i thought injectors would be the main problem. 30lbs are just way to small for a hot 383 like the combo in question

 

Yes, on 42's in, Sam was in mid of replacing intake gaskets on his 383 auto, when I relook at the HP vs inj size we were running, so he grabed a set of 42's to throw in. His build is same cam, but a heavy port super ram with 200cc ARF heads, 10.5-1 and all that. Sam ran at T&T about two weeks ago with not as bad as lean-out, but still leaning out

It wasn't till we switched on "single fire" that we had the fuel needed.

We are also working a mod'ed .ADS for Turner Pro for RPM logging over 6375, thanks to RBob's input.

Check back for up-dates! Pual's mini ram, six speed should be done from the chassie shop next week (that's the car that started all of this) 42's now also in that one.

 

if you get that worked out i'd love a copy

 

Are you guys really making more than 745hp?? That's what 8 42's .45BSFC, and 100% duty cycle can do.

The MAF, on the other hand, goes static at about 345hp (no matter what RPM), at .45BSFC.

 

No, we don't plan on makeing 745hp gen1, GT-1 motors. Sam and Paul had gotten a deal on some 42's for their 383's My thinking was more like some 36's, but so far no problems with the 42's (idle, etc.) Plus I don't like to see inj duty over 80% for a road course car which would now bring the 42's to more like 600hp tops. The 36's I factored for around 480hp

As for the maf maxing out, we have been able to limit what the ecm see's in the upper rpm's 5000 with the table "Maximum Air Flow vs. RPM" so as we have it now it dosn't see 255 till 6400. Sam has a AutoProm with a extra 5v logging input so I was thinking of adding a map, to see if the maf was holding up any air at WOT, If it is, a big tube maf mod may be next.

We all got day jobs, so it may be a week or two, before we get this all sorted out along with the mod'ed ads. So stay tuned.

 

what advantage does keeping those table values below 255 at rpms below 6400rpm, when the motor could be already maxing that MAF sensor out at rpms much lower than that, say 5000-5300 rpms? Why not make all values 255 in the table from 5000 on up to peak rpm?

 

Ratty,
You're missing my point that I was getting at - that single fire mode isn't necessary until you reach 99% duty cycle, and then it can save you by only 2-4%. If it was lean in double fire, something must have been wrong with the bin, calibration, or something else.

Limiting the max airflow has no use, except to reduce your accuracy.
If you set it all to 255, the MAF at least has a chance to work until 255 (no matter what RPM). Then, using a wideband, tune your PE to force the full throttle A/F to match what you want. Your method is wrong and confusing.

The MAF tube itself isn't much of a restriction, and it's not why it "maxes out". It's the sensing element inside that maxes out at a certain air VELOCITY (given standard temps and pressures). But, if you have a larger tube, the sensing element can pass more air (at same velocity, but different area) while thinking it's passing less. This will mean a real 400 gps will show up as 255 gps or something like that. Then, you'll have to fudge the injector constant to get it to work, and use NORMAL PE values.

 

Is it "twice per revolution" or "twice per cycle"? (two revolutions per cycle)

The reason I'm asking is that when I figure my injector on time % it seems that it would have to be twice per cycle, or once per revolution for an unmolested chip.

 

Twice per cycle (2 revolutions). That's how all GM "batch" fire systems work '165 & '730 included. It's all fired by one injector driver also, so there all firing at once. They're not synced with any particular event other than every 4th DRP from the distributor.

Single fire is sometimes used to help the ECU control a very small requested fuel pulse. A short pulse is not accurate because a large portion of the time is used to open and close the injector, and the flow from that can vary with age, voltage, and randomness. Single fire, though, can end up spraying a lot of fuel on an open valve which is bad for atomization, and can wet a plug - I've noticed and tested on sequential setups that emissions and idle stability suffer when spraying on an open valve.

 

Greetings. I have been following this thread and have a question about the single double fire. Is there any way to tell which ECM's can auto switch and when they do? Reading the code is not my strong suit. I have read a lot of posts refering to this but not how to tell when. Is it only at idle or at some injector DC (100%)? Also with this high RPM leanout, if at 6000 RPM there is only 10 ms, why is the injector time set at 9.4 ms ($32) 255 load? That does not include PE does it ? Is there some such limit in the $6E when it calculates values? If this is off topic please send me in the right direction.