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Hello all. I am finishing up my build and was considering getting an MSD 6AL ignition box. I was seeing if it was worth paying extra for the rev limiter or just getting the MSD 6A box without the rev limiter. I have a built 408W that I assume will be 500HP + with a built C4 automatic. Do I need the rev limiter with an Automatic? Im using a Mallory 4755401 unilite and a petronix flame thrower coil. Last question is if i get the MSD box do i still need my ballast resistor? Thank for the advice in advance.
 

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The rev limiter protects the engine from over - revving. An automatic transmission is not going to keep you from grenading the engine. You could stay in a lower gear too long and grenade the engine. The throttle could stick in neutral and you could grenade the engine. You could lose traction and grenade the engine. All sorts of things that can happen without the rev limiter.

The other cool thing about a 6AL box - you can pull the rev limiter chip and install a 2500 RPM chip if you drop the car off at a muffler shop for example. I call it "valet mode". There won't be any Ferris Bueller activity with a 2500 RPM chip installed.

You will need to read and follow the directions that come with your MSD ignition box. Typically you would want to use a coil with the recommended resistance as the instructions state, and wire that coil as the instructions state.
 

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I would also recommend a rev limiter, definitely if you plan on drag racing your car. If you plan on drag racing a lot, maybe a 2-stage rev limiter is your way to go.
 

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The key is what cam you have set up. Solid lifters must use rev limiter. Hydraulics will float the valves at high revs protecting a tight lower end. If the lower end is old or not blueprinted, then use rev limiter.
 
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