Do you change the Heat Range on your spark Plugs when you raise your compression, my LT 500 was useing heat range of 8 and now runs on a 9, the stock DS is a DR8

 

[img]i/expressions/face-icon-small-wink.gif[/img]

 

I ran the dr8 for many years on 11.5:1 compression, and now I'm 14:1 and still running the dr8. actually I'm running the iridium dr8, but yes the same heat range.

 

Im at 13:1 and HPR recommended dr10. quite a bit cooler but Im also on the bottle.

 

DR 9 here 12.5:1 w/twenty shot

 

HPR says a 9 with the 14/1

 

That is interesting. HPR sent me 10's with my 730 kit and I am 13:1. I wonder if conventional wisdom has changed with testing?

 

I upped my octane to combat the added combustion heat you would expect from a higher compression. my coolant temp is now Lower running the 14:1 with 110 octane than it was running 11.5:1 on 93 octane. I pondered going up to the 9 heat range plug, but since I cannot see any additional heat elsewhere, I am assuming I am okay. I may be wrong, don't take my word for it, I am no expert. there really shouldn't be any adverse effect going to a dr9 anyway, except maybe in extreme winter cold, so if in doubt better safe than sorry. and who knows, come summer I may need to go to the dr9, and if so then I will.

there are thermocouples you can get in the size and shape of a plug's cush washer, to be mounted between the plug and the head for the purpose of measuring temps right at the plug as a direct result of combustion temp. if this testing has been utilized with the 14:1 and appropriate octane fuel, and the results indicated the need for a dr9, then that would be a definite change in conventional wisdom through extended modern testing. has anyone done this? the results would be interesting.

 

The color of the porcelin should tell you if you are too hot or too cold.

For my 250R, I went from 180 lbs compression and a BR8ES to 235 lbs of compression and a BR9ES. However, if you are running cooler, I see no reason to have to change your spark plug (unless you were running a LOT cooler).