951 RAVE Valve Mod

[NCGator25]

So my thought on this is to ask why was the solenoid designed into the system in the first place......if leaving it off would make it function just as good? Only possible thing I can think of, other than it doesn't work (well) that way, is that it helps with emission standards of the time....we all know how the govt can make crap complicated.
Looking at the system, it seems like this mod is very similar to the "drill" mod, unless the pressures(exhaust vs crank case) are different in a way that would make this mod not work. I'm wondering if the solenoid acts like a pressure regulator to help smooth out the rave valve actuation, and without it you may get stuttering...just an idea!

Good points Grim. I'd be curious as to why they decided to make the change too since the raves designed differently in their earlier engines. The emission standards you mentioned makes sense to me.

I agree it likely comes down to the pressure created from the crankcase. I don't see why it wouldn't since the crankcase pressure has to be strong enough to open the solenoid to begin with. My assumption is the solenoid is simply opening and closing (ie. allowing the air pressure to flow through it or not). When the to solenoid opens the raves open, and when it closes the raves close. Someone can correct me if I'm wrong about that.

If it ultimately works the same as drilling the housing, I think that's a win as it's a much easier modification! I plan on giving it a shot once I get the ski back in the water. I don't see how it'd hurt the engine in any way. I've felt the on/off aspect of the raves opening through the solenoid, so if it can smooth out the powerband without affecting the lower rpms, I think it would be worthwhile.

 

[NCGator25]

Crankcase pulse is turned into positive pressure by one-way check valve. This positive pressure has the gas and oil mixture in it also. Until the rave valves are activated, this pressure flows thru the solenoid and out the back of the hull, we can’t be dumping fumes in there. When the mpem closes the solenoid, the pressure goes to the rave valve diaphragms, moving the guillotines and effectively changing the port timing. When the solenoid is deactivated, diaphragm pressure is released to atmosphere out the back of the hull.

This is helpful, and lets me know my thinking of how the solenoid works was backwards.

 

[etemplet]

I used to listen to people with their modifications. Stock is always best. As far as I am concerned the rave solenoids provide the absolute BEST TRANSITION and SMOOTHNESS. I restore a few Seadoos every year so I ride a lot of different models all two strokes. My wife and I ride 1996/1997 GTX 787s. They are definitely not as smooth in transition as the rave solenoid equipped engines. One can say it is the fuel injection but that isn't it. The computer OPENs the rave quickly and at the appropriate time, that's why Seadoo made the improvement.

I'll throw in this tidbit from experience **** No Seadoo 2-strokes run better than a DI that's working properly. Ferocious is the word I use.

 

[WhiskeyD]

I agree it likely comes down to the pressure created from the crankcase. I don't see why it wouldn't since the crankcase pressure has to be strong enough to open the solenoid to begin with. My assumption is the solenoid is simply opening and closing (ie. allowing the air pressure to flow through it or not). When the to solenoid opens the raves open, and when it closes the raves close. Someone can correct me if I'm wrong about that.

Its opened by an electronic solenoid controlled by the MPEM. I'm thinking it wont work well because the crankcase pressure is lower than exhaust pressure. Plus its pulsing and not constant like exhaust pressure. Will it work? It might, but you would have to dial in your spring weight to have the valve open at optimum RPM.

 

[mikidymac]

So let's break this down so it is easy to understand. This is why "Experts" on Facebook are not to be trusted...

A) The system as designed:
1. The crankcase check valve only allows pressure into the system on the positive pressure pulse and stops negative pressure as the check closes.
2. The solenoid opens at the pre set rpm and the RAVE opens from the positive pressure and changes the port timing and more top end performance.
3. The solenoid closes and the positive pressure holding the valve open is vented to atmosphere allowing the RAVE to close and gives more bottom end performance.
4. Very precise opening and closing of RAVE valves.

B) You remove the solenoid and connect the RAVE hose to the crankcase fitting.
1. The fitting on the crankcase is a pulse fitting just like on the fuel pump diaphragm and the piston moving up and down creates the pulse.
If you just connect the RAVE fitting to this pulse fitting the rave valves will pulse up and down at the same rpm as the pistons are moving which will do nothing.

C) You connect the RAVE hose directly to the check-valve at the crankcase fitting.
1. The check valve only allows the positive pressure of the pulses to the RAVE valve and it stays open all the time hurting bottom end performance.
2. There is nothing to vent the pressure from this line and the valves will be open all the time.

D) You disconnect the solenoid:
1. RAVE Valve never opens.

E) The 787 way (Same as "drilling the RAVE's"):
1. Exhaust back pressure increases as rpm increases overcoming the spring pressure of the RAVE valves and opening them at a general rpm for more top end performance.
2. Exhaust back pressure is less at lower rpm so spring pressure closes the RAVE valves for better bottom end performance.
3. Less precise opening and closing of the valves giving less performance in theory but very reliable.

