Dizzy mods. Changing the advance curve.
fzsk4p
Senior Jeeper
First off I am going to say that I am not familiar with how the dizzy`s are set up on emission regulated engines.
Sometimes I see folks making a reference to an ignition module. If this module is the same as the ignition module inside an HEI then we are good to go. If it is a stand alone then I am not sure.
I try to never post things that cannot be backed up with facts. So if I do not know I will admit so.
Carrying on..........
From Ignition timing - Wikipedia, the free encyclopedia
Mechanical timing advance
Distributor weights
An increasing mechanical advancement of the timing takes place with increasing engine speed. This is possible by using the law of inertia. Weights and springs inside the distributor rotate and affect the timing advance according to engine speed by altering the angular position of the timing sensor shaft with respect to the actual engine position. This type of timing advance is also referred to as centrifugal timing advance. The amount of mechanical advance is dependent solely on the speed at which the distributor is rotating.
Lighter weights or heavier springs can be used to reduce the timing advance at lower engine RPMs. Heavier weights or lighter springs can be used to advance the timing at lower engine RPMs. Usually, at some point in the engine's RPM range, these weights contact their travel limits, and the amount of centrifugal ignition advance is then fixed above that rpm.
The I6 engines suffer from a very slow mechanical advance. Kits from places like Summit.
Distributor Advance Kits - Ignitions & Electrical - SummitRacing.com
Offer weights and springs of different tensions. Plus some kits have a bushing that limits total mechanical advance.
By experimenting with springs/weights you can quicken up the advance curve and really make the I6 come alive. In the FL 4.0`s in YJ`s we swap in a XJ ecm that does the same thing. Only by ECM control.
Throttle response, acceleration and mileage can be vastly improved with just a few springs and weights.
Another consideration is the adjustable vacuum advance. Say your vacuum can is advancing a little timing at idle. (not gonna get into the ported vs. manifold vacuum argument). You can adjust it so it won`t. Want to add a few degrees of timing at cruise speed ? Crank it in with the adjustment screw.
A few bucks for a kit, vacuum gauge and an afternoon could be time well spent.
This link is kinda crude but you can get the gist of things.
http://www.73-87.com/7387garage/drivetrain/hei.htm
This one is OK
http://www.highperformancepontiac.com/tech/vacuum_advance_tech/tuning_vacuum_curve.html
Sometimes I see folks making a reference to an ignition module. If this module is the same as the ignition module inside an HEI then we are good to go. If it is a stand alone then I am not sure.
I try to never post things that cannot be backed up with facts. So if I do not know I will admit so.
Carrying on..........
From Ignition timing - Wikipedia, the free encyclopedia
Mechanical timing advance
Distributor weights
An increasing mechanical advancement of the timing takes place with increasing engine speed. This is possible by using the law of inertia. Weights and springs inside the distributor rotate and affect the timing advance according to engine speed by altering the angular position of the timing sensor shaft with respect to the actual engine position. This type of timing advance is also referred to as centrifugal timing advance. The amount of mechanical advance is dependent solely on the speed at which the distributor is rotating.
Lighter weights or heavier springs can be used to reduce the timing advance at lower engine RPMs. Heavier weights or lighter springs can be used to advance the timing at lower engine RPMs. Usually, at some point in the engine's RPM range, these weights contact their travel limits, and the amount of centrifugal ignition advance is then fixed above that rpm.
The I6 engines suffer from a very slow mechanical advance. Kits from places like Summit.
Distributor Advance Kits - Ignitions & Electrical - SummitRacing.com
Offer weights and springs of different tensions. Plus some kits have a bushing that limits total mechanical advance.
By experimenting with springs/weights you can quicken up the advance curve and really make the I6 come alive. In the FL 4.0`s in YJ`s we swap in a XJ ecm that does the same thing. Only by ECM control.
Throttle response, acceleration and mileage can be vastly improved with just a few springs and weights.
Another consideration is the adjustable vacuum advance. Say your vacuum can is advancing a little timing at idle. (not gonna get into the ported vs. manifold vacuum argument). You can adjust it so it won`t. Want to add a few degrees of timing at cruise speed ? Crank it in with the adjustment screw.
A few bucks for a kit, vacuum gauge and an afternoon could be time well spent.
This link is kinda crude but you can get the gist of things.
http://www.73-87.com/7387garage/drivetrain/hei.htm
This one is OK
http://www.highperformancepontiac.com/tech/vacuum_advance_tech/tuning_vacuum_curve.html
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