Hotrod Ignition advice wanted

[Trackrash]

I'm in the planning process of re-building and installing a 3.0 motor in my '71.

I would like advice in what ignition to use.

Basics of build will be a '78 SC motor with 9.5 J&Es, S cams, and Weber carbs.

I have two options on the ignition:

1: Use the SC distributor and 6 connector CDI.

The problem with this setup is my tac won't work and what do I do for a rev limiter?


2: Use a '74 distributor, which I have, by changing the crank gear.


What do you experts think I should do?

[304065]

Well, what is the date on the back of your tach? Is it before October, 1970 or after? If before October, 1970, you will have to use a tach adapter or have the tach converted to work with the six-pin box. If after, you might get away with using the +5V TD output from the six-pin with the later version of the tach that used an +11V square wave. Worst case is you have to send it to be modified to North Hollywood, but get to keep the six-pin, so it looks like the original 3-pin and the car can be made to look original.

If you need a rev limiter you can get an aftermarket one such as the MSD 8278.

Why don't you just use an MSD box with a built in rev limiter and trigger off the magnetic trigger inputs? You may need either a tach adapter or to have your tach rebuilt to trigger off the MSD's duty cycle.

MSD 6AL How to wire

The magnetic trigger was a forward step vs. points. I think I would trade a Pertronix in the '74-77 distributor for a magnetic trigger, however. Can you find a Turbo distributor that rotates the right way?

Why reverse rotation on SC distributors?

[MBruns]

We build a 6 pin and a 12 pin distributor that will plug into an MSD system which has a very good rev control, and can be set up many ways for your timing curve. The MSD will feed your SC tach as it was magnetic trigger from the SC dist.
Take a look at the web site for the dist.
Mike Bruns JBRacing.com

[Steve@Rennsport]

Originally Posted by 304065

Can you find a Turbo distributor that rotates the right way?

Certainly, the uber-rare '76 Turbo distributor works perfectly with an MSD or Bosch box (and matching coil).

[Trackrash]

Thanks, guys. I like the vintage 8k 1970 tac I now have. (It's one of those that has the factory tac adapter).
I can't imagine autocrossing or tracking a car without a rev limiter, so one is mandatory.

So my options are:

I can have my tac rebuilt and add an MSD rev limiter. $

Or use a MSD rev limiter, and a MSD tac adapter. Will that work with my tac? $

Or I can use all MSD stuff for even more money. $$

So what is the drawback to just changing the crank gear and everything I have now works with the '74 distributor I have on the shelf at home?

Thanks,

[E Sully]

SC distributor has opposite rotation from '74

[bullethole]

you could go all in and eliminate the Dizzy with a crankfire setup like an XDI (which I happen to have one forsale, as I switched to a completely megasquirt based system)

[Trackrash]

Obviously a number of options. Some pricer than others.

I'm leaning toward changing the crank gear and using my '74 distributor. It's basically plug and play. And at a later date I could still upgrade to MSD stuff.

At this point I can't see a down side to the backdated distributor option.

[MBruns]

What are you going to do about the rotation, the advance mechanism won't function, I guess you could lock it down and set it at full timing
Mike Bruns

[MBruns]

the best option might be to use your SC dist and trigger an MSD that way you will have a solid rev limiter, Send your early tach to North Hollywood Speedometer and for around 175.00 they will convert yours to be triggered by the MSD signal, I have one out there now for that Phone # 818 761 5136 speak to Kevin
Mike Bruns

[Trackrash]

I was under the impression that if I changed the distributor drive gear on the crank I could use the 1974 distributor.

I thought that by installing the correct crankshaft drive gear, on the crankshaft, for the '74 distributor it would turn clockwise and operate correctly. Is this wrong?

Thanks,

[Trackrash]

Originally Posted by MBruns

the best option might be to use your SC dist and trigger an MSD that way you will have a solid rev limiter, Send your early tach to North Hollywood Speedometer and for around 175.00 they will convert yours to be triggered by the MSD signal, I have one out there now for that Phone # 818 761 5136 speak to Kevin
Mike Bruns

I agree this may be, in the long run, the best option. Decisions, decisions. It's only money right.

[Trackrash]

After some more research I have found that there is a rev limiting rotor that works on an SC distributor. Pelican Parts - Product Information: 930-602-901-01-M14

And there is a tac adapter that is supposed to work with my tac. TACH-ADAPT

Any thoughts or experience with this setup?

[Walt Fricke]

You can get mechanical rotor rev limiters for 2.7 style distributors, which is what your '74 is. In fact, I'd suspect it has such a rotor. But if not, easy to purchase. I wouldn't expect that to have a 930 part number, though.

[turbo nut]

Originally Posted by Trackrash

I was under the impression that if I changed the distributor drive gear on the crank I could use the 1974 distributor.

I thought that by installing the correct crankshaft drive gear, on the crankshaft, for the '74 distributor it would turn clockwise and operate correctly. Is this wrong?

Thanks,

You are correct and can change the crank gear and use 1974 distributor.

[E Sully]

Originally I was thinking distributor gear, but changing crank gear is another story.

[Aurel]

You can save some money by using an MSD street fire instead of a 6AL. It also has rev limiter, smaller footprint.

MSD street fire in 78sc

[BURN-BROS]

Originally Posted by Trackrash

I was under the impression that if I changed the distributor drive gear on the crank I could use the 1974 distributor.

I thought that by installing the correct crankshaft drive gear, on the crankshaft, for the '74 distributor it would turn clockwise and operate correctly. Is this wrong?

Thanks,

hi Gordon,

Yes, If you put a crank gear from a 2.0/2.7 you will be able to use a 2.7 distributor which will work with your existing tach/cdi

[MBruns]

Aaron, how about the advance mechanism ?
Mike Bruns

[BURN-BROS]

Originally Posted by MBruns

Aaron, how about the advance mechanism ?
Mike Bruns

Hi Mike, I am referring to the gear on the crank, not the gear on the Dizzy.