Charley B

I changed plugs on the '88 today. The new Bosche plugs were gapped at 26 and the old ones coming out averaged a gap of about 45. It was obvious the difference was from the worn center electrodes. That's about an 80 per cent difference in gap and yet there was no discernable difference in performance.

Andre Hedrick

It has to effect your timing and how crisp the energy burn is ... no?

Lizard928

It depends on the strength of the ign system.

A larger gap will be able to make slightly more power, and increase economy. But a distributor ign system will run out of juice and start missing with a larger gap. If you run boost, the higher cyl pressures may snuff out the flame.

Trip..

Well said, Lizard.

Also if the gap is too large, it can burn up the coil.

928mac

I set mine at 36 but I have an aftermarket ignition system with seperate coils firing the plugs.

spark timing is a factor as well as temperature and the ignition dezign, so it is always recomended to stay with the manufactures specs.

I think for most of our cars it is around 32 but I am not sure.

Brad

PorKen

A little more hp, definately more torque, and better driveability with a larger gap. Emissions go down, and idle speed goes up when a bigger gap is used.

I found that my S3s started to fade over 5000 rpm with stock plugs past 0.035"/0.9mm. I recommend gapping them to 0.032", the high end of the 0.7-0.8mm WSM spec.

Using a non-resistor plug, however, (I use NGK BP8ES) I found I could increase the gap to 1.0mm/0.040" (faded over 0.042"), which I've been running in both cars for a while now. No problem with radio static or stock electronics - there are still resistors in the plug wire ends, and rotors. (I did have a problem w/aftermarket ignition amps.) Note this is w/dual coils, not sure a 16V could do this.



Note fancy, tiny tip plugs need a larger gap to compensate for the reduced energy required to fire them.

Lizard928

Ken, what about non resistor wires, with a resistor plug?

PorKen

I forget what the factory plug wire ends, and rotors ohm out to. (The wires are non-resistor.)

I suppose you could run thicker wires with a (ugly) non factory plug end, with a resistor plug, and may end up with less overall resistance, but then you might have radio/ECU EM problems.

Lizard928

I ran 8mm aurora wires (non resistor), with resistor plugs without issues. But I left my gap small and conservative.
The factory lead have no resistance, just the ends do. Each end (both spark plus, and cap ends) have 1k ohms of resistance iirc. As to the caps/rotors etc. No idea.
I never noticed any noise in the radio.