Ignition timing not correct

[ClausB]

Hi guys,

today I tried to adjust the ignition timing on my Chim 450. I wanted to adjust it to 8°BTDC at idle and 32° BTDC at 4000rpm, but that wasn't possible:

8° at idle ==> 26° at 4000rpm
32° at 4000rpm ==> 16° at idle

What am I doing wrong? Any guesses?

Thanks,

Claus

[Ozstyle]

Hi,

the distributor only has 16 degrees of mechanical advance.
So if trying to achieve, for example, 28 degrees at 4000 rpm then idle will be 12 degrees BTDC. If setting idle at 8 degrees BTDC then you will get 24 degrees max mechanical advance.

Oz

[ClausB]

Hi Oz,

thanks for your reply. So when I set the timing to 28° BTDC at full mechanical advance, it will be around 12° BTDC at idle, exactly what Rob wrote at the second to last post in this thread:
http://www.pistonheads.com/gassing/topic.asp?h=0&a...

BUT: What about the 8° BTDC at idle, which is the value I always read about? Just ignore it?

Claus

[Sardonicus]

Just set the total advance at 4k more advance on idle causes smoother running anyway, and you still wont have enough idle adv with a dizzy

[Ozstyle]

TVR usually specified ignition timing at max mechanical advance for a given rpm, thus 28 degrees BTDC @ 4000 rpm being a typical example.
Whereas the majority of car companies just specify ignition timing at idle.
Ignore the 8 degrees BTDC at idle, this might be OK for a Range Rover but not if you want the optimum performance for your TVR.
Oz