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Anyone Fitted A Vacuum Guage?


02GF74
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Has anyone fitted a vacuum guage to their inlet manifold and is using twin K&Ns? (referring to v8) 'coz I',m just wondering what vacuum you are getting at idle.

The info. I have is that at idle the vacuum should be 17-22 (ins Hg?) but I'm seeing just over 10 and wondering if it it the K&Ns that are making it breathe easier so less depression in the manifold. :huh:

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If they do electric vacuum gauges you could have one gauge, two senders, and a switch.

err, I do not wnat to fit more guages :o but wondering if having K&Ns, being less obstructive to air flow, is reducing the depression my guage is showing.

I will eventually wrap up the filtlers with cardboard to restrictthem and see what effect that has, just not gotten around to it.

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The vacuum guage measures pressure in the manifold, after the carbs as the air flows through the engine. The depression is caused by the pistons drawing air into the cylinders from the manifold, the air is restricted by the butterflys (or "throttles") in the carbs and so there is a depression in the manifold ie., lower than atmospheric pressure. Unless you are running almost completely blocked or unusualy small air filters then they should make little or no difference to the depression in the inlet - certainly at tickover.

Assuming that there is no problem with the engine and that the carbs are set-up correctly (ie. balanced) then the vacuum in either side of the manifold should be the same, eliminating the need for seperate gueages.

Chris

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cheers Chris, so I need to rule out engine probs and air leaks. (will need to do cyclinder compression test ).

For air leaks, can I fit two solid plates to the carbs to block them off, one with a hole connected to an air line and blow air into the intake system? So it will make air leaks easier to trace? (can't see why this should cause any problems as this would be in pricniple like super or turbocharging - engine not running so easier to hear anyu hissing?)

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Has anyone fitted a vacuum guage to their inlet manifold and is using twin K&Ns?  (referring to v8) 'coz I',m just wondering what vacuum you are getting at idle.

The info. I have is that at idle the vacuum should be 17-22 (ins Hg?) but I'm seeing just over 10 and wondering if it it the K&Ns that are making it breathe easier so less depression in the manifold.  :huh:

You are correct on the idle reading........... 10 may indicate a timing problem but in any event this link tells all

http://www.centuryperformance.com/vacuum.asp

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