02GF74 Posted September 15, 2005 Share Posted September 15, 2005 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. Quote Link to comment Share on other sites More sharing options...
fisha Posted September 15, 2005 Share Posted September 15, 2005 i was thinking that i'll need to start looking at the vacuum and the only way i could think of was to have 2 guages - one per carb. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted September 16, 2005 Share Posted September 16, 2005 If they do electric vacuum gauges you could have one gauge, two senders, and a switch. Quote Link to comment Share on other sites More sharing options...
02GF74 Posted September 20, 2005 Author Share Posted September 20, 2005 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 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. Quote Link to comment Share on other sites More sharing options...
fisha Posted September 20, 2005 Share Posted September 20, 2005 LOL - i too was going to duct tape over some of the filter as well! Quote Link to comment Share on other sites More sharing options...
GBMUD Posted September 20, 2005 Share Posted September 20, 2005 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 Quote Link to comment Share on other sites More sharing options...
02GF74 Posted September 20, 2005 Author Share Posted September 20, 2005 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?) Quote Link to comment Share on other sites More sharing options...
GBMUD Posted September 20, 2005 Share Posted September 20, 2005 You could pressurise the manifold but remember that you will loose air through potentialy leaking valves and piston rings. Remember that this is a system designed to operate under vacuum, not pressure so any leak may not show up. Chris Quote Link to comment Share on other sites More sharing options...
landi41 Posted September 20, 2005 Share Posted September 20, 2005 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. 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 Quote Link to comment Share on other sites More sharing options...
02GF74 Posted September 20, 2005 Author Share Posted September 20, 2005 You could pressurise the manifold but remember that you will loose air through potentialy leaking valves and piston rings. yep was aware of that; hopefully incoming airflow will exceed these leaks. Quote Link to comment Share on other sites More sharing options...
roguevogue Posted September 26, 2005 Share Posted September 26, 2005 Vacuum guage on ebay. Smiths, hard to find nowadays. Quote Link to comment Share on other sites More sharing options...
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