Individual trim estimation from injector flow test?

[jesse408]

I have upgraded to MS3X and I have been messing around with testing the injectors with the 3x drivers.
Most injectors flow pretty much the same, but there are 2 cylinders that consistently flow 3ml less than the others across a variety of commanded PW and on wide open flow test.
If all injectors flow roughly 86ml on a test and these other 2 only flow 82 and 83, how can I calculate the individual trims to help compensate for this?
Thanks.

[jesse408]

Would my thinking be correct to add roughly 5% to the injector that flows 82ml and 3.5% to the injector that flows 83ml to equal the 86ml flow of the other injectors?

[jesse408]

Okay, so obviously I cannot make an under-performing injector flow more by commanding it to flow more.
Do I therefore reduce fueling to all the other "good" cylinders in order to balance them with the under-performing ones?
Maybe I'm overthinking this and 2-3 ml out of 86ml is not a huge deal???
Thoughts

[billr]

Are you saying TS won't let you set + trims? (Obviously, I have never looked at that stuff)

My thoughts are that there are usually other significant variables in each cylinder that nullify any benefit to getting fuel flow to each cylinder exactly the same. Neither EGT or AFR, taken at each cylinder, will really tell you if you have the best power, fuel economy, or engine longevity; much less an acceptable combination of the three. Without a lot of dyno time, and a willingness to retest everything routinely, you are kind of wasting time. Professional racers will spend the money for that testing, but for many (most?) of us more displacement or more boost or less vehicle weight are more practical approaches to getting better performance. My *opinion* folks...

[jesse408]

Its easy to change the trims no problem.
I was just wondering if anyone had a CALCULATION of how many percent to trim based on injector FLOW difference rather than EGT or O2. I've heard O2's in charge pipes pre-turbine (under pressure) are innacurate and 8 individual EGT's can have hundreds of degrees difference per cylinder making that somewhat of a crap shoot as well. (Not to mention the cost involved.)
If there are KNOWN under performing injectors, is it just a guessing game to adjust trims without all the high dollar equipment, or can I calculate trims from the Difference in Percentage of Injector Flow?
If I can at least get close, that's good enough.

[jesse408]

The goal of adjusting injector trims in my particular case is an attept of Avoiding a potential cylinder burning down due to lack of fuel.
I only have a single wideband in the downpipe so it's just getting an average of all 8 cylinders. I may be targeting 11.5 AFR in boost, but the cylinder with the slightly lagging injector may be closer to 12.5 for all we know. That's Exactly the cenario I wish to avoid if at all possible.

[racingmini_mtl]

If you have characterized all the injector parameters such as the dead time and the the small pulsewidth curves as well as the injector flow then you could in theory adjust the trim accordingly to get the same amount of fuel to each cylinder. But that won't take into account the potential air flow difference between the different cylinders which could be more significant. So unless you actually measure the AFR for each cylinder, you're basically throwing darts in the dark.

There are ways to measure the AFR pre-turbo. You can use sampling chambers which put the sensors at the post-turbo pressure or you can use a controller that uses pressure compensation. By the way, the 14point7 MegaSpartan will soon have a pressure compensated version. But of course, that all comes at a potentially significant cost.

Jean

[billr]

Since TS does allow for + trims, why not just set the trims for those two low-flowing injectors to 3.5% (or so) in all cells? Won't that bring them up to the same nominal flow as the others?

[jesse408]

Thanks for the replies. I check and change plugs alot. I see the "timing" mark on the ground strap of the plugs that are in the cylinders that have the weaker injectors. Those marks are working their way around the bend toward the threads whereas the others aren't quite in the bend yet.
Perhaps I can simply add some fuel to see if the mark moves back a little to match the others?
Thanks.