HarleyTechTalk

I've been researching CDE. One thing I haven't found a  answer too is should CDE be increased when upgrading to a big bore. My bike started as a 107 with the 475. Now it's a 127 with the same 475 cam. CDE table stayed the same on both tunes. I would think actual CDE increased therefore the table should increase as well? Bike runs good, no issues just curious what is possible if the CDE should be higher and how much of a benefit there would be to retune. 

Short answer is yes they would change, up or down depends on the data, some software makes this process pretty easy, not sure how it's done with what you are using, following this to hopefully find out.

Cubic inch really isn't the deciding factor on this.  Combination of parts is.  You can have a big inch and pipe that is too small, a cam with no overlap and this will affect reversion one way.  A smaller cubic inch with a cam that is too big and short primaries and a dump collector will affect reversion another way.

Then it will always fall back on the base or starter calibration.  What was the state of tune the CDE tables was in the first place?  Was this table even addressed to make the cal you are starting with?

Tune seems to be good. No complaints. Yes the table was changed from stock to adding the cam. But was not changed when going from the 107-127, same cam. Seems if I add ci and use the same cam the CDE should increase? 

I have not seen it work like that.  If I understand your thought.  If CDE is x amount of units.  That x amount needs to increase with the same percentage as cubic inch increases.

It is all about cylinder fill and all we do to try and maximize it.  This includes intake velocity, wave scavenging, pressure in exhaust, overlap, time of valve opening.  Reversion can happen more when somewhere in this track the air slug slows down and looses it's inertia.  A cylinder that moves more cubic inch of air through the same cam timing events and port.  It increase the airs velocity to fill the larger cylinder.  This in turn increases it's inertia.  This is why the cylinder is still filling on the up stroke and why overlap scavenges the cylinder.  Reversion is never a problem when the cam turns on.

Not thinking it should change the same % as the ci increased but seems CDE would increase if the ci increase and the cam stays the same. I added a larger TB so that increase as well. I became curious from looking at other tunes that have a much larger CDE than what I have. Just curious if there is much a benefit from increase CDE and retuning. 

Are you running MAP or TPS VE tables? What are the VE values around 55-60 kpa from 1250 to 4500?

This is what I use to determine how I use the CDE table.

TPS
Using Excel to gather the info from 55-60 KPA and using the average for each RPM

Front                               Rear
RPM         VE                    VE
1250        76.1                 81.1                      
1500        93.8                 88.1
1750        117.5               87.2
2000        91.3                 99.9
2250        74.3                 81.9
2500        79                    79.7
2750        89.6                 86.4
3000        99.7                 111.1
3500        125.1               122.5
4000        112.6               111.4
4500        108.9               105.2

Doesn't look too bad.  Depending on how the CDE table is laid out.  If you could take away some percentage at 1700, and add some to 3000.  This might have a smoothing affect on the VE tables when you remap it or you might not see much change.

displacement isn't really the factor.  shape of the VE table is.  if i have a tune where the VE is pretty high (90s) at idle or in the 100s going through 2000 rpm and dropping into the 80s after that, then working on the CDE will change the shape of the VE.  i try to get it to be smooth changes from low to high in the areas that are below 60kpa. 

Thank you for the information.
I've been changing the CDE and have an idea what the effects are. I understand when we scale the ci higher to allow the maxed-out areas to be below the 127.5 limit, it lows the entire VE table. So should we raise CDE in the areas that lowered the VE, from the scaling of ci, to raise the VE back to somewhere close to the original ci. Example: I started off as a 107 and had to scale up to a 150. That took my VE at 3% throttle/1000RPM from 77 down to 44. Am I wrong thinking I should raise the CDE and get the VE back to the 70's or 60's?

The actually VE unit means nothing.  Just a part of the algorithm along with cubic inch, injector size, CDE table.......

The CDE unit in the table covers a block of cells.  If you can get the VE's smoother in this block of cells.  The algorithm will do heavier lifting as a constant with the CDE unit for this block.  While the VE's are used as a narrower variable.  Faster math, faster response for what is coming for next engine cycle.  Less viable, less tolerance of error.  Because what is the solution to the formula?  A time we are going to energize an injector.
 

Not trying to tell you how to suck eggs here just trying to help as I'm not sure how much you know, the biggest effect is under the 60kpa line, you can't do a lot about what's above, you are basically trying to smooth/flatten the ve out from below to 60kpa, you are only doing this step to compensate for dilution in the intake air flow, not to compensate for any other engine changes although those changes are probably why things need to be smoothed out now, does that help at all or am I just muddying the waters here?

I appreciate the info and yes I understand it affects roughly 60kpa and below and the intent is to make a smooth transition between cells. From what I've changed I see how much the VE table changes and smooths out. Now I'm just curious if raising the CDE up, which would raise the VE, in the areas that reduced from the ci scaling would have much of a noticeable difference in performance. Sounds like it won't but I'm bored soooo...

Where is you peak VE's at?  Is it in the area that will be affected by the CDE table?

CDE will not affect the peak VE. The CDE range for VE's is in the 40-50's until 3k then jumps to high 70's.