I bought the NGK-UR5 for my 502 carb with no blowers, what should I gap these at. I have heard both .035 and .040....thanks for the info

Those are a pretty cool plug for an N/A motor unless you've really upped the HP. I doubt you'll see any difference between 35 and 40.

What plugs should I be running in this motor then. It has a mild cam, alum heads, stainless marine exhaust, and 850 carb.

On NGK plugs the lower the # the hotter.. 6-7 heat range is a norm for a peformance motor.


Most people run the ac mr45t plug .

http://www.offshoreonly.com/forums/s...&highlight=ngk


http://www.offshoreonly.com/forums/s...ad.php?t=80948

I have had less than desirable results using the NGK UR series in a turobcharged application. However this was in a car. Believe it or not I have found the best plugs for boost applications were the AC Delco. Sounds strange but true. I thought I would share this incase you ever decided to get into abnormal aspiration.

Roby

I always used the R series plugs they are suppose to be made[assembled] in the USA they are considered a race plug.

The ur and br plugs are a standard automotive plugand most are a projected tip.
In a blown ,nos or turbo application if your not careful it will get the tips I have melted a few on the juice

I use NGK BR series plugs in my turbo cars...they came with them. I run up to 21psi of boost in one with no problems, key is tune and no detonation.

My boat engine, built by Innovation Marine uses NGK's V-Powers #7's in my 500hp 502ci motor and in their 600HP 540ci motor. So....the NGK works quite well for making power.