Fast355

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So I am helping somone with the old 1227747 that has a 350 Vortec with a 268 cam in it and some goodies. Asked me to look over some tuning for him. Found a few things, but let me know if anything sticks out to anyone that has been using the 7747 lately. I have disabled the EGR with the EGR patch since his engine does not have the EGR hardware in place. It has a Holley TBI unit that was running poorly, we first fixed by moving the MAP vacuum hose from the rear port that sits in the IAC passageway to one of the front fittings. Fuel pressure was 11 psi and VE1 + VE2 was way over 100%. We now have 14 psi and I left the BPWC stock at 135 so that I could bring the VE tables back to controllable. He had a high IAC count, up around 30 in park and 36 in drive. Got him to adjust them and they sit about 5 counts in park and about 7 in drive. After adding some timing and removing fuel it idles fairly well at 750 rpm and 42 kpa in park and 550 and 55 kpa in drive although it hunts occasionally between 525-575. If anyone wants to look over my work it would be appreciate. He verified it has a 369 module in it. I have the total timing set for 34* at 4,200 and he says it runs pretty well once the rpm rises. The converter was locking too early and dragging the rpm down in the 35-40 mph range in OD, so I delayed the lockup. He says the off-idle part-throttle runs great. My first .BIN revision and Datalog screenshots.

Fast355

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Revision #2

Fast355

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Revision # 3

Fast355

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Revision#4

Fast355

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I revised the calibration one last time and he took it riding around about midnight last night. Not sure the outcome yet, but hopefully with the PE re-enabled and a couple degrees more timing it will come alive. Should be 33-34* total advance at WOT now with about 14-16* at 1,000 rpm! He said before I touched it, it was a sloth, wouldn't spin the tires from a stop, had a horrible off-idle part throttle transition. Now it starts to spin the tires, bogs a little, and comes alive. I added a substantial amount of AE because of the heads and carb style intake. Debating pushing more into it.

RBob

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Tune came along quickly. Don't forget the ESC_Done patch. This one tells the ECM that the forced knock test was already run successfully.

RBob.

Fast355

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Thanks RBob! I forgot to mention ESC_Done and Highway mode patches are both applied, highway mode is currently disabled. A wideband would make things easier, but he doesn't have one atleast not yet. If he does not have plans to pickup a wideband, after the part-throttle VEs are nailed, I think a few pulls on the dyno with an AFR sniffer in the tailpipe and the matching graph would get the WOT 3,200+ RPM dialed in nicely.

I have a spreadsheet I made years ago to adjust the VE tables off the BLM data. Complete with an adjustable scaling factor that allows me to adjust the amount of change from the VE learn with each revision. For the last .BIN I reduced the compensation from nearly 1% VE change for every 1 BLM count down to 1/2% VE change. BLMs should be even closer to 128 this next pass.

Fast355

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So the verdict is back.....Don't ever let anyone tell you that timing does not affect air/fuel ratio on a speed density setup. 2* additional timing across the whole map caused a slight vacuum increase and a slight leaning effect. Also I am sure the change I made on the median 02 voltage from 450mv to 503mv at 0-16 gms/sec had an effect of driving the BLMs in that range higher as well. Trying to combat a slight surge at idle in gear with a slightly richer mixture. He also said my 2* PE spark I added from 1,200-2,000 rpm (total of 4* over what it was running in #4) had the effect of flashing the converter harder on launch. Its funny how these Vortecs LOVE the fuel when you up the timing. Probably need go add a small amount to the AE tables as well to help a small hesitation it still has.





Starting to show signs that the timing map is about as good as I can get without a dyno or premium fuel.

dimented24x7

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Yeah anything that effects how the engine runs will effect the VE. The improvement in performance means the VE goes up, and it needs more fuel. Especially true with a cam that has overlap.

