spark plug/heat range issue

[jon79flavette]

I am running into a problem with early fouling of plugs. The motor runs like a champ, then after an hour or so of run time it deterorates rapidly. new plugs and I am back to good. I am running NGK r-5673-7. I am going to try the 6 NGK instead of the 7. a little bit hotter plug. Does anyone know if this will make a significant difference??? Or any other plug suggestions? Will the 7 heat range have a tendency to foul that quickly? or are there other issues?? I have been doing more around town driving, so this may accelerate the problem. Any thoughts appreciated. Jon

P.S. motor is a 70 LT-1, modified to about 420 h.p. running a 280/520 cam, holly 750 double pump, dual feed, if engine info helps. ported cast heads with 1.6 rockers.

 

[cruzer99]

My own opinion NGK's are most of the problem. Try Autolite or AC's. I always used AC's in the race car without a problem.
Just my .02..........

 

[RLP]

My stock 350 with a spread bore Holley was running rich. A magazine article says to adjust the idle screws on the sides of the bowl using a vacume gauge. Adjust to highes vacume. This worked great. It worked out to about 3 turns out on each side. I never had a Chevy to idle so good.

 

[jon79flavette]

as far as the autolite or others, do you have any suggestions. The NGK is a race plug, and seems to be recommeded by several people. We have a moroso track near by, and while this is more of a strret car than strip, they seem to like the NGK v-power race plug.

 

[gary b.]

Sounds to me your plugs are too cold.
1 or 2 steps hotter should help your problem.
I also agree with Ron, lose the NGK's and put in AC or Champs!
Good Luck! gary.