Re: vacuum or mechanical advance
[Re: JohnRR]
#256554
03/17/09 02:42 PM
03/17/09 02:42 PM
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Joined: Dec 2003
Posts: 5,314 Carstairs, Alberta, Canada
dave571
master
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master
Joined: Dec 2003
Posts: 5,314
Carstairs, Alberta, Canada
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Quote:
You always have mech advance unless you LOCKOUT the dist. , Vac advance is for fuel economy under PART THROTTLE cruising conditions .
100% correct
A motor like that will need a custom curve on the mechanical to match the build. Cam, tire size, stall speed, weight, etc.. all play a part in the desired mechanical advance curve.
Vacuum advance is a feature for economy. Under hard throttle, performance should be unchanged, even on a mild build.
I curve deistributors on my sunn machine, and quite often will delete the vacuum. Usually on applications where the motor is radical enough the the mileage is not affected by not having it. Usually on these same apps, the initial value is so high, that adding vacuum at lower speeds gives it too much advance. Can creat a light throttle surge condition. Vacuum can also be a negative thing on a 4 gear car, as it comes up on the shifts, adding the possibility of theadvance plate sticking with too much advance etc..
Equally, on a milder build there is no reason not to run vacuum advance.
It only becomes a gray area in the middle
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Re: vacuum or mechanical advance
[Re: Mr.Yuck]
#256555
03/17/09 02:45 PM
03/17/09 02:45 PM
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Joined: Mar 2009
Posts: 1,169 Virginia Beach, VA
Old School
super stock
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super stock
Joined: Mar 2009
Posts: 1,169
Virginia Beach, VA
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on my my street cars with 500" motors,i use mech advance only. i tried to use vaccum adv.but it made the car surge and sputter at a steady throttle. when i unhooked it ,it went away.
Last edited by Old School; 03/17/09 02:47 PM.
68 cuda formula S 588" bb 5sp 70 CUDA CONVERT 500" 5SP (SUBLIME) 70 CUDA CONVERT 500" 5SP (PLUMCRAZY):TOO MUCH HORSEPOWER, IS ALMOST ENOUGH!
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Re: vacuum or mechanical advance
[Re: moretork03]
#256558
03/17/09 09:22 PM
03/17/09 09:22 PM
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Joined: Dec 2003
Posts: 5,314 Carstairs, Alberta, Canada
dave571
master
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master
Joined: Dec 2003
Posts: 5,314
Carstairs, Alberta, Canada
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Quote:
thanks for all the info guy's.I wanted to know which distributor to get and now I know.I bought the car from a car finder, not the builder who raced it in the 80's. The car had a crossover ignition with a computer and the guy did not know how to program it so he put a points dist so I could hear it run before I purchased it.I know its a radical build, i found time slips under the carpet running low 8's.I want to go with electronic ign.
Definately no vacuum advance on a car like that.
I doubt many 8 second cars run advance at all. More likely be a lockdown unit with a timing retard to start it.
If it has advance at all, it will be a really short curve.
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Re: vacuum or mechanical advance
[Re: dave571]
#256560
03/18/09 08:35 AM
03/18/09 08:35 AM
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Joined: Jan 2003
Posts: 24,562 Brookeville, Md
Mr.Yuck
Not enough dumb comments...yet
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Not enough dumb comments...yet
Joined: Jan 2003
Posts: 24,562
Brookeville, Md
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Quote:
Quote:
thanks for all the info guy's.I wanted to know which distributor to get and now I know.I bought the car from a car finder, not the builder who raced it in the 80's. The car had a crossover ignition with a computer and the guy did not know how to program it so he put a points dist so I could hear it run before I purchased it.I know its a radical build, i found time slips under the carpet running low 8's.I want to go with electronic ign.
Definately no vacuum advance on a car like that.
I doubt many 8 second cars run advance at all. More likely be a lockdown unit with a timing retard to start it.
If it has advance at all, it will be a really short curve.
yeah that, get a pro to set it up and lock it down.
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