Don't connect RAVE to crankcase pulse line, see B) & C) above.

 

[NCGator25]

Its opened by an electronic solenoid controlled by the MPEM. I'm thinking it wont work well because the crankcase pressure is lower than exhaust pressure. Plus its pulsing and not constant like exhaust pressure. Will it work? It might, but you would have to dial in your spring weight to have the valve open at optimum RPM.

I'm thinking it would work fine to open the raves when needed, but I now question how it would work when letting off the throttle and the rpms drop. I don't know how the pressure would get released from the raves, allowing them to drop.

Here's a pick of the system from the manual that illustrates the rave system. May be helpful for others.

 

[NCGator25]

So let's break this down so it is easy to understand. This is why "Experts" on Facebook are not to be trusted...

A) The system as designed:
1. The crankcase check valve only allows pressure into the system on the positive pressure pulse and stops negative pressure as the check closes.
2. The solenoid opens at the pre set rpm and the RAVE opens from the positive pressure and changes the port timing and more top end performance.
3. The solenoid closes and the positive pressure holding the valve open is vented to atmosphere allowing the RAVE to close and gives more bottom end performance.
4. Very precise opening and closing of RAVE valves.

B) You remove the solenoid and connect the RAVE hose to the crankcase fitting.
1. The fitting on the crankcase is a pulse fitting just like on the fuel pump diaphragm and the piston moving up and down creates the pulse.
If you just connect the RAVE fitting to this pulse fitting the rave valves will pulse up and down at the same rpm as the pistons are moving which will do nothing.

C) You connect the RAVE hose directly to the check-valve at the crankcase fitting.
1. The check valve only allows the positive pressure of the pulses to the RAVE valve and it stays open all the time hurting bottom end performance.
2. There is nothing to vent the pressure from this line and the valves will be open all the time.

D) You disconnect the solenoid:
1. RAVE Valve never opens.

E) The 787 way (Same as "drilling the RAVE's"):
1. Exhaust back pressure increases as rpm increases overcoming the spring pressure of the RAVE valves and opening them at a general rpm for more top end performance.
2. Exhaust back pressure is less at lower rpm so spring pressure closes the RAVE valves for better bottom end performance.
3. Less precise opening and closing of the valves giving less performance in theory but very reliable.

Don't connect RAVE to crankcase pulse line, see B) & C) above.

Good post! After reviewing the diagrams in the service manual and thinking through tobytd post previously, I started to arrive at the same conclusion you outlined.

It would be nice if it did work. I've already decided it's not worth me trying to drill the housings as that seems too risky. I've already put more money into my 2000 RX than it's worth!

 

[mikidymac]

Good post! After reviewing the diagrams in the service manual and thinking through tobytd post previously, I started to arrive at the same conclusion you outlined.

It would be nice if it did work. I've already decided it's not worth me trying to drill the housings as that seems too risky. I've already put more money into my 2000 RX than it's worth!

The only valid reason to reengineer the system is if/when the solenoids are no longer available and you want to keep the ski running.

You aren't going to get better performance than the ECU opening and closing the valves.

 

[Grim]

.

So let's break this down so it is easy to understand. This is why "Experts" on Facebook are not to be trusted...

A) The system as designed:
1. The crankcase check valve only allows pressure into the system on the positive pressure pulse and stops negative pressure as the check closes.
2. The solenoid opens at the pre set rpm and the RAVE opens from the positive pressure and changes the port timing and more top end performance.
3. The solenoid closes and the positive pressure holding the valve open is vented to atmosphere allowing the RAVE to close and gives more bottom end performance.
4. Very precise opening and closing of RAVE valves.

B) You remove the solenoid and connect the RAVE hose to the crankcase fitting.
1. The fitting on the crankcase is a pulse fitting just like on the fuel pump diaphragm and the piston moving up and down creates the pulse.
If you just connect the RAVE fitting to this pulse fitting the rave valves will pulse up and down at the same rpm as the pistons are moving which will do nothing.

C) You connect the RAVE hose directly to the check-valve at the crankcase fitting.
1. The check valve only allows the positive pressure of the pulses to the RAVE valve and it stays open all the time hurting bottom end performance.
2. There is nothing to vent the pressure from this line and the valves will be open all the time.

D) You disconnect the solenoid:
1. RAVE Valve never opens.

E) The 787 way (Same as "drilling the RAVE's"):
1. Exhaust back pressure increases as rpm increases overcoming the spring pressure of the RAVE valves and opening them at a general rpm for more top end performance.
2. Exhaust back pressure is less at lower rpm so spring pressure closes the RAVE valves for better bottom end performance.
3. Less precise opening and closing of the valves giving less performance in theory but very reliable.

Don't connect RAVE to crankcase pulse line, see B) & C) above.

