How to compensate for larger injectors?

[Zorganov]

I've installed 40% over injectors, but I'd like to tune the truck in such a manner that they behave as stock injectors would. I guess "dial them back". I just rebuilt the engine and would like a bit of a break in period before I pour the coals to it. Can anyone help me? Which tables do I change? Do I need to do anything with the pilot injection? Any help is appreciated!

[Zorganov]

There's got to be somebody out there that can help me with this! Please Please!

[Meshanic]

I'm in the same boat you are. I Just rebuilt my motor, 60% over nozzles, bigger turbo, etc. What I did right off was just adjust B0201 MAF Flow Rate. This allows you to pull back fuel all over the board. When you adjust the numbers down a little the ecm reads less air moving across the sensor & in turn injects less fuel. Easy way to clean up smoke and fuel rattle while you figure it out:good:

[THEFERMANATOR]

I'm in the same boat you are. I Just rebuilt my motor, 60% over nozzles, bigger turbo, etc. What I did right off was just adjust B0201 MAF Flow Rate. This allows you to pull back fuel all over the board. When you adjust the numbers down a little the ecm reads less air moving across the sensor & in turn injects less fuel. Easy way to clean up smoke and fuel rattle while you figure it out:good:Adjusting the MAF rate is simply for smoke control. You need to compensate your injection pulse width tables for larger injectors FIRST! Figure out your injector latency and subtract that from your pulse width tables, then make your percentage changes for the oversized nozzles(a word of warning, a 60% larger nozzle will not require 60% less pulse width), then add the latency amount back to your tables. Next you need to compensate for timing, and then your limiters.

[Meshanic]

Adjusting the MAF rate is simply for smoke control. You need to compensate your injection pulse width tables for larger injectors FIRST! Figure out your injector latency and subtract that from your pulse width tables, then make your percentage changes for the oversized nozzles(a word of warning, a 60% larger nozzle will not require 60% less pulse width), then add the latency amount back to your tables. Next you need to compensate for timing, and then your limiters.

Thanks Ferm. I'm still figuring this out myself. The MAF adjustment idea I got from Zach at Starlight Diesel. It allowed me to get mine to quit rattling at low boost and cruising.
I did the math & found in order to get these 60 overs to flow more like stock I had to subtract 37.5%.
Here's how I came up with that number. Say my fuel delivery per stroke is 50 mm3 and my commanded fuel rail pressure is 100 mpa, my stock main injection pulse is 776.
60% of 776 is 465.6. Added that equals 1241.6. In order to bring 1241.6 back down to 776, I subtract 37.5%.
Of course that is not accounting for the injector latency that Ferm mentioned.
Ferm is there a formula or table I can use to figure latency? I found on another thread where you said it was about 100 usec. Was that on a stock injector?
I think that is an important part of the equation I never considered.

[THEFERMANATOR]

Thanks Ferm. I'm still figuring this out myself. The MAF adjustment idea I got from Zach at Starlight Diesel. It allowed me to get mine to quit rattling at low boost and cruising.
I did the math & found in order to get these 60 overs to flow more like stock I had to subtract 37.5%.
Here's how I came up with that number. Say my fuel delivery per stroke is 50 mm3 and my commanded fuel rail pressure is 100 mpa, my stock main injection pulse is 776.
60% of 776 is 465.6. Added that equals 1241.6. In order to bring 1241.6 back down to 776, I subtract 37.5%.
Of course that is not accounting for the injector latency that Ferm mentioned.
Ferm is there a formula or table I can use to figure latency? I found on another thread where you said it was about 100 usec. Was that on a stock injector?
I think that is an important part of the equation I never considered.

For LB7 I found 100 usec to be pretty close. I found it by playing around with the minimum pilot quantity. I set the pilot to 0, and then started dropping the minumum pilot quantity until I found that it no longer worked(roughly 92-95 usec, so I use 100 to be safe). Not an exact science, but it got me pretty dang close. Makes for some wierd looking changes to the fuel table when you look at it with latency figured in, but when you subtract latency it all makes sense. Also you will find that at idle you will subtract a diffrent amount than you will up top as the changes are not perfectly linear.

[Quinton]

Subd.

[Meshanic]

Thanks Ferm. That's some good info.:)

[crash85]

subd

[Meshanic]

Ok got mine right where I want it. Pulled 100 usec from the pulse width as my latency, pulled my desired percentage and then put 100 usec back in. 37.5% worked great for my 60 overs. Once I got that it all started coming together nicely. Using the Josh H timing calculator made timing a breeze. Just used the same strategy I've been using for years with the new pulse width numbers.

I am loving tuning this thing! My street tune never exceeds 15' of timing & runs high 13's on a single CP3 with no lift pump. I have WAY less rattle than an LBZ with an edge. There is nothing like custom tuning:thumb_yello:

[Chiz1]

Subd

[Zorganov]

Ok got mine right where I want it. Pulled 100 usec from the pulse width as my latency, pulled my desired percentage and then put 100 usec back in. 37.5% worked great for my 60 overs. Once I got that it all started coming together nicely. Using the Josh H timing calculator made timing a breeze. Just used the same strategy I've been using for years with the new pulse width numbers.

I am loving tuning this thing! My street tune never exceeds 15' of timing & runs high 13's on a single CP3 with no lift pump. I have WAY less rattle than an LBZ with an edge. There is nothing like custom tuning:thumb_yello:

I'm curious how you're using the timing calculator with the bigger injectors. Maybe I'm missing something here, but would you be willing to share your formula?

[THEFERMANATOR]

I'm curious how you're using the timing calculator with the bigger injectors. Maybe I'm missing something here, but would you be willing to share your formula?

Injector size has no effect on the timing calculators accuracy. you just need to modify your base timing to work with your bigger inejctors(take some out in the mid to top end, but add some in at idle), and then use the calculator like normal.

[Zorganov]

The more I learn, the more I realize I have to learn still. I was under then impression with the latency you fellows were talking about, it would play into the timing via the pulse width. i will devote more thinking/learning time to the matter. Thanks THEFERMANATOR for your insight once again.

[turbo_bu]

I believe the "timing calculators" are being mentioned due to the shorter pulsewidth that a larger injector will have for a given commanded fuel value. Thus, if your old "stock" injectors were at like 2000 us and now your larger ones only need say 1200 us to inject the same amount of fuel .... then you should be able to reduce your timing value to try and center up where your start of injection and stop of injection are occurring. So people have mentioned shooting for like 50/50 split (degrees BTDC ... degrees ATDC).

[THEFERMANATOR]

Latency is pretty constant from stock to oversize inejctors, and is used in figuring out your modified pulsewidth's for oversized injecotrs. It has no bearing on timing or the calculators as they use RPM, pulsewidth, and rail pressure to figure your timing to obtain a certain amount of injection before TDC.

[pavetim]

I'm looking to do this for a friends truck who recently put in 30 overs. Where did you adjust the 37.5% in table? I was told to do like 22% at around 160mpa and starting at 1200us. And idle to only reduce around 5%. So did you reduce 37.5% on the whole table? or just the upper areas?