Posted by NITRO on June 04, 1998 at 16:33:33:
In Reply to: Re: NITRO can correct me if I'm wrong... posted by body on June 04, 1998 at 16:04:41:
Surprisingly enough, spark plug indexing had it's origins with some
of the high rpm small block Pro Stock engines of the '70's, and it didn't
have anything to do with power production by enhancing the burn quality.
Racers began indexing plugs simply because in an aluminum rod 10,500 rpm
drag racing engine, the rod stretch is about .060", and it doesn't take
much of a "tap" from the dome on the piston to close the plug gap. You
close the gap and you have no burn, so that's how indexing got it's start,
and people have been doing it ever since because "it's free power".
When all this started, we didn't have dyno's that were terribly sensitive. If a repeat run was within 2%, that was really good. Now we have dyno's that can measure the torque of an individual cylinder, as well as cylinder pressures/ degree of crank rotation. With this kind of accuracy, we can look at a lot of "little things". On engines which have one side of the plug shrouded due to combustion chamber shape, certainly can benefit from indexing the plug..in this case, the ground electrode should be in the shrouded area. The D16A6 Honda has the exhaust side of the plug in a small pocket in the chamber, and if the ground electrode is placed facing the intake side, there's very little accessability to the spark. The gain can be 4-8 hp depending on the chamber shape. On a really open chamber, the position would be relatively unimportant. On the "tiny" chambers that T.O.O. designs, we prefer to place the open side of the plug to the exhaust side, but there are a lot of other chambers that prefer the open side be biased to the intake side.
My best advice is to look carefully at your combustion chamber, and if it's configuration shrouds one side of the plug, index the open side to the unshrouded side.
Posted by 323racer (email@example.com)
on June 04, 1998 at 18:25:34:
In Reply to: Re: NITRO can correct me if I'm wrong... posted by body on June 04, 1998 at 16:33:33:
So you are saying put the plug gap towards the most open space in the combustion chamber. Most open space being determined by the amount of room surrounding the gap of the plug while the piston is at it's fullest position (TDC).
Posted by NITRO on June 04, 1998 at 19:30:49:
In Reply to: Re: NITRO can correct me if I'm wrong... posted by body on June 04, 1998 at 18:25:34:
You want to expose the "open sides" of the plug to areas where there's the greatest access to the mixture. The more you light innitially, the more you'll burn = more power + efficiency.