High comp piston
 

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.

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?

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.

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.

maybee you need some of this

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

????
:angel3:

Colin

OK so am I correct in understanding that:

1) We don't know of a high comp 'drop in' piston that is available for the XT660 motor?
2) A high comp Lets say (11.5:1) piston could yield anywhere from 1-2 hp though theoretically could be as high as 4.5hp?
3) No one has yet tried just upping the compression on this motor and measuring the results?

Both my Yamaha wr250 and wr450 had 11:8 compression ratios and worked perfectly on 98 octane pump gas. Why wouldn't the XT660 at the same compression or 11.5:1?

1/ We do not know of a HC piston of 100mm bore that will fit the XT.

2/ We do not know of a HC piston of a 100mm so the HP gain is theorey only if you are using a 10mm bore. We do know the HP gain with 102mm bore with a 11:1 piston.

3/ I have upped the compression from 10:1 to 11:1 using the Raptor 102mm piston & have full dyno results of Torque & HP gains.

I will make my next XT+++cc conversion 11,5:1. The Raptor boys run up to 14:1 with race fuel.

Is the 660 Raptor engine the same as the XT engine?
If so, these guys claim to have 100mm 11:1 pistons for the 660 Raptor engine.

The Raptor 660 piston is for a 5 valve motor with 5 cut aways on the piston crown for valve cleanace, the XT660 is a 4 valve motor with 4 cut aways on the piston crown, also the gudgeon pin is 1mm smaller on the Raptor piston..

Il pistone CP PISTONS � la stessa casa che da offtheroad da 102mm 11:1


Google
The piston CP PISTONS is made by the same factory to the one sold by off the road from 102mm 11:1

CP Raptor 102mm 11:1 piston sold by Off The Road 259 Euro

JE Raptor 102mm 11:1 piston sold on Ebay from the USA 108 Euro

Google:
Il pistone di 11:1 del raptor 102mm della CP in vendita presso Off The Road costa euro 259

Il pistone di 11:1 del raptor 102mm della JE in vendita su Ebay USA costa euro 108

So could you put the 5 valve raptor Head on the XT with the 11:1 piston?
:smilies0546:

No mate

why not?

Because it won't fit.

Different head, different camshaft lay out, 5 valve piston wont fit on the XT conrod & many other reasons.

OK I have not seen a Raptor.

It just seems a shame as it sounds like it has many things going for it.

In my simplistic world I imagined that at some point the build would be the same? Block gearbox mounting? Crankshaft? frame mounting points?:HeyHey_GOO2MN::HeyHey_GOO2MN:

If none of these things are the same then I guess it is not a compatible engine :walk::walk::walk::angel5:

quindi sono stato fregato ..avendo preso quello di Off The Road 259 Euro
non c'e nessuna differenza ?



Google:

then I was fregato .. having to Off The Road 259 Euros
there no difference?

A CP piston is better then a JE piston, but not at more then twice the price.

I fitted a JE piston to my bike & am happy with it so far.

Free translation:

Then I was conned when I bought the one from Off The Road paying 259 Euros when it's exactly the same as the other?

Maxx3 please note Kev is saying that the CP piston is better than the JE however that does not justify it being twice as expensive

Free translation

Maxx3 ascolta, Kev dice che il pistone della CP e' migliore del' JE pero' non necessita il fatto che costi il doppio, c'e' poca differenza

CP piston bought from the USA, 144 Euro

http://store.holeshotdesigns.com/cp-piston-raptor-.html

:incon_aargh[1]:

:incon_aargh[1]: azz che fregata che ne ho preso :sad10::076:
in pi� per la rettifica la moto � ferma pensavo che era in ghisa invece � nichelato

grazie CaptMoto

Which generally translate as a huge disppointment for having bought the wrong one and the fact that his sleeve can't be rebored apparently. Sorry to hear that Maxx3.

:bricks:

If it can't be bored get it resleaved.:smile[2]:

Be careful of some of the claims from the piston manufacturers. There are people claiming 14:1 and more compression. I have measured all of them, and I have NEVER seen one that could even get to 13:1 on a stock displacement Raptor 700. I have the largest dome available due to the availability of 3-D machining from Diamond racing (the manufacturer of my piston). My piston with a 9cc effective dome and a piston to deck clearance of .005", combined with the .028" head gasket comes to a total of .033" quench, will only do 13.3:1. That tight of clearance is really pushing your luck for a long term build. I promise there will be no carbon build up! Now you must take into consideration that other aftermarket pistons will have a piston/deck clearance of .050" or greater. When added to a gasket thickness of .028" that is a staggering amount of "quench" (.078" or more). They are just not able to get up to their rating. Even the pistons rated at a lower compression ratio usually fall well short of what they advertise.