Tuning for Larger Nozzles

[jfreemanak]

I just bought some 60% nozzles, and was wondering what the best way is to tune for them. Should I modify my Injection pulse width table to compensate for the larger nozzles? I was thinking of doing that, but then I noticed a fuel limit table with a max of 200mg. I am not sure if I will actually be injecting more than that, but that could turn into a problem. Or should I leave the Injection pulse width table alone, and self compensate for the desired fuel quantity?

Thanks for any advice.

Cheers,

Jared

[Jim P]

Lower rail pressure and or main injection pulse in smokey areas. Even if there is 200mg injection limit, if you got oversized injectors you will be flowing more fuel than oem injectors at a given rail pressure and duration. Listen to the engine, may need to reduce timing in some areas.

[jfreemanak]

Thanks for the advice Jim. For more clarification, here is the injection pulsewidth table, and the max fuel table.injection pulsewidth.PNGmax fuel limit.PNG

So, if I do nothing to the puslewidth table, then I will definitely get 60% more fuel that what the ECM thinks it is injecting. However, there is that limit table... I am definitely leaning on leaving the pulsewidth table alone, and self compensating for the amount.

[muz79]

Lower rail pressure. Really?? Bigger orifices and you want to lower rail? This forum has really turned to shit. I ask a simple question about benching an ecm and it?s crickets. Rail stays the same. Reduce duration if it?s more than you want. Also run a timing calc to see where you should be with tour new nozzles. Bear in mind, the timing calc doesn?t allow for spool areas.

[muz79]

And data log

[Dom_c13b]

Do not lower rail pressure due to adding bigger nozzles, that's poor advice. I would leave the idle range close to stock for the duration table and lower duration in the mid and upper range. Timing changes will also help a lot with smoke. If you're hazing at idle or low load try adding some rail pressure and lowering timing a bit.

[Jim P]

To each his own I guess. Lower rail pressure in certain areas even with larger injectors, sure does fucking help, even professional tuners that you pay money to for a tune lowers rail pressures in certain areas. But hey, what the fuck do I know? Not like I don?t keep close personal contact with a professional tuner who helps me out with many things in regards to tuning and more...

[Jim P]

Thanks for the advice Jim. For more clarification, here is the injection pulsewidth table, and the max fuel table.injection pulsewidth.PNGmax fuel limit.PNG

So, if I do nothing to the puslewidth table, then I will definitely get 60% more fuel that what the ECM thinks it is injecting. However, there is that limit table... I am definitely leaning on leaving the pulsewidth table alone, and self compensating for the amount.

Bear in mind that that 60% more fuel isn?t throughout the entire rail pressure/duration range. It?s at max rated rail pressure. A flow chart for your injectors if you can get one will be your friend on getting your duration table dialed in for what your injectors will flow at different rail pressure/duration.

[Dom_c13b]

@Jim P. I certainly meant no offense to you. The only place's I typically lower rail pressure is in the cruise range, and that's only to reduce parasitic drag on the pump. On a 6.7 it's already fairly low in that range so..

[Jim P]

It was more muz. I really don?t see the point of being a dick for not liking what another has to do say and that someone has responded to another persons thread that wasn?t his on a forum that for the dodge diesel community is quite inactive about a post that most people on this forum probably have absolutely zero answer to.

Lower rail pressure in cruise region, yes, duration, most likely that will damage performance and economy. Up in high loads or fuel command with oversized injectors yes you want to pull away more duration. But not down low. Your duration map you are ?programming? your injectors true time to flow x fuel at x pressure. An oversized injector isn?t very far off a stock injector at low fuel command and fuel pressure.

The idea of reducing rail pressure to reduce parasitic drag at cruise is ridiculous. The cp3 only uses some 3hp at full pressure. 3hp isn?t enough to make ones dick flinch in excitement, it?s not enough to make any real difference in anything unless we are counting milliseconds here at a drag race. Lowering the rail pressure will lower the fuel flow into the engine just as lowering duration will lower fuel flow into the engine. What you are doing is changing the way the burn reacts through out the cycle. At low/getting into medium and yes sometimes even at high loads, lowering rail pressure is better. Increase to rail pressure is relative to load AND rpm. Because remember, the duration table is really supposed to be real world time it takes your injectors to flow x fuel at x pressure.

Fuel required at different operating conditions of the engine IS controlled through rail pressure.

