Spark plug cap resistance ????

S

sxr700

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Looking at getting a new set for my machine. They have 0, 1000, and 5000 ohm caps. I think the stock ones are 5000. Would 0 ohms give a better spark??? anyone try or know if it will work
 
is there any other down side other than the interference. will it screw up the CID box????. and will you get a stronger spark with lower resistance.
 
From what I have read you need around 5k ohms to get good spark and keep the RFI down, this can be extended to 10k but performacne may suffer. when you run a BR9EV plug the R means the plug has a 5k resistance built in, plus the 5k at the cap. so you can either run a non-resistacne plug and 5k cap, or non-resistance cap and a 5k plug to achive optium spark, and not piss off the neiborhors TV.

does anyone have a different experience???

Also how long do spark plug caps last for ???
 
I really don't understand how the resistance would effect RFI? Isn't RFI a function of frequency (hz)? Can someone explain this to me.
As for going to 0 ohms in your cap I do think this is a bad Idea. I don't know what the voltage coming off the coil is but I suspect it's pretty high given the resistance spec of the cap at 5K ohms.
Ohms law, E (voltage) = I (current) x R (resistance)
Lets say for Kicks your getting 1 amp of current through your 5K ohm resistor.
Your voltage at the coil will be 5000V (I'm sure the current rating is lower)
If you go to a low ohm cap, say 1 ohm, and the voltage off the coil remains the same 5KV, your going to see 5K amps. (5kV = 5K amps x 1 ohm.)
That can't be good for the cap or the wires.
I think I'd stay with the specified resistance.
 
Last edited:
sxr700 said:
Also how long do spark plug caps last for ???
Click to expand...

I can tell you that at around 5000 miles on my 97 700SX that my plug caps were out of spec. Instead of measuring 5K ohms they were in the Meg area.

I installed some NGK caps.

Unscrew the old cap and snip off a short chunk of the spark plug wire so you get fresh wire to screw the new cap onto.

Tod
 
The resistence acts as a supressor to the "spark" noise in the RF band that you would hear if the resistence were not there. As the voltage jumps the gap a spike across all rf bands is heard during the instant of the spark (This is how early radio was achieved). Multiply this by 3000 at idle for instance, if your sled has a 1500rpm idle, and you can see where this could be an issue.

While there are non-resistor plugs out there why risk it. The performance increase if there is any is not worth the risk to your equipment. I'd hate to smoke a coil out in the woods and need a tow or worse have to hoof it out. Stick with the stock plugs and wires. BR9ES's are cheap and easy to find. The boots do seem to have a limited life span on some sleds but I have yet to replace a boot on a Yamaha. On a Polaris is another matter.
 
FuzzButt said:
The resistence acts as a supressor to the "spark" noise in the RF band that you would hear if the resistence were not there. As the voltage jumps the gap a spike across all rf bands is heard during the instant of the spark (This is how early radio was achieved). Multiply this by 3000 at idle for instance, if your sled has a 1500rpm idle, and you can see where this could be an issue.

While there are non-resistor plugs out there why risk it. The performance increase if there is any is not worth the risk to your equipment. I'd hate to smoke a coil out in the woods and need a tow or worse have to hoof it out. Stick with the stock plugs and wires. BR9ES's are cheap and easy to find. The boots do seem to have a limited life span on some sleds but I have yet to replace a boot on a Yamaha. On a Polaris is another matter.
Click to expand...

Thanks FuzzButt (first time I ever said that) that makes sense.
 
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