Thread: Mark U. and BOV
11-13-2005, 12:42 PM #1
Mark U. and BOV
The other day I orderd the new RR ECU and IC block off for my ski's. I also asked Mark about BOV's good or bad. After he explaind to me how things work it makes sense why BOV's are not a good Idea. It woud be nice if Mark could explain to every one himself
11-13-2005, 02:22 PM #2
he has explained it once before on this forum. I forgot the name of the thread though.
11-13-2005, 02:24 PM #3
I found the thread. He had this to say about it
heres my opinion on this subject. rotax tested engines on the dyno with and without a bov. the tests showed that without the bov the sc clutch slipped less. the impeller speed matched the crank speed more closely with no bov. the theory behind this is the sc impeller is using the air pressure behind the closed throttle body to slow down with the crank instead of free wheeling. with no air pressure present the sc impeller is affected more by inertia.( an object in motion tends to stay in motion unless acted upon by an outside force)
bov's look and sound cool but not a good idea in this application IMO
11-13-2005, 03:54 PM #4
but once again here comes the arguement of who has had a problem with a BOV? I have one and haven't had a problem yet. Who knows.
11-13-2005, 04:00 PM #5
I do not believe his theory. Just about every super charged and turbo charged automotive application uses some sort of blow off valve. The job of the BOV is to reduce strain on the SC, it is not there to help the type clutch used in the Rotax engine.
Just my opinion
11-13-2005, 04:02 PM #6
I think i'm with you on this one Rich.
11-13-2005, 04:39 PM #7
Just about every automotive turbo/supercharger application uses a BOV, but NONE of them use a clutch like we use in our application.
It's kind of hard to argue with hard data as shown by Rotax during dyno testing. "the impeller speed matched the crank speed more closely with no bov"
I also feel like these Rotax engineers that designed the engine would have implemented a BOV had they felt it necessary.
11-13-2005, 04:47 PM #8
Like i said before i dunno what to think. I hope this whole belt driven supercharger deal eliminates all headaches. I see potential problems though with a belt driven unit. It's probably going to be extremely costly as well cosidering all the internal components needed to change to belt drive. Not to mention the cost of an entirely new supercharger. I can't wait though. Time to turn the boost up on these puppies.
11-13-2005, 04:48 PM #9
And the debate goes on...I have heard of 3 hd clutches going bye bye...The only thing the 3 had in common was a bov...Over 40 hrs later...no bov...No clutch problems...
Jerry is right..Sometimes engeneers can be dumb...But the ppl at Rotax have tried bov's on the dyno, and after 3 yrs of this motor on the market and who knows how many years prior for testing...We still see no bov's.installed in the factory....None of the factory race teams use it..They are running over 300 hp @ 9000 rpm..So the back pressure they experience is tons more than we would..And they don't run bovs..
Trust me they are more harmfull than good...Especially on a modified motor..
11-13-2005, 04:49 PM #10
Yea, the belt driven will have it's inherant problems just like anything else, but it will sure beat having ceramic disks breaking inside your engine.
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