Hello again Jon

Although off the original thread of this post...I find your info. on 2 piece head very interesting.

Sorry to bother you further but you seem to be 'well up' on this technology of which I know little.

Are the inserts in low, medium and high compression with medium the standard fitment or is the range wider.

Are alterations to static timing and / or carb jetting required if inserts changed or is it just a straight forward insert swap.

Have you come across many riders using this option to adapt power output to their riding style or is it mainly for altitude tuning. Just wondering how many 'ordinary club riders' actually use this potentially useful 'tuning tool'.

Takes me back to the 80's when I converted motocross YZ400 monoshock ... which were been sold off new at mega discount.... into enduro trim.

Used the extra base gasket + 2 extra head gaskets method to tame the mega explosive power output which only a top rider had a chance of controlling...which was no doubt why they were been sold off cheap.

Also some good old Yorkshire "rack of eye and twist of mouth" porting mods as well as a bit of trial and error ignition retarding and carb jetting.

Surprisingly it was actually quite a success relative to cost and I kept bike for 3 years.

Assume power valves never made it to trials bikes due to weight as I found them very useful in tuning the 'hit' of the power output delivery via simple shim changes on 1990's KTM 300 enduro.

Trips down memory lane now halted....

All the best

david

Hello again Jon

Although off the original thread of this post...I find your info. on 2 piece head very interesting.

Sorry to bother you further but you seem to be 'well up' on this technology of which I know little.

Are the inserts in low, medium and high compression with medium the standard fitment or is the range wider.

Are alterations to static timing and / or carb jetting required if inserts changed or is it just a straight forward insert swap.

Have you come across many riders using this option to adapt power output to their riding style or is it mainly for altitude tuning. Just wondering how many 'ordinary club riders' actually use this potentially useful 'tuning tool'.

Takes me back to the 80's when I converted motocross YZ400 monoshock ... which were been sold off new at mega discount.... into enduro trim.

Used the extra base gasket + 2 extra head gaskets method to tame the mega explosive power output which only a top rider had a chance of controlling...which was no doubt why they were been sold off cheap.

Also some good old Yorkshire "rack of eye and twist of mouth" porting mods as well as a bit of trial and error ignition retarding and carb jetting.

Surprisingly it was actually quite a success relative to cost and I kept bike for 3 years.

Assume power valves never made it to trials bikes due to weight as I found them very useful in tuning the 'hit' of the power output delivery via simple shim changes on 1990's KTM 300 enduro.

Trips down memory lane now halted....

All the best

david

I imagine we can stray off a little and anyone who wants to put us back on target can chime in.

From what I understand, there are three choices as you describe. Not a lot of difference but the change is noticeable. For instance, in 2T stadium racing quads I would run a 21cc chamber at sea level and a 19cc chamber at the Denver, Colorado races (one mile altitude change). Static timing is not adjustable normally in the Pro's and mapping is handled by progammed electronics in the CDI module. For higher altitude you might want to set the switch to the "sun" setting (more agressive mapping advance)as due to the lack of available Oxygen and lesser barometric pressure, you need to start the combustion process a little sooner. This would also include using lower octane fuel, which burns faster than race fuel in most cases and part of the reason that the high octane pump fuel available in the Colorado mountain area is two points lower than the high octane fuel available on the "flatlands" here in the U.S. The riders I know who have used the high-comp inserts have not had to re-jet from what they tell me.

A rider who has used the lower-comp insert said he did not have to re-jet. I'm assuming that the overall configuration (which would include squish clearance, differences in piston/squish band angles, squish band width and radius measurement at the squishband/center chamber transition), other than volume in the center hemi chamber, is essentially the same in all three heads.

Jon

Thanks for response Jon

Helpful to get 'up to date' with latest developments.

When it comes time for a change from 'old yellow'....odds on another gasser.. it certainly helps knowing all factors available for tuning to personal preferences.

Given that change not envisaged in immediate future I think that my head insert query just about 'wrapped up'.

Thanks again for your time with your input.

All the best

david