Topic: Vaccum vs Mechanical advance??????????????
in Forum: C3 Engines
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Another doozie from mk's78...................
Just had my distributor repaired and both the vacuum
and mechanical advances work. The mechanic has the
vaccum side capped off and said it is better to use the
mechanical side only.........Any comments regarding this???
My guess is that the original setup used both sides together.
Would be interested in knowing the straight "skinny".
mk's78
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Take a look at these articles...I'm not sure how to make a link so I'll just give you the web address, vetteclub.org/technicaltips/techfiles.html. I have found some very good info here. I'm a little worried about your mechanics advice. 
Lifetime MemberEquinunk, PA - USA
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Vette(s): 1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.
Mechanical works o.k. on constant speed, but you NEED the vaccume when you GET INTO IT. They BOTH have to work for the engine to reach top potential performance.
Lifetime MemberModerator
Duncanville, TX - USA
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#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
It really all depends on the main use of the car...if you're running down the 1/4 mile only, mechanical is fine. For anything else, the combo will work best for all around performance, fuel mileage, and emissions...
Joel Adams
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Same what Joel said,.... you want somewhere about 34 to 37 degrees total advance all in at about 2500-3000 rpm for a sb chevy, these numbers may vary + or - depending on what you have done to the motor like a cam, compression, etc, so you put you distributor in a distributor machine and you spin it to 2500-3000 and you get your total mechanical by mixing different weights an springs to achieve 24 to 27 "built in" mech adv. at 2500-3000, the total "built in" adv should not go higher than 24-27 number no matter how high the motor is spinning even if its turning 10,000rpm, now you take you dist. and drop it into the motor and set your initial static timing to 10 degrees BTC, now what you have is 10 degs. static adv. + 27degs."built in" adv.= 37degs. total mech. advance.....the Vacume adv's job is to aid in a smooth transision from off Idle to your total by adding adv. till the mech comes into play, which helps with better gas mileage and smoother operation, Vacumn dashpots are like weights and springs, some come in faster or slower depending what number they are or if they are adjustable, all this has to be thrown into the mixing pot called the distributor machine and operated by someone who knows what the 
he's doing along with a curve that looks like a rainbow.......go to... Performance Distributors
(Inserted clickable link)
Adams' Apple 2009-07-01 05:12:51
he's doing along with a curve that looks like a rainbow.......go to... Performance Distributors (Inserted clickable link)
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Oak Creek, WI - USA
Joined: 5/21/2008
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Vette(s): 1981 Great White Shark. Red Interior, 350/190 hp. PS, PB (SS), A/C CC, T-Tops. Served three years in Active Duty Army, then Retired Air Force after 34 years! Badger State Vettes Car Club. 175,000 Original miles!! Now own a 1998 C-5!
Sounds like some sound advise from those that know!! Its nice not to be in an information vaccum.
No pun intended.
Dan
in Forum: C3 Engines
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