Started looking at the readings off Megajolt toady and got a little confused by the MAP values.

Could some one explain what I should expect to see and how it will change when the engine is revved but car is stationary.

Hope to do some runs out in the car next weekend and start to develop a map – But first have to get my head round the MAP readings

Paul

Been doing exactly the same myself today, at tickover was seeing 50 Kpa, 1.8 Zetec, ZZR1100 Carbs, MJLJ V3. This reading agreed with the balancing gauges, revving the engine to 3K saw a drop to about 15, then it recovered to 35-40 at a steady 3K.

I had 34 KPa at idle and dropping down to 19KPa when revved.

I just wondered how this will change when the car is moving ( under real load )

Paul

In an inlet manifold with the engine off you will have normal atmospheric pressure.

When the engine starts and idles you will have a negative reading (lower than atmospheric pressure) for the inlet manifold engine side of the butterfly.

You will get the greatest manifold depression when the throttle is closed and the engine is on over run slowing the vehicle down.

Unfortunately I cannot remember any of the specific values.

You need to log the car to determin the most used range then build the MAP scale against this.

I have throttle bodies on my blade engine but the priciple carriers across.

For WOT you will always have a high map value 95 - 100, on the overun low but its in between that counts.
Rescued attachment Blade MAP.JPG

So I built a VE table around the most used values.

With a V8 with a shared manifold your readings will be a lot more spread out than you get on throttle bodies as above.

[Edited on 23/11/08 by mark chandler]
Rescued attachment ve_table.JPG

This doesnt sound quite right, when the throttle is opened it should increase the map reading.I would expect to see 34 kpa idle, between 50 and a 100kpa under load and 20kpa or less on the overun.
Paul.

quote:

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Originally posted by Paul (Notts)
I had 34 KPa at idle and dropping down to 19KPa when revved.

I just wondered how this will change when the car is moving ( under real load )

Paul

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