[RR67GTO]

Greetings friends, I had Dave build a small body HEI for my engine and need some information on the best choices for plugs. Dave recommends an 045 gap according to the sheet he sends with his conversions. My engine is a 462 with SD built 670 heads with the CNC port work. SD Old faithful cam 236/245, and 1.5 roller rockers. The carb is a 76 Q-Jet rebuilt with a Kit from Cliff. I tried to do a search on here but I see so much information. Anything from a 045 gap to an 080 gap. So, I'm looking for more information based on the fact I have the 670 iron heads, and that my HEI is not a normal GM unit. Thanks for any help anyone may have. Good day friends. Mike

[rohrt]

I spent a whole night searching the archives and decided on getting the NGK plugs. No regets thus far.

[george kujanski]

Go with Dave's rec for the gap. A larger gap will require the coil to generate more voltage to fire the plug, that in itself is not necessarily good or bad, but as the coil voltage goes up, the spark energy may begin to leak off thru poor wires, etc. A .045 gap should give you no issues and still gives the advantages of the better ignition system...back then with points, the typical gap was .035, partially due to the limitations of the point-triggered system. In higher perf applications in the day, dual-point distributors were used to increase the dwell to improve ignitions, but that's another story.......

George

[David Jones]

I have a Dave's conversion (right now....) in my engine and have had for 7-8 years. I run .045 with mine and have found that Autolite's make the engine happiest. I've tried NGK's (XR4?)and Delco R45's and even a set of R44's.

Autolite 86's in my #48 headed 400.

[rohrt]

I forgot to add that I also have a Dave's small body HEI and I also used the recomended gap.

Originally Posted by David Jones

I have a Dave's conversion (right now....) in my engine and have had for 7-8 years. I run .045 with mine and have found that Autolite's make the engine happiest. I've tried NGK's (XR4?)and Delco R45's and even a set of R44's.

Autolite 86's in my #48 headed 400.

Dave, Just wondering what you like about the Autolite plugs over the others?

[RR67GTO]

So, if I use the plugs that come with an .035 gap, It's OK to open the gap to .045? I don't find any information on what the gap if the various plugs are. Just heat range. Thanks friends. Mike

[David Jones]

Originally Posted by rohrt

I forgot to add that I also have a Dave's small body HEI and I also used the recomended gap.




Dave, Just wondering what you like about the Autolite plugs over the others?

I feel like (strictly an opinion here...) that the Autolites have a smoother idle in my engine.

[David Ray]

ANY spark plug gap over .045 is begging for both coil and module failure. GM tried that with both .060, and .080 gaps for the HEI's, for leaner mixtures to meet increasing emissions jetting, and had to warranttee so many modules and coils, it wasn't funny. Dropping the plug gaps back down to .045 MAXIMUM STOPPED the coil and module failures.

Spark plug heat ranges are not set by ignition systems, but by actual compression ratios. So, just numbers thrown out, lets say an AC44 is for a 10.00:1 c/r, and that is what your engine has, run the 44 heat range. Adjust heat range as needed.

[grivera]

Originally Posted by David Ray

ANY spark plug gap over .045 is begging for both coil and module failure. GM tried that with both .060, and .080 gaps for the HEI's, for leaner mixtures to meet increasing emissions jetting, and had to warranttee so many modules and coils, it wasn't funny. Dropping the plug gaps back down to .045 MAXIMUM STOPPED the coil and module failures.

Spark plug heat ranges are not set by ignition systems, but by actual compression ratios. So, just numbers thrown out, lets say an AC44 is for a 10.00:1 c/r, and that is what your engine has, run the 44 heat range. Adjust heat range as needed.

Great to see you post on here Dave! I sent you a PM on an unrelated matter.

[Schurkey]

Originally Posted by RR67GTO

So, if I use the plugs that come with an .035 gap, It's OK to open the gap to .045? I don't find any information on what the gap if the various plugs are. Just heat range. Thanks friends. Mike

One of the plug manufacturers--might have been NGK--says you've got about + or - .008 leeway on the factory gap.

If the factory gap is .035, you could go .008 larger to .043. Or close it up to .027. Any more than that, and you need a different-length side electrode.

Given the popularity of the .040--.045 gap, might as well buy a plug intended for that gap distance.

Originally Posted by David Ray

Spark plug heat ranges are not set by ignition systems, but by actual compression ratios. So, just numbers thrown out, lets say an AC44 is for a 10.00:1 c/r, and that is what your engine has, run the 44 heat range. Adjust heat range as needed.

