Hey Kev, Freez, others...

Anyone know the effect of just a hight comp piston - now other mods?

- GF-

We used to race Supermono (single cylinder in road chassis - generally RGV chassis with XT600 motor) and we used high comp pistons, and bored out as well

Now, I don't know about the XT660X motor, but we had to run avgas (otherwise would blow head gaskets) and would crack crankcases fairly often - about every 18 months. But they went like you know what!

Also ran different camshafts.

As I said, don't know about the new engines, especially in regards to fuel injection over the carbs we used to run.

I reckon reliability would be compromised with a high comp piston.

That mod would be great & I have tried for sometime to find a piston that would work, I even had JE pistons doing some research for me on the dimentions I gave them.

Todate I have not found a straight drop in piston 100mm bore with a higher compression then 10:1.

__________________
Click here to join the XT Supporter's scheme

Mods that I have done to my XTX's

My 04 XTX
Stage 1 & 2 DNA filters / Kev fuel mod / snorkel mod / Drilled air box mod / Engine breather mod / Fork Spacer mod / 15w fork oil /
[
My 07 XTX
Raptor 700 cylinder 102mm / Modified Crank Case to take a 105mm Raptor Cylinder / 11:1 102mm JE Raptor piston / Stage 1 Raptor Hot Cam / Ported head / Colder Spark Plug / +2mm Throttle body / DNA stage 1 & 2 filters / Modified Air Box / Snorkel removed / Worry Brothers stage 2 filter cover / 6mm & 8mm Bolts Replaced with Titanium Bolts / Recovered seat in Black / O2 Eliminator /

My 09 XTX
59HP at the rear wheel / Stage 2 Raptor Hot Cam / DNA stage 3 Air Box / Carbon Can Exhausts / Modified Exhaust Link Pipes / PCIII With Custom Fuel Map / Wideband Commander O2 Data logger / LCD100 Dyno Jet display & fuel adjuster / 2500 OHM HT lead instead of a 10K OHM XT lead / Extra Coolant Cooler / Protaper Fat Bars / Tail Tidy With LED Tail Light / OKE Protection Knobs / LED indicators / AIS blocked / Modified rear sprocket rubbers / Rear Foot Pegs removed / 09 ECU With 02 Sensor Changed To A 06 ECU / Complete wiring harnes Changed from 09 to 04 / Home made LED resistor flasher / Hole drilled in the fuel tank filler neck to allow quicker filling / Modified Bar End Weights / Progressive front fork springs, 15W fork oil, forks lowered 25mm, used XTR rear links lowering the rear 20mm, rear spring one click stiffer / Changed front & rear guards from blue to black / 47T rear sprocket / Speedo Healer V4.0 / Kev throttle cam mod / Throttle grip mod / The new 2010 O2 sensor mod is out, works a treat, The new 2012 O2 Controller is out, PM me for details

Now ride a 2018 MT09SP ABS + TCS

My KTM 990 SMR Mod book. http://www.ktmsmt.com/viewtopic.php?f=13&t=4946

I have been doing a lot of research into all kinds of performance parts and if the XT and raptor sleeve length is the same, then it might be possible to increase compression without replacing the piston. Taking the stock XT's 10:1 compression to around 11 and maybe a bit higher. That compression should be fine with a nice high octane fuel you can get from a normal fuel station and should add 1 or 2 HP.

If not, we can still increase compression with playing around with the head, but both options becomes a bit more complicated than just adding a new high compression piston.

Kev, do you know the combustion chamber volume on the stock XT head?

__________________


Disclaimer: any mod undertaken, are carried out at owners risk

I was going to measure the swept volume when I stripped my motor but did not need to in the end to fit the Raptor piston.

It is easy to machine the cylinder base, to up the compression ratio. Then degree the camshaft to get the cam timing right. One would need a slotted sprocket & once the cam timing is set you would pin the sprocket to the camshaft.

__________________
Click here to join the XT Supporter's scheme

Mods that I have done to my XTX's

My 04 XTX
Stage 1 & 2 DNA filters / Kev fuel mod / snorkel mod / Drilled air box mod / Engine breather mod / Fork Spacer mod / 15w fork oil /
[
My 07 XTX
Raptor 700 cylinder 102mm / Modified Crank Case to take a 105mm Raptor Cylinder / 11:1 102mm JE Raptor piston / Stage 1 Raptor Hot Cam / Ported head / Colder Spark Plug / +2mm Throttle body / DNA stage 1 & 2 filters / Modified Air Box / Snorkel removed / Worry Brothers stage 2 filter cover / 6mm & 8mm Bolts Replaced with Titanium Bolts / Recovered seat in Black / O2 Eliminator /

My 09 XTX
59HP at the rear wheel / Stage 2 Raptor Hot Cam / DNA stage 3 Air Box / Carbon Can Exhausts / Modified Exhaust Link Pipes / PCIII With Custom Fuel Map / Wideband Commander O2 Data logger / LCD100 Dyno Jet display & fuel adjuster / 2500 OHM HT lead instead of a 10K OHM XT lead / Extra Coolant Cooler / Protaper Fat Bars / Tail Tidy With LED Tail Light / OKE Protection Knobs / LED indicators / AIS blocked / Modified rear sprocket rubbers / Rear Foot Pegs removed / 09 ECU With 02 Sensor Changed To A 06 ECU / Complete wiring harnes Changed from 09 to 04 / Home made LED resistor flasher / Hole drilled in the fuel tank filler neck to allow quicker filling / Modified Bar End Weights / Progressive front fork springs, 15W fork oil, forks lowered 25mm, used XTR rear links lowering the rear 20mm, rear spring one click stiffer / Changed front & rear guards from blue to black / 47T rear sprocket / Speedo Healer V4.0 / Kev throttle cam mod / Throttle grip mod / The new 2010 O2 sensor mod is out, works a treat, The new 2012 O2 Controller is out, PM me for details

Now ride a 2018 MT09SP ABS + TCS

My KTM 990 SMR Mod book. http://www.ktmsmt.com/viewtopic.php?f=13&t=4946

Kev, I have started to loose a bit of faith in these off the shelf high compression pistons, especially the domed type ones.

If I work out mathematically, based on Volumetric efficiency, then I should be seeing massive power gains when you add a high compression piston.

For example on my XT, making 44HP at 5800 RPM on my dyno with a 10:1 piston , VE works out to around 101% If I do the same calculations with an 11:1 piston and assume VE stays at 101%, then I should be gaining around 4.5HP@ 5800 RPM with just the piston.

Now, I have never seen that big a gain from just a piston alone. Maybe 1 or 2 HP, but that�s it.

I think the dome pistons mess with the combustion process and also the flow in some way and therefore don't see the big gains.

My next bunch of experiments will be to see if I can use the stock, flat top pistons, push up the compression and hopefully gain a bit more power than the dome pistons.

On the raptor, you have a massive potential to play around with and I hope the XT has the same potential. The raptor guys claim you can push the stock piston compression up by 1 to 2 points. That�s a lot.

I was also thinking of measuring the cam degrees and then just having the cam and "mounting plate' split, turned to the correct degrees and then pressed back into place.

Otherwise I will see if we can slot the cam sprocket or even have a new, adjustable cam sprocket made up.

__________________


Disclaimer: any mod undertaken, are carried out at owners risk

maybee you need some of this

http://www.gizmag.com/designer-fuel-offers-more-mpg-less-emissions-less-cost/9467/

????


Colin