Since the 800 twin thread is closed ? I'll post some things to think about the 800 here to think about.

Pull your y pipe, roll a piston to TDC, look into the exhaust port, what's not right? How would shimming the cyls up help?

Next time your out on the lake check your topend, now rig your raves wide open and do another run. Why aren't they staying open on their own?

Would retarding the timing 2 deg and running a protruded tip plug make the stock head work better?

Hillpounder...What are you seeing in the exhaust port that I am not? Unless you are looking at the rings that have just been murdered by heat. Or are you talking about that pesky little short circuit?

Yeah, I suppose that a extended tip plug would advance the timing some and get the flame front to the edges faster, but 2 degrees? I don't see that as a viable option. One thing to consider would be that the tip would tend to stay hotter wouldn't it? Maybe leading to pre-ignition?

Are you saying that you made a better hi end run with the raves tied open? Are they sticky? Boots in top form? I can say that I have never done a comparison run to check the raves. Interesting...

The pesky short circut in the wrist pin area?, forgot to even mention that, not much to do to fix that short of welding on the piston. What I wanted you to see (or not see) was the bottom skirt of the piston partially above the bottom port edge at TDC. Also at bdc where the piston are in relation the the port, comparing mag to pto, this is easier seen with the head off.

yes the protruded tip has a longer heat path, use a 10. The retard on the timing depends, summit or mxz mpem, 700 mpem, what compression and fuel? the usual timing considerations. Not as good as aftermarket head (setup properly). But improvements that can be measured.

The raves can "flutter" and do not always gaurantee the tall port height you want at wfo. The cleaner and looser they move the better, but even then they can't alway get out of the way fast enough. The spring/pressure method is simple but not the best. Look at any modern valved 2 stroke in the bike world, the raves are controlled by positive devices.

No short circuit using a Wiseco piston, in case anyone wondered.

I have also heard of some running extra RAVE gaskets to get them shimmed up to proper height.

If everything else is right, the short circuit doesn't come into play anyway. It begiins to show it's ugly face about the time you start changing things. Pressures in the case and pipe change from stock and then some problems arise. Nothing for the stocker to worry about.

Yup, running an extra RAVE gasket is a plus (on the 800's). I couldn't find it in my notes, but I think you also want to use the RAVE spring from a 98 583 MXZ. Maybe someone knows for sure and will post it. Anyway it's a lighter spring that will alow the blade to rise sooner.

I run 3 gaskets on my raves but thats just to make sure that they dont catch because of the massive porting i had DON E do for me. If your valves are closing at WOT that means you need more H.P. to keep them open wright ?? What an excellent excuse to do more mods. Seriously, if this is an issue for some, this is the reason your valve spring tension is adjustable, just back it off a bit, personally i run my valves all the way down and have had nothing but good luck. I would be intrested in the results if anyone sees a difference in their performance at any level be it low mid or top end using the spring from a 98 583mxz. :D

Speed...is that the right spring? Have you heard that before,too? I wasn't sure that was the right spring. I'm going to try a different spring on mine to see what happens.

I thought about this a few years ago when I was working on a FIII 700 that had a single pipe on it. Supposedly the Mach1 (same engine with 3x3 pipes) had a different rave spring. The only explination as to "why" the springs were different had to do with the pipe. Since the tripples peaked higher, they needed a stiffer spring (aka open later) to work with the peakier pipe.

It seems to me that the spring has to jive with the port timing and pipe. Keith, with the twins, you may actually want to try a stiffer spring. Just talking out loud. I actually have run my raves 1 turn out for quite some time. There are some issues with them actually not opening all the way, that is why I was told that the extra raves were to give the rave more room to move.

Shimming isnt the correction in my book, as it will lift the rave at lower RPM, and could effect bottom end power. IMO, one would have to machine the back side of the actual valve to provide the extra room to move.

I was thinking about using a softer spring so that it would lift sooner not worrying about power loss at bottom end because I feel that there is plenty to spare in these 800's for running on snow. Grass may be a different story.

Do you know for sure that the triple/triple had a stiffer spring or is that an unknown? I was thinking that maybe the single piped sled would have the stiffer spring due to increased exhaust pressures. But that is definitely a guess, since I don't really know.

Can someone enlighten us?

I think if there was something to be gained that an aftermarket spring would be available considering that there are aftermarket products that dont work, why not market these too. I think maybe we should start mass producing different strength springs and market them, kind of like clutch springs, watcha think. I still think that there is enough room on the adjustment dial to achieve peak perf. or at leats the max amount your going to get by changing springs. You have to admit that for a straight spring and a slide that this system works very good, but i have always said that there is a ton of room in the exhaust vale area for improvement do give us a better range and a more defined perf. adjustments. Now that would be a good thread to start, lets start swaping ideas on a new exhaust valve system.

