DTT question

[ICANTD55]

I always thought that manifold pressure went toward atmospheric pressure when you opened the throttle unless useing a blower or turbo it can become positive.

Is it me or is the DTT chart backwards?

[ICANTD55]

After messing with the neighbors nova it seems to drop initially then rise. Gonna hook a vacuum gage up to the bike this weekend and go for a putt.

[larluvssandra]

I've done the vacume gauge thing on my 95 w/55g cams.  The needle really jumped around alot at ideal.  I don't believe these vtwins run much vacume at ideal, or least mine didn't w/55 cams. I think a vacume tank would dappen the action on the gauge.  Let us know what you find.   Larry

[ICANTD55]

Thanks larluvssandra
I wonder if they make a liquid filled vac gauge. Trying to rig a gauge off my gps mount may be a little while, Were finally seeing sun in the N.E. been riding.

[Admiral Akbar]

I've done the vacume gauge thing on my 95 w/55g cams.  The needle really jumped around alot at ideal.  I don't believe these vtwins run much vacume at ideal, or least mine didn't w/55 cams. I think a vacume tank would dappen the action on the gauge.  Let us know what you find.   Larry

You need to add an orifice in the hose to filter the data vacuum pulses.. IIRC I used about an 0.030 inch jet.. Add it near the manifold not the gauge.. The gauge will be off a couple lbs since the DDT measures vacuum somewhere on the intake stoke and the gauge is only giving you an average.. Max
 

[Don D]

Be sure whatever you rig that it reads in the same units as the software. There are several methods and units to measure and report manifold pressure

[axtell]

The DTT isn't measuring vacuum its measureing absolute pressure. ie: 30 = sealevel and 25 = denver. Ron

[Don D]

There you go! What he said

[Admiral Akbar]

The DTT isn't measuring vacuum its measureing absolute pressure. ie: 30 = sealevel and 25 = denver. Ron

Well that sucks.. (or doesn't  )  You are right though.. Map is absolute pressure where the gauge operates off a pressure difference. Max

[05FLHTC]

This is why it's so important to have the ability to dump the data, something that can only be done on 04 & newer TC88a modules. Makes no difference what scaling is used if you can not determine what the module is actually applying in the real world when operating the motor / bike.

FWIW here is what I found when dumping the data off my module and comparing my data to others to validate it.

At steady cruise say 60~70ish 12 HG
WOT on the Dyno would drop to 30 HG & then slightly drop off to 27ish HG at 6K rpm's
Running through the gears the manifold vacuum would vary from 12~20ish HG pending how hard you pushed it.

HTH's
05

[ICANTD55]

I've done the vacume gauge thing on my 95 w/55g cams.  The needle really jumped around alot at ideal.  I don't believe these vtwins run much vacume at ideal, or least mine didn't w/55 cams. I think a vacume tank would dappen the action on the gauge.  Let us know what you find.   Larry

You need to add an orifice in the hose to filter the data vacuum pulses.. IIRC I used about an 0.030 inch jet.. Add it near the manifold not the gauge.. The gauge will be off a couple lbs since the DDT measures vacuum somewhere on the intake stoke and the gauge is only giving you an average.. Max
 

I was thinking of using a pneumatic line restrict that we use  to delay the actuators progress to slow the opening and closing of valves and dampers.So wouldn't that also affect the time that the gage moves. Messing with the tack = vac at that point depending on length of the hose?

Still riding looks like this is gonna have to wait I got a 3000 mile deficit to make up.LOL