CR500 Power valve

[searcher415]

Has anyone ever tried to design one. My thoughts were cutting apart bombardier mach z twin cylinders. It would take alot of fab work but the bore is 88mm and the mach z's stroke is only 3 mm longer. Maybe some fitment issues with the power valve. Just looking for some input.

[1550]

there is some discussion about powervalves. I think the mach z has gas operated powervalves which will not work good at motorcycles. Because of delay in powervalve use. Quite similar as turbo lag. And this is because those powervalves work with crankcase/cylinder pressure.

You can find more information with search.

[asteroid500]

theres an Aussie bloke thats at prototype stage now....

[Roostius_Maximus]

got a local guy wanting to mess with running the efi off the acrtic cat 1000, says it has a cable exh valve, could be decent

[craigf40]

Well im running the 04 gen 3 cr250 ignition system
and that has the electronic power valve system already wired
so to operate it i dont see a problem as that ignition
system works perfectly on the cr500.Just need to fab a
power valve thats where all the work is

[searcher415]

Are most cable exhaust valves EFI? I'm not really sure on how the cable system is timed? I know the rd350s have cable valves. Is the power difference that noticeable?

[OUTKAST INC.]

have lots of experience with snomobile exh valves . the ski doo exh valve work awesome and can be adjusted to open a different rpms , on sled motors we usually target about 6000 to 6500 open on motors that rev to 8000- 8900 , havent treid for sooner opening as clutch engagement is usually about 3800-4200 , mach z valves would not be a good choice , wrong shape , 02-06 800ho motors much better choice . bullet proof . who care how big the bore just cut the radius you need in the valve . of course you will need a billet or investment cast cyclinder to make it work and oh ya you will need to create a whole new kinda y conversion as the valve will sit directly above the pipe spigot and stick out toward the y , including an electronicly controled valve , which require a servo motor and matching 3d ignition cdi map to operate correctly such as 1998 yamaha srx 700 sled had good luck , best part if you get it all to work it will be awsome , even more 500 torque than any body thought possible and topend pull till tomorrow imagine raising your exhaust port like 8mm from stock for top end like the cart guys are doing yet starting out with like 2mm lower that stock for low end ,,, think about it. our 800 ho motors make 185 -190hp at 8800 or divide by 2 for about 75 hp on 400cc, think about that...

[2strokeforever]

think about it. our 800 ho motors make 185 -190hp at 8800 or divide by 2 for about 75 hp on 400cc, think about that...

how much nitrous you use for that dyno run

you also have to remember more cylinders = more power,even same cc, same port time, same exact thing
both have the same power, both have low port time, more cylinders = more power
cr 500 55 hp ish
333 cc 1976 twin gets 55hp

Working with engine supplier Fuji Heavy Industries, Polaris received a classic design, the 333cc TX-L twin. This was the heart of Polaris TX-L success. Ironically, with the historic success of the TX-L, you would assume it had the most power. Rarely was that the case. But, the 333cc engine with its approximate 55 horsepower output was one of the most reliable engines of the time.

i personaly think this would be more acurate
think about it. our 800 ho motors make 145 -150hp at 8800 or divide by 2.5 for about 60 hp on 400cc, think about that...

that being said i am thinking of making a powervalve for my bike as soon as i get a lathe, and i think its a great idea

[OUTKAST INC.]

no nitrous , porting and head redome , twin crank shop pipes , vforce reeds

[Roostius_Maximus]

OR i can port the cases and cyl for you and add 7ftlbs of tq, atleast 1 hp and make the power come on 1000 rpm earlier and smoother with the same or less jet than you run now and no harder on fuel, likely better for 600$+frt
If you're willing to hack out the bridge theres more to gain, that power increase is with stock port sizes at the sleeve, and stock locations

[Roostius_Maximus]

on a chassis dyno the stock bikes have shown 46-48 hp depending on pipe,carb+reed

[searcher415]

have lots of experience with snomobile exh valves . the ski doo exh valve work awesome and can be adjusted to open a different rpms , on sled motors we usually target about 6000 to 6500 open on motors that rev to 8000- 8900

Is porting or boring possible with out altering the exhaust valve or will it change the characteristics of the valve opening so much that a reshape is needed. Also, how do you adjust ski doo exhaust valves?

[Roostius_Maximus]

is that valve similar tot he old '94 670 mach1 valve?

[bearorso]

I think the bloke that I saw trying to do a PV was YLWRTGR ? - or something like that, on CR500riders site? He's in Melbourne, and is starting to sell / do AF conversions. I've not gone looking for him there for a while - I may have missed his progress on that project.

If I remember correctly, with where he situated what appeared to be the pivot mech, above the manifold, quite far from the sleeve / exhaust port, I thought that he was doing a 'drawbridge / flap" design for the PV. I enquired if that was the case, at the time, but didn't get an indication of what design he intended. Perhaps it wasn't a exhaust port height adjustment set up, it might have been an exhaust volume adjustment type. Goodness only knows, there's a million ways to skin a cat.....

Whatever you do, it could require extensive modification to the frame, be it a steelie or AF (though Gen 1 double down tube frames, perhaps not - there's a plus to them, perhaps). There's not much room at the barrel, frame interface area. I could see that you might be best to convert either a steel frame or later AF type to a double down tube set up, for a PV set up.

I had Maico's with the Vacuum / Diaphragm PV set up. It was a relatively primitive PV (but used for many years on the Rotax / Aprilia GP 250s, till they went electronic). And it's used on the KTM 65s now. Even though it was primitive, it worked well. And with the addition of a alloy top cap, that I made an external pre-load device for, and by using various springs, a very adjustable (and Very Easily adjustable) guillotine type PV.

I think a lot of the Snowmobile PVs, for special barrels and std barrels are vacuum types - I think I've seen them for Quad aftermarket barrels, such as Sabres and the CPI(?) types? That's what I would use - you can buy them from a few different suppliers, and it would be a pretty simple thing to do. Almost a pre-made, self contained unit. Well, compared to trying to do a spinning ball weight and rod arm unit, or electric set up. The KTM65 ones appear to be neat little things, perhaps you could use 2 of them, to the sides of the barrel, either as 'eyebrow" type PVs, or horizontally aligned exhaust width PVs, or as exhaust volume altering items, when opening to sub chambers. R&D, I think, do complete little units that replace the whole OEM KTM units, from what I've seen. 2 small ones, off to the sides, might mean that frame downtube mods would not be required.

It's something I'd like to try out one day.