Timing advance confusion

[nomuken]

Hi,

so I'm a bit confused at what advance I should set my L24.

My manual state 10° BTDC for engines with antipollution systems and 18° for engines without antipollution systems.

My engine is a L24 wich initially was with antipollution but the previous owner removed all that crap. Engine has roundtop carbs, headers,... No airpump, no EGR nor fuel reservoir recuperation...

 

So what timing advance should I adjust my dizzy at? 10° or 18°??

[240260280z]

Try to set max ~ 36-38 and idle ~15-18

[Zed Head]

Hi,

so I'm a bit confused at what advance I should set my L24.

My manual state 10° BTDC for engines with antipollution systems and 18° for engines without antipollution systems.

My engine is a L24 wich initially was with antipollution but the previous owner removed all that crap. Engine has roundtop carbs, headers,... No airpump, no EGR nor fuel reservoir recuperation...

 

So what timing advance should I adjust my dizzy at? 10° or 18°??

The first thing you should do is to stop thinking in terms like "all that crap".  Better to understand what the parts do and how they work so that when they're gone you'll also understand why the engine runs differently.

 

The factory timing specs. were set to meet emissions standards.  Since you're not worried about that any more just set the timing to where the engine runs the way you like it to run.  The specification is irrelevant now.  You're on your own.

[nomuken]

I do know what "that crap" actually does. No worries.

What I don't know is if the "antipollution" version has different camshafts or compression compared to the other engines.

Because after all it's mainly compression, camshafts and fuel wich affect ignition timing.

 

And I don't want to use the advance to max till pinging and then back off a bit.
I set it to 15° at idle for now (was 5°BTDC before), runs much nicer and easier up in the rev range now.

[240260280z]

If it is too advanced at higher rpms you will loose power and it may ping.

 

Remember that rotating the distributor changes both the idle advance and the max advance the same amount.

[djwarner]

Sometimes people are confused by the methods used in setting the timing. The factory manual set the timing with a light bulb and manually turning the crank of a stopped engine. Then adjusting the timing until the points just open. Dual point distributors repeat the process for the second set of points after disconnecting the first set of points. Adjustment of the second set is done internally with the distributor body locked down.

 

These distributor have centrifugal advance active at idle speeds and change the timing spec when using a timing light. This is why the Blue's 15-18 degree setting is correct. This is without any vacuum advance.

 

Blue's 36-38 degree number is with max centrifugal and vacuum advances.

 

Various distributors were used by Datsun over time. These had different advance schedules for centrifugal and vacuum and sometimes static timing. The Haynes Manual gives the specifications for each version as well as idle timings without vacuum.

 

You don't tell us which year/model/transmission you have, so we can't help much more. It would also help if you could verify the model number of the distributor as many owners have upgraded to electronic units from 280's.

Edited October 13, 2015 by djwarner