[F500] In summation........

[GaryK]

Art,

Thanks.  That puts a better perspective on the whole engine matter, debate, 
for me.

Gary Kramar
'89 F440 FM



At 10:57 AM 1/4/04 -0500, you wrote:
>F500 list,
>
>In the past week or so, I have conferred with Tony Murphy concerning the
>2 additional Rotax engines that we have been talking about. I was
>especially interested in getting information about the 494 Rave. Due to
>the realization that there are multiple heads and cylinders for this
>engine, I felt that it was necessary to get a better understanding of
>what we're dealing with, at least from the paper view. Tony was good
>enough to give Eric and the list previous information about the Rotax
>494s and 493, but some more specifics had to be noted. Please keep in
>mind that research is difficult on these engines because some information
>on a particular part may be listed differently from one source to the
>next(Bombardier, Rotax, and/or Ski-Doo).  If this is confusing to you,
>you may not be alone.
>
>The disclaimer. I offer this information because I believe that it is
>factual, but I offer no guarantee that it is( I've been flamed by some of
>you guys before :-) ). I am not a dealer. If you have other information
>from a parts list that would contradict the stuff provided, please post
>it so that it can be viewed.  At the very least, all of this information
>should be verified by your local Ski-Doo dealer, Rotax parts list, etc.,
>and etc. anyway to keep you happy and me from getting insulting
>comments<g>. There may be discrepancies between the Ski-Doo parts list,
>the Rotax parts list, and other agencies so let the reader be aware ;-).
>
>Below, I've laid out each engine's attributes so they can be compared
>easily for summation. The 494 Rave is detailed as best we know for the
>moment and offers a very complex picture.
>
>NOTE: Some part numbers may not have the starting "420xxxx....." and/or
>may be preceded by a "6"(6_ 420xxxx or 6_xxxxx). Keep that in mind if you
>look for numbers on a part.
>
>
>ROTAX 494 Non-Rave
>
>Bore              69.5mm                              Stroke
>65.8mm
>Compression Ratio    12.0:1 +/-0.5
>
>The 494 non-Rave has a 28.2cc combustion chamber volume and the published
>compression ratio is 12.0:1. It has only one legal head(923160) and
>cylinder(923148) available from Rotax. There may be other heads that were
>produced in 1996(923145/0) with a 11.5:1 compression ratio but with the
>same combustion chamber volume.
>
>There are a multitude of heads available for the Rave engine(see below)
>that will bolt on to this engine without any external indication that
>they came off the Rave. The cylinders are a different story. They can be
>externally ID'd due to an aluminum casting just above the exhaust port
>that has a black plastic cover with a red adjustment screw. This houses
>the Rave valve diaphragm. A "blocking plate" could be used to cover the
>opening if the valve has been removed. The part numbers are cast in the
>top of the head and the side of the cylinders for both 494 engines.
>However, the Rave parts are illegal and will be a continual problem.
>Since engines are not torn down in racing except under protest or at the
>Runoffs(top 3) and engines have never been torn down in Solo II except
>under protest, the suspicious among us may be inclined to do a lot of
>writing. Heads can be checked for part numbers rather easily by just
>removing the head cover.
>
>
>ROTAX 494 Rave
>
>BORE           69.5mm                              Stroke
>65.8mm
>Compression Ratio    12.0:1 +/-0.5
>
>The head part numbers are: 420923160, 420923162, 420923163, 420923166,
>420923167, 420923168, 420923168ZE, and 420923169. The Ski-Doo parts price
>list indicates that six of the original eight heads are still available.
>The 162, 163, 167 and 168 are the small volume versions with a volume of
>25.5cc.The other two have a combustion chamber volume of 28.2cc.There may
>be some other differences in these heads but they are minor, such as a
>slightly different water jacket. As far as we know, externally they all
>look the same but we are trying to find differences.
>
>There are three different cylinder assemblies. Part numbers 420923615,
>420923617 and 420923619. All three are still listed in the Ski-Doo price
>list. The 617 is 0.7mm longer(113.2mm) than the other two(112.5mm) and
>has different port timing.
>
>EXAMPLE: Use a short cylinder with a small combustion chamber head and
>the compression ratio will increase markedly. Put the 25.5cc head on an
>engine that had a 28.2cc combustion chamber and the compression ratio
>would jump from 12.0:1 to 13.5:1. Therefore, depending on your
>combination choice, compression ratio could be anywhere from 12.0:1 to
>13.5+:1. No matter what head/cylinder combination you use, the
>compression will probably be greater then the non-Rave engine and if you
>choose the correct cylinder, your port timing will prove to be even more
>beneficial. And, even if we were to approve one combination only, there
>would be no guarantee that this now "complete engine" ever existed, i.e.
>no junkyard engines. No on track testing of the 494 Rave has been done
>that we know of :-).
>
>
>ROTAX 493 RAVE
>
>Bore              69.5mm                              Stroke
>65.8mm
>Compression Ratio    12.0:1  +/-0.5
>
>The 493 Rave engine has only one head(420923882) and only one
>cylinder(420613605) available. The cylinder is112.5mm long, same as the
>non-Rave 494. A production 493 comes with 40mm carburetors and any dyno
>specs from Rotax would have been run with these units. Rotax people
>believe that if we install 38mm carbs, power will be reduced to a point
>comparable to our current engine. In initial testing by Don Clar and on
>paper, it looks to be as close to the 494 non-Rave as possible. Tony has
>stated that Rotax intended for this engine to be the 494 non-Rave and
>Rave replacement. We're going into our second year for testing without
>any consensus from this list. We're wasting time. QRE is willing to test
>if SCCA ever releases that other engine.
>
>
>Recently, I stated that I had hoped a 494 Rave could be included in our
>approved engine list. After researching and reviewing the data above, I
>think that would be out of the question now. As someone stated much
>earlier, the Rave valve seems to be a red herring. Although it may
>contribute some to the performance of an engine, the other factors of
>this engine offer more important benefits. There are just too many
>versions of the 494 Rave and testing /competition adjustments to the
>engine to achieve parity to the 494 non-Rave would be a nightmare.
>
>Therefore, in summation, I can't see the 494 Rave ever being acceptable
>to us or SCCA. IMHO, the 493 offers the best future for the class without
>hassles and I support it's inclusion to our rule book ASAP.
>
>Art
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