I received the bulk of my KTM LC4 inventory on Monday from Penco in Montana, including a new ’03 to ’05 “high flow” cylinder head.
I was completely surprised to see that KTM is hand finishing these heads. They have taken the time to match and blend seats and ports, as well as deburr the combustion chamber.
Photos are of the head as it came out of the box… all I’ve done is to begin measuring things.
It is a very rough finish… not at all “pretty”, but certainly effective. Suzuki is the only other major player I am aware of that does this is, specifically on the GSXR 750 sport bike series.
It would have been nice to see what the head looked like before someone at KTM attacked it with a porting bit… but it serves as an example of a company aware of the potential for improvement and willing to put in the extra time and effort to obtain it.
There is a bit more to be had by additional blending and smoothing … I’m sure the worker that performed the task had no idea this head would land in my lap to be scrutinized, with observations posted on the internet, rather than go on to become part of a motorcycle.
There are a few sharp edges left in the combustion chamber… potential “hot spots”, as well as quite a few casting “buggers” in all the ports. The happy-go-lucky KTM employee may have gotten a little over zealous around the spark plug hole, leaving some very thin areas… I’ll have to get a spark plug and see if I have room to remove the exceedingly skinny spots without exposing the plug threads to the combustion chamber.
Also of note are the valve guide shapes in the ports. The intake guides have a nice flow-enhancing taper on them while the exhaust guides are of full diameter and are supported by the head casting almost to the end of the guide.
Part of this disparity in shape is the size of the ports themselves, the tapered guides help to improve intake air flow... and with the exhausts, to improve in heat absorption and transfer.
The new seats are fully 3-angle cut and have contact angle widths of .045” for the intake and .050” for the exhaust.
All in all, it’s nice to see that KTM puts in the extra effort, and I’m sure there is a flow improvement vs. the as-cast version… but it may take more work to “clean up” what was done than if I had done it myself.
What will happen to this head?
At some point, after I’ve dissected it as far as I can, I’ll finish what KTM started as far as blueprinting, assemble it and offer it as a premium exchange piece for 2003 to 2005 LC4s.
That's about it.