Scaling the VE table for crusing resolution
 

I have made a ve table that ive scaled for off boost resolution and only am using the top 3 KPA bins for boost. They are in roughly 30 - 40kpa increments. Note that I am not actually boosted so dont bug me about the VE in boost, I already know. Also I have not tuned it at all yet, just scaled it the best I could based on my MSPNP scaled map that I had roughly tuned. I also attatched my AFR target table.

So any thoughts about this? Am I going to have any problems running it like this? My goal is to have better fuel economy and drivability, at the cost of possibly having to run slightly richer in boost if I have problems with lean spots.

Meh, I don't like that. IMO, you'll need more resolution in boost. The engines VE changes constantly with boost. So when you're at 100kPa, zero backpressure (more or less, but not really), but as boost builds, back pressure does too, affecting VE. Scaling from

I would want something like this if I were esentric about cruise VE.


190
170
150
130
110
90
70
60
50
40
30
20

That gives you 10kPa resolution from 10-70kPa. If I'm cruising at 70mph, I vary from 40-70 all the time. You can also get more resolution by adjusting the RPM columns in these rows.

Still, I like my 16x16 fuel table. I do kPa in 10 kPa increments from 20-100, then 110, 130,... 210, 230. RPM scaled from 500, 1000,....7500, 8000.

Not a word. ;)

So many of us run such simple boosted AFR targets I wonder myself how many boosted rows we really need. Mine is modeled after a table Joe posted awhile back, and IIRC the boosted rows started at 12.5 for one or two rows around 100kpa and then ran to 11.8ish for the remainder, starting just after crossover.

Yeah, I suck at sphelleng. :fawk:

AFR target table :ne: VE table. Agreed that a huge AFR table isn't really needed. But I think more resolution on the VE table is needed. It will be hard to dial in that table, and then it will still suck IMO.

I like my 16x16 table. :) MS2E FTW.

Well, I am going to run this table for now since I am NA at the moment, and once I get some boost, I'll see how it works out. The megasquirt's interpolation between cells will help a lot, meaning that if I have 110VE at 170kpa and 115VE at 210kpa, then 190Kpa will have a VE of 115, which is likely close enough to keep my AFRs within .2. I can just run slightly richer AFRs if needed.

By the way, Braineack posted up a VE table that was very similar. I'd like to know what he thinks about all this.

16x16 would be great, and 20x20 would be perfect. These 12x12 tables are like the bare minimum resolution needed. With 12 rpm bins, there is only one every 600rpm if they are spaced evenly. A lot can change over 600rpm.

I really don't get comments like this. A 20x20 table would be pointless. Frankly, a 12x12 table is probably overkill.

The MS interpolates the values in ALL the cells surrounding the MAPdot. It's not like your fuelling jumps between the VE numbers, it doesn't round-up or round-down to the nearest cell. With this in mind you basically already have a 1000x1000 table (maybe more, who knows, you get the point though!!!)

I bet an 8x8 table would work just as well in our application. They managed with a LOT les resolution in the good-old carb days!

12x12 is not enough resolution for me. As the RPM's rise, there are changes in the VE that are not linear and do not necessarially follow the interpolation of the fuel map. I have seen that between two points which are each tuned, the AFR will be off in between, and that was over a change of about 600 rpm.

16x16 is pretty good. I wouldn't mind a 20x20 actually. I'd like to be able to have more resolution in low boost actually. And a few extra RPM bins would be nice as well to better dial in off idle RPM and a couple extra columns in the cruise area.

I am not a 100% on this, but I remember reading somewhere in the MS documentation that spline interpolation is used for VE, not linear. Hence a 20x20 or a 100x100 wouldn't really help that much.

pff, after finally tuning a non-itb'd car, you guys have nothing to complain about. regular intake manifold cars are so much more forgiving. while in high revs cruising on the highway, my 20% cruising throttle puts me at 88kpa or so, while 70% throttle puts me at around 93. My VE table looks pretty silly to compensate. I'm probably just gonna give up and retune it for TPS instead of MAP. Right now my table is like
100
97
95
93
91
89
87
85
80
65
45
20

does this work:
use whatever scaling you want for the VE table in boost
give lots of authority and step value to EGO correction below 100kpa

this way you get the resolution you want in boost, and get the EGO correction "power" for target AFR in cruise...then you can make money, smoke trees, and get bitches.


I've owned another car with Haltech, and an "e-prom" tuned car and the 12x12 tables drive just fine. Actually, even with just MAP based enrichments my car has phenomenal drive-ability in comparison to my previous vehicles including a TT-coupe and STI.

yep, my fuel map has been scaled similarly for well over a year...

http://www.boostedmiata.com/timing/aug-2008-fuel.jpg

you need to switch to hybrid alpha n. I have mine use ve table 1, which is tuned to run speed density, when its below 85kpa and switches over to ve table 2, which is setup to run alpha n, over that.