Did a recent build on my 06. Did the timkin conversion, welded the crank, went to 95" Keith Black, 10.3:1 after gaskets, 55G cams, Dan Vance Heads, Pro Pipe, PCIII - wondering how that might effect plug gap? Factory says .040...nightrider says every 12.5 increase HP should reduce gap .004. So if factory is ball park 60HP on a TC88 - and my build gets me to about 105HP = .026. Seems way too low and will cause problems at higher RPMs. Currently at .038 but wondering if I might be missing any performce/power.

 

I run mine a .35 on NGK DCPR7Es, purs like a kitten

 

plug gap should be reduced with compression, not HP. it's compression that determines the resistance of the gap that the spark has to jump.

I'd second new_mentor70 at .35 gap....

 

I have the same build as yours New_Mentor. Btw, are you the same guy as
the "old" Mentor. Anyhow. I have the NGK DCPR7EIX on my bike and gaped
them at .040. Would you suggest I try .035?

 

I run .035 in mine as well. But if you have no running issues than .035-.040 is fine IMO.

 

Yes, im the dude formerly know as Mentor70. couldnt figure out how to get in after the change so I made a similar sig in hopes someone would remember me

If your plugs are the Iridium tip plugs i do not recomend messing with the gaps, for damage to the electrode may occur.

 

Folks,we have tested this out many years ago on our dyno.
.035" is in fact, the gap you want, for a street bike that has a increased compression ratio.
Double plugs, .025".
Our AHDRA Modified Class 108"(sits on showroom floor still) @ 17.25:1 CR,(167 hp) liked .020" gap, dual plugs.

 

here is what a very smart engine/motor builder told me regarding plug gaps. Use the smallest you can get away with. He said .040 works great on a stock engine becasue the spark (kernal) is large and can ignite the whole mixture but as you make more compression ie more power if you have too wide of a gap the force can blow the spark out so you want a small kernal of spark. He also recommended .035 to .038.

 

He is correct.
As the cylinder pressure comes up, the turbulence in the chamber increases dramatically,
and in the gap is too wide, it'll literally blow the spark out, as you have said.
When the gap is tightened, the spark intensifies, and is much harder to be disrupted at that point.
That was taught to us, by ourselves, while attending the school of hard knocks years ago.
Scott
BTW, a motor is an electrical device.

 

Good feedback - thanks all. Will drop to .035 tonight. Thanks.