Spark Plugs

[mikey]

Having suffered a backfire through one cylinder I found one of my plugs was not detonating properly. Further investigation revealed a second plug misbehaving.

A bit unusual as the plugs have done very little mileage - NGK BCPR7ES. The engine is well tuned so the heat range at 7 should be about right. Doing a bit of a web trawl, I found the following on the NGK site.

Mallory, MSD, Crane and Accel also produce a high output ignition CDI system, however, these should not be confused with a marine style CDI as mentioned above. For an automotive high output CDI system it is imperative you consult that manufacturer for plug specifications for their system. Some high out put systems specify the use of resistor plugs, while others will fry the internal plug resistor turning its 5k ohms into 60k ohms.

As a rule, performance is in no way impaired by resistor spark plugs. The only exception to this may be some models of high output CDI specify non-resistor plugs.

I am running an MSD with around 45 thou gap and I am just wondering if iy may be that the plugs have been cooked, especially as it had a bit of a session on the rig at Tims (makes me woder what the BHP would have ben with them firing properly).

Anybody got any knowledge out there and if you are a guru a good plug with a pretty well tuned motor. I will report further when I do a bit more research on MSD etc.
MIke

[mikey]

For your info - off the MSD forum.

These examples are just starting points to get you going in the right direction. Every application is different and should be tested and tuned:
Compression Spark Plug Gap
Up to 10.5:1 .050 - .060
10.5:1 – 13.0:1 .040 - .050
Above 13.0:1 .035 - .045

As for resistor or non resistor plugs we suggest the use of the resisted spark plug.(less RFI)

Your experience on plugs still appreciated
Mike

[wilf]

Can you tell us about the engine? What is it, what has been done to it etc.

I ought to remember but maybe too much wine last weekend killed off a few (more) brain cells.

[Clarkson]

Originally Posted by mikey

Having suffered a backfire through one cylinder I found one of my plugs was not detonating properly. Further investigation revealed a second plug misbehaving.

A bit unusual as the plugs have done very little mileage - NGK BCPR7ES. The engine is well tuned so the heat range at 7 should be about right. Doing a bit of a web trawl, I found the following on the NGK site.

Mallory, MSD, Crane and Accel also produce a high output ignition CDI system, however, these should not be confused with a marine style CDI as mentioned above. For an automotive high output CDI system it is imperative you consult that manufacturer for plug specifications for their system. Some high out put systems specify the use of resistor plugs, while others will fry the internal plug resistor turning its 5k ohms into 60k ohms.

As a rule, performance is in no way impaired by resistor spark plugs. The only exception to this may be some models of high output CDI specify non-resistor plugs.

I am running an MSD with around 45 thou gap and I am just wondering if iy may be that the plugs have been cooked, especially as it had a bit of a session on the rig at Tims (makes me woder what the BHP would have ben with them firing properly).

Anybody got any knowledge out there and if you are a guru a good plug with a pretty well tuned motor. I will report further when I do a bit more research on MSD etc.
MIke

Hi Mike,I got my plug gaps set at 50 thou with no misfiring, Can't really help with plug type,but if it was misfiring on tim's dyno, I am sure he would of picked it up!

Might need some help from you to fine tune my mighty demon on the idle circult?

[mikey]

Yes I am sure we would have although it may explain the range in exhaust temperature on a couple of the cylinders if they were only starting to break down - dont know enough about it I'm afraid.

However I am finding the analytical part of deducing which plug to go for at present a tad difficultas the manufacturers put pleanty of furry dice hype on the net, but little useful info.

Mike