XT660 to XT734 Conversion
 

I am using Steve Ruth in Suffolk UK, to build the engine, and Cuervo Racing / High Desert Dyno in the USA for the parts and Cylinder Head porting.

My bike is a 2008 XTR, fitted with a DNA Stage 3 Airbox, a Power Commander, and Carbon Cans Exhaust.

I have already sourced a spare engine to use.

Specifications

+1 mm Valves
Uprated Springs
Cuervo Racing Ported/Flowed Cylinder Head
High Desert Dyno HDD5050 Camshaft
Bored out to 734cc with a CP 105.5mm 11:1 Piston
Bored out throttle body 2 or 3mm


To fit this piston, Steve is going the route of : boring out the existing Cylinder, and fitting a liner. This seems an easier option than fitting a Raptor Cylinder, and doesn't need Nikasil Plating either.

A more "lengthy" thread on this conversion is at
http://www.xt660.com/showthread.php?t=14763

Richard, your parts will be on their way shortly, this will be a great build but require some tuning at your end, we hope all goes well!

thanks Dan...it will be fun!

this I'll watch with interest

Should fly.

looking forward to the dyno prints :-)

Since im making about the same convertion im going to write about my project too from 660 to 734
the final list of mods is:
+1mm inlet valves
stage 3 reprofiled xt660 camshaft
kibblewhite valve springs
ported head
otr oil cooler
105.5mm 12.5:1 piston
throttle body +2mm
fcr style air inlet
racing ecu with custom map and rev limiter @ 9000rpm
Termignoni exhausts
Termignoni headers
WP 48mm upside down front forks
WP rear shock fully adjustable

Now im waiting for the front fork and rear shock to be fit and then the cylinder....

Looking forward to see the torque gains with the 12.5:1 piston.

the difference in tq from 11:1-14:1 is minimal but more compression will support a cam with more duration with more efficency



My expectations of Richards build is as follows
the pipes used on the xt differ greatly from the ATV and may promote more mid rpm gains but this should be somewhat close
Peak hp of 70 @ 7200 rpm making 50 hp by 5000 rpm
Peak Tq of 54 @ 5200 rpm making over 50 tq from 4800 to 7200

:smilies0944:

cripes..my expectations are a little lower on 68hp, but hoping for 57 ft/lbs at 5200.
So, Dan, very close to my estimate! All in all, it will be a very noticeable increase.

But my torque won't drop away from 5000rpm like it does with the standard cam......I will be gaining loads of torque over my current spec. at 7000rpm as well!!! The trade-off will be a slight loss of torque around 3500rpm, maybe 6ft/lbs, against my current spec. which has 42ft/lbs @ 3500rpm. (standard 39ft/lbs@3500)

However, this is all guesswork....................

Whatever it says on the dyno, I will be looking at around and about a 50% increase in power and 40% torque over standard. (I will use a different dyno to set it up, and go back to my original dyno for the power run comparison.)

These figures should equate to a gain from my standard bike of
44hp-68hp = 24hp, and 42ft/lbs-57ft/lbs=15ft/lbs.

And from my bike as it is, with DNA Stage 3 Airbox, PC111 and CC exhaust,
49hp-68hp= 19hp, and 46ft/lbs-57ft/lbs=11ft/lbs

Just doing the Stage 3 airbox and Cans made a huge difference, so this is going to be alot of fun!