Speaking of which, how much overlap does the cam have? With overlap, the fueling at low RPMs from cylinder to cylinder varies quite a lot, and SD will tend to only respond to the average fuel demand, causing some cylinders to lean out. I ran into this when I tried using SD only on my SFI setup. Ran just as good as MAF at P/T and WOT, but it had a vicious off-idle stumble with the XE270 roller I have. Moral of the story is that there may be some low RPM bogging that cant be easily remedied.

Spaceboy1980

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Hey Fast355, if it is not too much trouble, what is it I'm looking at? Is the spark counts detected knocks? On the BLM, what is your target number?

Fast355

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Spark Counts = Knock counts

BLM = Closed Loop fuel correction

Higher than 128 is the ecm correcting for a lean condition. Lower than 128 is rich. I am attempting to get them all in the 124-128 range.

Spaceboy1980

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Thanks for the explanation.

RS-Chevy-SS

Fast I need to get you to tune my motor haha

Fast355

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HAHA! I am sure yours would probably be easier. This one has put up a fairly constant fight. Not sure if its the Holley TBI or the cam to blame.

Fast355

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Speaking of constant fight, finally starting to get the VE table and BLMs to cooperate.

In typical Vortec fashion it is wanting a ton of fuel early on in the midrange. My TPI setup had nearly maxed VE tables from 60-100 kpa. Weirdest shape to a VE table ever.



The good news is knock counts are practically non existant on 87 octane.

Fast355

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Duplicate post

Spaceboy1980

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How do you address the knock count? It started low is now about 25 times as many as it was. Bear in mind I have no clue what is normal and I am trying to learn from your tuning.

Did the bog clear up any? I can clearly see the improvement in the BLM, what changes did you make?

Street Lethal

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I bet I have your weird VE shape beat Chris, just ask RBob lol...

Coming along nicely btw...

Fast355

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Thanks! The surprise was just how much fuel it wanted clear down to 50 kpa.

This was my old 350.



My 310

Fast355

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Which ECM are you running? Every GM I have been around puts out knock counts in the datastream. To get it into a table view like I have, only need WinALDL or TunerProRT and the .ADS file for your ECM. The way to reduce the knock count is pretty simple. Reduce the spark advance by 2* in the cell that is knocking and 1* in the surrounding cells until you get no knock. If your tune started out rich it will have less knocks when rich.

BLMs are starting to get better as the fuel table progressively becomes more and more accurate. Considering the beyond slow 160 baud datastream and how far off the stock tune was I am suprised it is coming along as quickly as it is.

The bog has been greatly reduced maybe even eliminated. I asked him last night on a scale of 1-10 where he felt the truck was running and he said about an 8. Said it moves out nicely from a stop. Driveability is also remarkeably better at off-idle tip in and with the TCC adjusted not to lock below 45 mph in OD.

Fast355

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Its kind of a double blow when you tweak timing on a cam like this one. The performance increases, increasing the need for fuel and at the same time the vacuum increases across the rpm/load range. What was once ok now goes crazy. At first the BLMs were showing really rich, but he was out of fuel and had maxed VE tables. Increased fuel pressure and removed VE. Started to get it dialed in and found we had a huge vacuum leak aka the IAC due to the throttle plates being too far closed. Adjusted that amd boom, more vacuum, less fuel. Small tweak to the timing and again its lean. Beginning to gain the upper hand though as the tune and mechanical fall inline.

Dominic Sorresso

Pretty amazing how apparently "small" changes can impact fueling tables.

Fast355

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Yes it is and pretty annoying as well. Coming from tuning a 2012 and 2014 that have a MAF setup and a wideband on each bank. The data refresh rate when real time tuning on my Nissan Titan literally puts out 2-3 pages of data in a low 14 second 1/4 mile run.

Dominic Sorresso

I'm currently on the ZR-1 forum attempting to highlight how an incorrect Injector Bias has significant impact on tuning. The reaction you get is that you can "tune around it" or "the ECM will compensate for it".

Spaceboy1980

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I am running a 746 ECM.