rethinking expansion chambers

[Bike_Builder]

A basic baffle design, neat really.
Trying to get power all through is tough, but with use of a tuned air-box and pipe you can certainly get 5600 usable RPM with reasonable power throughout that range. I'm getting enough torque off the bottom to lift the front end with a vengeance, and wheel-spinning power starting at about 2500(the dyno was rolling on that take in the snapshot) right up to 5600. I used the header/intake lengths to produce bottom, the air-box ensures that those pressures are up, and pipe design carries her from there. I'm getting response from her like a real dirt-bike. Lift out of the hole with a Bwop. And Braaaapin' the wheel-spin on the pipe. The air-box gives an advantage and the fact she is a piston port makes the scavenging devices crucial and highly effective. I eyebrow my transfers to add boost for the low end while maintaining mid and high, and i use the curve of the top of the intake port to sort of variably time it. a 23mm exhaust port and 21mm carb work nicely together on a 66. I bet I still beat your dump-pipe racer.. Gears are my next thing to attack. If I had gears on Jenny she'd really be able to run! Gears are the answer really.. I want to get a lathe! I'm just poor.

 

[Deleted member 12676]

yeah the longer you make the intake and exhaust lengths the lower in the RPM range you get the most benefit. I discuss those lengths and what you might expect on my site.
I'd like to see the dyno of your engines power.

 

[Street Ryderz]

yeah the longer you make the intake and exhaust lengths the lower in the RPM range you get the most benefit. I discuss those lengths and what you might expect on my site.
I'd like to see the dyno of your engines power.

His dyno sheet is not what you would expect to see compaired to the claims made in the above post!In my post my bike running the exhaust has 20 inches of 19mm i.d header tube before a single stage chamber that has a 63mm dia belly with 104mm length the difuser is 408mm and divergent section is 178mm and having the header length it comes on around 3200-3300 and pulls well until the sweet spot at 5700 allowing it to pull thru the 3.09 ratio gearing then the engine does the work of achiving the higher rpm! In that video the bike ran an 1/8th mile in 6 seconds without even using above half throttle and hit 43mph in about 150 yards and yet I still dont have wheel spining or standing ability lol mind you I also have a 60 inch wheel base!

 

[Bike_Builder]

yeah the longer you make the intake and exhaust lengths the lower in the RPM range you get the most benefit. I discuss those lengths and what you might expect on my site.
I'd like to see the dyno of your engines power.

I've gotten the best results using two NT carbs for juice. This dyno chart was made using the Tillotson 21mm, it lacks mid and low power with the Tilly, but she will really tune nice for high RPM operation.

 

[Deleted member 12676]

I'd like to see someone saw through his expansion chamber and weld in a long belly and report back as to the difference.
I'd do it but I don't have a motorized bicycle now, just the cylinder/piston/carb/pipe from my last build before I moved to another country.
I think it's a great idea because a normal expansion chamber makes you only want to go at top speed and with it kicking in to the max there it is the most noisey and it is hard on the engine to run at top speed "on the pipe" (as dynamic compression is at the max and so the engine runs hotter).

 

[Bike_Builder]

I'd like to see someone saw through his expansion chamber and weld in a long belly and report back as to the difference.
I'd do it but I don't have a motorized bicycle now, just the cylinder/piston/carb/pipe from my last build before I moved to another country.
I think it's a great idea because a normal expansion chamber makes you only want to go at top speed and with it kicking in to the max there it is the most noisey and it is hard on the engine to run at top speed "on the pipe" (as dynamic compression is at the max and so the engine runs hotter).

I live on a mountain, and it's steep. I built this pipe for my chopper. The full length open to close is 30 1/4". The bike would pull a truck up hills I'm sure! I used your cones for the pipe. It climbs so good!! No matter what I'll be on the pipe around here. My initial compression is low anyways, I use a stock head, so I doubt my pressures are getting extreme. She runs just right with the BPR7HIX at .050, nice and normal, our ambient temp is closer to 30 around here this season.
The torque pipe hitting right as the air-box loses it's influence is working nicely. No real transition drag or loss. Jenny pulls the same hills with just as much torque(using the twins) only faster. I pull the same hills going just as fast as cars can manage, I pulled 1st. Ave. with a car behind me, the whole way! I rode up to where I took the second pick too. I ride some seriously steep stuff with her. It's a test of the clutch but with the 48 on a 26" it's not too bad, I like a 24" rear though. She was designed for that, better rake.

 

[Deleted member 12676]

Looks like what I've been talking about with the long belly. Can you tell me how long it is?

 

[Randall]

I like the Profusely Perforated Baffle Cone idea, Jag.

 

[Bike_Builder]

Looks like what I've been talking about with the long belly. Can you tell me how long it is?

The belly on the chopper pipe is 15", loads of off-the-line power.

 

[Archiwax]

I'd like to see someone saw through his expansion chamber and weld in a long belly and report back as to the difference.
I'd do it but I don't have a motorized bicycle now, just the cylinder/piston/carb/pipe from my last build before I moved to another country.
I think it's a great idea because a normal expansion chamber makes you only want to go at top speed and with it kicking in to the max there it is the most noisey and it is hard on the engine to run at top speed "on the pipe" (as dynamic compression is at the max and so the engine runs hotter).

I did on the one you (jag) already have seen, u told me 2 inch belly length and i did 5" with a 13" header (3/4") and a 7 1/2"(1/2") side stinger. It gave better grunt, no real #s available and good to about my max 6k rpm