CDE with a big bore

[Adams17RG]

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. 

[Hilly13]

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.

[hrdtail78]

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?

[Adams17RG]

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? 

[hrdtail78]

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.

[Adams17RG]

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. 

[hrdtail78]

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.

[Adams17RG]

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

[hrdtail78]

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.