distributor question

[newaccorddriver]

i was just wondering, if we use vacuum advance distributors on our cars, what happens when it see's boost?

[89T]

it doesnt advance the timming.

[newaccorddriver]

if it doesnt advance the timing, then what does it do?

[white ricer]

our distributor isnt computer controlled (hence vaccum advance) so it never "see's" boost yo

[buds302]

yea but boost pushes air through the vaccum system. it works the other way. but yea it wont advance the timing for you. but if you run boost you wil figure a way out to advance it.

[bobafett]

flatblackdime and zufer had thrown around ideas of a 'boost retard' distributor as opposed to a vac advance... they seem to think that by changning the springs and messing with it a bit, they could get a 'boost retard' function out of it.


not sure if this has really been pursued though...

[A20A1]

the one to the right is a universal metal distributor diaphragm welded / JB Welded to the distributor body.


Some vacuum advance bodies allow you to open them, that would allow you to adust the spring and swap it to the other side of the diaphragm to make it ready for boost.

if not
the one on the right with a washer welded to the arm/linkage will allow you to place the spring outside the distributor body so it doesn't interfere with the internal mechanism. Thats why I have the second red arrow pointing to that area.

Also with a longer rod you can add in adjustable spring stops to set the tension on the spring or possibly replace a section of the rod with a threaded bolt and then use nuts to adjust spring tension.

[white ricer]

^werd^ old turbo volvos came with mechanical dizzy's, has anyone figured out how those work?

[A20A1]

Some cool info on boost and ignition timing
http://www.fefcholden.org.au/techinf...e/norman5.html

[89T]

if it doesnt advance the timing, then what does it do?

under boost the dizzy stay's at base timing.
while not in boost the dizzy reacts normal, advancing timing.
easier starts ect.
the reason for retarding timming under boost is to control detenation.

i have heard that some of the 0bd0 crx guy's retard the dizzy by like 4 deg. to run boost without a boost timing master. I wouldent chance it but it has worked for them.(on a vacume advance system)

[A20A1]

^werd^ old turbo volvos came with mechanical dizzy's, has anyone figured out how those work?

There is a Turbo MG with a vacuum advance distributor... not sure if it was boost retarded as well or not.

[newaccorddriver]

under boost the dizzy stay's at base timing.
while not in boost the dizzy reacts normal, advancing timing.
easier starts ect.
the reason for retarding timming under boost is to control detenation.
i have heard that some of the 0bd0 crx guy's retard the dizzy by like 4 deg. to run boost without a boost timing master. I wouldent chance it but it has worked for them.(on a vacume advance system)

if i buy something like an boost timing master, itll automatically retard the timing based on how much boost there is?

[89T]

yup! it will retard timming upto 3 deg's per # of boost.

[newaccorddriver]

yup! it will retard timming upto 3 deg's per # of boost.

im not completely sure i know how the boost timing thing works. does it control the igniter and tells it when to fire the plug?(excuse my stupidness, im into stock related, not aftermarket parts...)

[89T]

while wiring the btm you remove the wires from the coil, tie them into the btm. then there are two wires that tie back into the coil compleating the circut.
you'r dizzy is now telling the btm when to fire the plug, but the btm is measuring boost via vacume line to delay the firing of the plug. A short answer would be: It delays the firing of the coil.

On the btm you also have a dial to adjust how much timming the btm will pull.

[newaccorddriver]

while wiring the btm you remove the wires from the coil, tie them into the btm. then there are two wires that tie back into the coil compleating the circut.
you'r ecu is now telling the btm when to fire the plug, but the btm is measuring boost via vacume line to delay the firing of the plug. A short answer would be: It delays the firing of the coil.
On the btm you also have a dial to adjust how much timming the btm will pull.

thanks for clearing it up for me . one more question though, you say that the ECU is telling the BTM when to fire the plug, but you also say the BTM is measuring boost through a vacuum line. how does our ECU tell it when to fire? i always thought our distributors were vaccum advanced and such.

[89T]

cough edit cough...