RPM vs. Temperature

[MacSeaDoo]

So this year, i noticed a drop in top speed RPM with my Speedster. Started out the season being able to hit 8060 RPM's, then towards the middle summer was noticing that I could only get 79/78 ish. Took it out last night and hit 8140. The water temp is now 64 Degrees and it was 67 Degrees in the start of the season and 76 Degrees in the mid end summer.

I have confirmed that there is a substantial range due mainly to the water temp. This makes sense as the temp affects air density.

Just thought I would throw that out there.

 

[Joe Starbuck]

2-stroke? The SC in the larger 4-strokes should make the engine a little less sensitive to air density changes (temperature and altitude).

 

[MacSeaDoo]

It is the 4 stroke 255HP Rotax 1503.

I noticed this at the end of last year too.

Also, I replaced the IC last year with the newer larger one with the integrated vent line.

 

[Joe Starbuck]

It is the 4 stroke 255HP Rotax 1503.

I noticed this at the end of last year too.

Also, I replaced the IC last year with the newer larger one with the integrated vent line.

Very interesting. Is the new SC supposed to raise the manifold (boost) pressure compared to stock? Did you make any changes to the intercooler?

 

[MacSeaDoo]

It was the Intercooler I replaced with the newer larger one from the 300Hp model.

The SC is stock.