749R Base Runs - Written Feb ‘05

The 749R is another of the new Testastretta models to vary significantly from its seemingly identical siblings.  The engine has a bigger bore, shorter stroke, bigger valves, another set of cam profiles (3 different 749 cam sets are now in production), different primary drive ratio (I'm told) and crank sensor provision hole in the alternator cover amongst other things.  Producing all these variants must be far more costly than the old system of making one thing and putting some cams in it for the hot one.

And it's not like they're going to wipe the floor in World Supersport with it – the 600's are just so amazingly fast and light these days that to compete with them using a slower and heavier bike is something of a costly exercise.  About 2.5 times more it would seem.  The 749R is one trick piece of machinery in its own right, but in the big scheme of things that guarantees no success.

But, it's still a very flash piece of kit.  We'll start with a bit of an engine comparison table to the other 749 models available.  The base model 749 (known as 749) is the same engine spec wise as the 749 Dark.  The 749S '03 model is also the same engine wise as these models, whereas the 749S '04 model is different.  As will be shown below.

Model

Bore

Stroke

Inlet / Exhaust

Valves

Duration

Centreline

Lift

749

90

58.8

37 / 30.5

241 / 244

105.5 / 111

10.1 / 9.1

749S ‘04

90

58.8

38 / 30.5

258 / 266

108 / 113

11.4 / 10.2

749R

94

54

39.5 / 32

254 / 260

106 / 110

13 / 11.5

Valve timing centrelines shown for the 749S '04 are the revised spec.  Initially they were 106 / 109.  The valve spacing is the same in all so you could theoretically interchange any of the cams as desired.  I'm not sure if the closing rockers for the R are different though – they may be relieved underneath to provide more valve stem seal clearance.  And the 749S '04 and 749R use the 6mm stem valves with the tapered collets.  Not sure if that changes anything else, I haven't looked.

 The first graph will be a comparison of the three above.  So far I have dyno'd two 749, one 749S '04 and one 749R.  So we'll have to assume they're going to be fairly consistant.  The graph below shows all std 749R in green, all std 749 in red and a 749S '04 with asymmetrical Termi power kit (the cheap one) in blue.  The 749R is running 105/109 cam timing, the 749 is as delivered (not far off spec, we checked it later) and the (somewhat lacking) 749s '04 has been reset to the revised 108/113.  I don't understand why the 749R is so much stronger than the 749S '04 in the mid range and top end given the similarity of head and cam spec, but there you go.  Maybe it's all in valve lift and the lessened valve shrouding due to the distance between the valves and the bore walls, though a little less duration always seems to help too. 

 [749rg3]

I haven't actually ridden a 749R yet.  The two I've checked the cam timing on (one of which I dyno'd) have both been in track trim, and I'm not at all keen to ride track trim bikes on the road these days, even if they are registered.  I imagine they'd be pretty flash, given the way they spin up on a free rev due to the light crank and rods and the amount of high RPM torque they make.  The next graph compares the above three again, this time torque.

 [749rg6]

I did come across something wacky when I dyno'd this 749R though, something I haven't had before.  When you transport bikes to the dyno, as this one was, you sometimes have real problems getting them to hook up on the roller.  You wouldn't think you'd get that much heat into a tyre during a 10 minute, 60 to 70km/h cruise to the dyno, but I rarely have wheel spin problems on bikes I've ridden there.  This is where the 749R's lower primary drive ratio and this bikes particular gearing (14/40 I think) showed up – sixth gear is just a little longer than fourth on the other two 749 I've compared it to.  Meaning fourth is quite a bit shorter than I expected.  On a full throttle run in sixth (where I started) it behaved as I expected.  In fifth I could feel the back of the bike lift a little as the torque curve started to rise around 6,500 RPM.  In fourth the back lifted and moved across.  Just to check the results weren't due to something else I did the final run again in sixth – same as the first.  The graph below shows the difference.  I haven't ever checked this before (I always use fourth gear), but the smoother line of the fourth gear curve is consistant with something that's wheel spinning.  You can feel it too, so I was aware of a problem.  Sixth is green, fifth is red, and fourth is blue.

 [749rg1]

 Finally I'll compare it to a 748R, in this case a conveniently 113Hp one.  The 748R has ported heads, reset cam timing, extended inlet trumpets, bored throttle bodies (to remove the restrictor), Termi 45/50mm half system kit and custom Ultimap eprom.  The 749R is all std.  The 749R, incidentally, has no restrictor in the throttle bodies below the blades – they are the same part as all the other 749 and 999 models.  749R is green, 748R is red.  Clearly the 749R is a better starting point than the 748R was, and this 748R was quick.

[749rg4]

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