1966 BB Question

[Darwin Kuhlmann]

HI,
I have a 66 390hp coupe. I have R43xls plugs, but my #5,7,4 and 8 cylinder plugs are carbon fouling. I read, I believe somewhere that the cylinders in front are hotter than the back ones, and GM realized that and installed plugs with different heat ratings. Would I be smart to put hotter plugs like R45xls in the back two cylinders on each side? (The R43xls plugs in the front cylinders look fine, without carbon on them). Any other suggestions for plug choices would be welcomed too.
Thanks!
Darwin

[Joe R.]

Re: 1966 BB Question

Darwin,

I've already been wrong once today in advice on the board so that's probably over for today. Maybe!

There could be many reasons for your plugs carboning up but the most common one is associated with valve guides. The heat generated by the BB detoriates the rubber seals on the valve stems under the valve springs and allows the oil to run down the stems into the cylinder.

This condition can be helped by installing new teflon seals on the valve guides. It can be done easily without removing the heads from the motor. This may help your problem and if you don't drive your 66 much it may be a quick fix.

Going to a hotter plug will only mask the real problem as it could be associated to a rich carb, rings or valve guides. If she is puffing the black smoke from the tailpipes, I would look to the carb. first.

Hope this gives you a starting place to fix the problem. Good luck!

Regards,

JR

[Duke W.]

Re: 1966 BB Question

GM never installed different heat range plugs on the same engine that I'm aware of, but their heat range choice for Corvette engines was about one range colder than what works best for normal street and highway driving.

In the case of SBs heat range "4" should be replaced with "5". and BBs should use one heat range hotter than OE, which would be "4", but some BB owners may run "5" which is two heat ranges hotter than OE. This rule of thumb applies to ALL horsepower ratings.

Since the Corvette is a relatively light car powered by relatively high powered engines, the engine rarely operates at more than a small fraction of full load, so a "hot" plug is required to prevent fouling. For race track hot lapping, one heat range colder than OE is usually a good choice.

The heat range is the second digit. The first digit - 4 - indicates a 14mm plug thread.

Carbon fouling can be caused by fuel or oil combined with too cold a plug.

Duke

[mike cobine]

Re: 1966 BB Question

#4, 7, and 8 are on the same manifold runner which would say one side of your carb is running rich. Why 5 is fouling? It could be the wire is cross-firing into 7 if the wires are non-shielded types (normal) and are wrapped around each other too much and thus losing some of its energy.

Go to the R44XLS in all cylinders and tune the carb. Different plugs in different cylinders would fall into the category of using different length velocity stacks on different barrels to equalize the flow length. Race only, not for the street and noticable probably only in the upper RPM limits if at all.

[Clem Z.]

for a street driven BBC corvette go to R45 XLS

the extended tip is cooled by the fuel wash so you can run a hotter plug with extended tips. check your plug wires with a ohm meter for high resistance or even open. also make sure that the plug wires are all the way into the distributor cap. the best way to do this is to slide the boots back on the wires,insret the wires into the cap and them slide the boots back onto the cap towers.

[Richard S.]

Re: 1966 BB Question

I have run 45XLS in my 66 427/390 for 8 years and 40,000 miles with excellent performance results....no fouling or any other problems.....and I usually add octane boost to every second or third fill up.

[Jon #40768]

Re: 1966 BB Question

My fouling problems pretty much ended when I also starting using the extended tip plugs, I believe 45s (I would have to pull a plug). The extended tip exposed the tip farther into the cylinder where it is exposed to combustion action, which helps garbage from forming. Heres what I used to do. 1. install a clean set of plugs. Run the car a day or however long it takes to color the plugs. 2. Pull the wires. 3. Before removing the plugs, mark the top sides of each plug, then remove the plug and keep them in order. 4. Examin the the plugs. What color is the plug. Oil or gas? Are the plugs colored on top or on the bottom. If the color is gas ( a gas smell can sometimes be detected), them look at your carburator. If the color is oil and the color is on the bottom, you have ring problems. If it is oil and on the top, it could be two things: a guide or guide seal problem, or and this was the problem with my big block, the intake manifold gasket leaked. On close examination, I found that the manifold casting hit the head castings just enough that the gasket was not fully compressed, resulting in leaks. I had to trim the head lips or the manifold (I cant remember as it was about 20 years ago). Between the plugs and the manifold gaskets, color my problem gone. If you ever pull the manifold, test fit the manifold on the heads to check the alignment without the gaskets before installing the gaskets.
Good luck.
Jon

[Darwin Kuhlmann]

Thanks everyone! *NM*