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i used this set up before. i found that the compexity was greatly reduced by completely defeating the stock retard in all situations. if you leave it in, even for low boost, you still get the timing dump at 3-5 psi causing a flat spot, which you have to compensate with by adjusting the btm. if you take it out and rely solely on the btm, the timing transition is smooth.
also, in dialing it in, do not rely on other's info. i got the greatest results, and learned the most, by using the btm to first duplicate the stock timing curve. meaning, using the stock actuator, set initial timing to 16 dbtdc. then hook up a hand pump to the actuator and pump up 1 psi at a time. check timing with timing light at each psi and plot a point. you will see that with the stock set up, you will start around 16 dbtdc initial and around 3-5 psi you will be at/around 11-11.5 dbtdc. next, defeat the stock retard and then hook up the btm. set initial timing to 16 btdc. hook pump up to btm and pump to max boost you are running (assume 12 psi for stock). so with hand pump set to 12 psi, check timing, it may read anything depending on where your btm gain is set. next dial in the gain on the btm to give you 11-11.5 dbtdc at your 12 psi. this means that at max boost, your timing will be the same as with the stock system. the btm gives a linear timing retard with each psi of boost. you will get more power in the bottom end because the timing will be more advanced throughout the boost range. then you can begin to tinker with the settings for initial timing while dialing in max retard at max boost for best results. this will allow you to run more initial advance and get more bottom end power.
the only draw back you may encounter is apc kickback before you hit your max boost. meaning, with the stock system (i'll pick a random point) say at 9 psi, the timing is already maxed out (since it hit 11-11.5 dbtdc at 5 psi). however, with the btm, you are not hitting max retard until your max boost. therefore, the timing may be too advanced at 9 psi and you may get predet and subsequent kickback of the apc. if this occurs, you will need to dial in the btm to give you just enough retard to get you past any hold up points in the curve. this means increasing retard. however, as may guess, this will result in even more timing retard at your max boost point, as the btm climbs linearly with boost, and therefore less power. this is where a pressure regulator comes in. following our previous example, say at 9 psi, you need timing to be around 12 dbtdc to prevent predet. therefore you adjust the btm to be at 12 dbtdc at 9 psi. now at 12 psi, your timing is more like 9.5-10 dbtdc. therefore you are losing power. this is when you first determine, with your new setting to get you past the hold up point (9 psi), at what pressure you get your max retard. for the sake of argument it lands on 11 psi. so at 11 psi your timing is at 11.5 dbtdc, but when boost climbs to 12 psi (your max setting) timing will be too retarded. this is when you add the pressure regulating valve and set it to 11 psi. so, when your boost climbs, you have enough timing retard to get you past 9 psi, and when 11 psi is hit, you reach your max timing retard, but the btm will never know you have hit 12 psi, because it only "sees" 11 psi. make sense?
sorry for the length. i spent quite a bit of time with this trying other people's suggestions, when in fact, you just need to look at max and min points for boost and timing and set the gain accordingly. i found that i was chasing my tail until i finally went through it in painful detail. keep in mind the numbers offered above are for example only, they should in no way equate to your actual settings unless by coincidence. hope this helps.
posted by 4.65.31...
, Mon, 15 Jul 2002 09:04:16
, Sun, 14 Jul 2002 13:04:20, Mon, 15 Jul 2002 00:00:23
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