Boost Port for reed valve conversion

[Andy W]

Hi all, hope someone can advise on the following:
I'm going to fit a reed valve to my iron barrel 200 I will be modifying the piston and want to cut a boost port in the bore. I have looked at a couple of reed valve barrels and the boost port seems to vary in height i.e. some are at the same level as the top of the transfers and some I have looked at are either above or below the top of the transfers.

Question is where should it be and how would it's height affect performance? Do I cut it to finish it at the same height, higher or lower than the transfers?

Any ideas welcome, Andy

[camel]

ive done a couple and i must say they do go well,one one an iron 200 is a peach to ride.
first job is to determine the ring peg positions,mark the top of the piston with a fine marker pen the EXACT points where the line up on the piston crown.
reassemble the piston onto your crank,no need for rings on,and put your barrel on.At tdc carefully mark the two ring peg positions onto the barrel.
Then using a good engineers square mark down the barrel into the inlet port,this gives you the exact peg positions the boost port(s) need to miss.id give a good 5mm gap from the peg position line to the edge of the boost port(S).
I keep the boost port height the exact height of the transfers.
you can also mark the piston window width through the inlet port while the barrel is on.
these are the basics i use
have fun

[bigmuff]

Roger at Pro design did an SR185 barrel for me to run with an RD350 piston and he cut the boost port level with the top of the transfers. Gets about 17bhp with JL3 and 30mm phbh and a homemade reed manifold. Cheers, Andy.

[pasner]

ive done a couple and i must say they do go well,one one an iron 200 is a peach to ride.
first job is to determine the ring peg positions,mark the top of the piston with a fine marker pen the EXACT points where the line up on the piston crown.
reassemble the piston onto your crank,no need for rings on,and put your barrel on.At tdc carefully mark the two ring peg positions onto the barrel.
Then using a good engineers square mark down the barrel into the inlet port,this gives you the exact peg positions the boost port(s) need to miss.id give a good 5mm gap from the peg position line to the edge of the boost port(S).
I keep the boost port height the exact height of the transfers.
you can also mark the piston window width through the inlet port while the barrel is on.
these are the basics i use
have fun

Have you got any pic Camel? this basic info is more than interesting. Thanks.

[camel]

yeah,pm me your email address and i,l mail you a few to get the general idea

[pasner]

PM sent.

[Speed Demon]

I think conventional tuning wisdom (if there is such a thing when tuners all disagree and hate each other but then end up copying what works best) is that the boost port should open last and therefore should be a little lower than the main and secondary transfers.

[a.j]

I think conventional tuning wisdom (if there is such a thing when tuners all disagree and hate each other but then end up copying what works best) is that the boost port should open last and therefore should be a little lower than the main and secondary transfers.

Yeah thats what I was gonna say.

[camel]

Also if your unsure about cutting the boost port, the artlicle in scootering mag just did the piston window mod(no boost port) with the reed valve manifold and got good results.
As a footnote. just the reedvalve alone without any piston windows reduced performance.

[fastfrog]

I think conventional tuning wisdom (if there is such a thing when tuners all disagree and hate each other but then end up copying what works best) is that the boost port should open last and therefore should be a little lower than the main and secondary transfers.

Yeah thats what I was gonna say.

+1 leave 2-3° less than main transfers.... As a boost port it blows straight in front of the exhaust window and needs less path than the two mains and therefore is sooner where it shouldn't be: somewhere in your exhaust especially at low revs... You can follow the beginning of my thread about the Lince 200 reed conversion. "Fastfrog o-tuning something..." can't remember the right title....