Most MSD distributors vacuum cans add about 15°, regardless of what they tell you in the phone.
I expect you would be fine at light throttle with 47° advance. You are probably getting quite a bit more. However, when you start to accelerate and the throttles open, the manifold vacuum should drop, decreasing the advance added buy the VA system. The problem with the cobra is that with such a powerful engine in a light car you don't have to open the throttle much to get light acceleration so the VA system doesn't drop out and you start to detonate.
Make sure you disconnect (in your brain) the amount of vacuum provided from when it is applied. The springs control WHEN the mechanical advance occurs. The bushing controls (limits) how MUCH advance occurs. You can still have it all in at 2500, but only get 18 degrees by changing to the black bushing. Leave the springs alone to keep the curve (the when) the same.
The two light springs are ok if your idle is less than 800. If your idle is over 800 you can start to get some MA at idle. I ran one light silver and one blue spring. That way the advance didn't start until 1200 but was still all in by 2800 (numbers from memory and are close but maybe not exact). If your idle timing fluctuates, try switching one spring to the light blue one.
Quote:
Originally Posted by cycleguy55
The curious part is why the VA and the same timing settings worked fine with the analog box, but not with the digital box.
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I agree. However, as Gaz64 mentioned, it has been noted there are significant differences between the analog and digital systems