390se Ignition Advance curve

[B-Reight]

I'm currently reading up on the issue of dizzy regraphing as both my centrifugal advance springs were a) loose on the spring posts b) had no springiness left.

Anyhoo it seems from reading around that what i'm aiming for is somewhere in the region of 10-14 degrees btdc at 1000rpm and 34 degrees total at anywhere between 3 & 4000 rpm.

I also have a photocopy of an old TVR datasheet which states;

Octane Rating - 98 ron
Ignition timing - 6' at 600rpm (vac hose off)
Centrifugal advance commences - 800 rpm
Centrifugal advance max - 28'/30' at 5000 rpm

all okay so far but what i have no clue about is what the advance curve should look like between these points (with vac advanced disconnected for measuring purposes, but i want to run with the vac advance connected). Linear? Curved? Anyone got an advance curve that has worked well for them that i could use as a starting point?

Edited by B-Reight on Tuesday 7th April 16:29

Edited by B-Reight on Tuesday 7th April 16:54

[ed_crouch]

The theory behind it is that for a given constant load, the spark wants to occur a constant number of milliseconds before TDC, in order to support peak cylinder pressure occuring about 20 degrees ATDC.

The reason you need to advance the ignition timing as engine speed increases is because the fuel mixture takes a constant TIME to burn fully. So if the engine's spinning faster, you need to ignite it earlier, i.e. more degrees BTDC (as RPM increases, the crankshaft rotates further in degrees per unit time).

[B-Reight]

bump

[TVRleigh_BBWR]

Looking at some Emerald Maps for TVR's most start at about 17 and go to about 38. they do go a bit higher and lower but this is mainly on strange loads. I think when I have my 400SE tuned for 4 star it was 7 deg on tick over. so you may want a bit more for 95.

The SD1 Emerald map does go as low as 5 deg. but not sure what fuel that was mapped for.

Sorry I cant help more the 400SE is still under wraps. else I'd check what mine does.