What can a high output coil do for performance?

Hi all…

Looking at a couple Accel high output coils for my 85 Olds Cutlass (305 Chevy V8, RWD, no real “mods”), just for a bit more response and power. What do you think of these coils, and will I get a noticeable increase in performance? Also, do I need to also install a “performance” ignition module to go along with these coils? Links are below…

High output coil: http://www…election=2

Really high output coil: http://www…election=2

Ignition module: http://www…election=2

Thanks for your opinions/suggestions!


It’s not going to make any noticeable difference at all on a low RPM street engine. The theory behind this stuff is that a coil with higher output voltage will somehow increase power, fuel mileage, etc. This is not the case.
A good spark plug firing in a normal engine will discharge around 8k volts or so which is way less than a coil that has the ability to put out 40, 50, or even 70k volts. The spark will jump the plug gap when it can and this is usually under the 10k volts mark.
The actual voltage that jumps the plug gap will vary a little depending on plug condition, gap, compression, timing, etc., but if one was to look at an oscilloscope on a running engine and saw a spark plug that was requiring even 15k volts then you would know there is a problem present with the plug or plug wire.

The plus to a higher output coil is that once the field collapses and the plug fires, the high performance coil may have a tendency to build itself back up a bit quicker.
However, this is still nothing that you’re ever going to notice at all. These super high output coils can help a microscopic fraction on race engines that are running at high RPMs. Since it’s unlikely you’ll ever be hitting 8 or 9k RPMs on a regular basis you should save your money.
The race coils are fine if used as a small part of an expensive, all out race engine, but on the street will do nothing for you.
The GM HEI stock setup you have is perfectly fine for all of your driving.
Hope that explains it without getting too deep into this. :slight_smile:

Someone or other on this board once made the analogy that the performance ignition stuff is like starting a forest fire with a blowtorch instead of a match. All the spark needs to do is ignite the fuel, and your stock system does that just fine.

Agree with the other posters. People tend to add high performance ignition parts when their old stuff is either dead or dying. They put on the performance equipment and WOW! Such an improvement. Well, usually ANYTHING is better than a 30 year coil. If you swapped that brand new performance coil for a brand new OEM coil, you probably would notice no difference.

The HEI ignition on those rigs is good stuff. Buy a new generic coil, get new wires, gap some new plugs at .045", and she’ll run like a bat outta hell.

It’s a fix without a problem.

I LIKE that analogy…I’ll have to steal that one.

High output coils are used on engines that have very high compression ratios. The higher the compression is in an engine, the harder it is to get the sparkplug to fire. This is called ignition spark saturation.

So installing a high output coil on a standard compression engine gains nothing.


If it has a carb. replace it with a higher performance one or better yet a fuel injection kit. You will get an appreciable increase in power with either and possibly fuel economy with fuel injection.

Thanks OK, awesome explanation as usual!

Thanks josh…I’ve done everything you mentioned in your post, except a new coil…I will get a generic coil and save my money.

Thanks everyone for your replies, and information. I love this board. While it’s not what I wanted to hear :), I can listen to sense. I will try to find a generic coil as I think the one I have is original…22 years old-ish. That is, after my current timing problems get sorted out (see other post about how I wrecked a distributor rotor…hoping it’s just a timing issue…still runs awful after I put a new rotor in). I will update the other post when I get the news.

Well, apparently I blew the coil when I installed the distributor incorrectly. I saw the old coil, the metal bracket had melted in 3 parts on the one side…ouch. I also had a few melted misc wires and the metal brush (?) with the spring attached to it beneath the coil was damaged. The timing was way off too, I’m assuming from my rotor incident.

A couple problems…the part # for the coil installed is D505A (ACDelco)…I looked it up on ACDelco’s website and it’s not the right one for my car…I have the less popular Chevy 305 engine, the D505A is for the more popular Olds 307…I need part #D573A according to the site (matches my VIN too - “H”, not “Y” or “9”). Is this a problem?

Second, while I gotta admit the car has TONS more power now with the new coil (I’m guessing more from the timing adjustment and advancement though - 5 degrees), if I punch the throttle, it hesitates, almost like it’s gasping really…just for a second and then takes off…when it does this the RPM’s jump up a tiny bit, then drop to 500 for that second, and then back up as it gets power. It does this at any speed, more noticeable at low speeds. If I gradually give it gas, it doesn’t do this, even if the gradual push quickly turns into hard acceleration. What could cause this? Wrong coil?

I’m posting this same answer in the other thread in case anyone is waiting for a follow up post on that thread only…Please help! I’m taking the car back to the mechanic tomorrow but I’d like to hear your opinions first. Thanks in advance…