Technical Tips > Engines - Carbies - Exhausts - Dissys
MSD dizzy mech. advance timing
Vettech:
Ok - sorry but I cant send pics. But!.
The HEI springs look identical.
The centre lobe #406 and two outer lobes #139 look non adjustable.
I would imagine they are changed as a set for differing engine needs.
They are held in place by the springs and tinsy circlips on the centre lobe.
The vaccumm advance which for some absolutely unknown reason people rip off, comes into play only when back throttling, ie foot off accelorator.
This changes the advance, and stops back firing, which could result in engine component failure..
As far as changing these bits I cant comment, I've always found std 350 has enough grunt for me.
My 78 runs great on an older std Kettering (points) style dizzy, put the original HEI in, gets me half way to W'pk then stops. That nite Tests ok, put it back all ok drive to work next day and stops in the same stop. Changed everything, but now realise maybe the Hall Effect pickup is the only thing original.
When the 78 runs I'll try again.
rosco:
It sounds like you have the heavy springs on it which is what they set them at from the factory. Just change them to the 2 light weight springs this will bring it down so that you should be all in at 3,500.
If it's a good 383 set initial at around 18 to 20 or where your vacuum level is best.
I don't want to get into a timing tuning report here.
But changing to the two light weight springs will get you on the right track
Regards Rosco
RHD.68.l89:
the stock points dizzy has a pin through the plate in the advance mechanism. put a sleeve/tube over the pin and the amount of advance is reduced. Lars recommends a total advance of 36 and all in by 3-3,500 (measured with vac advance disconnected) for best performance with small and Big blocks.
bfit:
--- Quote from: RHD.68.l89 on May 06, 2018, 07:47:12 AM ---the stock points dizzy has a pin through the plate in the advance mechanism. put a sleeve/tube over the pin and the amount of advance is reduced. Lars recommends a total advance of 36 and all in by 3-3,500 (measured with vac advance disconnected) for best performance with small and Big blocks.
--- End quote ---
The amount of advance that an engine we operate with is among other thing directly related to the fuel quality you use, the better the octane rating the more advance that the engine will tolerate , a little lead helps as well , avgas if you have the compressor ratio to utilise it, make good HP
RHD.68.l89:
for pump gas and streetable compression ratios Lars' rule of thumb works very well.
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