Indexing spark plug washer sizing....
Tourer
Joined: May 2010
Posts: 450
Likes: 2
High compression motors hide the electrode (so to speak) from the combustion chamber when the piston comes to TDC because of the dome of the piston. By turning the electrode towards the intake valve you are exposing the most intense part of the spark to the majority of the fuel mixture. Most of the increase in power comes from the fast, even burn of the charge. In any other motor your likely to see less then 3% of an increase in power.
As far as a source, the attachment I have in PDF form is too large or I would post it here. Send me an e-mail and I will send it to you.
Also, for whatever it is worth, I index the plugs in both of my bikes and do it with the crush washers from old plugs. I know, I know, heat transfer and whatever. Never had a problem with tune of a motor. Been in Phoenix in summer and Northern Michigan in winter.
As far as a source, the attachment I have in PDF form is too large or I would post it here. Send me an e-mail and I will send it to you.
Also, for whatever it is worth, I index the plugs in both of my bikes and do it with the crush washers from old plugs. I know, I know, heat transfer and whatever. Never had a problem with tune of a motor. Been in Phoenix in summer and Northern Michigan in winter.
Road Master
Joined: Mar 2010
Posts: 934
Likes: 54
From: SE Wisconsin
Outstanding HDF Member
Joined: Jan 2010
Posts: 2,916
Likes: 31
From: earth
I was under the impression the electrode needed to be pointed at the intake valve
...however the pics below shows it pointed in the middle of the valves:
perhaps fabrik8r could assist with explaining which was the electrode should be pointed to have the plugs properly indexed....?
...however the pics below shows it pointed in the middle of the valves:
perhaps fabrik8r could assist with explaining which was the electrode should be pointed to have the plugs properly indexed....?
Thread Starter
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Extreme HDF Member
Joined: Jun 2011
Posts: 10,216
Likes: 224
From: Glendale AZ
Thanks for the input everyone...going to index regardless, just makes sense pointing the plug in the right direction especially if the plug your using only has one grounding strap. I suppose if I were using a plug with four straps one or more would be pointing at the intake? But since I dont read much about those plugs being used much its best to keep it simple.....take care, Tucci
Road Master
Joined: Jul 2007
Posts: 914
Likes: 1
From: Republic of Texas
First I've ever even heard of this. Maybe it's because I don't have much experience with racing and high performance stuff - dunno. But if there really was all that much to be gained from such a simple idea, it does seem that it would be common knowledge everywhere.
Road Master
Joined: Jun 2011
Posts: 974
Likes: 13
From: Chesapeake Virginia
I won't commit to knowing what's proper, but I aim for the intake valve, that's about 4-5'oclock on the rear cyl, and about 7-8 'oclock on the front cylinder, using the same marking/ ground strap orientation technique as above. The bottom pic chamber view is "correct", but it doesn't match the top pic above deck view.
These heads are also no longer Hemi design and having a squish area should (by design) cause turbulence in the combustion chamber away from the wider edge of the bathtub shape as the piston approaches TDC.
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Road Master
Joined: Mar 2010
Posts: 934
Likes: 54
From: SE Wisconsin
Another non-expert here,
the way I always thought of it was, that it had nothing to do with the flame or combustion at all, but rather, the whoosh of clean fuel/air sweeping across the entire electrode for cleaning and cooling as the whole point.
Where as if the ground strap blocked the incoming clean fuel/air, deposits and uneven cooling of the plug would occur, slightly but more.
Nothing lost, (except spacer cost) something possibly gained.
the way I always thought of it was, that it had nothing to do with the flame or combustion at all, but rather, the whoosh of clean fuel/air sweeping across the entire electrode for cleaning and cooling as the whole point.
Where as if the ground strap blocked the incoming clean fuel/air, deposits and uneven cooling of the plug would occur, slightly but more.
Nothing lost, (except spacer cost) something possibly gained.
Outstanding HDF Member
Joined: Jan 2010
Posts: 2,916
Likes: 31
From: earth
I won't claim to be an expert either but in theory the main idea is to not have the ground strap in the way of the flame front towards the center of the combustion chamber. Picture one does that within the green arrows. The air/fuel coming into the cylinder should be flowing down with piston in all but the valve overlap portion at the beginning of the intake cycle where there would be intake air flow across the plug to the exhaust valve. Any flow across the plug is very short duration but will still tend to clean the plug without interference/turbulence from the ground strap when oriented this way. I would say 90* would be optimal and do not really understand any advantage of having it point toward the intake valve as it has been closed for almost the entire compression stroke when the plug fires.
These heads are also no longer Hemi design and having a squish area should (by design) cause turbulence in the combustion chamber away from the wider edge of the bathtub shape as the piston approaches TDC.
These heads are also no longer Hemi design and having a squish area should (by design) cause turbulence in the combustion chamber away from the wider edge of the bathtub shape as the piston approaches TDC.