Has anyone done spark plug gap tests?

[Otto]

This is apples vs. coconuts, but may have some relevance:

1. In BMW oilhead boxer horizontal twin 4 valve/cylinder motorcycle engines, surging is a big problem, so various sparkplugs and gaps have been tested. 4 prong and platinum or iridium plugs make the problem worse, impede the flame front, and degrade fuel economy and power. Best power, fuel economy, and surging relief are with plain old cheapo single prong Autolites set at 0.038 or as wide as possible as long as she runs well.

2. Aircraft Spruce & Specialty Company sell inexpensive cylinder head temperature sensors, actually little rings that fit between sparkplug and head with a wire to the readout gauge. Maybe such should be used in conjunction with testing various spark plugs and gaps among the cylinders.

[ziddey]

Nice. I've always stuck with traditional copper plugs. #2 is a very interesting idea indeed. I'll do some testing later this summer, but I have a feeling I'll be stuck with narrow gaps since I'm going forced induction.

For now, I pulled a plug today (installed last year around this time @ 0.028. got 10k miles on them) and measured it to be 0.032. Not bad. At this rate, I can imagine these cheapo coppers lasting at least 30k miles.

[bgd73]

from platinums to a classic style.. advance the timing a few degrees...and retard. See what works.

I went through this on a rock chunk steel 1950s style NGK plug in a 1987 subaru. the platinums fired so fast I had to retard the timing.

platimus are cheap.. just slap some back in? The inlines are sensitive however... hanging onto crud until chemistry is feeding the vents. The classic design must be a better choice? stay solid for the debris..

boxers do not need it. I am bragging.

[thecheese429]

Originally Posted by ziddey

holy smokes, 0.060! What ignition coil are you using?...

It is the stock semi-electronic ignition. It has a distributor, but it is electronically actuated (distributor cap has some huge contacts, so the computer can decide when to fire it).


But... yeah.... stock ignition

[Superturnier]

Originally Posted by thecheese429

I was wondering if anyone had done tests on this, then decided to do my own. I have a 4 banger, so changing gaps across the board is not time intensive at all.

I changed the gaps, and then checked the vacuum. Then I changed the gaps, and checked the vacuum again. Here's the data:

          Gap (inches)       Vacuum reading (In. Hg)
Test 1:    .025                       16
Test 2:    .040                       16.5
Test 3:    .045                       16.7
Test 4:    .050                       16.7
Test 5:    .060                       16.9
Test 6:    .080                       16.7

No, my gauge doesn't have decimals, but the needle moved so little between tests that I figured I should use decimals.

My question is how this relates to FE. Does higher vacuum mean higher efficiency?

Interesting results!
I quess you measured the vacuum at idle?

Did you notice any difference in RPM?
I'm just quessing, but maybe different gaps causes different ignition advance and that causes different rpm and also different vacuum

[Old Tele man]

...some dated, but still very relevant, SAE articles worth reading:

SAE 690018, "Inlet Manifold Water Injection for Control of Nitrogen Oxides - Theory and Experiment," by J. E. Nicholls, I. A. El-Messiri, and H. K. Newhall, Dept. of Mechanical Engineering, University of Wisconsin, 1969.

SAE 700081, "Spark Plug Design Factors and Their Effect on Engine Performance," by R. J. Craver, R. S. Podiak, and R. D. Miller, Champion Spark Plug Co., 1970.

SAE 700532, "Milage Marathon from 50 to 244 mpg," by D. C. Carlson and H. D. Millay, Wood River Research Laboratory, Shell Oil Co., 1969.

SAE 710832, "Effect of Compression Ratio, Mixture Strength, Spark Timing, and Coolant Temperature Upon Exhause Emissions and Power," by R. C. Lee, Phillips Petroleum Co., 1971.

SAE 710835, "Effect of Engine Intake-Air Humidity, Temperature, and Pressue on Exhaust Emissions," by S. R. Krause, Ethyl Corpoation, 1971.

...also, try contacting Champion Spark Plugs and ask them about the "real" relationships and effects of gapping, compression ratio, and A/F-ratios.

[thecheese429]

Originally Posted by Superturnier

Interesting results!
I quess you measured the vacuum at idle?

Did you notice any difference in RPM?
I'm just quessing, but maybe different gaps causes different ignition advance and that causes different rpm and also different vacuum

Yes, the vacuum was measured at idle. The spark advance, EGR, and even idle speed are computer controlled, so I believe that the spark did change stuff, and then the computer compensated for it.

For those who are wondering, I am running a .040" gap now

[2009Prius]

Originally Posted by thecheese429

I was wondering if anyone had done tests on this, then decided to do my own. I have a 4 banger, so changing gaps across the board is not time intensive at all.

I changed the gaps, and then checked the vacuum. Then I changed the gaps, and checked the vacuum again. Here's the data:

          Gap (inches)       Vacuum reading (In. Hg)
Test 1:    .025                       16
Test 2:    .040                       16.5
Test 3:    .045                       16.7
Test 4:    .050                       16.7
Test 5:    .060                       16.9
Test 6:    .080                       16.7

No, my gauge doesn't have decimals, but the needle moved so little between tests that I figured I should use decimals.

My question is how this relates to FE. Does higher vacuum mean higher efficiency?

Originally Posted by thecheese429

Yes, the vacuum was measured at idle. The spark advance, EGR, and even idle speed are computer controlled, so I believe that the spark did change stuff, and then the computer compensated for it.

For those who are wondering, I am running a .040" gap now

And what is the manufacture's gap spec for your car? Thanks!

[thecheese429]

Originally Posted by 2009Prius

And what is the manufacture's gap spec for your car? Thanks!

.035 inches

[Duffman]

Dont be afraid of the big gaps guys, GM spec a .060 in 1975, they backed it down the following year but for FE it wont hurt you.