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09-03-2012, 12:12 AM | #1 |
Member
Join Date: Oct 2011
Location: Chattanooga, Tn
Posts: 73
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Ported or Manifold vacuum
As you guys can see by my join date I do more lurking than talking. I modified a Chevy distributor 6 or 7 years ago and have always run ported vacuum from 390 Holly. The engine is a fairly well built '51 Merc with Crower Cam, 1.6 in chevy valves, heads, headers etc. Is this correct or should I be running manifold vacuum? I have tried to research the issue but find both opinions. I see Bubba recommends no vacuum and do not doubt his opinion but since mine is set up for vacuum I would like to be sure it is set up for best performance. Thanks for putting up with the newby
John L. |
09-03-2012, 12:51 AM | #2 | |
Senior Member
Join Date: Dec 2010
Posts: 696
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Re: Ported or Manifold vacuum
Quote:
Set your maximum mechanical advance at 20°, then adjust your vacuum canister (assuming it it adjustable) to add 8° in high-vacuum regimes like cruise and idle. You'll cruise at 28° which will make your engine happy, but the instant you go to WOT (Wide Open Throttle) the vacuum drops out and you're back to 20°, which is ideal for WOT. The higher advance at idle will let your engine idle cooler, too. Works very well that way. |
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09-03-2012, 07:53 AM | #3 | |
Member
Join Date: Oct 2011
Location: Chattanooga, Tn
Posts: 73
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Re: Ported or Manifold vacuum
Quote:
I am driving to the Shades of the Past this weekend and will change it to manifold vacuum. I have total advance set between 26 and 28 degrees already. |
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09-03-2012, 11:41 AM | #4 |
Senior Member
Join Date: May 2010
Location: Chester Vt
Posts: 8,913
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Re: Ported or Manifold vacuum
What roller cam are you useing??
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09-03-2012, 01:27 PM | #5 |
Member
Join Date: Oct 2011
Location: Chattanooga, Tn
Posts: 73
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Re: Ported or Manifold vacuum
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John L
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