Poll: Who thinks exhaust valves are a marketing gimmick?

[Thundercatrev]

On my skidoo 800 twin, I run them in a fixed wide open position so they cannot slide down ever.
I cannot tell any difference in throttle response!
If anything it almost seems like it gains bottom end!

So my question is: Are exhaust valves really needed on a big bore, reed valve inducted motor?

They certainly seem to have absolutely no benefit for some engines.

Speaking to people to have done similar things to their rave valves and dyno tested on the series 3 Ski-doo motors, they all seem to have experienced similar results.

So in my opinion, Exhaust valves rank up there as one of biggest marketing scams that the sled makers have ever dreamed up... next to the Ski-doo's Dpm marvel of engineering, but that is a different story....

 

[MARV1]

Doo was the first to come out with them, and everyone else followed. Probably all depends on your arse dyno, mine likes the feel of them opening up at 7k rpm and surging up to 75-7700rpm and pulling so much harder on top end. Oh, and my sleds use alot less fuel lower than 7k rpm when I'm heading out so fuel economy is a must when going 180 miles/day and can only carry extra fuel to make it home.

 

[Thundercatrev]

Thats exactly my point. When skidoo came out with rave valves, they put them in the original ancient rotary valve engines. I can totally understand the benefit of rave valve on a rotary engine. Without them it would be a slow revving unresponsive pig.

Exhaust valves on reed valve engines are redundant. A modern reed engine is a completely different engine from the engines we had back in the eighties as far as throttle response is concerned. Throttle response is not an issue, a larger two stroke twin has enough bottom end torque to cancel out any benefit an exhaust valve would gain.

Why would anyone want a exhaust valve hanging down in the exhaust ports? (If it doesn't gain any performance)

How many people who claim exhaust valves work and are *needed* on big bore reed valve two strokes, have actually disabled them and tested if there is a noticable *loss* of horsepower and throttle response?

Just curious to find out what other peoples experiences are.

 

[Thundercatrev]

Of course 2 stroke dirtbikes have had them for years, but how can you compare a manually shifted low torque motorcross bike to an cvt shifted snowmobile engine that is 2 to 3 times larger and a lot torquier..!?

 

[Ove]

I really notice the differece running the valves, but it is only out of the hole. The engagement can be set lower and there is less spinning.

 

[Thundercatrev]

With the skidoo engine I can set the engagement as low as l want. No sputter or hesitation. Like I said, if anything it almost seems like it revs quicker, and is more responsive out of the hole.

This is when the exhaust valves are fixed in ther wide open position.

Since their disablement has no negative effects, I can only conclude that they are a uneccessary feature. ( at least on the skidoo 800 twin motors

I think more people should experiment with their engines. Disabling the exhaust valves on a skidoo is easy. It just takes a minute and requires no tools. (just move the spring underneath the exhaust bellows so the sping is expanding to force the valve open, instead of pushing down to force the valve closed)

I think we should petition skidoo to remove the exhaust valves on certain engines that do not need them. They are just an unecessary complexity and add weight. They do not enhance throttle response or facilitate lowering of enagement (on the skidoo motors).

The interesting thing is, people have dyno tested a skidoo with the valves stuck down, and it results in a 10 hp loss. So my question is: If they can have such a detrimental effect on performance (if they malfunction and stick in the closed position), and meanwhile have no bad effects when they are disabled to the wide open position..... why would anyone want the hassle of one more thing to worry about on your motor?

For me, a 10 hp loss is too much of a risk to take that is why I run my valves fixed in the wide open position to gaurantee there is no chance of this! Since I do not lose throttle response, it is a win- win situation in my opinion.

Again this is on a skidoo motor. Other brands may respond differently.

 

[freak58trio]

If I remember right IndyDan had some good info on the exhaust valves. I know they create a lot of heat around the piston where the valve is due to limited amount of coolant in that area. I've also heard that non valve motors generally make more hp whether this is true or not I don't know.

 

[MARV1]

There was a good discussion like this on the old forum a couple years ago, something like build the engine you want and port it to the max for the most HP you can produce out of it and it will pull harder on top and upper midrange, but be kinda doggy in the midrange. Yet, lower that exhaust port 1/4", 3/8", 1/2" or whatever a valve actually does and you gain a bunch of bottom end torque and HP that will pull harder off the line. And then when they open up you'll pull harder yet as you get into the full porting.
Try go race one of your buddies that has their valves intact to work properly.

 

[Monty]

I preferred my non ves 800 polaris twin, with twin pipes it just felt like it had longer legs.

 

[Beels]

I'm going to go with gimmick on a reed valve 2 stroke.

