Hey guys, 13B 4 port here, turbo. I have two MSD 6a boxes and just picked up a BTM unit for one of them. I know I have to retard the timing under boost to prevent detonation. Money is short so I could only afford the one BTM, which timing is the more important to retard for now, Leading or Trailing, or do I even need to retard both??

 

Retard both. Here's a scenario: If you are running 10 degrees of timing split between leading and trailing and you are running more than 10 psi of boost what is going to happen? The BTM is going to retard the timing at least 10 degrees (or more if you set it up that way). Now your leading/trailing split is 0 degrees. The car will still run OK but what happens if you run 11 pounds of boost? BOOM!!! Trailing fires before leading and goodbye to engine. Remember you'll be under boost at this point. If you put the BTM on trailing you are still firing the leading plug just as early but now the leading/trailing split will get much farther away from each other and you'll lose power with no real benefit towards detonation protection. Just back off your timing a few degrees on the crank angle sensor if you are running higher amounts of boost than normal or just keep the boost down. I don't know your setup so its hard to tell what is best.

 

good stuff