MSD ignition
3.0 BAR
Joined: Mar 2003
Posts: 4,217
Re:MSD ignition
a msd btm is a msd 6a ignition amplifier with a built timing controller that adjust timing for each pound of boost it sees, you controll the degrees of the retarded timing,with a control **** provided. I think it also have built rev limiter. they also have one that come separate from the ignition it just a timing control box, that you hook to the vacuum, and controlled the way as the btm.
0.0 BAR
Joined: Jan 2003
Posts: 24
Re:MSD ignition
Why you need to retard timing under boost:
Hard to imagine, but it takes time to burn a cylinder full of fuel and air. If you want the explosion to happen just as the piston travels past top dead center --so that it pushes the piston down just after maximum compression-- you need to fire the spark a little before (called timing advance). The faster the piston is traveling (higher RPM's) the sooner you need to fire the spark so that the explosion happens when you need it.
Your stock ECU takes care of this by knowing when the piston is at TDC and what RPM's your engine is at. It adjusts the spark timing accordingly.
The problem: compressed air/fuel burns faster than regular air/fuel. But your stock ECU doesn't know that you are running boost, so it keeps advancing the spark anyway.
THIS IS VERY BAD
If the spark fires while the piston is still on the upswing the full force of the explosion works AGAINST the piston finishing its stroke you not only loose power but put a TREMENDOUS strain on your Piston/Rod/Crank/Cylendar walls. Break/bend any of these parts and your engine is basically toast. 
(This premature ignition is ofter referred to as "knock" and results in an audible click or ping.)
The Boost Timing Module "tricks" the ECU into waiting before it fires the piston (called retarding timing). This ensures that the full force of the air/fuel explosion occurs after TDC.
Some people don't bother with a BTM. They manually retard the timing by physically rotating the distributor. This changes the ECU's point of reference. It still advances the same amount at the same RPM's, its just starting from later in the stroke. The problem is that this method sacrifices low/no boost performance and efficiency. Also, under some high boost situations the distributor cannot rotate enough to solve the problem.
Should you get a BTM? Well, this forum is called homemadeturbo not ifIhadamillionbucksturbo, so no one is going to fault you if you go ghetto. It depends on how safe and efficient a set up you want and what you can afford.
Hard to imagine, but it takes time to burn a cylinder full of fuel and air. If you want the explosion to happen just as the piston travels past top dead center --so that it pushes the piston down just after maximum compression-- you need to fire the spark a little before (called timing advance). The faster the piston is traveling (higher RPM's) the sooner you need to fire the spark so that the explosion happens when you need it.
Your stock ECU takes care of this by knowing when the piston is at TDC and what RPM's your engine is at. It adjusts the spark timing accordingly.
The problem: compressed air/fuel burns faster than regular air/fuel. But your stock ECU doesn't know that you are running boost, so it keeps advancing the spark anyway.
THIS IS VERY BAD
If the spark fires while the piston is still on the upswing the full force of the explosion works AGAINST the piston finishing its stroke you not only loose power but put a TREMENDOUS strain on your Piston/Rod/Crank/Cylendar walls. Break/bend any of these parts and your engine is basically toast. (This premature ignition is ofter referred to as "knock" and results in an audible click or ping.)The Boost Timing Module "tricks" the ECU into waiting before it fires the piston (called retarding timing). This ensures that the full force of the air/fuel explosion occurs after TDC.
Some people don't bother with a BTM. They manually retard the timing by physically rotating the distributor. This changes the ECU's point of reference. It still advances the same amount at the same RPM's, its just starting from later in the stroke. The problem is that this method sacrifices low/no boost performance and efficiency. Also, under some high boost situations the distributor cannot rotate enough to solve the problem.
Should you get a BTM? Well, this forum is called homemadeturbo not ifIhadamillionbucksturbo, so no one is going to fault you if you go ghetto. It depends on how safe and efficient a set up you want and what you can afford.
