LCGB Forums

Posted: **Sat Jan 24, 2015 3:27 pm**

Getting ready to build an engine for my series 2 project and have an alloy 185 barrel which has been taken out to 66mm and the ports tidied up by AF , so what benefits ( if any ) would I get by fitting something like an atomic or LTH small reed valve with a 24mm carb on it ??

Posted: **Sun Jan 25, 2015 1:02 pm**

Better fuel consumption,less spit back from the carb.Would benefit from a hole in the piston as well.There is a thread about that recently on here.

Posted: **Tue Jan 27, 2015 5:36 pm**

More speeeeeeeeeeeeeeed!! :lol:

Posted: **Tue Jan 27, 2015 6:39 pm**

^^^
Why?

Posted: **Tue Jan 27, 2015 9:35 pm**

Scooterlam wrote:^^^
Why?

I agree, fitting a read valve on it's own won't give more speed. In fact you will lose some performance unless mods to piston and ports are undertaken. On the other hand, it will allow you to run with more radical port timings by managing the spit back associated with overlapping port timings.

Posted: **Wed Jan 28, 2015 1:09 pm**

coaster wrote:
Scooterlam wrote:^^^
Why?

I agree, fitting a read valve on it's own won't give more speed. In fact you will lose some performance unless mods to piston and ports are undertaken. On the other hand, it will allow you to run with more radical port timings by managing the spit back associated with overlapping port timings.

Reed valves are basic and can enhance performance simply because they keep the fuel in the engine. Simply stated, a reed valve is a one-way check valve that allows fuel to flow into the engine and then closes, making sure the fuel charge doesn’t spit back. The reed valve works off the engine’s internal pressure changes. When atmospheric pressure in the 2-stroke engine’s crankcase is low, the valve opens and allows fuel to flow in. During compression of the charge the reed valve is closed, keeping the charge in to be combusted.

That is an oversimplification, but it is fundamentally how the system works. The result is improved low end and generally an increase in performance

.

Posted: **Wed Jan 28, 2015 1:55 pm**

Reed valves are basic and can enhance performance simply because they keep the fuel in the engine. Simply stated, a reed valve is a one-way check valve that allows fuel to flow into the engine and then closes, making sure the fuel charge doesn’t spit back. The reed valve works off the engine’s internal pressure changes. When atmospheric pressure in the 2-stroke engine’s crankcase is low, the valve opens and allows fuel to flow in. During compression of the charge the reed valve is closed, keeping the charge in to be combusted.

That is an oversimplification, but it is fundamentally how the system works. The result is improved low end and generally an increase in performance

. [/img][/quote]

That is indeed an oversimplification, the reed valve itself presents a significant obstruction to inlet path which will harm performance further up the rev range. That's why 360 inlet duration and finger ports etc are needed to compensate for the losses.

Posted: **Wed Jan 28, 2015 6:31 pm**

That is indeed an oversimplification, the reed valve itself presents a significant obstruction to inlet path which will harm performance further up the rev range. That's why 360 inlet duration and finger ports etc are needed to compensate for the losses.[/quote]

+1

Posted: **Wed Jan 28, 2015 8:02 pm**

Is a finger port a boost port?

I'm thinking of adding a reed valve with boost port and piston cut-outs, but am slightly concerned that I'll sacrifice top end.

Will the piston cut-outs and boost port compensate for flow restriction caused by the reed?

Posted: **Wed Jan 28, 2015 8:21 pm**

dickie wrote:Is a finger port a boost port?

I'm thinking of adding a reed valve with boost port and piston cut-outs, but am slightly concerned that I'll sacrifice top end.

Will the piston cut-outs and boost port compensate for flow restriction caused by the reed?

Finger Port = Boost Port and yes, you should be able to get the top end back and more if you tickle the exhaust port while you're at it 8-)

Re the finger port, I cut one on an ally 225 cylinder and found it quite easy to break through the outside wall :shock:

Posted: **Wed Jan 28, 2015 11:17 pm**

coaster wrote:
Re the finger port, I cut one on an ally 225 cylinder and found it quite easy to break through the outside wall

So you mean that you wrecked the barrel?

Posted: **Thu Jan 29, 2015 12:06 am**

interesting thread this!!
as me mates wanting to add a boost port with an atomic reed-valve manifold
his kit is a 200cc for a small block - alloy fins/steel liner

Posted: **Thu Jan 29, 2015 12:20 am**

dickie wrote:
coaster wrote:
Re the finger port, I cut one on an ally 225 cylinder and found it quite easy to break through the outside wall

So you mean that you wrecked the barrel?

It was only a small hole the size of a match head visible between the fins so I cut a small piece of ally and glued it in place over the hole using JB Weld. It was going to be a temporary fix but was on there for around 2k miles, Norfolk to Kilarney and back (650 or so miles) 2 up and it was still firmly in place when I replaced it with an Avanti top end 8-)

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