Big injectors??

[dc_justin]

Ok, I see the flaw (I think) in my theory. Changing the displacement will lean out the mixture, but will still change the grams/cyl. calculation too because you are altering the known volume of the cylinder. Fudge the VE and you fudge the numerator (grams/cyl.).....fudge the cylinder volume and you fudge the denominator (grams/cyl.).

Not quite... It's grams / cylinder, not grams / cylinder volume... if it was, then displacement would be a factor. As it is, the units are G of air, Temperature and manifold pressure, displacement doesn't play a factor.

[SSpdDmon]

Not quite... It's grams / cylinder, not grams / cylinder volume... if it was, then displacement would be a factor. As it is, the units are G of air, Temperature and manifold pressure, displacement doesn't play a factor.

Damn....

So, you're saying if I double the size of my displacement in B0104, it won't change my AFR to run pig rich?

[turboberserker]

Rats... This is pretty much what I thought but had hoped to avoid -- a complete retune. Or is it as simple as dropping my known VE table by 12%?


Anyone know why this artificial limit is imposed? PCM, OS limit, or software? From another issue, I know there are buffer imposed limits because of how GM put the OS together, but in this case, 100 and 112 fit in the same number of bits so it doesn't seem like the OS limit is insurmountable.

Oh lord... I can see it now... Me + assembly code = yech.

[dc_justin]

Damn....

So, you're saying if I double the size of my displacement in B0104, it won't change my AFR to run pig rich?

Yep, should run identically. Give it a try.

[dc_justin]

Rats... This is pretty much what I thought but had hoped to avoid -- a complete retune. Or is it as simple as dropping my known VE table by 12%?


Anyone know why this artificial limit is imposed? PCM, OS limit, or software? From another issue, I know there are buffer imposed limits because of how GM put the OS together, but in this case, 100 and 112 fit in the same number of bits so it doesn't seem like the OS limit is insurmountable.

Oh lord... I can see it now... Me + assembly code = yech.

It looks to be an EFILive limit... Change your units to metric, and you'll see a limit of 511.922 g/sec. That's considerably more than 100#/hr.

[turboberserker]

It looks to be an EFILive limit... Change your units to metric, and you'll see a limit of 511.922 g/sec. That's considerably more than 100#/hr.

3962 lb/hr more!

[turboberserker]

So...


112 lb/hr * 0.126 = 14.112 g/s

That is sooooo strange that the limits are so far apart. PM'ing Paul

[redhardsupra]

IF i was to hack up a tune, and i hate doing such things dearly, i'd cut the displacement exactly in half. it's the most universal, linear term in the whole airflow equation. all the other linear relationships will also be cut in half, so it's easy to make sense out of it: if you hit .5g/cyl, you know it really means 1.0g/cyl; if your airflow says 500g/sec you know it's 1000g/sec, etc... this way all your fuel needs are going to be halved too. this way you can exactly half your IFR too, and it will produce the correct final IPW:

.39g/cyl of air at 13.0AFR needs 0.03g/cyl of fuel which at 6.11g/sec yields 4.9ms IPW
but double airmass and double IFR would yield:
.78g/cyl of air at 13.0AFR needs 0.06g/cyl of fuel which at 12.22/sec would yield the same 4.9ms IPW!

so knowing you're exactly at double the airmass your scanner shows would be a good thing also for all the other airmass/airflow based tables, like spark: if you really need 19* spark at 1.0g/cyl, now it's gonna be 19* at 0.5g/cyl.

so basically all your airmass based table are going to lose half of resolution for the sake of double the range, as you suddenly can really dictate parameters for 2.0g/cyl that you couldnt do before because you 'ran out' of tables. just remember to 'move' your spark before you start tuning, or you're might have a nasty experience if you're really flowing 1.0g/cyl but commanding stock 0.5g/cyl spark (usually around 30*)

the problems will show up in all the nonlinear relationships, like short pulse adders, as you will be dumping an unknown amount of fuel, and simply halving/doubling the value might put you in the ballpark, but it wont be anywhere near the real values. so watch out, think twice, and quadruple check everything. go through every table you can find, and if it's airflow or airmass dependent (actually fuel flow dependent too since you're 'lying' about it as well) make sure it makes sense.

good luck, this is not the easiest task, but with some planning and common sense you should be able to get around the limits. hack the planet!

[turboberserker]

Paul just confirmed in a PM that everything is converted to metric in the PCM anyway, so the 100 limit in the imperial side is indeed a bug. For now, the work around is what Justin found -- USE METRIC

Thanks all.

[Chuck L.]

A dumb ??
Is the added volume gained by running the injs at 58PSI, something you have to do to get the amt of fuel required?
Is this a FI application?