Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Power valves. Some say half your manifold vacuum, some say 2 hg below. Who is right?
View Single Post
  #3 (permalink)  
Old 11-20-2012, 10:18 AM
cdminter59 cdminter59 is offline
Registered User
Last photo:
Join Date: Jan 2011
Location: Hopewell, Va
Age: 65
Posts: 1,684
Wiki Edits: 0

Thanks: 1
Thanked 192 Times in 179 Posts
Originally Posted by Zerocyde View Post
Half the people I talk too say you cut your idle manifold vacuum in half, and round down to the nearest .5, so with 10hg you want a 4.5pv, etc. The other half of the people I talk to say you want 2 hg below your idle manifold vacuum, so with 10hg you would want a 7.5pv.

Who is correct, and why?
If you use example #2 what if your engine vacuum is 15 hg at idle and you -2 hg the largest PV number you can get is 10.5PV Everytime your engine vacuum drops below 10.5 the power valve opens feeding more fuel. If driving in a hilly countryside and the vacuum stays at 8.5 cruising this would be rough on gas mileage. If using example #1 with the same engine vacuum and 15 hg*2 = 7.5PV. If driving in the same conditions the PV never opens until 7.5 hg so you have a lean condition which could cause severe complications.
Reply With Quote