Before getting started however, we'll briefly discuss the purpose behind the selection of the MSD BTM. Upon the venture past vaccume, we find a new term called Pounds Per Square Inch (PSI), or more commonly refered to as boost. This pressure starts to build as the turbo spools and foce induces mass amounts of air into the engine. While forcing more air into the combustion chambers, static compression starts to rise as the pressure increases. While increasing the pressure inside these combustion chambers, heat begins to build, and the engine becomes unstable. Having the ignition timing off just a bit can cause detonation and or pinging inside the chamber which in turn can produce holes on top of your pistons and or even blow a connection rod in half. In order to prevent such problems from destroying an expensive and timely engine replacement, an MSD BTM unit is used in sieres with the MSD 6AL to allow for safe and reliable ignition timing adjustabiblity while under pressue.
Knowing that we're going to be using the MSD BTM unit, it's time we take a look at the items we'll need for the install. You will need:
- Soldering Iron
- Fine Point Solder
- Wire Stripers
- 1' Heatshrink Tubing
- 12' 5/8 Wire Loom
- 1 Roll of Black Electrical Tape
I'm going to make reference to my previous article on Installing the MSD 6AL and MSD Blaster2 Ignition System before going any further. You can do what I did for this install and relocate your 6AL box as to make it easier for the BTM's wiring, or you can locate the BTM in a different area. The pics below are going to be shown as splicing into the 6AL's wiring harness, and my previous article goes into further detail as to where everything is wired in at prior to the BTM's install.
The first true step in all of this is to completely dissconnect the battery. Last thing you need is to suprise yourself while installing the power wire for the two units. Accidently touching the ground wires to a positive can have the same effect, so be forwarned by this precaution.
In Figure 1, you'll see what I'm going to refer to as my desired mounting place for both of my units. Mounting is important, and careful decisions are to be made when it comes to choosing a spot. You need to make sure that there's an ease of access to both the 6AL and the BTM, you'll need to make sure you can supply a vaccume source to the BTM, and you'll need to make sure that you can run the wires to the engine bay (if mounting inside). These specific MSD units are water proof, so mounting in the engine bay won't hurt them if you decide to place them in that location. Once again, make sure you can easily mount the boxes before you start running wires. With the 6AL, make sure you mount it in such a place that you can change out the Rev Limiter Plug as well if needed. Once mounted in place, you can begin to measure out your wires as to how you want them run so they'll fit inside the wire loom. And finally, make sure you use something between the unit(s) and the surface you mount them to. I used rubber gromments that were just thick enough to space the backplates of the units away from the wall.
Once all of the mounting issues are taken care of, it's time to measure out your wire lengths and decide how it's going to fit inside the wire loom. Wire loom is very important when it comes to electrical automotive work as it protects the inner wires from rubbing up against something and causing a short due to a break in its insulation. Once I placed my units side by side as in Figure 1 above and mounted them, I knew that my 6AL wires were longer and would be running to the engines componets that it needed to operate where applicable. Also, I knew then that I could use some of the same 6AL wires to provide my BTM with what it needed. Remember though, it's best to leave some slack in the wiring so that you can fit the loom around the wires as well as looping a roll of electrical tape around the loom as to prevent any wires from coming out.
Figure 2 goes into detail as to how you need to wire the BTM in series (same circuit) with the 6AL. Your BTM unit has 4 wires: Red, Black, White, Orange. As is commonly known, Red and Black are your + and - wires. By splicing the two units' black wires together, I was able to run one wire through the floor board to produce the ground. Our red wires are almost the same way, except for the fact that the BTM unit doesn't use a power source of its own; the BTM receives its power via the 6AL. As for the 6AL, MSD says the power wire needs to be run to the positive side of your battery, but with the battery in the trunk as I have mine, I decided to run the wire to the positive side of the fuse box. The 6AL obviously doesn't have that long of a wire harness, so you'll need to add in the same gauge wire to the end of the 6AL's heavy positive red wire provided you need to extend the wire for your application. By using wire strippers, you can create a clean break in the + wire shielding from the 6AL, strip the same amount off of a same gauge wire, and solder the connection. Make sure to cover every connection, and when possible, use heat shrink. I used tape quite a bit on my splicing, yet for all my wire extentions, I used heat shrink.
