Indexing Sparkplugs
Elder User
Joined: Mar 2004
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Originally Posted by Brian460
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.
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Posting Guru
Joined: Jul 2002
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From: Paola, KS
On a flattop or domed piston in a street driven application cutting off the ground strap can cause the spark to occur between the spark plug and the top of the piston which when driven in a non-race or street application it will eventually burn a hole in the piston.
Elder User
Joined: Mar 2004
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The spark going to the piston top wont burn a hole in it, the inability to time the engine due to that occurrence will destroy the engine. I do not think that you could make it happen with a flat top unless you had done some serious milling. The piston would have to be closer to the center electrode than the side electrode for the fire to go to the piston instead of side electrode.
Senior User
Joined: Apr 2003
Posts: 432
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From: Oregon Coast
I have to do it on my dragster on one cylinder only as that piston doesn't have enough of a plug relief cut and when reved up it will close the gap on that plug. On the dyno,no engine I have ever owned or my builder has built ever gained one horsepower to indexing plugs. When done it has always been for clearance more than in search of power. Ground strap up way from piston dome and gap favoring the exhaust valve is the accepted way if you are determined to do it. Their small blocks are around 2.6 horses per inch and if it was a plus they would say so.
No trick plugs will add horsepower as long as the one removed was still firing to spec. Platinum, four electrode or split grounds all do nothing for horsepower unless it's special plug that it's resistance is programmed into the computerized engine controls. Then the wrong plug will slow you down. For the street you will see no measurable change from indexing your plugs.
As far as burning holes in the pistons that is a Top Fuel thing where they are running dual 44+amp magneto's. They even burn cranks and bearings if the heads are not grounded properly and the current grounds through the block instead. That's when they have a problem.
No trick plugs will add horsepower as long as the one removed was still firing to spec. Platinum, four electrode or split grounds all do nothing for horsepower unless it's special plug that it's resistance is programmed into the computerized engine controls. Then the wrong plug will slow you down. For the street you will see no measurable change from indexing your plugs.
As far as burning holes in the pistons that is a Top Fuel thing where they are running dual 44+amp magneto's. They even burn cranks and bearings if the heads are not grounded properly and the current grounds through the block instead. That's when they have a problem.
New User
Joined: May 2004
Posts: 14
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From: Arkansas
Thank god someone else knew that indexing was for clearance from piston domes. It is really not a super technical thing. Just make a mark on the insulator in line with the ground strap and use washers to make sure that the line and ground strap are up and away from the piston dome when torqued.
