LB7: SAC 45 overs, who is running them?
- Thread starter THEFERMANATOR
- Start date
If running stock tuning, then stock replacements, if you're tuned then the sac's seem to be a nice improvement. I actually haven't been able to drive mine much since I did them, but they will take some tuning to get them to where I'm truly happy with them. It's the little details that bug me, and there are some quirks that need to be worked out in the tuning with them.
I've got a DSP5 tune from Duramax tuner and have already talked to them concerning changes. They are very familiar with the SAC nozzles and have tuning for them. I was thinking about changing the out of spec injectors and changing the nozzles while I'm in there but I'm contemplating just changing the nozzles and seeing how much my rates change but that is a lot of extra work if I do need to change some injectors.
Was going to post some of my findings on sac 45%...Had them all installed and truck runs pretty good so far but not sure if the balance rates and fuel rates are normal. The fuel rate is 5mm3 according to my insight and balance rates are all +/-.5 except for number 1 @ -2.3, #2 @ 1.4 and #6 @ 1.2...does this seem fairly descent? Ill post mpg here soon. Smoke doesn't seem real bad but too soon to tell. Haven't driven it a whole lot as I'm tracking down what appears to be my lift pump putting out too much pressure.
I've had to add fuel at idle to mine to get it where it should be. Stock tuning is NOT your friend with them. I'm still ironing out my pulse tables, but these things LIKE timing. Both main and pilot needs to be bumped up to make it happy at idle. And the lly rail pressure table with a few tweaks made a night and day difference. So far mine is running cleaner than the stockers ran, and if I'm not carefull, it will break the tires loose on me without boosting it(nothing lime rolling into it in 2nd, and losing traction once it comes on boost all without any smoke). I know it's out there that you can run stock tuning(I even repeated this), but you shouldn't run stock tuning with them imo. Mine was a dirty smelly pig with some misfires off idle with stock tuning. A few changes and it's night and day difference. As to the balance rates, yours are about inline with mine. If I ramp up rail pressure they go all over the place. But when I bring it up on fast idle, it runs so smooth, it doesn't worry me.
Your last statement in this post concerning idle...can you lower fuel pressure, and then decrease timing, in order to smooth out the idle? I don't know much about tuning, just taking a stab at what seems logical because of the amount of fuel that's going into the cylinder (more than a stock injector) at idle. Leave the table alone at whatever rpm it runs smooth at high idle though.
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Doesn't matter what size injector you run, it still takes roughly 8MM3 of fuel at idle to make a DURAMAX engine idle at 680RPM's. The larger injector injects the same amount of fuel in a shorter amount of time is all. The problem I see is the LB7 tables are mapped for VCO injectors where there is no delay between the injector opening to inject fuel, and fuel coming out of the nozzle. In a SAC injector nozzle this is not the case. Since you have one sealing surface, then a small pocket, and then the fuel goes out the nozzle orifices, you have a slight delay for that pocket to pressurize. So even though you have a larger injector, at small lower pressure pulsewidths it actually injects less fuel due to the pocket having to pressurize before injection takes place. At higher pressures it switches back the other way as the higher pressure pressurizes that pocket quicker allowing the larger orifices to let the fuel out quicker since the pocket pressurizes so much faster when the pressures turned up.
I'm actually using a pretty UNIQUE pulse table right now to say the least trying to get my idle and off idle transition tables back to stock. Stock fuel tables are very jumpy I've noticed from where the pressure ramps up and the injector begins injecting more fuel than a stock one VS where in the lower pressures it is actually injecting less. Mine was actually popping and missing just off idle with a stock fuel table in it.
As to reducing pressure, this increases the lower injected amount, reduces fuel atomization, and all around doesn't work well with bigger nozzles that tend to run dirtier to begin with. As to timing, due to the delay of that pocket pressurizing, I've found that you need to bump the timing up to account for the injection delay of SAC's VS VCO's, and since they inject the fuel in a narrower window in most areas, you have to also account for this in your timing. So I found that changing idle timing from -3.6 to -2, and bumping pilot up from 4-4.3 range up to 4.5-5 range reduced fuel useage at idle by almost 1MM3 of fuel by itself as well as smoothed out the raspiness I had at idle that I thought was too small of a pilot shot. Little by little I'm getting the tuning ironed out. So far my mid and upper ranges are good to go, just trying to get a handle on my idle and off idle areas where the SAC's go from flowing less to flowing more fuel is giving me some issues right now. So far I have it down to less haze than before on spool up, but the power increase is "IMPRESSIVE" to say the least.
Ferm...power is impressive I have to agree! Ive got tonys tuning and on the DD "75" horse tune at 15mph in 2nd gear i bust the tires loose completely free, not a chirp. This runs like a whole different animal than my lly with tuning and trans. I think this truck is putting down way more than 75 horse, has to be. Not sure if Tony knows how much these injectors flow. Ill be calling him tomorrow to talk to him about them. My main issue is at idle in gear, its rpms vary and I'm quite sure it has to do with the tuning and these injectors. Overall I'm happy, just want the idle better. Smoke considering the power is very good imo. Tonys tunes are good driving around and at wide open! Id recommend these injectors if you have a built trans! Thanks for the tips on the tuning. Ill pass it along and see if it helps!
OK...instead of seeing it as the same amount of fuel in a shorter amount of time, I guess I was taking a different perspective. I am seeing it only as more fuel in the same amount if time. Some people might say it's the same thing, but it isn't from my vantage point... Like I said, I don't know about tuning. Wished I did.
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Off idle they do inject more fuel in the same amount of time. The thing is though the engine at least at idle doesn't care how big the injectors are. It takes X amount of fuel at idle to run the engine. So when you go to bigger injectors, the pulsewidth has to go down to keep the fuel amount going in the same. I'm not the best at explaining things though, so I'm trying not to muck it up to much.
I'm running nearly smokeless, far less smoke now than with stock injectors. I'm beyond ocd about my tuning, so I'll be ironing it out for the next year or so until I'm somewhat happy with it. I know Tony is a top tuner and should have no troubles getting you sorted out. I will say the idle and off idle has been difficult to get to a tolerable point. Stock fueling even with the timing and pressure changes left me with an off idle cackle/miss, so be patient as these things respond completely different from stock lb7 injectors. The flow charts resemble those of a lly tune, but lly tables do not work. If I get my off idle issues ironed out to where I'm happy, I may post up the tune file for others to have to start with.
No, you're fine. Thanks for explaining. I can understand what you are saying. Hope you get her worked out how you want it.
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Ferm, thank you for all the information about the tuning. Makes perfect sense. 
Stock lb7 injectors are larger than lly injectors
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Until the lml the lb7 had the highest flowing injectors with each generation flowing less than the last until the lml when GM went to piezo injectors with higher flowing nozzles.
