Has anyone done a test to see what the actual power/performance gains are??? Like on the dyno...?? It makes scence to do it, but I haven't seen any physical #'s on the deal. My second question is have you guys played with their clocked location in the port?? My final question is how are you guys actually indexing them when you put them in?
Brian
Most of the time plugs are indexed mainly to keep them from hitting the piston. That's on close deck motors, dome pistons and tight quench clearances. The plug is indexed so as the ground strap is straight up. Most of my high compression stuff requires it. As far as Hp gain, I have no clue. But it does help in reading the plugs since they all see the chamber in the same position.
As Fiat said it is used to clear the piston dome mainly but many years ago a big time roundy-round racer did some dyno testing on indexed plugs and he found only 1 or 2 hp by indexing the plugs. Keep in mind this was 25-30 years ago and dynos weren't as precise as they are now. Now plug location in the combustion chamber is a whole different story. In the 60s when Ford was developing the SOHC 427 they were down on their projected power estimate with the plug located in the center of the chamber, they moved the plug to the top of the chamber and picked up 50 hp.
I tried it and nothing noticed.I used a marker pen to see where the plug was pointing.
Only time I index plugs is if I know they are too close to the piston. Also I've never noticed any difference in power, but I've never played with that on a dyno either!....
roughly 600 HP NA SBC
gained 7ft-lb of peak tq by indexing the plugs
No peak HP diff.
Dont remeber the rest of the curve.
BJH
I put some "extended tip" plugs in and apparently had one that wasn't indexed and it got banged by the piston. Closed the gap and jacked up the valve lash.....fortunatley no real damage but be careful with those extended tip plugs.
mirvin
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