Also set by throttle position. A spark plug heat range that's perfectly fine for normal driving will burn an engine when used at WFO for minutes at a time.

This is one reason why outboard motors used to have "surface gap" plugs--you just can't get any colder, because the outboard might run full-throttle for an hour.

[David Ray]

I am extremely familiar with the "surface gap" design spark plugs. Kawasaki used the NGK BUHX part number, or Champion UL17V or UL19V surface gap spark plugs in the then new Kawasaki 1969 thru 1971 H1 500cc two stroke triple motorcycles with battery/distributor CDI Ignition Systems. Those systems were set up to use the .135 inch gap of those design spark plugs, an HEI ISN'T. In the H1R 500 triple, and H2R 750 triple road race versions (considerably modified from stock, minimum 45 to 50 percent more power output), with an even hotter magneto CDI, we used Champion E56R to E58R retracted gap spark plugs, gapped at .022/.024 because of the added compression ratio. H1R ran at top RPM of 10,500, H2R was red lined at 9,800.

One thing we all have to remember is, as a spark plug operates, wear of the center and side electrodes erodes metal off them, increasing the gap. .045 takes into consideration the .003 to .004 gap increase as the plugs wear, from those that never seem to get to changing/re-gapping their spark plugs regularly.

[77 TRASHCAN]

I've used auto lite plugs in every type and make of engine. Never had one problem, and their regular plugs are usually the cheapest...

My engine builder favored non extended tip plugs, usually gapped at .035, for reasons stated above about the widest gap plugs...

[Schurkey]

I was posting from another computer, didn't have an easy link to my photos or I'd have included them in my previous post.

These are the surface-gap plugs Dear Old Dad's 125hp Mercury Outboard ran--I found these plugs in his garage after he shucked his mortal coil. I have the sense that most folks haven't seen spark plugs with a heat-range this cold--but what do I know. Maybe this is old-news to you folks.





I don't know how that engine idled without fouling plugs. (but it did...) Mostly, that engine pulled a 16-foot boat with at least one water-skiier, WFO for miles and miles. Stop, drink beer, hook another skiier to the back...WFO for miles and miles.

I similarly don't know about Kawasaki spark plugs, the surface-gap plugs I've seen have a much smaller gap than .135.




I used to love Autolite plugs. Hard, long-wearing electrodes unlike Champion's soft, short-lived, fast-eroding electrodes, and Champion had the most-brittle porcelain in the industry thirty five years ago when I swore I'd never buy another one. Then Autolite moved production to China, and I started buying NGK for most stuff.

[David Ray]

Yup, them's the ones, and, with the way the body is rounded at the edge of the porcelain, the gap ends up being about .135 or so.

These design have been around since the early 1950's, didn't work well until capacitor discharge ignition systems came along. The NGK's I mentioned, BUHX for the 500 triples, had a serious cold heat range, well past the bottom of any scale. The only thing that kept them from fouling was the CDI volts/amperes output.

Funny thing, about a year ago, I started seeing ads for new versions of this design spark plug, touted as being THE answer for four stroke car performance engine applications. Haven't seen those ads for a couple of months now.

One thing these spark plugs don't have is issues/problems with them trying to fire past increased compression resistances, as the CDI systems needed to make them fire efficiently feed them serious output.

[george kujanski]

Had a kawasaki MAch3, 3 cyl 2 stroke...bullet without brakes had a CD ignition with surface gap plugs....would idle all day long without fouling.

george

[David Ray]

My 1973 street H2 had Morris Mag wheels, 3 disk brakes, Dunlop slicks, Koni's, H2R front fork innards, special 6 speed, added plate clutch, under slung pipes, braced frame, 70 lbs removed, special crank, better pistons, ported, heads were redone to H2R catherderal domes, 40mm carburetors, and made an honest 162 horsepower.

Stock H2 made 74 horsepower, and weighed 419 lbs.

It was fun to ride, but you never drilled the throttle in 1st gear, or the thing would go straight over backwards, and pole drill you straight into the ground. It helped to work on the Road Racing team at Kawasaki.

One of my street bikes sitting in the garage is a 1986 Yamaha RZV500 V4. It has a very rare 700cc factory top end kit, porting, special heads, bigger reeds, big carbs and good pipes. 70 year old fart has to have a nice sport bike to go tear up the country side on.

[george kujanski]

Dave, you are a crazy man!
At least yours had disk brakes!
On the 500,you would crank on the throttle and nothing much would happen until it hit 3000 rpm. Then it would be warp drive.

George