17 replies to this topic

[germini30]

Anyone know what kpa you should have in the inlet manifold at idle.

[mini13]

Depends a lot on the cam, but 40-55 kpa probably covers it

[germini30]

I have an mg metro cam and mine is sticking at 34kpa

[paul748]

This is so weird!

I have just replied to exactly the same question on another (MINI) forum, but for the R53 cooper S.

I know it's not relevant but it's the same …..42 kpa.

[germini30]

Mine is 34 kpa. What does that mean

[Spider]

Just to be clear, is this Manifold Vacuum?

[germini30]

Yes

[Spider]

Yes

 

OK cheers.

So in numbers I can understand, that's just a whisker over 10" mg Vacuum.

 

Where are you measuring this at? Direct off the Manifold or from a Port on the Carb?

[germini30]

This is what my megajolt is saying the kpa is at the inlet manifold

[Spider]

This is what my megajolt is saying the kpa is at the inlet manifold

 

Is it calibrated to measure absolute pressure or pressure from atmospheric pressure?

 

Also, have you check it with a separate known gauge?

[germini30]

I have no idea sorry. It has a vacuum pipe from the unit itself to the inlet manifold.

[mini13]

34 is lower than I would have thought, but not out of the realms of possibility, certainly I have heard of high CR short cammed engine that pull similar,

Just to clarify. 0 kpa is an absolute vacuum, 101.3 kpa is atmospheric pressure at sea-level,

[RooBoonix]

Usual vacuum at idle on an SPI is around 30kpa I believe and I normally get between 30 and 34kpa measured by my ECU.

Just for reference.

Cam.

[germini30]

Thanks so I am about right

[mini13]

Yep, bigger cams with more overlap will make less vacuum (higher kpa) on full race stuff with itbs I've heard of idle figures in the 60s-70s,

A method of tuning idle advance is to tune it for the lowest kpa, but it sounds like your right in the ballpark anyway.