Help appreciated please.
Holdens are rebuilding the distributor on a 318 cu in A series engine for me. The engine is in a Bristol 410, car is for normal street use. What should the mechanical advance settings be please? I can't find the info anywhere.
Thanks
Andrew
Distributor Advance
Moderator: Moderators
Re: Distributor Advance
You want 34 degrees total with whatever initial the engine wants, that usually falls in the 15 to 20 degree range with todays E5 fuel.
“This ain’t no party, this ain’t no disco, this ain’t no foolin’ around”
Re: Distributor Advance
Hi Andrew, there are lots and lots of threads on the forum about things such as Ignition timing.
However, in essence, you need to set the timing at full advance and set it to 34 Degrees, with any Distributor vacuum pipes disconnected and plug as appropriate.
Then check the initial timing. If it is an older Distributor this will not be adjustable without significant fettling / Welding up, and filing.
If it is of later construction there may be screws / Torx fittings that allow the top plate to be moved to change the relationship between Initial and full advance.
The other option is to fit a restrictor plate if the advance is excessive. Not a fan of these, my guess is that the gap will be too big and you will end up with about 34 degrees all in and about 14 degrees initial.
With modern fuels you want as much initial timing as possible for a leaner burn and to reduce overheating where possible.
However, in essence, you need to set the timing at full advance and set it to 34 Degrees, with any Distributor vacuum pipes disconnected and plug as appropriate.
Then check the initial timing. If it is an older Distributor this will not be adjustable without significant fettling / Welding up, and filing.
If it is of later construction there may be screws / Torx fittings that allow the top plate to be moved to change the relationship between Initial and full advance.
The other option is to fit a restrictor plate if the advance is excessive. Not a fan of these, my guess is that the gap will be too big and you will end up with about 34 degrees all in and about 14 degrees initial.
With modern fuels you want as much initial timing as possible for a leaner burn and to reduce overheating where possible.
Pete Wiseman; Cambridge.
Mopar by the grace of God
Mopar by the grace of God
Re: Distributor Advance
unless you can find a service manual for a car with the same motor i doubt it will be easy to get a advance curve graph for holdens to look at, and even if you did, it would be applicable for the equivelent of 4 or 5 star leaded petrol.... not the ethanol soup we have to use today.
as stated by blue and pete your best bet is more initial timing and limited total.. to take that into account.
few pitfalls that holden should be able to cater for.
the dizzy will probably have a standard spring and a long loop spring
standard spring lets advance come in fast up to a certain point when the long loop spring reaches the end of its loop and comes into action for the last 1-2000 rpm that it advances for i.e steep graph followed by a less steep graph.... once you have the total advance limited that long loop spring may become irrelevant, becasue the weights can't swing out far enough.
just add in a light spring with standrad loops instead.
if you plan to run vacuum advance and i think if it works, you should, (if the main focus is driving rather than racing definitly should given the cost of fuel) you may not need as much initial because the vacuum can will pull in a load of advance as soon as the throttle blades go past the ported vacuum port. especially with a standard cam in the motor.
more initial (which is a good thing) could potentially mean you now have too much vacuum advance which may or may not be hard to limit depending on which manufactuer made the vaccum advance can on your dizzy. some are adjustable via an allen key down the vacuum pipe and others are not. ask holden to check
when you get it back it will pay to go round and check cap, cap button, cap contacts, plugs, leads, and igntion power supply connections.
with a different curve you will be asking more or less of your igntion system at different rpm points
be a shame to be blameing the dizzy work when actually all it has highlighted is marginal spark power or grubby plugs or gapped too small.
just like the orginal advance curve the plug heat range specified in the manual for the car may no longer be appropriate for modern fuel blend
if using points igntion, a move to a "Hidden if necessary" electronic set up may make sense. (but beware of advertsing hyperbole or as i like to call it Bull.....)
loads of options some are just "eleiminate the points" upgrades, which are beneficial if its a dialy drive and you don't like setting or changeing the points, every 3 to 5 K miles, some actually provide more spark power...one focused on the latter is a much better investment.
buy once and never need to buy again....
i think in a poly 318 you have a nice semi hemi 1/3 of a sphear shaped combustion chamber traditionally they don't need as much total advance as a wedge or small heart shaped chamber, but static CR and your cam choice come into play here as well. if holden didn't ask maybe they already know.... but worth checking
in theory the 1957 1960 or 1966 service manuals here will cover a 318 A engine i.e a poly.
https://mymopar.com/service-manuals/
Dave
as stated by blue and pete your best bet is more initial timing and limited total.. to take that into account.
few pitfalls that holden should be able to cater for.
the dizzy will probably have a standard spring and a long loop spring
standard spring lets advance come in fast up to a certain point when the long loop spring reaches the end of its loop and comes into action for the last 1-2000 rpm that it advances for i.e steep graph followed by a less steep graph.... once you have the total advance limited that long loop spring may become irrelevant, becasue the weights can't swing out far enough.
just add in a light spring with standrad loops instead.
if you plan to run vacuum advance and i think if it works, you should, (if the main focus is driving rather than racing definitly should given the cost of fuel) you may not need as much initial because the vacuum can will pull in a load of advance as soon as the throttle blades go past the ported vacuum port. especially with a standard cam in the motor.
more initial (which is a good thing) could potentially mean you now have too much vacuum advance which may or may not be hard to limit depending on which manufactuer made the vaccum advance can on your dizzy. some are adjustable via an allen key down the vacuum pipe and others are not. ask holden to check
when you get it back it will pay to go round and check cap, cap button, cap contacts, plugs, leads, and igntion power supply connections.
with a different curve you will be asking more or less of your igntion system at different rpm points
be a shame to be blameing the dizzy work when actually all it has highlighted is marginal spark power or grubby plugs or gapped too small.
just like the orginal advance curve the plug heat range specified in the manual for the car may no longer be appropriate for modern fuel blend
if using points igntion, a move to a "Hidden if necessary" electronic set up may make sense. (but beware of advertsing hyperbole or as i like to call it Bull.....)
loads of options some are just "eleiminate the points" upgrades, which are beneficial if its a dialy drive and you don't like setting or changeing the points, every 3 to 5 K miles, some actually provide more spark power...one focused on the latter is a much better investment.
buy once and never need to buy again....
i think in a poly 318 you have a nice semi hemi 1/3 of a sphear shaped combustion chamber traditionally they don't need as much total advance as a wedge or small heart shaped chamber, but static CR and your cam choice come into play here as well. if holden didn't ask maybe they already know.... but worth checking
in theory the 1957 1960 or 1966 service manuals here will cover a 318 A engine i.e a poly.
https://mymopar.com/service-manuals/
Dave
The Greater Knapweed near the Mugwort by the Buckthorn tree is dying