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Old 07-20-2014, 02:47 PM   #1
OldDog OP
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Yes I know this stupid, but why not?

Howdy everyone,

Well with the help of some of the ADVers I've managed to identify the CR500 motor I have, its an 87, which has had some port work done, and has had a late model clutch cover / water pump housing fitted and has the later model 8 plate clutch.
It looks to have the longer rod, but has the lower engine cases so that can't be right. My plan is to pull the engine done in the near future and have a good look, it was raced in an offroad sidecar rig so who knows whats in there?

Anyway, I have a shedful of bits and pieces and I'm known for building things that don't make a lot of sense...
Tinkering around in the shed yesterday produced this very rough mock up




An XR600 frame, CR500 motor and a 500cc twin lobe supercharger. The frame will need mods obviously, but it is registerable and has enough space for the blower.
I've supercharged a few engines in my day, but never a 2 stroke, I guess the question is, has anyone here done such a thing?
It looks deceptively easy actually.
At this point I'm really just kicking the idea around, looking for constructive comments / ideas. I have more than enough projects to keep me busy for years yet.

Cheers

Bill
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Old 07-21-2014, 04:04 AM   #2
woods wizard
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Oh my.......
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Old 07-21-2014, 04:08 AM   #3
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Yes I know this stupid, but why not?

Happy to be wrong but I wouldn't have thought you could supercharge a two stroke. Don't you have to blow the fuel/air mixture through the crankcase? Do you really want to pressurise the crankcase?

Edit: apparently you can do it but there are significant issues. Good luck

squarebore screwed with this post 07-21-2014 at 04:13 AM Reason: addition
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Old 07-21-2014, 05:49 AM   #4
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watch how much pressure you are running or find a new way to retain the crank seals before you blow them out of the case....and good luck
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Old 07-21-2014, 05:23 PM   #5
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Quote:
Originally Posted by squarebore View Post
Happy to be wrong but I wouldn't have thought you could supercharge a two stroke. Don't you have to blow the fuel/air mixture through the crankcase? Do you really want to pressurise the crankcase?

Edit: apparently you can do it but there are significant issues. Good luck
Thanks for the comments guys,
Yeah with a 2 stroke you push into the crankcase, the charge is then squeezed up the transfer ports into the cylinder, so in affect a mild form of supercharging I guess. The seals could definetly be in trouble for sure, thats a good pick up. The other issue I see is that a blower would simply blow the mixture straight through into the exhaust port as there is an overlap when both intake and exhaust ports are exposed simultaneously.

The blower I have in the pic is off my supercharged 990 KTM project and thats where it'll stay. This is an exercise in working out if I could eventually build a blown 2 stroke as well. There are those that say a well modified CR500 is overkill as it is, without extra pressure, that's probably quite true too....but what the hell!

SB when you say "apparently you can do it" where are you looking? I've found some stuff via google, but want to see what other people are finding too.

Thanks
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Old 07-21-2014, 05:28 PM   #6
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Hey olddog, no great info, just what I have seen on Google as well. Go for it. Sounds like fun
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Old 07-21-2014, 06:21 PM   #7
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Trucks (Lorries?) used to have two stoke diesels that where supercharged!
Cool idea you got there!!!
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Old 07-21-2014, 08:36 PM   #8
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Trucks (Lorries?) used to have two stoke diesels that where supercharged!
Cool idea you got there!!!
They do! Thats one of the reasons I'm scratching my head. How the hell do those big Jimmies work, they're a two stroke diesel, but they call the blowers "scavengers" on them. I'll just keep doing my research, I'm sure theres some way to do it!
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Old Yesterday, 12:47 AM   #9
PSchrauber
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Yes two stroke diesel are mostly supercharged, but these machines are huge in displacement and they habe valves to control the flow if mixture and fumes. As these engines are running at low rpm there is no timing problem with the valve drive..

If you add additional pressure to the mixture you will have a lit of mixture loss as the two strike when controlled by ports and reeds have a moment when both ports the one of the intake and the one of the outtake are open.

That's I think is the reason why no one has dine a charged port controlled two strike yet.

The the port controlled two stroke was invented by Schnürle in the 20's it's also called Schnürle Spülung (flush). The reeds installed by most two stroke yet does prevent that mixture is pressed backwards into the intake. So we can assume a ported two stroke has an I build charger it's the piston when going down.

I think if you want to get a tiny little advance from a turbo charger you need a rotary valve controlled engine it has the same benefit as the reeds but it will stop additional air when it is not useful.

Look at a Rotax engine for that.
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Old Yesterday, 02:26 AM   #10
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Valves!

Nearly all supercharged two stroke deisels (except opposed piston deltic) use normal poppet valves in the cylinder head to control the exhaust. The transfer ports in the cylinder walls allow passage of air only from the blower, crankcase does no pumping work and is pretty much the same as a normal four stroke motor, pressure fed bearings etc. Look for EMD locomotive engines gives you an idea.
I love a mad project and would always say "why not". But whilst cool, would be a huge amount of work to achieve the same result by a different method.
Good Luck.
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Old Yesterday, 12:24 PM   #11
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DKW did a blown two stroke it was kind of like a split single two rods two pistons etc, but never did work out how it worked can remember seeing drawings in a book of this engine at school.

Searched it its number 3 down, how is that for a memory 40 years since i left school. LOL!

http://www.motohistory.net/news2009/news-mar09.html
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Old Yesterday, 03:44 PM   #12
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aussies and kiwi's do a hell of a good job being innovative. Just look at the Britten. Then it'll probably work
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