The BTM's wire harness so far has been grounded, and currenlty has 3 wires remaining to be connected. This unit is special in that it takes the factory pulse signals and modifies them to the point of reduced spark under boost if so desired via a potentiometric dial. Since our 6AL is a spark multiplier to the ignition coil, where should the BTM go to reduce the signal when needed under boost? The answer is, before the 6AL. In order to create this effect, your going to have to do some cutting and splicing under the hood to the factory pulse wires. With just the 6AL installed, the red and white wires from it lead to the positive and negative sides of the ignition coil. With the BTM being wired in series, some modifications have to be made. Since our BTM is being wired in pre 6AL, you'll need to make the BTM's white wire take the place of the 6AL's white. Both of the factory negative pulse wires will now lead to the BTM's white, and the heavy black/yellow wire will lead into both the BTM and 6AL's red wires. Now that 3 of the BTM's wires are connected, the orange, and final wire, needs to be addressed. Believe it or not, the ornage wire provides the only signal output to the 6AL. The BTM's orange lead wire conncts tot he 6AL's white, again, to provide the BTM's signal output. All that's left from this point is the 6AL box, and we're left with just the paired black and orange wires. As when wired before the BTM's installation, these two don't change; orange to ignition coil positive and black to ignition coil negative. I know it's easy to get lost in what I just said, so I spent two hours producing this wiring diagram in MS Paint for the ease of installation sake.
Once wired in as Figure 2 displays and the writing above explains, your pretty much done. Quick note though, in our diagram above, the solid dots are wire splices and the X's are where you need to cut the factory wires so that they don't lead to the ignition coil. From here though, it's nice to start the car up just to make sure your still in check with where you need to be. If your car doesnt start, disconnect the BTM's harness from your wiring and try to restart. If the vehicle starts where as it didn't the first time, recheck your wiring as stated above for the BTM. Though the diagram looks like a mess at first, it should prove very easy to follow after reading the explanations as to where everything should go. Now that it's all soldered together, it's time to start running wire loom. Place the loom around the wires, and make sure that you can tape the loom shut once completed. As long as your wires are protected inside the loom, your going to be good to go. After securing the wiring inside the 5/8" loom and taping the loom shut, you need to secure the wires to the vehicle. I placed my wires as close to the units as possible so that a pasanger wouldn't hurt the wires by stepping on them. I also used a few self tapping screws to clamp the wiring down and make sure it wasn't going to move. Remember that anything that loom rubs up against if let loose will eventually rub through the loom and through wires. Figure 3 below shows the loom job and mounting process I performed on the units.
Just as a final piture, I thought I'd show where my wires perform a 90 degree turn and exit via a hole in the floor board to run up towards the engine bay. If you mount yours as I did mine, that hole could prove bad if you don't use a rubber grommet to protect the sharp edges from rubbing a hole in your wiring. Creating a short can sometimes cause sparks, and if in the right place at the right time, produce a fire. My interior is stripped as you can tell, and I don't plan on installing carpet. However, if the carpet were there and a spark was to produce, I very well could get a nice carpet fire. Be safe with your wiring and routing. Make solid connections with enough solder, and always use heat shrink when applicable.
Before ending this article, I wanted to take a brief moment to explain what the MSD BTM unit does. After looking at why it's selected, you should have noticed that pinging and detonation are very prone to happen in a turbocharged application. To help prevent this, the MSD BTM is an ignition timing retard unit. The BTM activates under boost only, and uses a manual dial knob to control it. This dial knob reads 0, 1, 2, and 3 representing degrees of ignition; in this case, ignition retard. Set at 0, your engine will produce power and act as if the BTM isn't there. However, when you turn the dial to 1, your setting the BTM unit to retard the ignition timing by 1 degree per PSI of boost. 2 on the dial would be 2 degrees per PSI, and 3 would be 3 degrees per PSI. The only way to really know if your BTM is fully operational, because it functions under boost pressure only, is to set it at 1, 2, or 3 under pressure and see what happens. At 3 degrees of retard, any amount of boost you throw at the engine will be all but canceled out. In my own personal experiance, I've produced less power under pressure than when off boost.
The Reason for the BTM is to prevent detonation and pinging concerns with the engine. If it starts to sound funny under pressure, crank the dial over a few numbers and see what happens. Don't shut the engine off, rather get down under pressure, let the blow off valve do its job and drive safely to where you can park it for a while if you think you did any damage. If you've got to drive far, set the dial to 3 as to really cancel out the boost and don't worry about having to half throttle it home on a 70mph road. If you've got a turbocharged application, the BTM unit can and will do wonders for you if you don't have any other kind of an ignition retard device. Being that it's MSD, the name and reputation follow the product in mention. Email me with any questions you might have concerning this install and or topic; I'll do my best to reply promtly.