 512g/s, or is it the max the stock LS ECU can handle? The latter actually sounds more probable.

[Yves]

I don't know for sure, but I remember something about the maf voltage reaching 5.0 V at that airflow.

To me it seems logical in the sense that you can always flow more air if you speed it up. The fysical limit is normaly around half the sonic speed (300 ft/s, which should be limited to below 180 ft/s in all cases to prevent losses and best performance - explanation from D. Vizard ). So I think a 3.5" maf could flow more at higher airspeeds, but it will max out the measureable range of the maf when the voltage reaches 5V. The usual solution to this is increase the diameter, but that creates another problem. In essence I would need a tube of 115 mm to get the same airflow as the dual 90 mm's.

[subwoofer]

512g/s was conspicuously looking like a logical limit, but it makes for easy calculations... The MAF voltage output may well be calibrated to that.

But are you sure you are not overestimating your airflow needs? 800cfm of air is an awful lot, approximately 1650kg/hr or 460g/s - needing 126kg(170l)/hr fuel for 13:1AFR? An 800cfm rating for an intake is completely another matter, that is how much air goes through for a depression (pressure drop) equal to a 10" or 28" vertical water column (depending on measurement standard).

http://www.gregraven.org/hotwater/calcu ... low-hp.php suggests 1150hp for 800cfm of engine air flow.

[Yves]

Engine has 95% VE right now at 7000 rpm . 347 ci, redline 8000 rpm.


So 8 intake strokes equal 347 every 2 rotations. So with (7000/2) x (347 X 0.95) = 1153775 ci of air per minute = 667 cubic feet per minute or roughly 700 cfm.
It should be able to run at least to 7500 and I'm not sure what VE will be at that rpm, but at 8000 assuming the same VE you get 763 cfm.

VE is an underestimation as my dead times were set too high and my actual fuel flow too low. It will be closer to 100% VE at 7000 and hoping to still have 95 at 7500.

I have no actual data on hp, except a short blast with a gps connected to TS to calculate hp. I was getting 504 hp at 5000 rpm which is where I stopped. This is of course rear wheel hp I believe.

[bradyzq]

All LS1 MAFs _ARE_ frequency-based.

As subwoofer said, the 512g/s is a GM ECU limitation. There are ways around it, but you don't need them since you have a Megasquirt.

Air speed through the MAF should have no impact on how much air mass the MAF can measure. Of course it makes a difference in how much air can actually flow through it, just not on how much it can measure.

[Yves]

http://chevythunder.com/ls1_page_1.htm
http://www.lsenginediy.com/sensors-inputs-guide/

The 3 wire and 5 wire maf were both used on the LS1. The early ones got the 3 wire voltage maf.

What is the basic ls1 transfer curve in TS ? Voltage or frequency ?

[dontz125]

I can't comment on the default in TS, but the MS2 can only use voltage signals. The signal-summing circuit you and I have been discussing is voltage only. MS3 can handle voltage or frequency inputs for MAF, but I would think the standard filter circuits on any ADCs used for logging purposes would absorb fairly wide swathes of signal - note that this applies to your IOx project.

[Yves]

These are 3 wire mafs so voltage mafs.

[bradyzq]

I'm not guessing here. I'm trying to save you from wasting time and money.

All LS MAFs are frequency MAFs. The 3 wire ones simply have a separate air temp sensor, whereas the 5 wires have an integrated MAT.

[dontz125]

Yves - the documents you are referencing above state quite clearly that these are frequency MAFs. Sorry ...

[Yves]

Ok, I see the mistake. d***.

[jsmcortina]

The MS2 Hardware manual says:
"MS2/Extra supports voltage MAFs only. Frequency MAFs (such as LS1) are not supported."

James

[dontz125]

James - you've missed an episode; he's moved on to MS3X.

[jsmcortina]

James - you've missed an episode; he's moved on to MS3X.

My post is still correct, even if irrelevant!

James

[dontz125]

Ah, the thrill of duelling pedants - listen to the crowd roar ... er, snore ...

[Yves]

The MS2 Hardware manual says:
"MS2/Extra supports voltage MAFs only. Frequency MAFs (such as LS1) are not supported."

James

I was aware of that, but I thought I had voltage mafs. The thing is that gm only had voltage mafs in the tpi era. They only went to 255 gr/sec, which is way too low.

A frequency can be converted to voltage again in some circuitry and then the voltage can be averaged, but it gets complex as Don has figured out on my iox project.

The problem could be that the airflow into one bank maybe different than the other bank. When one using the maf for one bank that one bank will run right, but the other might be way rich or way lean. Averaging the mafs, would put them closed together with EGO being able to smooth out the rest.
If of course in MS3X sequential injection it's possible to correct fuel based on the respective O2 per bank it would make it possible to just use one maf and the other as a dummy to do fueling and let EGO sort it out. Less complex in any case.

[PMAS]

Here is the transfer function for the 5 wire LS maf. Sorry about all the extra digits. It was from a 37 point flow test on our stand and extrapolated to 50 points. this way you can pick points in the range you are using. I'm assuming MS has you enter less points and uses linear interpolation between them.

FLOW KG/HR KHZ
0.73334773536772 0
1.1559866368771 0.24489795918367
1.838765386492 0.48979591836735
2.8591751120985 0.73469387755102
4.2784635908902 0.97959183673469
6.151180434972 1.2244897959184
8.5337649099529 1.469387755102
11.487777903676 1.7142857142857
15.080493316054 1.9591836734694
19.384725578129 2.2040816326531
24.478524364531 2.4489795918367
30.444886907935 2.6938775510204
37.371503934264 2.9387755102041
45.350530743599 3.1836734693878
54.478370398283 3.4285714285714
64.855462685227 3.6734693877551
76.586075872183 3.9183673469388
89.77809548378 4.1632653061224
104.54282015562 4.4081632653061
120.9947489202 4.6530612244898
139.25137743354 4.8979591836735
159.43299680948 5.1428571428571
181.66249394417 5.3877551020408
206.06515854597 5.6326530612245
232.76850134134 5.8775510204082
261.90207898617 6.1224489795918
293.59731674194 6.3673469387755
327.98735797405 6.6122448979592
365.20691514015 6.8571428571429
405.39211332798 7.1020408163265
448.68038892746 7.3469387755102
495.21033763885 7.5918367346939
545.12162208557 7.8367346938776
598.55486154556 8.0816326530612
655.65153956413 8.3265306122449
716.55391454697 8.5714285714286
781.40494823456 8.8163265306122
850.34823417664 9.0612244897959
923.52791428566 9.3061224489796
1001.0886609554 9.5510204081633
1083.1755757332 9.7959183673469
1169.9342012405 10.040816326531
1261.5104198456 10.285714285714
1358.0504655838 10.530612244898
1459.700858593 10.775510204082
1566.6084051132 11.020408163265
1678.9201498032 11.265306122449
1796.783387661 11.510204081633
1920.3455805779 11.755102040816
2049.7544407845 12

[Yves]

Thanks

How much influence can be expected from the intake tubes and turns in those tubes ?

[PMAS]

A lot. a filter or at least 12" of straight inlet tube is needed for this Xfer function to apply. A 90 degree bend can throw it off by as much as 25%. changes in the outlet aren't that critical.

[Yves]

A lot. a filter or at least 12" of straight inlet tube is needed for this Xfer function to apply. A 90 degree bend can throw it off by as much as 25%. changes in the outlet aren't that critical.

Hm, in other words, not much use in real life situation.