1966 Chevrolet Sportvan HEI distributor

[Registered6Offender]

I am in the process of building a Megasquirt for my 1966 250 L6 Sportvan. The van came with a 230, so I'm converting to the nearly identical 250. I have assembled the PCB and loaded firmware. Right now I'm kind of in a get-the-parts-together and define-the-system mode. I have a new alternator (upgrade current) and gear reduction starter, welding up exhaust system (needed to run/tune), etc. The engine is back in and I've fabbed a throttle body to replace the Rochester 1bbl. So...my question (this is a huge learning experience for me) is: I have a GM HEI ignition, upgrading from the old points style. My engine rebuilder found a billet HEI distributor, bought it, and stuck it in when he was buttoning up the engine. Apparently there aren't a million distributor options because I'm not working on a small block V8, ha ha. I've looked for a HEI myself, and can't find one. Don't know where my rebuilder found the one he got...Anywho, its got a 4 pin module, vacuum advance, and centrifugal weights. I think the old-school hot rodders prefer this as they are most common even for V8. Can I just pin the weights, remove the vacuum advance, and replace the module with a 7 pin? My reading of the various references on this site do not reveal an issue? I'm ready to order an ACCEL 7 pin module and get the pieces flying in loose formation. Am I making a stupid mistake?

[jsmcortina]

Yes, that modification to the dizzy should work. I've converted a vac/mech points dizzy to a locked dizzy. It was however a PITA to get the phasing correct.

The MS3 distributor manual page has details of input and output phasing. http://www.msextra.com/doc/ms3/distributor.html Most of the notes there apply the same to MS1 or MS2.

If possible consider setting up a crank trigger (e.g. 36-1 wheel)

James

[billr]

I don't think you even have to "pin" the weights, just remove them and let the springs hold it in the full-retard position.

[DaveEFI]

I don't think you even have to "pin" the weights, just remove them and let the springs hold it in the full-retard position.

It's more usual to make up some sort of adjustable clamp between the moving and fixed parts of the advance mechanism so you can adjust the phasing of the rotor arm - it no longer tracks the advance curve, and you can end up with cross-firing if it's left in the 'rest' position. And as James said can be a PITA to get right. Personally, I'd not bother - easier to go for a trigger wheel and wasted spark.

[billr]

Agreed, getting the rotor to point (as best possible) to the towers is always tricky and a compromise with a dizzy. Honestly, I was thinking more in regards to using the dizzy only for a CMP sensor. Fit it with a 36-1 or 60-2 crank wheel and use waste-spark. Trouble-free and you can get it up-and-running without any signal from the dizzy at all.

[Registered6Offender]

I can see how pinning the weights will be a pain to get right. I could be convinced to add a trigger wheel. If I do that, than I am only using the coil in the distributor? Might as well get a coil pack and ditch the distributor completely? That's the lost spark right?

[slow_hemi6]

Usually referred to as wasted spark, but yes that's it.

[billr]

Understand, the dizzy, or remnant of it, must still be there to drive the oil pump, and it makes a convenient place to put a cam sensor if you want full-sequential fuel.

[DaveEFI]

Understand, the dizzy, or remnant of it, must still be there to drive the oil pump, and it makes a convenient place to put a cam sensor if you want full-sequential fuel.

Yup. Other advantage of using a trigger wheel on the crank is it's way more accurate - no 'slop' from the cam and dizzy drive.

[Registered6Offender]

Oh, yeah. I almost forgot I still need to drive the oil pump! OK, off to the DIYautotune website for some more stuff...I'll be back with more questions I'm sure. I still feel like I've bitten off more than I can chew. I'm drowning; somebody throw me an anvil!!

[jsmcortina]

One option to keep things simple...start fuel only.

Use the HEI dizzy as-is and take a coil-negative tach signal into the Megasquirt.

Once you have fuel-only control up and running you can consider switching to full fuel and spark control.

James

[Registered6Offender]

That's not a bad idea to get me running. Would I use the 4 pin HEI module then? Of course, I'd keep the vacuum and centrifugal advance for phase 1 of this project, but is there anything to be gained by goofing around with the 7 or 8 pin HEI (which I'd have to convert to)? Then for phase 2 I pitch the distributor and use a trigger wheel and coil pack.

[Registered6Offender]

OK, I've taken a slight diversion to get the fuel delivery system done (pump, filter, return line), and cooling system (electric fan and new radiator), and I re-did the exhaust system...now I'm back at the Megasquirt fuel and ignition piece of the pie. I've decided to go ahead with a Megasquirt for fuel injection only for the first phase and leave the 4 pin HEI for ignition. Once I get the car running, I will come back and visit the Megasquirt for ignition control. So, where do I find a schematic for how to hook up the HEI? I've stripped all the old wiring out, so I've got nothing to crib from...

[slow_hemi6]

This is the Basics. But I would recommend an ignition relay as in the bottom example and a fuse.

[Registered6Offender]

Thanks. That looks so simple even I can do it!