Clarification on RS Rotax 998cc

[figmotoday]

Does someone know how different RS years have different hp and torque rating? Are there modifications to Rotax 998cc, gearing, or methods of measurement? Marketing reasons?

Or is it because the GS/RS 2008-2012 106 hp (79 KW) is measured @ 8500 RPM & torque 77 lb.-ft. (104 Nm) is measured @ 6250 RPM
VS the RS 2013-2015 100 hp (74.5 KW) is measured @ 7500 RPM & torque 80 lb.-ft. (108 Nm) is measured @ 5000 RPM

From yearly pamphlets and BPR website, the Rotax 998cc specs for RS are below.

2008-2012 specs are: bore & stroke 3.82 in. x 2.68 in. (97 mm x 68 mm); power 106 hp (79 KW) @ 8500 RPM; torque 77 lb.-ft. (104 Nm) @ 6250 RPM.
2013-2015 specs are: bore & stroke 3.82 in. x 2.68 in. (97 mm x 68 mm); power 100 hp (74.5 KW) @ 7500 RPM; torque 80 lb.-ft. (108 Nm) @ 5000 RPM.

My stock RS 2012 measured the above 106 hp and 77 lb.-ft. on my buddy’s dyno to get pre mods measurements. I have put mods on & we are going to get post mods measurements on the dyno. We wanted to clarify how RS Rotax 998cc were measured each year.
Thanx in advance for your feedback.

 

[billybovine]

The 990 series engines used in 2008 to 2012 GS/RS. The 991 series engines used in 2010 to 2013 RT, 2013 to 2014 RS/ST.

The 2 difference that I know of are the compression ratio and cam. The higher compression in the 991 series was done by reducing the squish volume. Off hand I don't remember if it was done by changing the shape of the head, piston top or both. As you figured out no change to bore and stroke. The effect was a broader flatter torque and horsepower curve.

 

[DrewNJ]

The only difference (other than the obvious dbw/throttle body/tuning) is in the cams. The slightly higher compression is a dynamic increase due to the cam profile. Static compression is the same.

 

[Chupaca]

Curious..!!

opcorn:opcorn: for those dyno results...:thumbup:

 

[DrewNJ]

opcorn:opcorn: for those dyno results...[emoji106]

I'd like to see that too! Maybe even with some Aprilia cam profiles too!

 

[Bob Denman]

10.8:1, versus 12.2:1 is considered "slightly"? This increase is probably why the 991s need to run 91 octane, while the 990s can be happy on 87.
:shocked: Uh-Oh... Is this gonna start another octane discussion?

 

[billrob71]

Hmmm 2012 cams in a 2013 :chat:

 

[billybovine]

Hmmm 2012 cams in a 2013 :chat:

The heads and pistons are different part numbers as well. I would want to know what the actual difference is first and how that would interact.

 

[billrob71]

Would be a $120 guess
One cam cost about that would need to measure the cam journal mounting diameter if it is different and fits loose in the head won't need to go any further anyway. The valve reliefs cut in the top of the piston should be enough for the bigger lift cam.


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[DrewNJ]

Heads are the same part number. Pistons/matching cylinders are different though...missed that. Sorry guys.

What's odd is that the two listings for 13' pistons are 96.945 and 96.955 and for the 12' they are 96.944 and 96.956. That is some strange ranges for the same application for an oversize on the 12'.

 

[Flanker]

Does someone know how different RS years have different hp and torque rating? Are there modifications to Rotax 998cc, gearing, or methods of measurement? Marketing reasons?

Or is it because the GS/RS 2008-2012 106 hp (79 KW) is measured @ 8500 RPM & torque 77 lb.-ft. (104 Nm) is measured @ 6250 RPM
VS the RS 2013-2015 100 hp (74.5 KW) is measured @ 7500 RPM & torque 80 lb.-ft. (108 Nm) is measured @ 5000 RPM

From yearly pamphlets and BPR website, the Rotax 998cc specs for RS are below.

2008-2012 specs are: bore & stroke 3.82 in. x 2.68 in. (97 mm x 68 mm); power 106 hp (79 KW) @ 8500 RPM; torque 77 lb.-ft. (104 Nm) @ 6250 RPM.
2013-2015 specs are: bore & stroke 3.82 in. x 2.68 in. (97 mm x 68 mm); power 100 hp (74.5 KW) @ 7500 RPM; torque 80 lb.-ft. (108 Nm) @ 5000 RPM.

My stock RS 2012 measured the above 106 hp and 77 lb.-ft. on my buddy’s dyno to get pre mods measurements. I have put mods on & we are going to get post mods measurements on the dyno. We wanted to clarify how RS Rotax 998cc were measured each year.
Thanx in advance for your feedback.

:cus:! I wish your buddy's shop was closer; haven't been able to find anyone with a dyno that will let my Spyder on it! Were your pre mod numbers R wheel numbers or corrected for at the crank?