which plugs

[nitrotommy]

I have twin 540 cube engines with B&M 8-71 blowers, I is hell to start after sitting for a week, which plugs should I run, now i'm running NGK V-9's, so I ordered a new set and they are not the same, longer threaded section, any idea's, I think they might be too cold of a plug, when it starts it doesn't run on all cylinders, but after 2-3 minutes they all start to work and it runs great.

[obnoxious001]

The 9's are a cold range, what I used to run in my race engine. Depending on your ignition system, and the rest of the engine components, and even the speeds you run, you may have fouled the plugs.
You brought up an interesting point, saying the replacements you ordered are different. Are you certain the plugs that are currently in the engine have the correct thread length? You didn't state what heads you have, but if you have a shorter plug in a cylinder head that actually requires a plug with 3/4" of threads, it's not going to want to run right.
Give us a little more information?

[nitrotommy]

MSD ignition, brodix heads, the boat was used for racing, now I just use it for running the chesapeke bay, but not wide open, usually around 3000-3500 RPM's. Thread length is different because of different part number plugs, they had the smalled threaded plugs in the boat NGK said go with the longer shaft, I still think a -9 is too cold for just running around.

[DUCKY]

The length of the threads depends on what the heads are machined for. Thread length has nothing to do with heat range. Considering the fact that the stock plug for a BBC is a NGK BR6FS, I think you are right about the 9's being too cold for a non-racing application.
If the heads require a long reach 14mm thread with gasket seat and 5/8" hex. (most aluminum heads do) I would suggest NGK's R5672-A8's if you have no clearance issues, or the R5671-A8's if you do have clearance problems between the plugs and piston. Keep in mind that these are a non-resistor type plug and may not be ideal for your application depending on ignition system, and other on-board electronics.

[DUCKY]

I just re-read your post...Did someone put a short reach plug in heads that are machined for long reach? That will make all kinds of problems, as will a long reach plug in a short reach head. I think you need to figure out what you heads are machined for if you can't tell for certain. Get the numbers off the heads and call Brodix.