I've heard that it can add a couple of horsepower to flow the crankcase while you have it apart, removing rough casting burrs and radii the edges. Can somebody explain how to go about this, and what to look out for. I don't want to make a mess...
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MC21 Honda NSR250. TYGA 300 conversion.

Stephen could, though I wouldn't expect him to since that's how he earns money to feed his exotic two strokes addiction!

anonymous.shyster wrote:I've heard that it can add a couple of horsepower to flow the crankcase while you have it apart, removing rough casting burrs and radii the edges. Can somebody explain how to go about this, and what to look out for. I don't want to make a mess...

I believe there was a thread on this not long ago, which had some words of wisdom from Matt and links to these:

http://www.dogfight-racing.co.jp/race/f3photo.htm
http://www.hm3.aitai.ne.jp/~aichi/kaizou2.htm

Looking at the RS cases the main area you want to open up is the area up into the upper cylinder transfer ports.

Dave ripped Tuckerbag to bits recently telling him to try having an NSR website for himself, well here's a pic from the site in question;



And on the RS barrels the boost port on the barrel is as big as the one on the cases.
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The pics Fontyyy posted definitely give you a good headstart in what works with the NSR cases.

However, you don't need to go all out crazy with the grinder as just knocking off the corners and smoothing things here and there gives good results

i think i have a pic of mine,but dan would cut my balls off for showing it
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Sounds like there is some hidden science behind this, secret handshakes included.

I suspect there is, amd of course some folk do make a living by doing this kinda thing - Stephen is working on my engine for me since I don't have the facilities or the nerve to do it myself...

For what it's worth, as already alluded to by Fontyyy, I blogged my crankcase flow from here onwards.
The material that I removed, was balanced out by adding some material elsewhere to keep the two crankcase volumes quite near to equal.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...

IMO all this is a complete waste of time and makes little difference to the output. I wouldn't put any faith in someone who still knife edges transfer dividers.

Make up your mind, is it a complete waste of time or does it make a little difference to the power output?

There are no big gains anywhere, ever. You get a bhp or 2 here, another one there, another 1 or 2 somewhere else and suddenly instead of 62bhp you have 67.
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Fontyyy's on the money there. I wouldn't run std cases on any of my bikes.

fontyyy wrote:Make up your mind, is it a complete waste of time or does it make a little difference to the power output?

There are no big gains anywhere, ever. You get a bhp or 2 here, another one there, another 1 or 2 somewhere else and suddenly instead of 62bhp you have 67.

I'll agree with Jan Thiel's assesment that this type of thing makes little difference, the spoiler is the spinning crank and rod, that creates much more turbulence. A very clever South African ex GP enginner told a his friend that spending 20 hours on F1 boat cases that it was a WOFTAM, left the cases stock(except for removing a few casting dags) the dyno nor a world class driver could pick the difference.I my local dyno can't pick the differnce between cases with and without this mod.
Big gains come from the ignition, pipe and specific time areas.

Surely 'shaping' is the main thing.
Several ( ) years ago me and my mate were in the pits at Silverstone as guests of Dino Karts in the year that they won the world Superkart championships. Not only were their karts the pick of the crop but their 250 Rotax twin motors were also the fastest.
My mate (himself more than a bit of a wizard with 2 strokes at Fowlers) said to me to take a look inside one of their motors as it had the barrels off. We were amazed by how rough looking it was inside! Everything was matched/shaped but no area had any sign of smoothness, no nice polished surfaces. We did chat with one of their tuners and he explained that you can get a faster, more pressured charge if you just shape correctly but with no polishing.

Mike
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It also depends how good the original case are, it looks like both the early NSR (r2jmc18) and NF5 RS cases start out as the same casing, opening up the top transfers (stock on the left, modded on the right in the above pic) is one of the mods that is done to the RS cases.

Matt@TYGA wrote:Fontyyy's on the money there. I wouldn't run std cases on any of my bikes.

You ever back to back test modded vs stock cases them Matt with no other changes?

I know Mark Jordan reckons case work on his KR1S racebike is worth nearly 6 bhp
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