I thought I would bring up a subject which has been touched on elsewhere on the web, but is still unclear. I was just going to make it an article, but thought I would place it here for a while to gather more input.

-This according to Corvette Central

This is the only rotor on the market that has the correct extended copper tip that closes the gap left by other rotors between the rotor tip and the distributor cap terminals. All rotors since the 70's have a 1/8" gap between the rotor tip and the distributor cap terminals. In the 60's this was the rotor that was used by all the Hi Performance GM Engines! No matter what ignition system you have, you need this rotor.

This is transcribed from "Performance Ignition Systems" by Chrisopher Jacobs.


While you've got the distributor out you can improve engine performance by modifying the rotor in two ways. First, grind the rotor tip back to make a bigger air gap (race application only, illegal for street use). This acts like a booster gap in sparkplugs in thaI it allows coil voltage to build up behind the gap. After this voltage has built up sufficiently to easily jump the spark gap in the combustion chamber. Then and only then will it be strong enough to jump the distributor gap. In other words, it takes more voltage to jump the distributor gap than the spark gap, so if there's sufficient voltage to jump the distributor, you can be absolutely certain there will be enough to jump the spark gap.

What's the advantage of letting coil voltage build up before connecting it to the sparkplug? Because it takes time for coil voltage to increase. If the voltage reaches the spark gap before it's ready to make the jump, the spark gap, if fouled or wet, will suck so much energy out of this voltage, it will never get strong enough to make the jump.

By grinding back the tip of the rotor blade about 1/8-in. shorter, you can enhance this booster, gap effect.

If you've phased the distributor-race application only-you'll also benefit if you grind the tip of the rotor blade to a point. A pointy rotor has two advantages. First, the spark jumps cleaner and crisper; that is, more yes/no rather than a gradual arcing. Second, the pointy tip increases the precision of the phasing. The problem with grinding the rotor for street application is that the sharp tip will erode in about 500 miles. Remember, the rotor passes eight times the sparks that a spark*plug passes. Also the tip needs to be wide enough to tolerate the variation in phasing caused by the vacuum advance.

It is said: At some point in the late 60s the rotor gap was widened to about .125" to better control RFI.
Many wide gap rotors are listed as "Extended Tip Rotor". The best way to identify the real extended tip rotors is to look at the tip. The tip of the extended tip rotor is tapered to a slightly narrower tip. The wide gap rotors have a wider tip.

The easiest way to find the correct rotor on ebay is to search like:
Corvette extended tip rotor