All about reed spacers -

[KXcam22]

I wanted to consolidate the various tidbits of info on the reed spacer:

A reed spacer is one of the best mods going for the KX500 and makes a noticeable improvement in low to midrange power quantity and smoothness.  It is even better when combined with good jetting and aftermarket reeds such as the Vforce (or boysen dual-stage for cheapskates like me).  Moose racing makes a nice 10mm thick one for cheap or it is very easy to build one out of a 3/8" (10mm) piece of aluminum.  You could also use other materials such as phenolic or micarta.  3/8" is the best thickness in terms of carb clearance. I made mine out of 1/2" aluminum but the carb barely clears the frame.

How to build:
   From experience, I would recommend no thicker than 3/8".  I built mine in under an hour, using a drill press to cut out the inside with a series of small fast holes.  Cut the outside contour with a hacksaw and file to a nice finish.  The inside contour doesn't see flow so can be left rough. As a suggestion measure the reed cage (don't just trace the gasket) otherwise the spacer may be too large inside.  I have some pics in my gallery.

What it does:
   The reed spacer increases and focuses the power down lower in the powerband at the slight expense of top end power. The loss of top end is often not noticable.  Combined with reeds, this gave my bike the midrange bark I was looking for.

How it works (or at least as I understand it):
   The reed tips protrude slightly into the transfer port flow (up & down) at the rear of the cylinder, causing turbulence at the reed tips which impedes the intake flow at lower RPM.  The spacer pulls the tips back out of the flow. The increase in intake volume and length also tunes the power lower in the band.

Hope this consolidation helps somebody. Cam.

[Danger4u2]

Thanks for your indepth reply.

  Danger

[Johnniespeed]

Thanks KXcam22  I just bought one and have not installed it yet, the weather is almost too cold now to ride, so I think it will be a spring thing. The insight on theory is always appreciated.

[alan]

I still need more INFO!

When I first joined the forum I ask "what mod should I do first"? Unanimously the answer was reed spacer, pipe and V -Force reeds! So I installed a reed spacer and FMF Gnarly pipe and was amazed in the change in performance!         

This is my Question: What is the technical explanation for why it works so well? What is the limits in performance based on the thickness of the spacer, the one I installed in my KX5 was .308 inches! What if 1 inch would fit?

So has anyone done any research on when and how they work?

Alan

[olddirtrider]

I just found this!

Simply put, the Reed Spacer improves the velocity of the air/fuel mixture entering the cylinder. The result is; Increased Mid-Range Horsepower and widening of the midrange (where most of us ride) torque = pulling power. The spacer goes between the cylinder and the reed cage. Why is our kit the best on the market ? Because; First the Trenga Racing Reed Spacer is the correct thickness, determined from bench-flow testing, to give you torque and horsepower gains. Some of the kits being sold aren't even thick enough to do what they are supposed to.

[Timbowe]

Soo what is the correct thickness? Do different thickness's make for varying engine torque ranges? Like the thinner the less torque and thicker more low end? Also back in the day, those who knew, used to bead blast the enterance of the intake port. This would mix up the fuel better. As opposed to smoothing the port off to resist drag. So many theorys, so little time, so little money!

[Paul]

Correct, Timbowe. Rough on the intake is supposed to help keep the fuel / air charge atomized, and smooth on the exhaust to help flow.

[hughes]

I made my spacer out of 3/8 alumn. This might be stuid but I am going to throw it out there. I was thinking about tuning the thickness of the spacer by adding a extra reed gasket on before I mount the spacer(two gaskets, same as a thicker spacer, maybe three gaskets) What do ya'll think.

[alan]

From Boyesen

THE GATEKEEPERS OF POWER

Looking to increase the performance of your Polaris watercraft without making a large investment? Try the new Reed Valve Spacer Kit from Boyesen. The Reed Valve Spacer Kit increases the intake tract length by moving the reed cage away from the crankshaft. This increases the flow volume under the piston and the rear boost ports in the crankcase. In this position, the reeds are allowed to function more efficiently. The action of the reeds are no longer impeded by the adverse effects caused by the rotation of the crankshaft. What you feel is improved low to mid-end response, more torque and horsepower.

[KXcam22]

Alan,
   I like that last explanation. My understanding is that (beside increasing the intake tract length - which you could also do after the reed cage) the spacer pulls the reed tips back away from the turbulence caused by the transfer ports. Without the turbulence, the flow through the reeds becomes more laminar (even).  That is why a spacer is not a universal hopup for every engine. Depending on the amount of turbulence, the spacer will help or not do much at all.  The increasing the thickness will likely make it work better (to a point - that why I made mine 1/2") but it would probably take something like 1/4" increments to notice (or measure) an improvement.  Would be a cool test to do if someone had an engine mounted in a cart. You could build a 2" one to see what happens. Heck for a test you could build a quick one out of hardwood. Cam.

[dennis]

I don't think the spacer helps because of the tranfer port distance. since the ports are in the crankcase their pretty far from the reeds. The change of the length of the intake track is prbibly the main cause of the torque increase. The volume of the crankcase is changed somewhat if the spacer is between the reed cage and the cyl.. The crankcase volume would stay the same if the spacer was between the reed cage and the carb. Has anyone tried this? I've heard that manufactures try to keep the crankcase volume as small as possible to get as much horse power as they can. Putting the spacer between the cage and the carb might be a better way.

Dennis in Arizona

[hughes]

That's called stuffing the crank case. Some enignes have wasted space inside the crank case. If the fuel/air mix doesn't have to go through or fill these wasted spaces the mixture gets into the combustion camber faster. The kx500 has very little wasted space but some one could stuff the lower end of the crank case. I agree the spacer increase the length of the intake track. If you could shortin the intake track you could make a more higher reving engine. Same goes for the pipes. Longer header pipe can make better power over a wider power band. Shorter pipes will make a short peak power across a narrow power band.

[Polar-Bus]

I just installed my Moose torque spacer, can't wait to try it out. I was very concerned as initially when installing the kit, you are effectively moving the carb and the carb to airbox boot closer to the shock spring. I thought for sure the boot was going to be rubbing up against the spring. After everything was tightened down, and properly put in position, there ended up being a small amount of clearence between the boot and the shock, so all seems ok.

[alan]

Yeppers! She be tight! But she make the grunt power!!

[Polar-Bus]

A GEORGEOUS day to ride today! Had a lenghtly opportunity to shake down the Moose torque spacer. Overall I am very happy. The torque spacer makes for a far smoother torque hit from off idle right into the midrange. All's I had to do to avoid a huge 20ft. puddle was stand, lean back a bit and abruptly roll the throttle, and instant power wheelie! The biggest advantage I felt with the spacer was the consistancy with the torque. I definately also agree this is a sweet mod to compliment the 5's beastly power. I still need to jet down a bit, but I am running straight CAM II race fuel, and the 5 really likes straight race fuel as far as crisp throttle response. I have an idle dialed into my bike, as I find it much easier to ride trails.