Just to better my understanding, your saying the pulse line generates enough pressure to open the raves at the low RPM range so that it would open up the raves pretty quickly if not immediate when the engine is started.
Also, by what I read the raves are either open or closed, so they are not variable based on pressure?

 

[mikidymac]

.

Just to better my understanding, your saying the pulse line generates enough pressure to open the raves at the low RPM range so that it would open up the raves pretty quickly if not immediate when the engine is started.
Also, by what I read the raves are either open or closed, so they are not variable based on pressure?

In normal operation the valves are closed at low rpm.

Yes, they are either open or closed and is why you feel the hit of power around 4,500 rpm when they open or it gets stuck at 4500 if they don't.

If you plumbed them directly to the check valve then they would open once you reach high enough pressure but then would never close as it would be a sealed system. Even with the engine off they would be held open by the pressure as it should be sealed.

 

[etemplet]

Good discussion. if one is simply trying to understand how the raves work. For me, there is absolutely no reason to eliminate the rave solenoid.

I accidentally left the rave solenoid unplugged during a final break-in test ride on a RFI. When I got home I noticed the rave solenoid was unplugged. The ski was sluggish of course but got up to high RPM. I was a little surprised but put 2 and 2 together pretty quick. LOL My next ride on that ski was definitely more spirited and I had some Yeee Haaa !!! moments. LOL

Great write up @mikidymac as usual.

 

[Grim]

Good discussion. if one is simply trying to understand how the raves work. For me, there is absolutely no reason to eliminate the rave solenoid.

I accidentally left the rave solenoid unplugged during a final break-in test ride on a RFI. When I got home I noticed the rave solenoid was unplugged. The ski was sluggish of course but got up to high RPM. I was a little surprised but put 2 and 2 together pretty quick. LOL My next ride on that ski was definitely more spirited and I had some Yeee Haaa !!! moments. LOL

Great write up @mikidymac as usual.

I agree, I am a "WHY" person myself and this helped me grasp the functional system of the raves. The book has some good details but not a lot. It seems the only way to make that mod work is to put a dump valve inline with raves...which defeats he purpose of the mod...simplicity. Leaving it as designed seems to be the best action...especially since there isn't high failure rate with the solenoid. Now when there becomes a supply issue this might be something to further investigate and design. but then again you have the drill method as a backup.

NCGator25 if you still are going to experiment with this...let us know how it turns out...enquiring minds and stuff!

 

[NCGator25]

I agree, I am a "WHY" person myself and this helped me grasp the functional system of the raves. The book has some good details but not a lot. It seems the only way to make that mod work is to put a dump valve inline with raves...which defeats he purpose of the mod...simplicity. Leaving it as designed seems to be the best action...especially since there isn't high failure rate with the solenoid. Now when there becomes a supply issue this might be something to further investigate and design. but then again you have the drill method as a backup.

NCGator25 if you still are going to experiment with this...let us know how it turns out...enquiring minds and stuff!

Will do! I still plan on giving it a shot, but I'm not confident it'll work based on the discussion in this thread. It seems really easy to test while the ski is on the trailer, and I can't think of any damage from testing it, so why not.

 

[mikidymac]

The only damage that could be done is.....

Remember it is a closed system so if you have the crankcase open to atmosphere it will either have a pressure leak and not scavenge the air/fuel mixture correctly.

Or even worse, if it is a vacuum leak that cylinder will run lean and run away. A runaway 2-stroke is just like a diesel, the air/fuel ratio is so lean the engine will ignite on the compression alone and will run to full rpm with no spark until it either blows up or you add fuel to cool the spontaneous combustion or remove air. Easiest way to stop a runaway is to pull the choke until the engine dies.

 

[Wolverine]

Hey y'all: I was reading this fairly recent (Jan 2024) post, I am at the tail end of my 2001 XP rebuild, with much help from many of you. I two am at the RAVE solenoid conundrum. Here is my question... I cut/pasted the 1st portion of the awesome technical design post.
A) The system as designed:
1. The crankcase check valve only allows pressure into the system on the positive pressure pulse and stops negative pressure as the check closes.
So, when I tore out my 951 engine, the was no crankcase check valve (#2 in above illustration). The hose ran from crank case to solenoid directly. I am original owner, this is the original engine so there was never a check valve. Back in the 2000s the ski ran at peak (65mph, 6800rpm). So how does that align with the design? Not trying to be difficult, but I truly am trying to understand how this operates, if I didn't have the check valve, why did the engine run so well? With no check valve stopping negative pressure how did that effect the performance? The ski ran awesome, but would a check valve have made it even better?

 

[etemplet]

Without looking at the engine it may utilize another path. The only thing "not having the check valve" would have done for performance was give you an air leak and the ski would run lean. Lean is always fast until it melts parts. The check also provides crankcase ventilation which removes moisture.