I'm never gonna know.
I can't get caught up with stuff that needs done.

Might want to ask more specifics, such as stock or hi compression piston?
Carb off?
Stock carb?
With a CV carb, even with the throttle open all the way, the slide sits down. Prob get a lower reading than with a slide carb.
Warm or cold?

@Batman, still you'd think that a bike that's just done 1000 odd miles would be at least in the high end of the spec range rather than the bottom end.

@Armen, good point about the slides, however the specs would certainly be for a stock slide.

DBM with a DR cam I would expect to see a compression test with lower pressure, with valve overlap the exhaust valve is also open. I don't think you'll notice any less low end torque/hp  , if your using the DR cam with a stock piston, the cam dino's for the DR still show the torque peak at around 3400-3500 just like the stock cam . I think you would have to go to a larger piston (with 10.5 ; 1 compression) before you see a higher peak torque , somewhere between 3500 and 4000 rpm, and some low end losses.  

@Armen,

If a motorcycle is barely using any oil, say 300ml over 6000kms, would that indicate that rings are OK? Or can they still be a bit worn.

Quote:


I'm not sure what you are getting at Batman.  Valve overlap occurs at the end of the exhaust stroke.  It should have no effect on cranking pressure.  Intake closing point determines how many degrees of crank rotation are left to compress the fresh charge of air.  Close the intake at BDC and you have 180 degrees of crank rotation to compress the charge.  Close the intake at 20 degrees ABDC and you have 160 degrees of rotation to compress the charge.  Close the intake at 48 degrees ABDC (stock cam) and you have 132 degrees of crankshaft rotation to compress the charge.  Close the intake valve at 42 degrees ABDC (DR cam) and you have 138 degrees of crankshaft rotation to compress the charge (6 degrees > than stock).  How does the valve overlap event that occurs at the end of the exhaust stroke affect the compression stroke?

Regarding low end torque, my stock engine dyno run showed 30.5 max HP, Suzuki says it makes 31 HP so I'm pretty comfy with the results of the dyno pull.  I think it was accurate.  The stock engine made 30 ft-lbs at 2000 rpm.  The guy in Finland with the DR cam in a 692cc engine and 10.?:1 compression makes 25 ft-lbs at 2000 rpm.  That's 5 ft-lbs less low end torque.  I attribute that to the valve overlap.  The intake & exhaust are swappin holes at low speed.  Fresh charge is running out the exhaust.  Also, he runs a straight pipe so there is most likely quite a bit of reversion during overlap (sonic wave running back up the pipe, through the open valves, and back out the carb).

I put that DR cam in my engine over the weekend and have been fiddling around with it.  Of course I checked compression before and after.  It was interesting.  To my surprise, it didn't change a bit (155 psi before, 155 psi after).  Since I had the head cover off and the cam out, I checked the stock cam timing.  It's a bit different than what I recorded when I checked it through the valve covers with everything together.  That's understandable since you have to fight the valve springs and alternator, and access doesn't permit optimum placement of the measuring instruments.  I will be posting an update to the valve timing data I previously posted.  For this discussion, we only need to know the intake closing point, which is 48 degrees ABDC for the stock cam, and 42 degrees ABDC for the DR cam.  The 6 degrees of additional rotation did not increase compression pressure.

Keep in mind that as the piston moves further up away from BDC, the movement accelerates (the piston moves further for each degree of rotation).  At some point, the intake valve closing is going to start having a significant effect on compression pressure.  That point is obviously somewhere past 48 degrees ABDC.

I can tell you this much for sure, the DR cam does not produce low end torque like the stock cam.  The stock cam pulls harder at slow speed on surface streets.  The DR cam comes into its own on the freeway.  I'll post the results shortly.

It seems everyone knows more about this than I do, but it seems to me that turning the crank 90* from BDC gets it to TDC,