Low MAP Values

[Don D]

What would one consider to be the issue if the MAP values on a 10.5/1 95" motor with a Woods 6H hit 80 and then at high rpm dropped back to 72? Power is about on par torque a little low. I have my own ideas but I would like to hear from some SMEs

[eddfive]

Not sure I qualify as an SME?? but when I see this on the dyno it is usually a bad MAP sensor or air box restriction of some kind.  Have you checked the MAP sensor hole where it plugs in to TB for a restriction or blockage?  What kind of air box is on this bike?  I am suprised it only gets to 80kpa, something is blocking the hole or the MAP sensor is bad.  Just my $.02 cents worth.

[Don D]

Have you seen bad MAP sensors?
I am very curious with this build, the owner has tried many different parts including cams and heads and tunes and the results stay the same like it hits a brick wall.

[05FLHTC]

Don,

Brain at Valley Racing spotted a similar slight loss in manifold vacuum looking at my DTT data dumps on my build...

I'm not an expert by any stretch of the imagination, but I'll throw out my swag, could the slight loss of manifold pressure at WOT be attributed to my big ole S&S G carb & my motors ability to maintain velocity at WOT for extended period of time?  We adjusted my timing table to account for the MAP loss, at least it's not also pulling timing for the map pressure change at WOT.

I'm all ears! 

[eddfive]

I have had a couple of bad MAP sensors, they were cracked at the interface where they plug into the Throttle Body.  Just a thought.

[Steve Cole]

The MAP sensor is easy to check. Just key up the bike and do not start. Then test the value being report. It should be the same as the Baro for the area that you are located in. If it is then its OK and you've got a restriction happening.

[Don D]

Thanks Steve
Looks like sea level would be 100 KPa or close to it.
Can this be checked by voltmeter against the reference voltage, 5V isn't it? The bike owner has no SERT or TTS.

It is one of those things that gets a lot of jarring if the tech is not careful when tightening the intake bolts. Never thought about a crack sure that could happen, you betcha.

[notarheli]

Additional info.  Condition remained virtually the same with air cleaner off and on.  A/C is SE with zippers high flow filter.  Stock TB.