FD3S MSD and FC3S Ignition Coil Conversion




Introduction: FD3S MSD and FC3S Ignition Coil Conversion

First of all I believe a congratulations is in order!  You have reached the point of your RX-7 build where your stock ignition just isn't cutting it anymore.  Well I have a surprise for you.  In this tutorial you will learn about ditching that FD3S leading coil for the beefier FC3S leading coil.  Along with this I will walk you through adding a MSD 6a/6al to give your system the needed oomph to power through even the richest of tuning!

Do you suffer from any of these conditions?

     1) A turbo large enough to make a nice party piece as a very expensive fruit slicer?
     2) Fuel injectors that flow enough to reverse the flow of many mid sized rivers?
     3) Frustration of having your entire attic filled with fouled spark plugs that you "don't have the heart to throw out?"

If you do, then read on my friend.  There is no need to go ahead and buy a system that will cost you an arm and a leg (because how would you drive your car without those?!)  The goal of this tutorial is to try to use as much of the stock ignition system as possible, while still having enough power to put you in the 5-600 whp range.

Remember!  This project will take some work.  The time to wire everything up will take no more than 2 hours to complete, but before you start working on the project please consider where you will be locating the coil bracket.

What do I need to buy......

     - An FC3S leading coil of course!  These can be found used frequently.  Generation does not matter as they are all the same.
     - MSD 6a or 6al.  Do your research on which fits your needs best.
     - 2 male and 2 female, 2 wire weather seal plugs with correct male/female pins
     - SHRINK TUBING!  Lets not make this look sloppy!
     - Soldering iron and solder
     - A few feet of 16g and 12g wire
     - Circular eyelet crimp connectors
     - Strippers (No! WIRE STRIPPERS)
     - Don't forget blood, sweat and tears!  Those are very important!

Are you scared yet?  I sure hope not, you'll have this project done in no time.  I think we have chit chatted long enough, lets get to work!

Wait... Don't leave yet!  Let's read step 1 first!

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Step 1: Putting Two and Two Together

So we have wires right?  And they have to go together right?  Without going through electricity 101 we need to consider how we are going to do this.  I used a 2 wire weather seal connector that can be found at many auto parts stores.  I decided at the beginning that I was going to use terminals marked "B" as my universal ground pin.  On the MSD these will be your white wire on the igniter side of the harness and the black wire on the coil side.  I started by grabbing my orange and black wires included with the MSD unit. 

First grab your male pins and strip the wires exposing around a 1/4 inch of wire.  Because I did not trust my crimping abilities I used a bit of solder to make sure I had a solid connection.

Step 2: Time and Time Again

Repeat this step for the white and red wires also supplied.  I hope we haven't forgotten step one already!

Plug these into your male weather seal connectors where one connector has red in the "A" slot and white in the "B" slot.  And the other has orange in the "A" slot and black in the "B" slot.

Step 3: Grab Your Leading Coil and Lets Put Things Together!

Strip the ends of the black and orange wires and attach two ring connectors.  The orange wire will go to the positive marked terminal on the coil, and the black will go to the negative terminal.  Make sure you bust out the shrink wrap here to give it a nice clean look that will have all your friends telling you how crafty you really are!

Step 4: The Tricky Part

Now we have to remove the coils from under the upper intake manifold.  There are several tutorials online on how to get to this and I don't want to get into too much detail on the removal process.  Remove the coils and unplug the coil harness from the main harness.

Here is the result!  Look at them, they are filthy!  I bet that leaf added at least 10 hp though.

Step 5:

AH!  That's better.  As you can see I decided to machine out a bracket to relocate the coils to beside my brake booster.  Location of the coils will greatly depend on what your engine bay setup looks like and your space requirements.  Figuring out where you are going to put your coils could be a harder decision than deciding if you wanted to wear your favorite Scooby Doo underpants this morning or not.  I will discuss possible locations in a video later in this tutorial.

Step 6: Igniter Side

Now we need to solder the red/white connector we made on to the harness for the coils.  For this we will be cutting off the black coil connector.  The white wire will be soldered and shrink wrapped  to the red/black wire, and the red wire will need to be soldered to the yellow wire.  After everything is done you should have a snazzy harness that looks similar to this.

Step 7: Putting It Together

So now we have our coil harness finished! Easy, right?  This next step is just as easy!  Now we are going to attach our female connectors to our MSD box.  Following the same convention as the coil side of the harness we will now put our red/white wires in one connectors, and our black/orange wires on the other.  Make sure you pay attention to which one goes into the "A" slot and which goes into the "B" slot.  After this is done you will be able to mount your coils and plug everything in!

Step 8: Finding a Solid Ground

One method is to ground your MSD box directly to the battery ground.  This was not an option for me as I had to relocate my battery to my rear bin because of the front mount intercooler.  I chose to just find a nice solid chassis ground.  This proved to not be an issue in the least bit for me.

Step 9:

Now on to the last step!  We need to power this system right?  Along with the negative, MSD suggests that you run the power directly off of the positive battery terminal.  Lucky for us the stock fuse box off of the positive battery terminal is still there even if you relocate your battery.  I ran my eyelet to this position.

Step 10: Food for Thought

CONGRATULATIONS!!!  You are done!  In this video I will discuss possible locations of different components.

Step 11: Conclusion

Alrighty, now its time to start your car up and enjoy the awesome power of the MSD 6a system, but first wash up.  I wouldn't want you getting your car dirty!  Throughout this tutorial we were able to identify that our ignition system needed a bit of boost, and complete the project in a timely manner.  This setup will work just as good as many of its more expensive competitors and should be able to easily support 600 whp.

If you have any questions or concerns, please feel free to send me a private message on rx7club.com, username Hisupyo.

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    3 Discussions

    Tex Arcana
    Tex Arcana

    5 years ago

    1) nice instructable, decently detailed; 2) you might want to add a diagram of what exactly you're doing, I'm an experienced car guy, and I can't quite visualize this; 3) you might want to add some pics showing the whole setup, and why you're doing it; 4) also, toss in an 'ible on face shields to guard against flying apex seals (J/K!!!). Otherwise, great 'ible, keep up the good work.


    Reply 5 years ago on Introduction

    Also, to answer a few of your questions. Without going into the science of it, when you reach a certain pressure inside the combustion chamber the dense air is very hard to spark across. By adding the MSD ignition system you can overcome this resistance by driving more current through the coil packs internal windings.

    One reason I did not locate the box on that cross member was because it is kind of flimsy, I did not want it vibrating too much and for the wiring to potentially hot the fan. From the factory the radiator position is also very different, and that location might be unusable.

    As far as A/C I deleted it because I am simply going for performance with this vehicle. With r22 gas prices to refill my system being as high as they are I could not personally justify the cost of trying to fix the A/C.

    I appreciate you asking the questions and will continue to update this instructable after I receive a grade on the project for my engineering technical writing course as I did not want to go outside the boundaries of the assignment.


    5 years ago on Introduction

    I will be updating this instructable with wiring diagrams, more pictures, and CAD files for those who would like to replicate my work in the near future. Thank you for reading it!