[Jim P]

Something to bear in might when only changing nozzles, you are still running high mileage bodies. With high mileage injectors there may be a chance that down low and in the cruise region you will benefit from bumping up duration a little bit, nothing crazy though, even though larger nozzles were put on.

[Dom_c13b]

Yes, lower pressure will reduce total fuel volume per time. That's not at debate. But adding pressure with bigger injectors/nozzles will almost always make for a better running truck. Reducing pressure in order to reduce total fuel flow will push you further into the commanded fuel to maintain the same torque. With big nozzles you will need to adjust duration. Will it run with stock tables, sure. But it will be a smokey touchy mess. If you're not tuning duration, pressure and timing when doing a nozzle change of this size you really shouldn't be tuning these trucks. A set of 50-60hp injectors really don't need much, 60%'s should really be tuned correctly.

[Jim P]

If you look at a flow chart for stock injectors you are literally looking at a line graph representation of the stock duration table. A properly tuned duration table for oversized injectors will be matched to those oversized injectors flow chart. Increase injector size absolutely duration, pressure and timing will need to be adjusted. Duration down low even on 60% over injectors is more than adequate to leave at stock value. When I ran 60% over and most others I know running larger injectors, down low rail pressure and timing is most often lowered. Adjusting pilot timing and quantity with oversized injectors can be very beneficial as well. You really only see major fuel flow differences between a stock injector and an oversized injector when you start hitting higher pressures. High pressures are really needed most when at high load and high rpm when the optimal window to inject large amounts of fuel is very small. When a duration table is matched to an injector as a good tune should be, focus should be on rail pressure and timing for troublesome smokey areas of the tune and desires power output. While lower rail pressure will require longer duration for the same amount of fuel I have not seen it cause the engine to start working harder, engine load increase, unless you are way too low on pressure. Pressure is used to control the amount of fuel required for the objectives, whether it be emissions, economy or power. Pressure also affects the to ignition delay and burn of the fuel, timing can be used to shift where that ignition begins, optimal is to have ignition just after top dead center.

[Jim P]

I dunno man. I?m just sharing what I?ve learned from my experiences over the last 7 years, what worked well for me and what I?ve learned from professional tuners. If fuel flow is not supposed to be controlled through rail pressure I guess Cummins R&D really screwed up by compensating for altitude and temperatures by applying correction factors to rail pressure and not duration. The 6.7 does run lower rail pressure stock versus the 5.9 but the 6.7 has a lot emission equipment to allow running the lower pressure it does the pass emission standards. If rail pressure is too low it will cause more smoke, at that point I would agree with raising rail pressure.

[jfreemanak]

Wow, I step away for the week to take a PSV sizing course and all kinds of good discussion happens!

Jim, it sounds like you do not recommend multiplying the fuel quantity axis on the Injector Puslsewidth table by 1.6 to compensate for the larger nozzles? Also, looking at the fuel pressure table, it appears the correction table makes the pressure 1800bar at all rpm and commanded torque when the engine warms up. Are you suggesting changing that?

[Jim P]

No I wouldn?t recommend reducing duration across the board by 60 percent because your injectors are 60 percent over stock. They will flow 60 percent over stock at full pressure. At lower pressures they won?t be flowing 60 percent over stock, the flow differences at the same duration at lower pressure will be slightly higher than stock but nothing significant to really worry about. Lowering duration at lower pressures and quantity can cause suffering of performance and economy. Higher pressures and quantity it?ll be more worthwhile to lower duration. If you can get a flow chart for your injectors that would be the best of options to see where you need to adjust your duration table to for your injectors otherwise if you feel it?s too much lower it in the upper pressure/quantity section of the table. With the duration table you are defining how long it takes your injectors to flow x fuel at x pressure. Optimum would match a flow chart, without one it comes down to what ?feels? right, that?s a refined skill pro tuners have developed over time.

Play with your rail pressure and timing. If it sounds like you are betting too early of ignition is some areas, lower timing in those areas. Areas of smoke, try lowering pressure some, of smoke increases try giving more pressure in those smoke areas. Do same with timing in the smoke areas and find which direction helps clear the smoke. Small adjustments at a time and only change one thing at a time so you know if the change you made has made any difference. If you change a bunch of things at once. You?ll just be doing circles trying to find what helped or made it worse.

[Jim P]

Down low something you will probably notice when changing duration is if you decrease duration your commanded quantity will go up if gone too far if you add duration the commanded quantity will go down