If you were running 87 octane in your DS to advance the timing did you find that when you went with an aftermarket CDI you had to go back to 91 octane. Would this be true if you were running a Procom CDI that seems to add to much advance to early in the rpms? Would the 91 octane help? Not that I think the advance is the same for White Brothers and Big Gun CDI's but what about them? I am wondering if twenty cents more for 91 octane is a little insurance against kick back on these units or am I all wet in my thinking. Just a thought and I would like to get your imput. Thanks

 

Hey 400EXerciser,

I was kind of thinking the same thing... as I run 91 octain Union 76 gas all the time and have had vary little if any problmes (knock on wood) with my Procom CDI unit.
I am wondering if the combination of 87 octane and the CDI from Procomm may be a bit to much for the timeing ?

ILIVSD

 

I don't believe that a CDI box makes a big enough change in timing to worry about chaing octane. At least when I tested that theory with my Vortex I saw no change.

 

Has long as your total timing is 26 degree's and you have stock compression, 87 is fine.
If you raise your compression or advance your total timing above 26, then run 91.

 

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Thanks, makes sense. Its the total advance that can cause the problems. The CDI only advances the timing on bottom and mid I guess, leaving total advance at factory specs? I know that in my rail I took and advanced the timeing on the distibutor on the bottom but then modified the distibutor so I would not get more than a total of 32 degrees total. This gave me more bottom end yet did not go past the spec sheet for total timeing on the cam and compression I run(no spark knock). I guess the aftermarket CDI does the same.