vaccum advance
Thread Starter
|
Posting Guru
Joined: Jun 2004
Posts: 1,133
Likes: 3
From: Dracut, Massachusetts
vaccum advance
hi all,
i have a question about the vaccum advance. first and formost can someone explain what it does? and is it a neccessity? the reason i ask is in all the cataloges, the 400 has two different dizzys. one without v/a and one with. whats the difference? thanks for any help!
i have a question about the vaccum advance. first and formost can someone explain what it does? and is it a neccessity? the reason i ask is in all the cataloges, the 400 has two different dizzys. one without v/a and one with. whats the difference? thanks for any help!
Elder User
Joined: Jun 2003
Posts: 886
Likes: 1
From: Houston/Hope BC
Vacuum advance is for efficency. All distributors have some mechanical advance that should be curved vs RPM to give the engine the timing it wants to see (max HP). This varies on different engines and is primarily dependent on the style of the combustion chambers. 400's have an "open wedge type" which will like to see in the area of 34-36 degrees total mechanical (if memory serves me well). When the engine is operation at partial throttle (cruise) it can tolerate an additional 10-15 degrees of advance (45-50 degrees total) and this will get you 10-20% more mileage. Race engines are technically always operating at zero manifold vacuum and, therefore, don't need a vacuum advance. It is also something to go wrong on a race engine that could destroy it if it got stuck in the advance position. All modified engines should be recurved, typically to get the advance in earlier.
Thread
Thread Starter
Forum
Replies
Last Post
66flareside
FE & FT Big Block V8 (332, 352, 360, 390, 406, 410, 427, 428)
46
Oct 16, 2008 03:30 AM
Greg Schretter
1987 - 1996 F150 & Larger F-Series Trucks
1
Dec 20, 1999 09:37 PM
