How Important is Cranking VE?

[Rinkrat456]

Through my searches it seems as though even the best tuners on here are sometimes hit and miss on describing exactly how important Cranking VE is. Does anyone have a clever way to describe what the Cranking VE table does for us, how long it's used during starts and how important it is to have this table dialed in? And how would one tune this table?

Here's how I tune Cranking VE...thanks to RedHardSupra. Anyone see anything wrong with this?

I downloaded Marcin's Excel Spreadsheet that takes the VE table and figures out the in-between values.
http://www.marcintology.com/tuning/crankingVEv1.1.xls Starting with an 'untuned' VE table you can see the Cranking VE table doesn't follow the primary VE as close as it could.


Untuned Cranking VE table


I tune the Primary and/or Secondary VE tables by logging some time with the vehicle...which gives me this.


From there I take the tuned VE table data and put it into RedHardSupra's Excel sheet...


Which then on the next tab spits out...


Followed by me pasting the 'hackish' Excel data into the "new Cranking VE table".



It seems to be working for me but I don't quite understand it all. Anyone have some input?

[kjhallex]

In for learning more about this table also!

[jimmyblue]

Cranking VE should match running VE where the RPMs overlap. What's unknown
is how your cam overlap weakens pumping and blows intake charge out to the
exhaust side at the lower RPMs.

If you have trouble catching at warm starts (and your IAT reading is not
simply jacked) this is the table to work with. Cut and try pretty much.
All you know is it's going to fade as RPM goes lower. What slope, I dunno.
I just massaged it to something that looked eyeball-reasonable and it's
good enough.

[Ricardo]

I dont have cranking problems, neither cold nor hot.
I had previously applied an 85% reducing factor to the whole cranking ve table, but I will give this method a try.

[Rinkrat456]

I dont have cranking problems, neither cold nor hot.
I had previously applied an 85% reducing factor to the whole cranking ve table, but I will give this method a try.

Please pay attention to how smooth the vehicle cold starts, warm starts and anything else you can describe before and after you make these changes. I've been curious to hear about more experiences with this.

[jegten]

i have wondered about this, but, the y and x axis are switched in my ve table compared to the spreadsheet. and, really i have not taken the time to figure out if i can swap the axis in either table. lol

your pics show a nice change.

EDIT:umm..nvm, found it in the spreadsheet! lol

[Ricardo]

I just did it.
Cold start went perfect. I did the Russ K thing and let it idle till it reached 100 C temp. Shut it off, reconnected the fans and started again on the first try.

Will have to see how it behaves after sitting for a while and trying to start.

[Higgs Boson]

You don't have to unplug the fans, FYI, you can turn them off in the BiDirectional tool of the scanner.

[Nitroused383]

Honestly I've never once messed with this table. I've always been able to get hot / cold starts perefect by playing with the startup airflow tables and the afterstart enrichment fueling tables. If you look under airflow > dyanmic > cranking to run time it's all the way at the bottom left. My stock value is .125 which states time to transition and ramp from cranking airmass to dynamic airmass calculations. I've done cars with up to 25 degrees of overlap @ .050 (242/248 110lsa) in a 346. Almost all open loop hot starting issues are caused from a heat soaked IAT sensor. Car's run much better when you reclocate the IAT if possibly to an ambient air source. I like to keep things simple and change as few tables as possible to run good.

[Rinkrat456]

Car's run much better when you reclocate the IAT if possibly to an ambient air source.

Is there such thing as relocating it too far away? I'm building a snorkel for a 5.3L off-road buggy and could easily put the IAT in the snorkel always drawing ambient outside air.

[Ricardo]

You don't have to unplug the fans, FYI, you can turn them off in the BiDirectional tool of the scanner.

Thanks for the reminder I completely forgot about that one.

[wyochimneysweep]

I was always under the impression that the iat should be close to the maf to more acturally measure the air flow. thats why some mafs include the iat

[Rinkrat456]

Nitroused383, to go a little further with your suggestion to move the IAT sensor to some place cold, what about those of us who are using the truck MAF?

[Nitroused383]

Relocating the IAT sensor is a good idea when running open loop speed density tune. If you're running off the maf you will have far less issues regarding a heat soaked iat. I tried to search around as someone recently posted some part numbers and info on exactly what is needed to relocate the IAT on a MAF that has the IAT in it. I couldn't find the thread I was looking for but there is quite a bit of info on this floating around.

[ari666]

sorry to bump and old thread, but was wondering if the xls sheets are available anywhere else, cos' looks like that source doesn't work anymore.

cheers

[jimmyblue]

The in-MAF IAT is still going to follow the MAF body temp
absent any great airflow, and the whole body soaks in the
engine bay heat. The truck MAF was better than the air
box MAF, for this, but only partly. My IAT sensor is now
tucked up in the cowl inlet vents, outside the engine bay
altogether. Much easier hot starting.