Screamin' Demon coil review

So I threw in of these ignition packs in this weekend. The truck runs good and everything but I'm 100 miles or so in and I'm thinking I've lost about 4 mpg...

It advertised "open sparkies up to .065" ... Mine are are at about .060 and I'm seeing a lag in acceleration and fuel mileage drop.

No... I didn't buy the recommended "live wires" but I bought some good Bosch wires...

I'ma re-gap down to .054~ish and see where that leave me, but uh, not super impressed.

Just a product review for anyone interested.

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What engine?

1992 can have either distributor and single coil or Coil Pack(distributorless)

Spark plug gaps really are not related to the coil, unless you are talking very old, 50 years old, coils.

Engines spark plug gap is set for average driving needs and longevity.
Wider gaps are better for starting and lower RPMs, but have less recovery time for coil at higher RPMs
Narrower gaps are better for higher RPMs, and have better recovery time for coils.

We are talking +/- .01, .005 is better
So if recommended gap is .054 then .059 would be wide, .049 narrow
And you would still have OK starting and OK higher RPMs

Engine is a '92 4.0L OHV.

the coil pack manufacturer says to open them up as wide as .065....

I think I'm just gonna put it back down to stock spec.

RonD, do you know what the stick coils packs put out, 35,000 volts?

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Yes, I would say 30k-40k, 4.0l is only 9.0:1 compression ratio so doesn't need much.

Not sure why they would recommend that big of a gap on a 4.0l OHV.
I know sellers of Cold Air Intakes(CAI) recommend changing thermostats to 160degF, CAI's don't really do anything on fuel injected engines but the lower operating temp does, which is why they add that part, lol.
Yes, I would think .065 gap would cause issues on the stock 4.0l OHV

When super or turbo charging an engine higher voltage is better, or if engine has a higher compression ratio to start with.

Stock coil, wires and spark plugs in good working order will give maximum performance from the engine.
Nothing can be "upgraded" for better performance, spark system simply doesn't work that way.
If only 20k volts is needed to "jump the gap", at idle, then that is all that is used, even if it is a 60k volt coil.

If 40k is needed to "jump the gap", engine under load, and coil is only 30k then you can get misfires.

Spark plug gap can be changed for driver preference, as said earlier.

Screamin' Demon coils are fine as far as I know, but they don't increase performance over a working stock coil, unless engine was modified to need a higher voltage output to "jump the gap" under load.


Any spark that can ignite the air/fuel mix works.
The spark comes at approx. 30deg before top dead center, as the air/fuel ignites around the spark plug the pressure increases which snuffs out the spark, so minimum voltage spark, rest goes to ground.
The ignited air/fuel burning spreads and complete explosive combustion should happen at about 10deg After TDC, that gives the best leverage to push down on piston to give crank the most power.

So voltage needed from coil is based on the engine , higher voltage certainly won't hurt anything, and no it can't burn pistons, popular myth, lol.
But it also doesn't really do anything to have more voltage than engine requires at maximum load.

Weak spark, to low a voltage from coil or bad spark plug or wire, nothing manufacturer would install, weaker spark can't ignite richer fuel mix, so slow cold starts and misfires under load

You Sir, are a wealth of knowledge.

Thanks for taking the time to write all that out, much appreciated!

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chewy012 said:

You Sir, are a wealth of knowledge.

Thanks for taking the time to write all that out, much appreciated!

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Click to expand...

as usual, outstanding concise and easy to understand answer to the application ron, i try to rep ron but it wont let me...so please add to his rep thing chewy if you can...

Thank you both

may need to get a bigger hat
until a goof something up......again

bobbywalter said:

as usual, outstanding concise and easy to understand answer to the application ron, i try to rep ron but it wont let me...so please add to his rep thing chewy if you can...

Click to expand...

Would love to help! .... How do i do that. I use this forum from a phone, and I'm not overly savvy with this stuff

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So just an update on the speed demon coil pack;

Doesn't seem to have any real benefit over the stock one I had. Again, it claims you can open the spark gaps to .065, but doing so gave me a loss in power/response and mpg... I'm running them at stock gap and it's smooth, but, nothing more than the stock one.

As RonD stated, on a stock engine no real improvement.

It may have some benefit in off-road low rpm applications, but daily commute not so much.

Just some two cents for anyone thinking they want one. I don't know

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