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How close can I move my reed cage forward with obstructing air flow?

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I posted this here a week ago but it got moved for no reason.

 

I want to move the reed cage forward by shaving down the spacer plate.

How close can I get to the booster port inlet (the flange that hangs down in the intake port) such that it doesn't obstruct the airflow.

 

If I get it too close it will probably cause turbulence and the air/fuel will not have adequate distance to change its direction to go up into the booster port.

I don't know anything about fluid dynamics which you probably need to answer this question.

I just need a rough estimate or rule of thumb so I have an idea of how much to shave off.

IMG_2311.thumb.JPG.f477cda6110f3c3c3f1e4a5b813b8cbc.JPG

 

 

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Used to notch the reed stops to match the rear bust-or boost port. Can't see enough to tell if that's an option.

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The stop plate is just a thin strip of metal. It isn't in the way of anything.

Without the spacer plate the cage just barely contacts the rear bust.

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So you just ave a thin plate (rev plate) where the reed screws are? reed tips don't have stops.   Consider, the mix isn't having to make a hard right turn up that boost port when the case is being filled on upstroke.  The mix will blow up through that port from the case, that's the direction any obstruction will have effect. The notch in the cyl skirt looks like a attempt to minimize that?   Purpose for moving the cage in ? better signal at the reed tips? reduced case volume ? 

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I figured reed spacers shift the power band down and I want to do the opposite.

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59 minutes ago, 2strokezuke said:

I figured reed spacers shift the power band down and I want to do the opposite.

You need to do a whole bunch of reading on the subject before you do something like this.

How the powerband is generated and over what rev range is a complex balance of intake and exhaust, which are all influenced by the cylinder porting.  Simply shaving down the reed spacer won't likely have the effect you think it will and it will potentially compromise the engine mechanically.

I have a pair of 80's vintage 2-stroke street bikes and can tell you that additional crankcase volume (larger reed spacers) helps to smooth out the powerband where it transitions from off to on the pipe. 

IMO you'd be better off looking at porting in order to tune the powerband.

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Its already ported. I'm just trying to squeeze an extra ounce of power out of it. 

The stock spacer plate is 6mm. I figured I'd get a few and make a 5mm and a 4.5mm. But maybe its not worth it.

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I added a 6mm spacer plate to my RD350 and it did not shift the powerband at all.  What it did was fill in the 6500 rpm hole in the powerband. 

Shortening the spacer plate is unlikely to give you more power and I would also doubt that it would do anything to shift the rpm at which the powerband starts.  

On a 2-stroke, more power is a complex thing.  Exhaust, porting, transfer porting, carburation etc.  Its a lot more than shaving down a reed spacer.

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The plot thickens. KTM didn't always use this spacer plate.

 

They kept the same jug for all years.

They kept the same reed cage from 2001 to 2006.

From ~2000 to 2005 they did not use a spacer plate.

For 2006 the changed up the intake port slightly (see picture, 2005 style on the left) and added the spacer plate while using the same reed cage.

Then in 2007 they switch over to a Boyesen cage keeping everything else the same. I guess the Boyesen cage is longer than then 2006 cage because it does require the plate to not contact the cylinder.

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If the bottom edge of the cylinder skirt protrudes into the intake it needs to be rounded off as much as possible. That might give you the clearance you're looking for.

I would also cut the left case to match the right side.

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