The Oldsmobile Connection

[88 Coupe]

Hello All

I thought this thread might be of interest as it is more detailed than any I have posted here.

Regards, Norm

[speedy266]

Ok so what that thread was talking about was if it takes x amount of volts to jump the gap, applying kx volts (k>1) wont make the spark stronger or help it produce the spark faster because it only requires x volts to jump a specific gap.

Ok so the stock system is lets say 30000volts, and the gap is .060, and it only requires 25000volts to jump the gap. Someone installs an aftermarket coil to boost the total output to 60000 volts. Keeping the same gap wont yield any significant power increase. Lets say the gap is uped to .120, not saying the calculations are this easy, but now it requires 50000volts to jump the gap and u have more than enough now so technically it would jump it. In that case i would assume there would be noticeable power increase on a dyno of a couple of hp or more depending on the car and the compression ratio because of the bigger spark more fuel would be getting burned if all of it wasnt getting burned to begin with or it would get burned faster.

i know the gap of .120 is crazy big and unrealistic but im sure u get my question.

[88 Coupe]

Hi speedy266, hello All

88 coupe in the MSD thread in ROP wrote: ............In carbureted applications, using .035 plug gap and "street" compression, a points distributer/stock plugs, coil and wires work fine, as they have for me for a lot of years...............The spark needs only to contact one fuel molecule to start the combustion process. Any more is redundant.............
The leaner mixture used in the newer cars requires a wider plug gap in order to make sure the spark contacts the one required molecule.

If two or more molecules are ignited, there will be no difference in the combustion process, and no extra power will be made.

Just to stay crazy big and unrealistic, lets use a 6 inch gap. It would be that much more likely to strike that one molecule and start the same fire that a .010 gap might have.

Regards, Norm

[speedy266]

with that said, why do car manufactures change the gap specs to a wide variety?? I know that compression would play a big role and also if the engine is like a pick up wit lots of low end torque or the corvette wit lots of hp.

If you just need to contact one molecule, the gaps can be made quite small. Ive also searched this and it appears that on some cars if the gap is 2 big and the engine is revving high the coil doesnt have enough time to recharge and u get misfires?

So wouldnt really small gaps be wat manufactures are aiming for? With more compression its hard to jump the gap so usually high compression engines have small gaps.

Ive been searching through the acdelco site at various vehicles, seems that high performance vehicles have small gaps like the porsche 911 has .032

Just wondering cause my factory recommend .080 seems 2 large havent seen anything recommend that big or bigger.

[88 Coupe]

Hi speedy266, All
Quote: ..........If you just need to contact one molecule, the gaps can be made quite small.......... A lean mixture has less fuel molocules, and they are farther apart. The gap has to be wide enough to insure contact at idle, and at maximum expected RPM.
Higher cylinder pressure (more effective compression) reguires more voltage to jump the same gap, but that applies to racing engines.
Quote: .........Just wondering cause my factory recommend .080 seems 2 large havent seen anything recommend that big or bigger. In that engine design, that's what it takes to fire the mixture under all conditions.

When you change the engine design, change the settings.
If you don't change the design, you already have the best settings.

Regards, Norm

[Turbocharged400sbc]

dont forget that too small of a gap can give you problems with plug fouling out, and that too big of a gap (especially high compression engines) requires High voltage that means everything else in the system have the dielectric strength to prevent voltage loss/missfiring.

[speedy266]

Sorry to start this old topic up again...but i had a question relating.

Refering back to the original gap for my engine of .080 with a regular ac delco plug. The Rapidfire plugs for my engine says gap to .045, but i believe all engines that use the same rapidfire plug as my engine are said to be gapped at .045 not sure though.

The rebuilt engine has about 25000km on it now and runs real good, acceleration is great, id like to get some drivetrain work done this summer to strengthen it and hopefully get some extra hp and more power to the ground.

[Brando]

That's very interesting...
I looked it up, and indeed, your spark plug gap is supposed to be .080".
That is for 1984-1985 3.8L with FI.

Now, the 1986-1987 3.8L with FI (VIN Code 3) says to gap the spark plugs to .045".

What changes that makes the large difference in spark plug gaps? :-k

TOC Admin
Brando

[88 Coupe]

Hi speedy266, All

Quote: Sorry to start this old topic up again .........
Not a problem, it's why we are here.
Quote: .......... gap for my engine of .080 with a regular ac delco plug. The Rapidfire plugs for my engine says gap to .045 ..........
Use the gap recommended by the manufacturer in either case. Unless you've made internal changes to your engine, changing plugs or gaps will not increase your power.

Quote: ............ hopefully get some extra hp and more power to the ground.
Other than small gains from fresh cool air, an efficient filter, and the 180 stat you already have, there's not much left.

You can change tire sizes, but it makes the car set funny.

I'm sure if there were anything out there that could help you, it would be common knowledge.

Properly set up, nitrous oxide works very well and is the only practical option I see at your financial and skill level, although you'd still need to freshen your engine first.

Regards, Norm

[88 Coupe]

Hi Brando, All

Quote: What changes that makes the large difference in spark plug gaps?
That would be about the time they found the technology to meet EPA regulations without running excessively lean mixtures that needed such large gaps.

The lean mixtures and the wide plug gaps were the reason the HEI was designed.

But what do I know? I'm just a kid with no automotive experience.

Regards, Norm