Performance reeds: How do they increase power and do they decrease fuel economy?

VenomRS4

Member
Jan 12, 2007
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As stated in title. I'm having an argument at my place of work and I may be wrong. So I need an answer from some pros! How do they work? And at wide open throttle, I understand an engine with performance reeds will have more power. Will it also use more fuel while doing it compared to an engine with stock reeds at wide open throttle? Thanks!
 

RM_guy

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Damn Yankees
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Nov 21, 2000
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They work better by allowing for better flow. Some will open further or have less restriction in the flow path and others (V-Force) increased the number of pedals so they don't have to open as far to get the same flow. The better the flow (more gas and air in the combustion chamber), the more the power.

Generally you get better low end power if the reeds are more flexible. It takes less pressure to open them so they respond quicker and open further at low RPM. They won't help at the top end because they don't close fast enough at the higher RPM. Each revolution needs the reeds closed on the down stroke to prevent backflow...which reduces the amount of charge going into the combustion chamber through the transfer ports. Stiffer reeds will give you more top end with a loss of low end power.

Fuel consumption is a good question. I never noticed any change (read: I’ve never checked it) but I’d guess that is has to be higher since you are improving the air flow but not much higher.

I’m curious what the other theories at your work are.
 

_JOE_

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May 10, 2007
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I've never noticed, and wouldn't expect, much of a change in fuel economy. The engine isn't trying to pull more fuel, simply getting it where it needs to be more efficiently. In my experience they impact starting ease and throttle response most.

I too am interested to hear the workplace theories....
 

2strokerfun

Member
May 19, 2006
1,500
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_JOE_ said:
I too am interested to hear the workplace theories....


OK. I am at work. So, in theory, if you have a high performance reed capable of completely closing and stopping backflow at 8,500 rpm, you might slightly increase efficiency of engine, thereby increasing mileage from 20 miles per tank to 20.003 miles per tank.

I would be shocked if there is a SAE paper on this. But maybe:
Evaluation of Reed Valves in High Performance Two-Stroke EnginesDate Published: 1994-12-01Paper Number: 942528
or
Mathematical Modelling of Reed Valve Behaviour in High Speed Two-Stroke EnginesDate Published: 1997-09-08Paper Number: 972738
or
An Improved Model for Predicting Reed Valve Behaviour in Two-Stroke Cycle EnginesDate Published: 1987-09-01Paper Number: 871654
or
Theoretical and Experimental Study of Gas Flow Through Reed Valve in a Two-Stroke EngineDate Published: 1996-08-01Paper Number: 961802

Problem is you have to pay for these papers. Then you have to be smart enough to read them and understand them. So do what I normally do: Ask Rich.
 

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