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07-16-2018, 04:46 PM | #1 |
Member
Join Date: May 2010
Posts: 62
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Engine Vaccum readings
What vacuum should a good Model A engine pull at say 40 miles per hour.
At Idle my engine pulls a steady 18. At 35 - 40 it drops to above 10. |
07-16-2018, 04:56 PM | #2 |
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Join Date: Feb 2015
Location: Lone Jack Missouri
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Re: Engine Vaccum readings
Man pulls 20 in at Idle and the same at 40 miles per hour steady speed
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07-16-2018, 05:13 PM | #3 |
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Join Date: May 2010
Posts: 62
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Re: Engine Vaccum readings
Could this indicate a muffler restriction?
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07-16-2018, 06:38 PM | #4 |
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Join Date: May 2010
Location: on the Littlefield
Posts: 6,159
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Re: Engine Vaccum readings
were is the spark advance ---too retarded and vacuum will be low
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07-16-2018, 10:48 PM | #5 |
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Join Date: May 2010
Posts: 62
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Re: Engine Vaccum readings
spark is fully advanced.
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07-17-2018, 09:13 AM | #6 |
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Location: SW Idaho
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Re: Engine Vaccum readings
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07-17-2018, 11:25 AM | #7 |
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Join Date: Nov 2017
Location: Terre Haute, Indiana
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Re: Engine Vaccum readings
Look at these
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07-17-2018, 02:59 PM | #8 |
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Join Date: Aug 2011
Location: Battle Ground WA
Posts: 293
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Re: Engine Vaccum readings
Depends on several items, but mostly it is power output vs wind resistance. At around 40 mph, out are getting close to using most of your power just to push the car through the air. If you have some modifications that allow more power to be generated than the stock 40hp, then you would expect less vacuum loss at that speed. However, on Elvira, my mostly stock, but high compression head, model A, the vacuum drops off pretty quickly between 40mph and 50mph (and above). I made several measurements when installing the Honda vacuum advance distributor, and I was at 10 inches of vacuum at about 43-45mph. I was down to 6 inches, where the vacuum advance drops out on the Honda Distributor at around 50mph.
It all depends on how far your foot is into the carburator, which is based upon how much power your engine puts out, vs what the resistance to vehicle motion is. For a totally stock engine in no wind conditions, 10 inches at 40mph is not too far off based on my measurements.
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