3.0 from CIS to Carbs

914obsession · 11-12-2009, 10:20 AM

I'm sure that there has been a lot said on this, can someone either provide me a link or enlighten me a bit. I have a 78 3.0, the dizzy came from this engine (ie. it's a 78). I will be running a set of carbs. I have a 81 CIS wiring harness (I believe it is an 81 or 82 because it has the green wire for the O2 sensor). I'd like to modify this harness (take off what I don't need) and use it for my engine. I have several 3 Pin CDI boxes, but it seems as if I'll have to run a 6 Pin. My questions:

- Do I need to run a 6 Pin CDI because of the 78 dizzy (stock magnetic pic ups), or can I sue a 3 Pin?

- There are quite a few wires from the CIS harness that go back to the 6 Pin CDI plug, the O2 wire, several of the plugs (I believe the WUR, and a few other similar connectors), are any of these required in order to "complete a circuit" or allow the 6 Pin to work properly?

- The dizzy connector on the harness I have is different than what is needed for my 78, can I just find a 78 connector and solder it in place of what's there now?

- Assuming I have to use a 6 Pin CDI box, can I still use a standard tach from a 70-74 car or do I need to use a tach from a car with a 6 Pin?

- Do any of the factory CDI boxes, 3 or 6 Pin have built in rev limiters, if so how do you know what the redline is?

Thanks in advance,

Dan

Carrerax · 11-12-2009, 12:37 PM

Hi Dan, Do a search for a thread by "James Brown". He goes into detail about how he did it. I am doing the same thing. I do know that you wull need to run a 6 pid because of the Dizzy. In James thread he tells you what main jets (160) and idle jets (65) you need to use and also the contact info for a guy here that makes 40mm Venturis for Zeniths. Hope this helps!

914obsession · 11-12-2009, 08:37 PM

I looked at the thread James Brown posted, there was very little info other than carb jetting (I've got that covered). Does anyone have any answers to my questions? Any links to any related threads?

Thanks,

Dan

Eagledriver · 11-12-2009, 09:26 PM

Your dizzy is only compatable with a 6 pin CDI or an aftermarket CD ignition like an MSD 6A or AL. The required connections are in the instructions for the aftermarket system. Since your car currently is a 3 pin car (I think based you your questions), you will need to add the connections for the 6 pin or aftermarket ignition. It's not hard to do for the aftermarket system, but slightly harder for a 6 pin system since you don't have instructions on what wire connects to which terminal on the box.

Many of the aftermarket systems have rev limiters. The 6 pin doesn't. Your Tac should work fine with an aftermarket (my 72 did), don't know about the 6 pin.

I don't think you need any of the extraineous wires (o2, WUR, etc.) for either ignition system.

-Andy

tom1394racing · 11-13-2009, 01:27 AM

Dan

I did something similar with my RSR clone.

You will need to run either the 6 pin CDI or aftermarket system like MSD. The 6 pin will be needed to get the tach to function properly. The 3 pin CDI will not convert the magnetic pick-up signal from the dizzy for the tach.

I had to to make significant modifications to the wire harness to remove all the extra CIS connections. You'll need to understand which wires you need for the dizzy, sensors, alternator, starter, back-up lights and 6 pin CDI. Do some searches on the tech forum, The information is all there in detail.

Carrerax · 11-13-2009, 03:22 AM

Tom, I am doing the same thing that Dan is doing. Putting a 3.0 in 1970 and using carbs. will it be easier to wire in the 6 pin (with the 3.0 harness) or should I go aftermarket? I want to do what will be the cleanest and easiest. Thanks! Mark

Eagledriver · 11-13-2009, 07:42 AM

When I put a 3.0 in my 72 I went with an aftermarket ignition system. It was very easy to do. You can still use your old wiring harness for everything except the ignition. This keeps you from rewiring things like the backup lights, oil pressure sender, temp sender etc. I even used my old fan and alternator so those wires would be the same. I had to transfer my pully from the old engine to the 3.0 engine so the fan would be compatable.

For the aftermarket ignition all you do is mount it (I put it on the relay panel where the old CD unti was). It needs to connect to switched power for one lead, unswitched power for another (these are both available at the relay board where the 3 fuses are. It needs a ground (also available at the board). The rest of the wires go to the coil, and dizzy wires. Hook the green dizzy wire to the green magnetic pickup wire on the aftermaket CDI. Purple goes to the wire mesh jacket on the dizzy magnetic pickup wire.

I used a Mallory hyfire 6AL for many years. It ran the tac just fine. I can no longer recommend Mallory as I've had 3 boxes fail, 2 in less than 1 hour of operation. I have an MSD now but I haven't installed it yet. I'll try to get it done today and let you know if the tac works.

You need one with a rev limiter. Don't worry about the instructions to wire the aftermarket directly to the battery. The unswitched power fuse at the relay panel IS wired directly to the battery. The units draw less than 10 amps.

-Andy

Carrerax · 11-13-2009, 07:49 AM

Andy, That is a huge help. I would much prefer to use the original harness. Please let me know if the MSD unit works properly with the tach. Also what model is the MSD and is there a more prefered unit available?

tom1394racing · 11-13-2009, 09:55 AM

Yes

MSD with original harness modified to remove the CIS components. You'll need to have the Tach modified to work with the MSD.

Eagledriver · 11-17-2009, 05:50 PM

Ok, so I installed my MSD today. The tac works fine above 2000 RPM and is jumpy at idle and below 2000 RPM. Car runs well. I think I may have a weak signal from the dizzy due to an extra connector I have to adapt from the old Mallory box. Installation was very clean by connecting as I described above. I used the MSD 6AL. This is the old school model with analog technology. I would say that the old Mallory worked better with the tac at idle and low RPM and the car idled a little smoother with the Mallory, but the Mallory was completely un-reliable.

-Andy