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1500 Intake Vaccuum

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Morris

Morris

Yoda
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Can anyone relate to me the intake vaccuum charateristics of a healthy 1500 engine?

What is a healthy idle vaccuum? How much, if any, needle wiggle is tolerable?

Thanks,

morris
 
I can't offer information specific to the 1500, however, a lot of things can change the readings and how the reading behaves. Assuming your car is "stock" and that you haven't put in a performance cam you can look at the following pages for the general idea:
https://www.centuryperformance.com/vacuum.asp
https://www.free-ed.net/sweethaven/MechTech/Automotive/Automotive02/lessonMain.asp?iNum=01030305

As soon as you change cam or make exceptional changes to the head or carb(s) these figures change because the engine breathes differently.

In general on a stock engine I like to tune for the highest vacuum I can at idle. If I'm lucky and things are in good order this is around 20" of mercury. Fluctuations will be more noticeable if you set your idle speed below 1000 RPM. When idling near 1000 I see the value drift slowly within a window of +/- 1 or 2 inches. These figures are for my Mini with a 1275 but I've seen similar on other non-British cars I work on.
 
My 1500 is less than healthy but I have never been able to get more than 15 inches or so at idle. I know I have worn rings but have sorted out most everything else. I feel like I will be able to get 18 to 19 with it once I finish the motor rebuild.
JC
 
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