Measured friends 01 DS650 compression, and it read 110psi. After putting in a new stock piston & rings, ran another compression test=185psi. Ran on the dyno today, dyno showed 42hp & 41ft lbs torque. Does this sound about right for a stock DS with Alba pipe and TM45 170 main jet, and RWR CDI?

 

Did you dyno it stock? The numbers can range greatly depending on the dyno, it's the increase you wanna see over you're stock number. One quad can dyno 50 HP, and then 35 on another, so it's hard to make a judgement.

 

No, we didn't dyno it before the rebuild. I'm going to take my 04 BajaX over for comparison. I have the RWR Stage2 kit in mine. I just thought his compression seemed a little high (185psi), for a stock piston.

 

also did you have stock tires or smooth tires, Iwas told that one needs smooth flat track tire for top numbers. as said dynos will vary. those are stock numbers on some dynos Ive seen. a ds with those mods push almost 50 hp again dynos and tires will vary, this dyno is prob. conservitive. was that 170 main recomended ? seems kina big but if thats whats recomended.

 

On the two dynos I use the stock DS's clock in around 36 to 38HP. With pipe, jet kit and new air cleaner they tend to clock in at around 40 to 42HP. This is with stock tyres and measured in summer. They tend to gain about 4 to 5HP with jet kit, new pipe and air cleaner.

The other day I racked my brain to figure out why the dyno runs from so many people tend to differ. Even on the same dyno they will differ on the exact same quad.

Tyres play a big role. The pattern and even the tyre pressure make a power difference.

Then since the air temperature and atmospheric pressure is changing constantly, you need to compensate for it before each and every run.

Then the latest theory I have is in air temperature.

Sure the dyno can compensate for air pressure and temperature, but it is a straight forward mathematical formula where they use a fix temperature and they work the power output back to the fixed temperature. The problem with the formula is that it cannot predict engine power and the way it behaves under different conditions.

Here is my thoughts. As temperature goes lower, the motor will pick up HP. So far the dyno math can compensate, because its simple. After spending lots of time doing all sorts of runs I noticed that the same DS or Raptor made completely different curves depending if you run them in winter or summer. For example, the Ds's and raptors will produce max HP around 7000 to 7200 RPM in winter, but in summer they will produce max HP at around 6200 to 6500 RPM. This is the exact same quad. The dyno math CANNOT compensate for this engine behaviour. If it produces max HP at 6200 RPM in summer, then the dyno math compensates for the temperature BUT it is not able to predict the actual HP curve it will make at a much lower temperature. The motor will produce much more power in winter, even after all the match is compensating for it, purely because the power output curve is way different.

Does it make any sense?

Like it was said on here already, you need to test the same bike before and after the mods and try to do it at the same temperature. Testing a bike in summer and testing that same bike in winter produce completely different results in HP, torque and power curves and no dyno I know of will compensate and predict power output correctly.

 

The stock tires were on the bike, and the max hp was made at 7200RPM, and it took 8 seconds to get to 9700 rpm.