I just got a set of champion RS15LYC plugs but the reach is way more than the stock plugs for the 305 tbi will if have any clearance problems inside the engine?... here are the plug specs so you dont have to look them up


Resistor plug, 14mm, .708" reach, taper seat, 5/8" hex head, extended gap, projected core nose, copper core design

 

No clearance problems. The plug points basically straight in from the side so unless you're running domed pistons (stock motors haven't had domed pistons since the early 70s) it can't hit anything unless it sticks in so far a valve whacks the side electrode (very unlikely).

 

thanks

 

Whatever you do, don't put a longer reach plug in a head than the stock spark plug! The stock champion plug for that engine is a RV19YC with a .460" reach.
The RS15LYC has a .708" reach.
It's not the danger of hitting the piston, there's plenty of room. The engine will run fine.
The problem is that the threaded portion that sticks in the combustion chamber will become coated with carbon.
When you unscrew them you will unscrew the threads right out of the heads.
Needless to say, I've had to clean up somebody's mess like this before. (can you say "new heads"?)
On the other hand, using an "projected core nose" spark plug (longer electrodes) won't cause a problem in a (newer than '70) stock engine.

 

Supervisor's right- I didn't know we were talking about a plug with longer threads- I thought we were just talking about a projected nose plug (longer center and side electrodes). Definitely DON'T use a plug with a longer threaded portion.