Author Topic: Non Specific: VE dip  (Read 261 times)

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Online Frédéric CM

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VE dip
« on: January 04, 2018, 09:46:19 AM »
Hi Guys,

Finally decided to started a thread.

I've a big dip in the VE at 2750-3000rpm (front cyl, mainly 3000rpm for the rear).
From what i've read here & there, I supposed it to be caused by exhaust reversion, because of too big baffles diameter ? Am I right ?

Bike is a 2014 Street Bob 103, 57H (0.030"HG), SE Air Cleaner and V&H Twin Slash Slipons (stock spiral louvered baffles, don't know the size).

Thank you for watching and for your help !



Offline Gordon61

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Re: VE dip
« Reply #1 on: January 05, 2018, 01:36:06 PM »
Hi Frederic, I gave you my map, if you have a look it has kind of the same shape as yours ...which isn't very surprising given our two builds were almost the same.

I spent a long time trying to get to the bottom of that as well ...both at the higher TPS but, note there is also a hole in the 2% TPS in that area as well which no amount of CDE tuning would take out.

In general, I came to the conclusion it was just what the build wanted.  But, I had both std and quiet baffles for those Twin Slash and found the quiets gave a slightly lesser dip than the std's

What was really funny tho was if you data log and then create a MAP vs RPM table to look at, there doesn't seem to be much of a dip if any??

Online Tail Ridr

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Re: VE dip
« Reply #2 on: January 06, 2018, 02:42:57 PM »

 V&H Twin Slash Slipons (stock spiral louvered baffles, don't know the size).
Been trying to find this out myself, it seems the general consensus is 2" spiral louvered is desired and it has been mentioned that 2.25 is too much in a 2-1-2 and that V&H looses numbers...from what I have been able to determine with what I had available at the time, the twin slash is 2.125 (2 1/8)...may be just too much still?
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Online Frédéric CM

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Re: VE dip
« Reply #3 on: January 07, 2018, 08:26:08 AM »
no others opinions ?

Offline rigidthumper

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Re: VE dip
« Reply #4 on: January 07, 2018, 09:58:10 AM »
Looking at a lot of graphs, i see waves in VE- very typical. VE is representative of airflow through the system. We ask for 1 AFR at a specific throttle position ( say, 13.0 @ 100%).  Because we are changing the time (RPM) allowed for events to occur, with fixed length & diameter intakes, fixed length & diameter exhausts, fixed size/shape combustion chamber, cams that dictate where in the RPM band best torque is achieved, etc; and all of these things have specific times (in the RPM range) where they work in concert, requiring more VE, and other times where they fight each other, ( add in reversion, too) so less VE is needed to attempt to maintain a steady, measured,  AFR.

tl:dr - VE is adjusted to reduce or increase the fuel flow to maintain a requested AFR
Bottom line?  Tuning is calibrating the ECM to the components installed on the MC