NGK UR-4 OR UR-5 Spark plugs?

So its time for new plugs and im trying to find out what ngk's are right for my application should i go with ur-4 or ur-5 for a stock 72 455ci with a K&N filter and i will be installing a MSD blaster coil and some day new wires which i dont know if that changes anything. does weather or climate matter? what about gap should it be .040 or something different with a msd coil?

 

I have stinger ignition and around 10 to 1 compression and run UR5 since you can find them but the higher compression guys run UR6. I ran UR6 once and the seem to foul out in about 2 months of drag racing. I copied this from a website. "For NGK, the higher the number, the colder the plug". If you have lower compression you might be ok with the UR4's. Google NGK spark plug heat range.

 

Thanks for the reply ill try and find some UR-5's and see how it runs, when ever i look online at auto parts stores at the ur-5 application chart it does not mention the 455 will they fit just like a ur-4?

 

I gap my UR5 at .035 and it looks right.

 

That's awesome but just putting this out there has anyone tried changing the gap and see if it helps the performance?

 

I do not know if the same is true for the 455 engines but here is some info about a test with different plug pags:

http://www.mazda3forums.com/index.php?topic=162848.0

A quote from the famous Joe Sherman:

I have been dyno testing for over 40 years. The ONLY time I have ever seen plug gap make any difference is when you make it BIGGER.. I one instance, I got a 22 horsepower INCREASE by going to an 080 gap, from a 035 gap. I will admit, that is a real big difference, but I have had several guys tell me that the big gap was a big HP increase. I always run them at 055 to 060 in my serious race engines- The big gain was on a 990 HP big block, and the engine just would not make over the 1000 HP number.. When I did this, it was a really big deal, to make 1012 HP


JOE SHERMAN RACING

And another good quote from david Redzuds:

The size of the spark plug gap has three effects to be considered.

The larger the gap, the more voltage is required to jump the gap and to ionize the air space. If sufficient reserve voltage is available, a larger gap can be used. If not, the gap size must be reduced.

The larger the gap, for a given reserve voltage, the shorter the spark duration. If the gap is reduced we can increase the length of the spark duration, but at some point, it no longer makes any difference.

The larger the gap, the more advanced the equivalent ignition angle. The size of the initial flame kernal is determined by the size of the spark plug gap. If the gap is increased in size, the flame kernal is larger, giving the same effect as if it had been ignitied earlier. In most cases, the range of gap sizes available will have no more than a 3-4 degree effect on equivalent ignition timing. If slightly advanced timing can improve engine performance, then a larger gap is beneficial. If there is already too much ignition timing (or an excessively fast burn rate) then a larger gap will be non-beneficial and perhaps even destructive.

Now we have some trade-offs to consider. Which is more important to the performance of a given engine: longer spark duration or advanced ignition timing?

If spark duration is adequate (a spark lasting until TDC) and ignition advance timing is correct at each throttle and engine speed, then it becomes quite difficult to extract more power by use of spark plug gap. Now things like electrode tip heat range and tip temperature, squish velocity prior to TDC, chamber temperature and pressure emerge as dominant variables.

 

Wow Sean thats some good info. Thanks.