Daveinet

I'm running a set up on my 502 that was done by some else and am trying to understand why they made the choices they made. For some reason, the injector constant was increased over actual, as well as the cylinder volume. This seem counter productive, as telling the ECM you have a larger engine, but then telling it the injectors are larger, wouldn't one setting cancels out the other. Is there some unique way in which the ECM responds to these changes, that makes it work better for a specific situation?

set up is :16197427 BJKW 502HT W/ Edelbrock MPFI

Nub383

The only thing I can think of is that it was a "cheat" to get the BLM's close without doing a whole lot of work to the VE table.

JP86SS

iTrader: (1)

Injector constant could be due to higher than stock fuel pressure.
I would guess the cyl constant was to fudge something like stated above.

Daveinet

Does the ECM respond to lower the injector constant in the same way it responds to increasing the cylinder size?

Nub383

I would set it all correctly in the bin and tune the VE table. Of course I don't even own a roll of duct tape so "quick fixes" don't go over well in my book.

Daveinet

That is the precise context in which I ask the question. It doesn't run bad, and the table is pretty close, but do I gain much by having the constants correct? I have set the constants correctly, but then it is too lean. The VE table is maxed out 70 KPA and higher, so it does require fooling the computer somewhere. Which is better, tell the computer you have a bigger engine, or tell the computer the injectors are smaller than they are?

I'm trying to asses what impact fudging either the injector constant, or the engine size constant has on other parameters. Will fudging either one impact anything beyond giving me better range on the VE table? If so, what other effects does each have?

pandin

Just my two cents, as soon as you install a different motor size, cam, intake, fuel, gears, ect... you are "lying to the computer". In fact any major change from "Factory original" is a "cheat". So by trying to keep some of the numbers "exact" it forces you to "fudge" other numbers.

Just remember they are all "just numbers" the computer (it is a calculator, that is all). One set of what I call "magic numbers" are as good as the rest. I try to keep the numbers with in a range that the computer works in (did you ever notice how many multipliers and scale factors there are in these programs). The only way this stuff even works is everything has to be close to the middle, of it's range, so you are not at the max or minimum any of the ranges (0-255) any time the values are over 255 or under 0 then something has to be "fudged" or nothing will work.

Nothing is perfect, so if the tune works, accept it for what it is and try to under stand, if what you see is a good "fix" or just a "fudge" for some underling "problem" that is not immediately apparent.

We use standardized parts so every time some part is changed, you don't have to "reinvent the wheel" to get back on the road.

A leaking injector could be one of these unnoticed problems, you can replace the injectors or retune the VE tables to "fix" but when the injectors are replaced, the tune will have to be "corrected" too.

Everything going into and out of the system, has a real world meaning, but that is only as seen through our eyes. The system doesn't have a clue.