202 ignition coil versus 204

[D S.]

Are the 202 12V and 204 12V ignition coils the same output? What, if any, is the difference between 287 BR and 287 B-R? And what is a 238 B-R? A service replacement to the 287 B-R (or 287 BR)?

Thanks,
Scott Sims
Texas Chapter

[Ken A.]

Re: 202 ignition coil versus 204

Internally they're all the same.

[D S.]

Re: 202 ignition coil versus 204

Internally they're all the same.

If that is fact then why isn't just one generic coil used for all sizes of engines? Why is there a 202 for one type engine, and then a 204 for another, a 270, a 293 B-R, a 287 B-R, etc? Isn't there an output difference to compensate for the demands of the firepower of the engine, i.e., a 327/300 would need less firepower than a 427/435?

[Ken A.]

Re: 202 ignition coil versus 204

Actually, the 427 would need less "firepower" than a 327. The science of coils is pretty straight forward, but there a lot of myths about "blaster coils" and 40-50,000 volt coils.. A coil will only produce enough voltage to overcome the resistance it "sees", which is around 12-17KV. The key to a good coil is "arc duration" which is measured in milliseconds.. Most of the embossed numbers refer to a coil & bracket assembly. If you bought a service coil over the parts counter, then you got a "generic" as you call it, coil.

[D S.]

Re: 202 ignition coil versus 204

Then why the different coil designations for specific applications? I was running a 202 coil on my '66 Impala 396 until I learned that a 204 is correct. Now I have a 204 on the Impala. I have a 287 B-R on my '70 454 because the manuals say that is what is supposed to be on there. Based on what you are saying I could run an MSD coil or a 202 or a 438 B-R on either car and it wouldn't make a difference. Right?

[Jack H.]

Re: 202 ignition coil versus 204

Well, there's at least one reason for specific coil PN's that don't equate to what was available from service as replacements OR the coil PN's you see on 'equivalent' Chevy passenger cars...

Joe Lucia has told us in prior posts that some of the factory original coils were NEVER carried by service because the PN specific to them was a production factory 'bundle'...coil + engine mounting bracket.

Since Corvette typically used radio RF shielding and passenger cars didn't, the Corvette coil mounting bracket was sometimes specific to Corvette in order to position the coil properly for distributor shielding clearance.

Asking, "What's the difference?" may entail a larger/longer answer that what you intended. What's correct original from a factory concours viewpoint is often quite different from what will substitute and function without appreciable difference...

[D S.]

Re: 202 ignition coil versus 204

The point of asking is that I thought that there were varying outputs on ignition coils related to the performance of the engine. Contrary to that what I think I am reading is that if people didn't give a hoot about having the correct ignition coil on their cars people could put Massey-Ferguson (MF) tractor ignition coils on them and they'd run just fine.

[Jack H.]

Re: 202 ignition coil versus 204

It's not magic... It's just a step-up transformer.

Get the recipe 'close' to design center and it will work, mon!

That's one of the reasons why service replacement coils were often NOT the same number as the factory original and the service substitute PN sometimes changed over the years.

[Ken A.]

Re: 202 ignition coil versus 204

Then why the different coil designations for specific applications? I was running a 202 coil on my '66 Impala 396 until I learned that a 204 is correct. Now I have a 204 on the Impala. I have a 287 B-R on my '70 454 because the manuals say that is what is supposed to be on there. Based on what you are saying I could run an MSD coil or a 202 or a 438 B-R on either car and it wouldn't make a difference. Right?

Yes to all except I would NOT use a MAY STRAND DRIVER part, even if it was free. And no, you can't use a FORD coil on a Chevy.

[Duke W.]

Re: 202 ignition coil versus 204

The point of asking is that I thought that there were varying outputs on ignition coils related to the performance of the engine. Contrary to that what I think I am reading is that if people didn't give a hoot about having the correct ignition coil on their cars people could put Massey-Ferguson (MF) tractor ignition coils on them and they'd run just fine.

The primary factor in ignition energy output is primary current. That's why models equipped with the 0.3 ohm ballast have different coils than those equipped with the 1.8 ohm ballast.

Primary and secondary resistance varies with the number of windings and these values are listed in service manuals. Inductance also varies, but these values are not specified, and they are not easy to measure unless you have an electronics lab handy.

TI systems have different coils because they offered more primary current than any of the breaker point systems.

Add to the above that there will always be some debate among engineers as to what constitutes the "perfect coil" for a given primary current.

Then add various manufacturing changes to all of the above and you end up with a proliferation of part numbers.

Duke

[Jack H.]

Re: 202 ignition coil versus 204

Tidbit: when you DO measure primary vs. secondary inductance, everything falls into place clearly. You'll see the actual step-up ratio fall out of the numbers...

The resistance/turns ratio that's often taught only applies when the primary/secondary wiring gauges are identical. If dissimilar winding wires are used or the consistency of the wires are erratic, you won't see the true step-up/step-down ratio.

But, as Duke says, you need an inductance meter to capture this information and most auto mechanic literature tries to 'simplify' things by reducing tests to what can be done with common tools like a continuity lamp or ohm meter...