RD 266

[BlueSmoked]

1976 RD250C

Not the beautiful, but I like that I can hop on and ride! Technical and safety first!

Engine rebuild in 2019
56mm R28 Cylinders
DT125 Pistons
0,35mm polini membranes
Homemade exhaust for more mid range performance. Now ready to make new ones for more top performance.
Tyga short exhaust muffler

Electric wire harness
YSS rear shocks
Racetech front springs 80+ kg, fork filled with 10W oil
Taper steering bearings

Fitted the new rear shocks and stiffer front springs combined with the steering bearings gives much more handling on high and low speed corners. Even when there are bumps on the road.

https://www.youtube.com/watch?v=oRqxFLGbKek

[robrd]

Sounds good, looks good, looks like it rides good, what is there to dislike about the bike. Thumbs up from me!

[GAZZATT2]

nice
can you tell more about polini membranes ?  fibre reeds ?

[BlueSmoked]

Thanks guys! Bike ride today on dike roads sweet, but need some little more top end power to make it finish!

Yes fiber reeds GAZZATT2. You could get Polini membranes as sheets and cut them by your self. Easy to do and deliverable on different sizes, I saw a shop that sells 0.25 0.30 0.35 0.45 mm thickness.

Before I could consider which one I would take, and to backward test the expansion chamber ASC1.0 and ASC1.1(now with larger outlet pipe to muffler(15->26.5mm) and design new expansion chamber ASC2.0 (more top performance, little bit less mid-low range) I used software ENGMOD2T.

Pictures are from the ASC1.0 version to compare as baseline the original steel membranes. What make the difference in weight of membranes and stiffness to 1st graph the power curve. 2nd graph intake pressure curves and 3nd the exhaust pulses. All from 6500 rpm where the difference between baseline is at his largest.

All simulation data from one cylinder! So double power curves for engine!

What it makes on real street, that is not day/night difference comparing with suspension upgrades(!). Maybe dyno would measure a bit of gain.

[BlueSmoked]

Last year I did a dyno test with the original mufflers and with oem membranes, running on E5 gasoline.

28.4 hp on the wheel. Efficiency of the geartrain?? I don't know.



Al simulation on ENGMOD2T are pure theoretical. Put in a lot of dimensions of cylinder ports and intake volumes etc. Could play with theoretical setups.

The software could set you a hint of needed expansion chamber on Blair design basis. For ASC2.0 expansion chamber I used now this software before an other. Now I want more top performance. ASC1.0 was designed for a okay mid-range and top performance at higher rpm's 8000. But practical the engine runs to a "wall" when driving to max 7000 rpm. Where 6000-7000 rpm is a little bit flat.

The muffler broke off the bike with version ASC1.0, so for ASC1.1 I modified it to weld the muffler connection direct to the baffler (26.5 inside diameter over 15 mm) to have more meat to weld on.

Black power line is ASC1.0 , red ASC1.1 with larger outlet pipe

[BlueSmoked]

New ASC2.0 expansion would give a power curve like 1st graph. Compared with ASC1.1.

I can't find data of the graphs of the exhaust pulses in suction(before closing transfer ports) and compression state( between closing transfer ports and closing exhaust port). There you could see huge difference between the two pipes. ASC2.0 much wider (degree of rotation) suction and higher compression pressures. Mostly because ASC1.1 is designed for 8000 rpm and engine can't go to there.



Picture shows the dimensions of the pipe. There could be a better and stronger pipes. But they don't fit the bike or get to large. This one is almost from cylinder to end muffler 1200 mm. 3.5L. Belly 93 which is 30 +- mm smaller than ASC1.1

[BlueSmoked]

So first step on making new expansion chambers!
Cut out the raw sheets and for one pipe rolled the cones. Only need some material for the long belly.

[BlueSmoked]

Front and rear brake upgrade.

Both Brembo PS13 master cylinders. Fitted with HEL brake lines and fresh caliper pistons and seals (rear was really corroded and not good seals). Did a quick hone on the rear caliper.

[BlueSmoked]

Last week fitted the new made expansion chambers. Runs great, nice powerband from 5.5k!

https://www.youtube.com/watch?v=WL4ZXKMMVoU&t=124s

[tore]

Last week fitted the new made expansion chambers. Runs great, nice powerband from 5.5k!

https://www.youtube.com/watch?v=WL4ZXKMMVoU&t=124s

The boots, are those to catch the bike at a wheelie out of control?

[BlueSmoked]

Hehe . The boots are to push the bike when it is up-side-down

[BlueSmoked]

Last summer big trip with the RD 3500 km without missing a hit. Stock exhaust. Netherlands start, Germany, Swiss, Italy, small part Slovenia to tank cheaper, Austria, France, Luxembourg and than via Belgium back home.

[BlueSmoked]

In Januari, cold weather, dyno tested the ASCH2.0 exhaust!!

https://youtu.be/ewC8X5Ad_MU

I just want to see what it made of power. Put in a fat 180 jet and go with the banana like we say in Dutch.
30 hp at wheels. Sparkplugs tells very rich when running part load back home. The sound so loud riding 7-8 am in the morning.