Fluted crank webs

[bigk]

I as having a clean up the other day and found a CR250RZ bottom end I'd forgotten I had. It's interesting in that 1. it has a full circle crank and 2. the crank webs have been "fluted". It's a work of art and I imagine it would have cost a few bucks as it looks like a professional job. I have asked a few people as to the theory and where it would help the power, but have had answers completely opposite. Some say it will improve the power only in the top end by "supercharging" the fuel driven by the crank and is best for speedway/flat track racing, while others say it will help everywhere and would be good in an MX bike. Any ideas or has anyone done or had a crank modified like this? I'm led to believe it's half common amongt the go kart fraternity. I'll see if I can get a photo uploaded.
Cheers,
K

[paul]

[Lozza]

I as having a clean up the other day and found a CR250RZ bottom end I'd forgotten I had. It's interesting in that 1. it has a full circle crank and 2. the crank webs have been "fluted". It's a work of art and I imagine it would have cost a few bucks as it looks like a professional job. I have asked a few people as to the theory and where it would help the power, but have had answers completely opposite. Some say it will improve the power only in the top end by "supercharging" the fuel driven by the crank and is best for speedway/flat track racing, while others say it will help everywhere and would be good in an MX bike. Any ideas or has anyone done or had a crank modified like this? I'm led to believe it's half common amongt the go kart fraternity. I'll see if I can get a photo uploaded.
Cheers,
K

Turbo cranks make an reappearence every few years......................like every good scam. They are not used in karts sprint or super.If you really believe they make a difference it will. The dyno knows the answer

[DR]

I wonder how much weight it removes and I wonder how much it increases crankcase volume. I wonder if this would be a neg or pos and I wonder..wonder I do sorry..when one is wondering so much Rodriguz normally comes to mind

[EML]

I know a guy that raced minis as a kid and his dad made their YZ80 crank like a Swiss cheese, all drilled in a spiral direction. It was very fast and he one many champs with it. Always on dirt track though.
A Yamaha mechanic asked about it at a Title meeting and bought one off them-to take to Japan and test I am told.
Like it was said, probably a good idea at the time but too expensive to produce in numbers??

[firko]

I have a works 250 Maico crank that had supposedly been used by Adolf Weil that's drilled in a similar way to what EML describes and has the "turbo" grooves ground into the outer flange.Ony difference is that there's only four of them, placed  every 90 degrees. When the big end let go my mate, the third owner pulled the engine down he replaced it with a stocker he had on hand to save time and money. From didtant memory the bike was nowhere as quick as it had been but for various reasons he never used it again.
I've been thinking of using it for years and may fit it to the 250 squarie going in the Metisse. Being a 'philistine' on such things, I don't totally follow the science behind both the drilling and the turbo grooves. I presume the cranks been drilled to make it lighter but wouldn't the increased crankcase volume be detrimental? One theory we thought was that perhaps Maico was experimenting with flywheel weights and had tried plugging some of the holes with various amounts of Mallory metal or something similar. I've seen drilled cranks plugged with cork to retain crankcase volume but this one hasn't been plugged. Unfortunately the crank sat in a set of cases with in the elements for years so it's pretty rusty but nothings unsavable if you want it bad enough.

[Freakshow]

I thought crankcase Volume was a good thing ?

 Anyhow, I know some guys that make them little planes and boats, Turbo's the cranks and like you said its grooves cut into the outsides of the Webs like a pump side on, they reckon its for pullin the charge in and spin it around and creates a little bit of force in the small window of opening.  They sware buy it on the high end jobs that rev there guts out 20k but dont do it on the lower revvers.

I got a mate who has some stupid nitro alchohol boat he races with it and if you heard it run it sounds like its doing 100K rpm but the minute charge in each rev is liek an eye drop so im guessing that little bit of spin ight make some differance in suck a small motor helping push scavange, he reackon if you put it to full scale the things doing like mach 1, they litterally throw it over hand into the water as soon as its ready to run, then you cant see it, its so fast i get dizzy watching it go around

Im not sure if it would do anything on an old bike with such low revs, it might, but it would only be masking other flaws id say in other things like elect, ports etc etc.

HAving said that if i had a bike that sounded like that little boat i would be happy, then again i think its worth double the price of a bike, so maybe not.

[EML]

With four strokes you drill the crank out to lighten it but then fill the void with the lightest thing you can find-and in old fourstroke workshops wine corks are plentiful so lets use them.
With tow bangers the more you can fit into the crankcase the better because thats where the transfer gasses go, so it would be better to have no crank at all as they take up all the room-so drill some holes in the bastard to make some space-drill it on an angle to make a turbine and then rev the shite out of it.
That's the concept anyway.

[Lozza]

Some INTERESTING READING on this subject, light crank and boost bottles(just for you Rusty ). One poster refers to 'his boss' which I'm pretty sure is Dan Wade from Patriot Racing.

[Freakshow]

When Jesus spoke, he said leave me and my 2eee for we  not need these trinkets,  then he turned water in Avgas, grabbed a handfull and rode across the water at full noise.  TWas not the parting of the sea it was Rooost.

[Freakshow]

ahh and forgot to also say i quizzed Ian willaims on this about a mod to the bikes after i saw it on the Remotes, and he said they tried all sorts of mods even Vaining on the go karts, all run on there dyno.  Didnt show any gain on the  graphs so they have sheveld it over the years.

What they have found make HP was pissing about with the inlets, reeds and of all things the manifold material and width's, length's and inside shape.  Didnt get the full story cause i was shattered the turboing was a dead duck, but thats where they have been getting gains even on the controlled engines like the rotax's.

[Lozza]

You wouldn't want to use a modified Rotax MAX in NSW. You will soon find yourself on the sidelines. A few items we started to use a few years ago have been subsequently banned.

[lukeb1961]

a control engine means don't touch - and you had to do it, right? 

[Lozza]

trust me there isn't much room to move Luke, we found some bottom end and then got it to rev again through gaskets, that changed to had to have OEM gaskets. There was an opening with bearings but that's been closed. Never found what we did to the pipe though

[Freakshow]

Nothing is controlled, when they used those so called Customs locks that were supposed to seal motors and had never been apart or so "Customs thought", within 2 weeks the guys had them off and put them back on and you couldnt tell.

People will always tinker with the boundries, thats how progress is made, Risk vs result. someone will always give it go.