MOPED ARMY

If you are on 2stroke research and development most guys that port that step out get a quick lesson as to why the step is there. Something something return wave. If you get a good comprehension on it let me know what is good about it. I've not put much thought into it.

And most of my "race" scooty cylinders ha ve that step cast in. If that means anything.

I would think being so close to the boundary wall layer where the flow is already low on exit having it would not affect exit flow that much

its pretty common on like nascar style roundy round cars, especially dirt track with a restrictor plate. i'll see if i can find a good article i read on it, basically it stops the reversion pulse you get from the end of the tailpipe

if you have a multi-cylinder engine with a collector, the exhaust pressure wave goes down the tube to the collector but when it hits the end a reversion pulse comes back, those four stroke motors are turning like 6000 rpm maybe so you're talking 1/2 that for it being a four stroke and the tuned length gets pretty long, so the reversion pulse is in theory coming back while the exhaust valve is still open.

the stepped port like that stops the reversion pulse or at least significantly reduces it so you don't get back flow in the exhaust port. this also is the same reason you hear about four strokes liking 'back pressure'... basically if you don't have a blower or something a 20 inch whatever zoomie or open header is gonna send back one motherfucker of a reversion pulse. if your intake port pressure is already on the low side (i.e. restrictor plate)

as far as how it would work with an expansion chamber, i dunno, seems like most high performance two stroke cylinders i've had apart, like factory dirtbikes and snowmobiles and stuff, have a pretty smooth transition for whatever that is worth.

When you have 10 to 15 year-old bikes that start and take you 20 to 30 miles in every direction and iand run for hours let me know, r Hard to start

but being a musician you rock! You are talented!

I tried a few years ago to see you in Akron but I couldn’t make it there in time, keep posting because some of these belt drive moped people counting on you! I like gear drive chain drive or nothing,

either chain drive or gear drive everything else fail oall four seasons!

Are you saying I don't have those reliable bikes riffroff? Shame on you.

I'll race your old ass for a thousand miles for pinks and we'll see if all your big reliability talk holds up.

Jbot vs riffroff 2021

The ds7 step is just how the gasket seats on there, if there is any step other than that it would have been somehow missed in it’s finishing. This is only useful with aux exhaust ports and they never had 3 exhaust ports on the rd series bikes. Rd means race developed, it is essentially what you say, r and d. It being a culmination of the 1960s-early 70s yamaha road racing efforts, but de tuned for reliability, consistent power delivery and noise compliance of course. Jbot, when are you gonna make a power valve already? (edited)

Maybe I'll do it.

I'd need to see one in person someday.

Stock cr 250R with power valve geared correctly is a 10 second bike, quick shift at the next gear to bring the front end down and being only a four-speed and close ratio within mili seconds the front and came back up I never was scared in my life the 5-6 times I rode these bikes in my life! And I rode 360s Husks in hair scrambles back in the day and got finisher pins, Though I didn’t finish in the top three I finished ninth place and they were nothing like these wicked Honda 250cc powervalve bikes!

jbot what tools are you using for your auxiliaries? I feel like I gotta open up the tract and flange a fair bit to be able to get the bit deep enough at a good angle for shaping. angled exhaust flanges are kinda dumb

I needa find some longer bits, im just using hardware store Dremel tungsten carbides. it seems like the ebay/amazon diamond and carbide ones dull or get bent easily

Yeah long shaft carbide eBay blue packs like $8 or something.

But I use a drill bit usually.

Just aim well and take your time.

Then after the drilled hole is cut, nibble away with the carbide cutters

I've only fucked it up once, (cue Jackers) but the cyl still ripped. Did one aux port and then made the 2 ports like an off center bridge..

http://www.dragtimes.com/Yamaha-YZF-Timeslip-9916.html

Some guys with the new R1M broke into the 9's with one in Canada.

But for the most part I stand by what I said. Most liter bike crotch rockets are 10-11s bikes.

I followed this process. Was awesome 10/10 would recommend. That blue pact of carbides is the best porting bits.

Get the diamond dental burrs for plated cylinders. Much less chipping.

You can still use carbide burrs on all the aluminum stuff.