My 999 Mad Max Cat big bore has the valves bolted open and I can't see there being any bottom to mid range power being gained with them operative. Out of all the sleds I've ever owned without exhaust valves, I can't ever remember sitting around thinking, "Gee, I wish I had more power from idle up to 6 or 7000 RPM."

 

[CO 2.0]

If I remember right IndyDan had some good info on the exhaust valves. I know they create a lot of heat around the piston where the valve is due to limited amount of coolant in that area. I've also heard that non valve motors generally make more hp whether this is true or not I don't know.

This is what he told me as well so I had him rebuild my edge motor with non VES cylinders and a high comp head for this season. Butt dyno feels like it added 15-20hp with the combo up top. Fricking rips now. This is also with getting rid of the Vforce 3 reeds I had in last season and putting in the stock reeds again for this year Wish I could see where my temps are at before/after...

 

[Thundercatrev]

Yes, I agree about the heat issue associated with exhaust valves as well.

According to a guy that I know running a turbo skidoo the exhaust valve creates a hot spot, especially when they come down, they create backpressure, and depending on the situation can make you melt a piston a lot easier than if there was no valve there at all. I think he said he finally resorted to taking the valve out, and filling the hole with weld and streamling it for smooth unimpeded flow.

I also agree that some engines with radical port timing can sometimes benefit from exhaust valves. Problem is, many engines such as the skidoo 800 have very un-radical port timing, making rave valves on that particular engine especially redundant.

Friend of mine rides a non-Ves Polaris, and I agree they seem to put the power to the ground better than what I've seen when compared to the later VES motors.

 

[turbo800]

I know that in my first turbo motor('02 800) the valves were bolted wide open. This created a noticeable increase in lag. I know apples and oranges.... but with the bases welded closed and pressurizable, noticable less lag.
It sounds like with the P'tek and R motors the computer is holding them closed longer for emmisions and sound db's.

 

[SnowSnob]

If you get BJ's Trail Torquer kit or 840 kit they come with stiffer rave valve springs. The bottom end is noticably stronger with these stiffer springs.

 

[Angermangement890]

I feel exhaust valves are not a gimmick when used on an engine that needs them. A 700+cc twin/tripple does not need exhaust valves, as pointed out previously they do not seem to add a whole bunch. Pin the valves open on a 440 or eliminate them and tell me what your butt dyno says. I personally think that the VES is benificial on the smaller engines so you can maintain good bottom end but still pull good HP out of the engine due to the more agrresive porting you can use. The 98-00 XC 600 Big block engines made 110 hp, the 00 600 VES engine made 115 HP.

 

[stevemartin]

for one, on a stock motor they cannot be set to a "fixed position" you can run the red adjuster all the way in, but that just means the spring has maximum pre-load,but they will still open, just at a higher rpm. if you dont think they do anything other than a sales gimmick. remove the springs and ride it, it will be a dog. Its an adjustable exhaust port. A higher exhaust port is more HP at a higher RPM and a lower exhaust port is more mid range, more grunt. this is a way of having both. thats why every modern 2 stoke (motocross bikes, sleds) have a variable exhaust valve of some kind.

 

[ROOSTKING]

I don't think the entire reason for valves is for increased power but for better economy at part throttle. Compare the average mpg for a pre valve engine to one with valves. From what I've seen there's a 5-6mpg increase with a valve motor when run at partial throttle.

 

[Ill Named]

I have had the red adjuster pop out and the spring dissapeer on me twice with my 827 and it runs like sh it when that happens, but only in the bottom end. So I guess my engine needs them.

 

[2zeros]

Exhaust valves on a two stroke.

Exhaust valves make the engine have a wider powerband. Try disabling the valves on somthing small, or somthing with a real narrow powerband. You will notice a huge differance. I agree that they might be less noticable on todays large cc engines, but still an improvement. The manufacturers dont spend the time and money to install them for no reason, or just for marketing. You are proving your real knowlage of two strokes with this post. Rotax has used them for years, now others follow suit. I like the concept of the gas operated ones the best, continuously variable. I am no expert, but mine are working fine.-00's

 

[joshkoltes]

big -small

the motor size will amplify the loss. in larger twins will be less noticable being everything is big. big intake, big chambers, big ports, big volume. with the smaller motor there is less, volume. the same amount taken away by closing a small port cuts a much larger ratio of flow amplifing the power loss to where it can be noticed. in my 800 tripple it is obvious when i lose a valve but that is three small cylinders. so dyno it with stock components to get your answer, gain or loss. a good motor builder should be able to overcome the loss of a ex. valve with their own mods but thats nowhere near stock.