critter

iTrader: (9)

So, for my new high compression motor, I decided to get real racing plugs. I studied, cross referenced, and finally picked up a set of Autolite AR93 plugs and a set of AR473 plugs. I put a junk set of TR6's in to warm it up and break it in a bit. The I put the AR93's in gapped at 0.040". The next day it would not start. An occasional pop and bang, but that was it. I changed computers back, and not wanting to waste my good plugs, put the TR6's back in. The car ran again. I put the AR93's in and it would not start. So I put 4 TR6's in and it started with a bit of difficulty but ran on all 8. So I tried the AR473's at 0.032" (they came out of the box at 0.025") and it almost starts but not quite. Maybe I should have left them at 0.025 .....

Has anyone seen anything like this before?

simple

iTrader: (8)

are the plugs the same size physically, maybe the new ones arent protruding into the combustion chamber enuf?

i'm sure you already checked that over but thought i'd ask anyway.

88blackgt

what are the tr6s gapped at? are they the same style(are autolites too far out into the chamber and the spark is getting blown out?)

critter

iTrader: (9)

They are the same in that they are tapered seat, 14mm x 18mm, but they do project less into the chamber. But then that is part of the point - they should be colder than TR55s for the 13:1 compression. However, I don't know what "protruding enough" is on these engines.

critter

iTrader: (9)

The TR6s are gapped at 0.045". The Autolites protrude into the chamber less since they are colder plugs. I don't think the spark is getting blown out, but don't really know whey it won't light off with the Autolites gapped much closer than the TR6s.