Indexing a spark plug

A

Antracer88

Member
Building a flathead and was wondering about spark plug indexing any info is appreciated a question I have is which way should the plug be in when it’s inside the engine does it matter what the end is pointing to?
 
Flathead indexing is necessary so the valves do not hit the electrode when the valves come up to max lift, it is not a matter of increasing flow by one orientation or another.. I always did it by having the electrode point to the left rear head bolt. Some may say that other positions are "better" but your goal is to not have a valve hit and close up the gap on the plug. There is actually quite a bit of latitude but figure out a method stick to it out of habit. To adjust you use thin copper washers that are easily available at any kart source. When racing FHs I would pre index the plugs by engine so i could make quick changes at the track should the need arise.
 
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By using thin washers you slightly change the orientation of the electrode. Are you using a stock class slapper cam? Stock size valves?
 
Lkerley said:
Gas or alky? gas autolite 458,alky autolite 411 as Flattop stated shouldn't be a problem with stock lift.
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Your recommendation is to use a very hot plug with a 3/8 reach for gas and a very cold plug with a 1/2 inch reach for methanol? Interesting. If you set up your cam correctly with the proper valve springs indexing is absolutely needed for all plugs with a wire electrode.
 
Run the same 411 plug (or my preference, an ND W24FS-U) for either gas or alcohol and you'll be fine. You can run a slightly hotter plug on gas if you like, but there is no need to if it is fueled correctly.

I prefer to index my plugs so that the ground strap opening is facing the middle head bolt on the right side of the cylinder head. You can also point it toward the exhaust valve if you like. There is a reason that I do it the way I do, but the important factor is that the intake valve cannot hit the ground strap of the plug.

We stock the indexing washers if you need. Just give us a call at the shop number as we are still open and still able to ship for now.

CatIndexWashers.jpg



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Technically, since the air/fuel ratio within the combustion chamber is not uniform, there is a spot within the combustion chamber where
the mixture is closer to ideal and will ignite better/more quickly, so proper indexing could yield a minor increase on any engine. YMMV
 
So true .
The second time , the intake vale shut the plug gap . You typically have learned your lesson and have become a staunch beliver in indexing the plug .
 
I'm a believer now.I indexed to approx in between the two valves never ran 1/2 reach because of valve hitting issues always ran the the short reach plug...I can tell it runs better.currently running gas mikuni carb a w16 fsu..plug looks like it's burning great.will running the w27fsu really run and burn correctly with gas I thought that was an alky high timing plug or is the cold plug also for lower exhaust temps.I use only for short quick runs.denso or ngk which would be a better fit for gas.great learning experience.thanks
 
I find it strange that everybody seems to think that alcohol runs cooler than gas. How can that be? Alcohol, if run properly, makes more horsepower than gas. How can it do that if the temperature in the combustion chamber is lower? I'm sure that there is a small increase because there's more alcohol in the combustion chamber, but is that the only reason? I've always had this idea that an engine is a heat pump, more heat, more HP. How can alcohol make more HP with less heat in the combustion chamber?
 
alvin l nunley said:
I find it strange that everybody seems to think that alcohol runs cooler than gas. How can that be? Alcohol, if run properly, makes more horsepower than gas. How can it do that if the temperature in the combustion chamber is lower?
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Al,

I believe that the amount of power an engine can produce is based on the *delta* in temperature in the combustion chamber between the fresh charge and the amount of heat/energy produced in combustion, as well as the total BTUs created from combustion. It's not an absolute temperature thing. Methanol can show a lower EGT number than gasoline, yet still produce more power/work.
 
To add to above posts, the heat required to evaporate methanol is greater, resulting in a colder, denser charge entering the cylinder.

More dense equals more oxygen molecules in the cylinder.

Also, burns slower, so more timing is required.
 
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I know with nitrous on our drag car we run 3 degrees colder plug. nitrous when it ignies is hot like alky...gas is not as hot of a charge when it ignites like alky."alky fires hotter " that's why you get more power than gas"so if you want more btu's for power why run 11 degrees colder plug with gas? gas calls for a w16 fsu I've been told run the w27fsu....I might be wrong idk I know alot of you guys know these 4 strokes.im just asking because I'm trying to learn what works best.
 
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Pete_Muller said:
Al,

I believe that the amount of power an engine can produce is based on the *delta* in temperature in the combustion chamber between the fresh charge and the amount of heat/energy produced in combustion, as well as the total BTUs created from combustion. It's not an absolute temperature thing. Methanol can show a lower EGT number than gasoline, yet still produce more power/work.
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Could you give me some references, that I might read up on this thing you're talking about? And thank you.
 
95 shaw said:
To add to above posts, the heat required to evaporate methanol is greater, resulting in a colder, denser charge entering the cylinder.

More dense equals more oxygen molecules in the cylinder.

Also, burns slower, so more timing is required.
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I only see one oxygen atom in all of these components. I didn't find a picture of
gasoline ,if there is one. From Wikipedia.


Some of the main components of gasoline: isooctane, butane, 3-ethyltoluene, and the octane enhancer MTBE
 
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