I was wondering if there are any people out there that know what reed spacers do, and why they do it.

 

The larger the spacer is the smoother the power will hits. If your machines power hits so hard that you have a hard time holding on, then your in need of a reed spacer.

Waymod

 

What a reed spacer does is increase your intake volume. This makes the fuel/air mixture move faster at slower rpms thus giving you the added bottom end power that these spacers produce. Hope this helped.

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Jayson Blough '99 Banshee, '97 Warrior, '96 Blaster Yes I like Yamaha

 

The spacer spaces the reeds back so that the fuel has more time to mix completely and at the same time the flow smoothes out and increases in velocity. It becomes more of an "injection" than just a flow. It really doesnt make that much of an improvement, but it can be noticed.

 

On cylinders that have auxilary transfer ports (aka finger ports, boost ports, so on), the tips of the reeds and the reed block assy. are moved further back away from the opening to the aux. transfers. This in addition to what was mentioned in the previous post(s), allows more air/fuel to enter thru the aux. tranfer ports. Thereby trapping(and slightly compressing) more air in the bottom end of the motor when the piston is rising to TDC. More air, more fuel, more power...

 

With the larger volume in the crankcase, there are two things I am thinking of that will HURT performance. First, the extra volume the reed spacers provide reduce the "pumping ratio". This is the volume of the crankcase at TDC/volume at BDC. It would seem that since the case pressure is REDUCED with the reed spacers, that LESS air would be pumping into the cylinder via the transfer ports, and this would mean LESS power, especially at high rpm. Secondly, with the reduced pressure ratio, there would be less velocity through the transfers, which would again cause a loss of power due to a less efficient swirl in the combustion chamber.

Could it be that the actual effects of the reed spacers is that they reduce the top end hit, which FEELS like an increase in bottom end?

After all that I have read and learned about the two stroke engine, reed spacers don't make sense to me. Any comments???

 

This message has been edited for some clarity, I was trying to cram the original in during my break at work.....

...Good points, but...one of the factors of modern two stroke motors are the tuned expansion chamber exhaust systems. The tuned pipe offsets almost all of those "bad" characteristics with the suction phase and stuffing return pulse. This is where the increased volume is good.

The suction pulse, created from the diffuser cone(s), is able to pull(scavenge) more mixture down the head pipe, then the baffle cone sends a return wave, "stuffing" the mixture back into the cylinder before the piston closes off the exhaust port, thereby almost "supercharging" the cylinder. A cylinder with a tuned pipe is able to actually allow the cylinder to displace more than the swept volume that it is (i.e. 125 can displace 175cc's)while "on the pipe".

Again a greater volume created by a spacer, is able to be trapped in the cylinder which in turn can be drawn down the head pipe and returned to create more power.

The tuned pipe provides a stronger return pulse that effectively and positively helps the reeds shut and lessens cylinder primary pressure losses.

The transfer ports don't account for a whole lot of swirl in the combustion process. Often the sum of the angles of the transfer ports dump the mixture towards the rear half of the piston. The transfers are often aimed rearward to prevent too much from being sucked down the pipe(at lower RPM's where it will hurt), as well as preventing exhaust gas entering the ports, thereby short-circuiting them. The entering intake charge coming from the boost port and intake also help "bring" mixture up from the transfers, but on a limited basis, much like a suction paint gun works. The swirl imparted in the combustion pocket is far more influenced by a properly set-up squish band.

A reed spacer should be viewed as a part of an entire package of how a motor is designed to create maximum(or nearly max) power. A spacer isn't going creat neck snapping power differences, but the subtle differences that each modification that an engine builder may make begin to add up to create more power overall. I really can't reccomend running reed spacers on an otherwise stock motor, but if you have even just pipe(s) then I would reccomend them.

Remember that getting the full potential out of a motor requires careful planning and attention to small details. The sum of many changes brings about a complete and potent motor...80% of the work is getting the last 20% percent of the power...

Reccomended reading--Gordon Jennings, Two Stroke Engine Theory. Mr. Jenning's book humbles most and makes you realize how little we all really know...

[This message has been edited by Backcountry (edited 01-10-2000).]