Scooterotica

i,m playing with an early bike barrel which has a reed valve fitted and it raised a few questions as to what works and how.
I,ve got the basics that positive pressure in the crank case will close the reeds enabeling longer inlet timings to be run.

now this is where it gets fuzzy.

some set ups run pistons with no holes, like the barrel I,ve got. the skirt is short on the inlet side so it gives longer inlet duration.
most people talk about 360 degree timing but is that absolutly necassary.
if due to the size windows in a piston it only gave say 270 degreed would that be ok.

any other info gratly apreciated.

Same as you, I don't fully understand all the theories surounding reed valve induction. But, I believe the reason for 360 inlet timming is to counter for the loss of 'flow' through the inlet due to the obstruction caused by the reed valve itself. This is really only a problem at higher revs apparently so I would imagine wouldn't make much difference until the engine is under load. What is your objection to drilling holes in your piston? The TS1 piston I'm using on my reedvalve set up also has a 3mm cutout on the inlet side of the skirt and I've also added a boost port.

Same as you, I don't fully understand all the theories surounding reed valve induction. But, I believe the reason for 360 inlet timming is to counter for the loss of 'flow' through the inlet due to the obstruction caused by the reed valve itself. This is really only a problem at higher revs apparently so I would imagine wouldn't make much difference until the engine is under load. What is your objection to drilling holes in your piston? The TS1 piston I'm using on my reedvalve set up also has a 3mm cutout on the inlet side of the skirt and I've also added a boost port.

Essentially some of the early reed valve barrels developed a process they termed as power porting where the process used was partially reed induction but also used the piston skirt as a cut off. The bottom line is that there is a huge variation in the application, use and terminology of these type of induction systems. They have been around as long as the hills 40 odd years (in the form we see in most Lambretta), much much longer if consider DKW engines in the late 40's.

If you want to get your head around it I would recommend you read a couple of books to give you some history, examples, process descriptions and port timing - application advice. Otherwise you'd be asking questions for ever and a day and getting yourself frustrated and or more confused.

The best book by far is John Dixon's The High-performance two-stroke engine ISBN 1 844250458
The Graham Bell book Two Stroke Performance tuning has some good general reference information for application of port timings. ISBN 1 85960 619 9
The John Robinson book is better presented than the Bell book but I thought it the least useful and a good 20% of it is dedicated to writing out DOS programs for port timing etc.
A great book in general but a real rare find is The Romance of Engines by Takashi Suzuki ISBN 1 56091 911 6 not specifically related to 2 strokes but historically and development wise it is a very interesting book with some really funny author cartoons (my favourite is the Nazi's with the VW bettle, you wouldn't get away with that these days).
Finally, there is a set of Roy Bacon paperback books from the late 60's that are quite fun and a nice reference to that time.

If I had to boil it dow to two essentials it would be Dixon and Bell in that order.

Here's Bell on 'Power Porting'

Thanks for the replies.
I'll find my glasses and give it a read.

Interesting reading.
I'm building a ts1 and with a Suzuki dt piston it could give me around 200 degree inlet.
I could try power porting and with a revvy pipe might work well.
Shame there's no graphs to show any difference with 360 timing and no boost ports.

Out of interest which way did the gt kit go.

GT kits and virtually all other modern reed engines I know run 360 degree timing. Holes in the piston are only used where the reed is mounted in the barrel. Most karts and moto X run the reed direct into the casing so the piston can have more bearing area and the big end gets a nice cool fuel charge. The current trend on some karts is to position the reed into the base of the transfers.