Indexing Sparkplugs
Senior User
Joined: Oct 2003
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From: in a house
its mainly done for close valve to piston clearances in a higher compression race engine or people runnig big shots of nitrous. you may not get much benifit on a daily driver.
maybe a true race engine builder here can elaborate on this.
maybe a true race engine builder here can elaborate on this.
Senior User
Joined: Oct 2003
Posts: 347
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From: in a house
no. that I wouldn't know much of so you can understand my confusion.
I was on the line of orienting the opening of the plug for the purpose of clearance or for controling the burn of the mixture from the quench area by usaully setting the plug to face the exhaust valve.
like to know more about the firing order change but I don't think thats the heart of the question. but maybe, Brian?
I was on the line of orienting the opening of the plug for the purpose of clearance or for controling the burn of the mixture from the quench area by usaully setting the plug to face the exhaust valve.
like to know more about the firing order change but I don't think thats the heart of the question. but maybe, Brian?
FE "Freakin Expensive"
Joined: Dec 2003
Posts: 6,461
Likes: 4
From: Smith Mountain Lake, VA
Well sorry about that...the plug indexing to the face of the valve Im not firmiliar with?
There is a set-up tho that some of the Heavy Hitters use..they have a cam ground to change the firing order of 2 cylinders..to make a slightly less load on the lower end..
was what I was thinking you meant..LOL!! Have a good day. Russ
There is a set-up tho that some of the Heavy Hitters use..they have a cam ground to change the firing order of 2 cylinders..to make a slightly less load on the lower end..
was what I was thinking you meant..LOL!! Have a good day. Russ
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Posting Guru
Joined: Dec 1999
Posts: 1,903
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From: Copley, OH
You orient the plugs so the gap faces the intake valve. It's supposedly worth a couple of HP. I do it on the racecar; it's not worth the time or effort to do it on the street.
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Elder User
Joined: Jun 2003
Posts: 886
Likes: 1
From: Houston/Hope BC
And even more on the subject:
>Last night when reading thru some old hotrod mags i have, i came across
>an ad for sized washers that you put on your spark plugs to assure the
>plug gap is facing the proper direction for maximum burn of the air-fuel
>mixture. Does anyone out there know if this really helps performance and
>if so how much??
The purpose of indexing plugs is to a) place the ground electrode where it
will cause the least disturbance to flow and b) where there will be
maximum exposure to the mixture flow at the instant of ignition.
The direction of mixture flow is variable and may even change with RPM
and tuned header/intake action.
Like a lot of other things you can do, indexing the plugs may or may
not help your particular engine. The only way you can discover
whether it helps or not is to try it and carefully record the results.
Note that extensive testing may be required because the proper direction -
if any - of the ground electrode must also be determined experimentally.
This is absolutely not a "bolt'n'pray" type of tuning tool.
Sourced from: http://yarchive.net/car/spark_plugs.html
(no copyright)
>Last night when reading thru some old hotrod mags i have, i came across
>an ad for sized washers that you put on your spark plugs to assure the
>plug gap is facing the proper direction for maximum burn of the air-fuel
>mixture. Does anyone out there know if this really helps performance and
>if so how much??
The purpose of indexing plugs is to a) place the ground electrode where it
will cause the least disturbance to flow and b) where there will be
maximum exposure to the mixture flow at the instant of ignition.
The direction of mixture flow is variable and may even change with RPM
and tuned header/intake action.
Like a lot of other things you can do, indexing the plugs may or may
not help your particular engine. The only way you can discover
whether it helps or not is to try it and carefully record the results.
Note that extensive testing may be required because the proper direction -
if any - of the ground electrode must also be determined experimentally.
This is absolutely not a "bolt'n'pray" type of tuning tool.
Sourced from: http://yarchive.net/car/spark_plugs.html
(no copyright)
Thread Starter
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Posting Guru
Joined: Jul 2002
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From: Paola, KS
Yes I was reffering to the orientation of spark plugs.
So which way should they point I have the indexing washers. My head man told I should index them for a few more horses but, I thought he said to point the opening at the exhaust valve. There are no clearance issues in this motor.
What rapidruss is refering to is the same reason a 302 firing order is different than a 302HO and a 351W. A stock 302 fires 4 and 8 (if I remember right) in sequence in the order which they say causes heavy load on the rear main bearing.
So which way should they point I have the indexing washers. My head man told I should index them for a few more horses but, I thought he said to point the opening at the exhaust valve. There are no clearance issues in this motor.
What rapidruss is refering to is the same reason a 302 firing order is different than a 302HO and a 351W. A stock 302 fires 4 and 8 (if I remember right) in sequence in the order which they say causes heavy load on the rear main bearing.
Last edited by Brian460; Jun 17, 2004 at 06:08 PM.
Posting Guru
Joined: Dec 2003
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From: Northern California
I have also heard that when indexing your plugs, have the opening face the intake valve. It's only good for a few HP, and I doubt you will feel a difference.
I've never heard anything about it being due to piston clearance to the electrode.
I've never heard anything about it being due to piston clearance to the electrode.
Elder User
Joined: Mar 2004
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I have personally never tried it, but I have seen other drag racers that in effect cut the ground electrode off. They leave just a nub at the side of the plug. If you have the ignition system to jump it, it throws a heck of a long spark.
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Posting Guru
Joined: Jul 2002
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From: Paola, KS
Originally Posted by ga302p
I have personally never tried it, but I have seen other drag racers that in effect cut the ground electrode off. They leave just a nub at the side of the plug. If you have the ignition system to jump it, it throws a heck of a long spark.
Not saying that drag racers don't do it, but that is a good way to burn a hole in the top of your pistons. I have seen it happen.
Elder User
Joined: Jun 2003
Posts: 886
Likes: 1
From: Houston/Hope BC
I can assure you indexing works. The jap's call out a spec for their modern outboard engines. Why? For the two reasons above, flow and flame front. I expect flame front is about 90% of the reason. With precise engine controls and sensors, they are getting every last molocule they can to burn at exactly the right time to squeeze everything out of the fuel and the engine is so sensitive to variation that the plug orientation will upset the system. If you do not have the sensors (like a G-tech) and a digitally controlled engine, indexing has got to be a lot of hours invested for little or no return. So....
Brian, I see how removing the ground electrode is a bit radical but I don't understand why it is linked to burning holes in pistons. Please explain. Thanks
Brian, I see how removing the ground electrode is a bit radical but I don't understand why it is linked to burning holes in pistons. Please explain. Thanks