Computer controlled electronically actuated according to RPM's, signal sent for every 100RPM change in run condition. I'm not an electronics type person, but how hard could it be?

Doo has suddenly fallen behind the times in the variable exhaust valve arena.

I have some extra springs here. Could paint different colors on them... :devil:

idooski: Here is a trick that will work to see if the raves are opening all the way...drill a 1/2" hole in the side of the rave covers so that you can see if the valves are opening the way they should...hope this helps...Al.

Doo has many different tension rave springs available, and the diamater on the Mach1 springs were larger than that on the F3 springs. But the mach was happy at 8400 or so and the F3 at 7800 also. The spring allows the valve to open at a specific pressure. I believe that Summits come with softer springs to compensate for altitude.

Originally posted by idooski@Jul 17 2003, 10:47 AM
Computer controlled electronically actuated according to RPM's, signal sent for every 100RPM change in run condition. I'm not an electronics type person, but how hard could it be?

Doo has suddenly fallen behind the times in the variable exhaust valve arena.

I have some extra springs here. Could paint different colors on them... :devil:
One could create a pressure accumulator to supply needed diaphram pressure to overcome spring resistance (electronically controlled of course!) assuring full RAVE operation at given RPM values. I personally think plumbing an adjustable rate bleed down check valve to dampen the closing rate of the RAVE valves thus maintaining the power peak when the throttle is lifted and reapplied quickly instead of having to "build a new head of steam" to reopen the valves. The same theory of bypassing the inlet side of a turbo compressor to keep it spooled up when changing gears or backing off the throttle breifly.

I haven't looked at my 800 RAVE assemblies since last winter so I may be missing something. But doesn't the RAVE stem stopper bottoming in the cylinder recess control the guillotine clearance to the cylinder wall? So, when you install the RAVE assembly the valve bottoms in the cylinder before the RAVE housing touches the cylinder. Pushing the housing up against the mount for bolting then loads the spring. With this configuration I don't see how the gaskets make a difference on the guillotine in the closed (low end) position. I can see where it would make a difference on the top end if the spring is fully compressing.

SummitAK

Basically, adding an extra gasket effectively makes the spring seem a bit softer at the bottom and allows the blade to push up a little farther at top end.

idooski, e-rave buy ski-doo.

I agree with summitAK. Adding extra gaskets will allow the rave to pull back farther the thickness of the gasket, but will not change the intial location. The accordian boot has enough stretch to it that it still allows the rave stem to sit against the cyl.

Some of my thoughts FWIW: The cylinder pressure (CP) that opens the rave varies with throttle position and rpm. At WFO@ mid rpms produces more cylinder pressure than wfo@shift rpm, the raves open earlier. The big gulp of air without the rpms to swallow it produces more pressure. Example pulling a steep hill in your car and you get some ping, back off the throttle and it goes away. The design criteria for when (rpm) to open the rave is a function of exhaust port timing, when do I need the extra port timing? The avg exh port timing change on doo rave is about 10-12 degrees, a 7800-8000rpm twin rotax measure out to about 180-190 deg with the rave closed and 190-200 deg with it open. The advantage of the increased port time occurs at about 6500rpms, if a postive device was used to open it this could happen every time. But CP (dependent on throttle position and rpm) is used so there is some inconsistancy. The CP is variable but the spring is not so there is some inconsistancy. If you watched the rave pop open on a dyno under load (not on a track stand) it may come open at 6000 rpm on a throttle pinned wfo run, if you gradually opened the throttle it may not open till 7500. My concerns with the way the rave works: A spring selected to it pop open when desireable and not too early or too late, MAY be too stiff to keep it all the way open on a wfo pull (rpm is digesting the airflow easily and CP is lower). I think the port times on the rotax motors sorta give hint to this. If you look at the exhaust timing with the raves open and the actual hp peak rpms, the motors should be reving more than they do. 583 rotax, 202 deg exh rave clear open, 190deg closed. These motors run best at 7800? closer to the 190 timing IMO? standard 800 twin, 190 deg what did doo do to wake it up? the HO, just raised the exhaust ports, they ported around the problem. If the rave was staying open 190 would have been a good spec. IMO if rotax used a more positive method of rave control the motors could be stronger and more consistant. I think the devopment of the SDI mapping forced skidoo to deal with the issue and hopefully will move into the other sleds. sorry for the long post, hP

Originally posted by X-it@Aug 1 2003, 10:15 AM
idooski, e-rave buy ski-doo.
?huh?