a good tune will map the VE tables for all loads ...but sticking to the CDE/EGR topic given Wiz gave us a Sticky...

a configuration that has MAP based VE tables is much easier to see and adjust CDE/EGR

Throttle position based VE gets a little more awkward.

 

Credits:
Most of the credit for the following information goes straight to Steve Cole for the excellent TTS guides, and Mr Wizard for the Dummies guide to TTS ...as well as Steve, Mr Wizard, Jason, WOC and others on the forum here that were such a huge help getting the message across. Otherwise with some snippets of what I saw and learned and all worded maybe a little bit different, hopefully it might help others ...and at least it is here in the forum easy to find

PS: If you have a TTS and VTune3 software ...you don't need any of this, it does it all for you. Maybe the others will catch up one day but until then...


So, my understanding of CDE/EGR is that it is not a value that you can work out necessarily. Rather, it is like a slightly wooly fudge factor that helps smooth the VE tables …and may give you an “indication” of what the dilution effect may be at certain revs.

Unless there are some really bloody awful exhaust designs out there, my thought is that the CDE/EGR tables should be a reasonably smooth curved line - I doubt there are any weird flow harmonics that would produce a spike up or down in the line.

The task at hand
(as stated by quite a few of the Pro’s) is to adjust the CDE/EGR tables to smooth your VE tables in the lower load area …NOT to calculate the actual CDE/EGR and populate their tables with real numbers as such. Do NOT manually adjust your VE tables to get them smooth

The TTS manual kind of tells you that, and it was the likes of Mr Wizard, Ed, Jason and Steve that tried to tell me that was what it was about. I thought there had to be a calculation there somewhere, especially when Steve/and TTS are able to work it out. Well I was wrong, I doubt there is a calculation as such …as Steve and others have said above, there are simply too many variables that go into how well the air flows and at what rpm.

Why do we care?
Well my experience of tuning (cough) one bike, is that if you have big differences between adjacent cells in your VE tables, especially at low load/low revs, the ride will buck hesitate and surge like nobody business (…and no! I’m NOT talking about lugging your engine …a term often misinterpreted in the Harley community, I suspect grown out of poor tunes I’m talking about the 0 to 5% TPS tootling around in town/traffic/parade riding type stuff)

So how do you work it out?
The TTS guide hints at it but quite a few of the Pro’s, including Steve have said in many threads to look at the 60kpa and 70kpa columns and to make adjustments to CDE/EGR to get the 60kpa column VE value (<=60 is subject to the effects of changing the CDE/EGR) equal or close to that in the 70 kps column (>=70 is not affected much if at all by changing the CDE/EGR).

The calculation
There sort of is a suggested calculation but it is more of a “rule of thumb” “starter for ten” “all bikes and builds are different so ymmv” kind of thing. It didn’t quite work for me …but it does get you moving in the right direction, so rinse and repeat. So expanding the example from Jason in post #8

• Work out the percentage difference between the 60kpa value to get to the 70kpa value
• Multiply that percentage by a factor as follows - this takes into account that CDE/EGR has more effect at lower RPM

• Increase or decrease as required the current CDE/EGR value by the resulting percentage
  
• You must re-tune your VE tables
  
• Rinse/repeat

I did quite a lot of testing over the last couple of years and found the actual changes to be much less than the rule of thumb calculations suggested. But, it does take you in the right direction so rinse/repeat will get you there.

It's not just the 60kpa column that changes but all of the columns below that as well. I found that the lower the kpa the bigger the change in VE value for a change in CDE.

However, sometimes the left most column would start going the other way to where you were trying to get to. I think that is maybe where you are starting to go too far.

I realised that you will maybe not get the 60kpa column value to equal the 70kpa column ...what I think is more significant is getting a smooth trend going from left to right in the rows, and up and down in the columns.

 

So, about the 60kpa and 70kpa columns …if your configuration has MAP based VE tables you have it easy.

If you have TPS based VE tables then this is when it gets 1) awkward, and 2) rather prone to potential errors and chasing your tail.

What you have to do is work out for each RPM line in the VE tables, what the maximum TPS is that records 60kpa ...to do this you need a nice big log with lots of varied riding.

I then used Excel to create a scatter graph of RPM vs TPS. Then I filtered the results to only show data where MAP was less than or equal to 60 (or for more of a line try filtering the data to only show 58 =< MAP <= 60)

You should get something like this (sorry the sample log I had to hand didn't have much data in it, but you get the idea)



So in this example, your 60kpa cells on the VE(TPS) table would be those highlighted in yellow ...with the 70kpa calls being the next higher TPS to the right.



So looking at the VE table and the 1125 rpm line, you might want to raise the CDE value a touch to get the 5% TPS VE value closer to the 7% as follows...

The 70kpa cell is 93, the 60kpa cell is 88, the rpm is below 2K so multiply by a factor of two((93-88)/88)*100*2 = 10.4%

If the current CDE value were 105 adding 10.4% would make the new value 116

• Now the main problem here is how good was the data in your log file and did you get enough to accurately "guess" what the max TPS is for 60kpa?
• Did you actually collect any 70kpa and above data in your logs (especially below 1500 rpm, that is tricky on the street) - no point trying to alter your tuned under 60kpa to what was the original stock 70kpa and above values, is it
  [TIP: it's easier if you have a table that only has the tuned cells populated, that way you know what you actually have]
• Trying to work out where the 60 and 70kpa cells are ...are they really 5 and 7% ...or should they have been the 3 and 5% or the 7 and 10%

This is why I bought MLV - it can take the same log and build a VE (MAP based) table.

So much easier to read and work out any CDE changes you may want to make. And it can remove transient data that may cause errors and you can see how many hits you managed to get in each cell to decide if you want to make a change or get more logs

 

I thank Steve every time I use the "cam estimator" to get proper MAP poling for some of the cam/exhaust combos out there.
Bob

 

Couldn't agree more Bob ...and TTS does the EGR for you as well. But you are right - you have to get the cam timing set properly to start with

It's only reading these forum that make you realise that Harley tuning is...

1. not easy
2. difficult to get good VE(TPS) data tuning on the street
3. and most importantly - not all tuning devices are created equally (for my scoot I already have an FP3 and a Power Vision ...and still wish I had a TTS)

note: part 2 finished

 

Gordon

Looks like you read our early DataMaster manuals before we automated it all for you in Vtune3! Here is a screen shot in DataMaster doing it all for you for those TPS calibrations. Now days Vtune3 solves all that.

 

I read it many times Steve, it just took a while of trial and error and looking at spreadsheets before it sunk into my thick head

I added a bigger credit at the top for you

 

Just so people understand the smoothness of the VE tables is the RESULT of getting EGR Effect set properly, NOT the other way around. I see way to many people who mistakenly believe that they should just adjust the VE values to make them smooth and believe it is doing the same thing as properly adjusting the EGR.

 

I made a minor edit to emphasis that point, thanks

 

OK so I said I would so here you go ...an example of applying the "60 vs 70 kph columns" to work out CDE (EDIT: tuning with a Power Vision)

...or not ...I think there are maybe a few tricks missing from the advice we have so far because it doesn't look as if my tuning will ever finish, and shows a couple of anomalies that I will leave hanging in the air if anyone wants to comment.

The following graphs were for the front and rear CDE. I started with a half tuned map that was not completely dreadful, and set the CDE to the Stock 2014 103 values.

Blue - stock CDE
Orange - first adjustment
Grey - second ...then yellow, light blue, Green, Dark Blue