Wiring a blown small block

[NOBLNG]

I have only built one supercharged engine before and never wired it. I am working on the Revell ‘29 model A roadster and have started wiring the engine. I can’t seem to find any pictures anywhere that shows a coil mounted. Can I put it anywhere? Does a blown engine even use a conventional coil and distributor? Forgive my ignorance, but I think a poorly wired engine may look worse than no wiring. Any advice appreciated.

Edit: I’ve used a shapeways distributor which is a touch large, so I will have to modify the firewall slightly.

Thanks in advance. Greg.

Edited December 5, 2020 by NOBLNG

[gman]

A blown engine certainly can use a standard coil, but depending on the era of the build and what the vehicle's intended use is, it may be more likely to use a magneto or an electronic ignition module. I'd shoot for the latter if replicating something street driven from the 80's to present.

[Ace-Garageguy]

Everything depends on the era and application you're building.

A blown car in the 1960s would most likely run a magneto setup, as coil-type ignitions would be on the ragged edge of not being able to make a hot enough spark to light off a blown engine consistently...but the amount of over- or under-drive on the blower is part of the equation. An over-driven blower on a drag car would need more gutsy ignition than an under-driven blower on a street machine. Cylinder pressure in a racing engine will usually be higher than a street engine, requiring a "hotter" spark.

There are a few coil ignitions that could handle it back then, like a Spaulding Flamethrower, or some of the other two-coil rigs. Coils would be external on those.

On the other hand, a GM HEI distributor, made from about '74 onwards (and looks kinda like your model) makes a much hotter spark than some of the earlier hot-rod setups, should be able to handle a street-driven blown engine without huge boost, and has its coil inside the cap. It only requires one small wire to power it...no coil wire.

The first-generation HEI rigs had some limitations, but GM and the aftermarket quickly solved the problems. People dissing the HEI today are generally just rebleating what somebody else said, and most of 'em don't know what they're talking about.

A stock HEI distributor with vacuum advance won't work with a blown engine, because there's no way for it to get a boost reference to vary the timing as the blower blows harder. There are, however, plenty of HEI-look distributors that WILL do the job on a blower motor...and none of the differences would be visible. Again, both the "module" and the coil are inside the typical HEI cap, so you don't need to worry about coil wiring (remove the nipple for the coil wire from the cap). HEI caps are usually larger diameter than older coil-type caps, and usually look like this...more or less. 

Another popular (external-coil) electronic distributor that will do the job is the Mallory Unilite, and its relatives. Use a separate coil, and wire it like you normally would.

There's a lot to getting the right ignition system on a real engine, but the info here should be plenty to get your model reasonably accurate.

If you're building an earlier car and want to run a magneto or a Flamethrower, I've got posts that show the correct wiring for all of 'em. Just ask.

 

Edited December 6, 2020 by Ace-Garageguy

[NOBLNG]

Thanks Guys. For simplicity’s sake, I think I will snip the coil wire and go for the after market coil-in-cap electronic ignition look. So if one was to use the kit distributor on the blown engine version, the vacuum canister should be removed.

[Ace-Garageguy]

3 minutes ago, NOBLNG said:

... So if one was to use the kit distributor on the blown engine version, the vacuum canister should be removed.

For simplicity's sake, yes.

A sloppy real-car builder could leave it in place but inop, or a more knowledgeable real-car builder might even rework it to function as a pressure-retard, but the most likely scenario would be to just get rid of it.

[Dave G.]

A lot of people mounted  with rear distributor engines mounted Accel Super Coils on the firewall fwiw. Basically a yellow box looking thing. When I drag raced I used the Accel replacement coil mounted on the fender well (  Ford FE engine) which had quite a bit more than stock spark in itself, between that and Yellow Jacket wires, my own internally modified distributor and ignition was never my problem. I used the Accel cap and rotor too which were tan colored. The Accel system I'm sure would fire a street/strip blown small block.

[Force]

Today many or even most who builds hot street and race engines use MSD distributors and coils together with a MSD ignition box like MSD 6, 7 and 8 and on the digital programmable versions you can do your own ignition curves and lots of other stuff.

Edited December 6, 2020 by Force

[Dave G.]

1 hour ago, Force said:

Today many or even most who builds hot street and race engines use MSD distributors and coils together with a MSD ignition box like MSD 6, 7 and 8 and on the digital programmable versions you can do your own ignition curves and lots of other stuff.

Indeed, that stuff was all coming in to mainline as I was getting out of racing. Be good to know the era being modeled here in the thread.

Edited December 6, 2020 by Dave G.

[Ace-Garageguy]

56 minutes ago, Dave G. said:

...Be good to know the era being modeled here in the thread.

Yup. I kinda seem to recall somebody said that earlier...

[Dave G.]

3 hours ago, Ace-Garageguy said:

Yup. I kinda seem to recall somebody said that earlier...

?

[NOBLNG]

I figure it would be late 80’s to early 90’s. It looks like 700r4 tranny which I believe were produced between ‘82 and ‘93. GM was also using HEI in this era, so that works for me.?