Build the pipe. Watch the wave do the work.
Weeks Pro Pipe is a two-stroke expansion chamber designer that shows you the pressure waves inside the pipe while you build it — header, three diffuser stages, belly, rev cone, stinger. Live, in your browser, on any device you own.
THIS IS NOT A VIDEO. The animation above is computed live from the same equations the app uses — and the degree wheel works. Drag it and turn the crank yourself.
A two-stroke pipe is an engine part made of sound
An expansion chamber doesn't just carry exhaust — it times pressure waves against your port windows. Get the timing right and the pipe supercharges the cylinder for free. Get it wrong and you built an expensive muffler. The app shows you all three acts, on every crank degree:
Blowdown
The exhaust port cracks open and a pressure pulse leaves at the local speed of sound — set by your exhaust gas temperature. The app computes it from your EGT and RPM, in inches per crank degree.
Suction
Each diffuser cone reflects part of the pulse back as a negative wave that pulls spent gas out of the cylinder and drags fresh charge up through the transfers. Three stages, three returns — you see each one peel off.
Plugging
The rev cone bounces a positive wave back toward the port that stuffs escaping charge into the cylinder right before the port closes. That's the free supercharge — if it arrives on time at your tuned RPM.
Design tools that answer while you type
Change a cone angle and the whole pipe recalculates — geometry, tuned length, powerband — with the wave animation updating live so you see what the change did, not just read a new number.
Every section, your numbers
Header angle and outlet ratio, three independent diffuser stages, rev cone angle, stinger ratio, flange diameter — the complete stack, built on fluid and thermal dynamics, with the belly length solved automatically so the pipe lands on your tuned RPM.
Turn the crank yourself
Drag an on-screen degree wheel and watch the waves move with the crank. Exhaust-open and transfer-open marks sit right on the wheel, so you see exactly which wave is at the port at which degree.
Speed of sound from your EGT
Wave speed is computed from your exhaust gas temperature — not a fixed constant. Change the temp and watch the tuned length move. Hot pipe, short pipe. Cold pipe, long pipe. The app makes it obvious.
Over-rev and low-band, instantly
Live stats for over-rev RPM (how far past peak the pipe keeps pulling) and low-RPM band, plus displacement, sound speed, and piston-to-stinger length — updating on every edit.
Rotate the metal
A rendered 3D chrome pipe built from your exact cone stack — orbit it, inspect the profile, show a customer what their chamber will look like before a single cone gets rolled.
Browser-based, no install
Laptop at the bench, tablet in the shop, phone at the track. No Windows requirement, no .NET, no license tied to one hard drive. Your license follows you, not your computer.
Formulas tell you a number. This shows you why.
The established tools are Windows programs from the desktop era — formula calculators that print dimensions, or full engine simulators that need an engineering course to drive. Weeks Pro Pipe is the only one that lets you watch the wave while you design.
| WEEKS PRO PIPE | WINDOWS FORMULA CALCULATORS | FULL ENGINE SIMULATORS | |
|---|---|---|---|
| PLATFORM | Any browser — laptop, tablet, phone | Windows install, licensed to one hard drive | Windows install |
| WAVE VISUALIZATION | Live animated pressure waves, tied to the crank | None — static numbers | None — curves after the run |
| DESIGN FEEDBACK | Instant — pipe and waves update as you type | Re-run the calculation | Re-run the simulation |
| LEARNING CURVE | Minutes — it shows you the physics | Moderate — formula inputs | Steep — full engine model required |
| CONE STACK CONTROL | Header + 3 diffusers + rev cone + stinger, per-cone angles and ratios | Classic formula outputs | Muffler geometry inside the engine model |
| POWERBAND READOUTS | Over-rev RPM and low-band, live | Not typical | Torque/power curves |
| UPDATES | Instant — it's the web | Versioned installs | Versioned installs |
Comparison reflects the typical feature set of established Windows-based two-stroke exhaust calculators and engine simulation packages as published by their vendors. Verify current versions before purchase.
Built for engineers. Priced for builders.
Design the whole cone stack before you cut a single blank. Show a customer the wave working in their pipe — nothing sells a custom chamber like watching the physics that justify the price.
Moto, kart, sled, drag, vintage — if it has a piston port and a chamber, this shows you where your powerband comes from and what moving a cone does to it. Before you commit to sheet metal.
Pair a ported cylinder with the pipe it deserves. Design against the customer's actual port durations and EGT, and hand them a combination — not just parts. We're a shop too; that's why it exists.
One license. Every pipe you'll ever build.
Less than one custom chamber. Less than one wasted set of rolled cones. Yours forever.
- Full designer — every cone, every input unlocked
- Exact buildable dimensions for the complete pipe
- Live wave simulation with interactive degree wheel
- 3D pipe view, powerband readouts, live stats
- Runs on laptop, tablet, and phone — no install
- All updates included
- Direct support from Grand River Racing
Instant license by email. Questions first? Call the shop — (616) 755-3101.
Straight answers
What wave model does it use?
A kinematic slug model — first-order acoustic wave timing computed from your exhaust gas temperature, port durations, and RPM, with reflections generated at every cone transition. It's the same physics reasoning a professional pipe designer works from, made visible. It's built for designing the pipe and understanding why it works — the dyno still gets the final word, but you'll arrive with a pipe that's already close.
What do I need to run it?
A web browser. Laptop, desktop, tablet, or phone — Windows, Mac, iPhone, Android. Nothing to install, and your license isn't chained to one computer's hard drive.
Will it work for my engine?
If it's a two-stroke with an expansion chamber, yes. Enter your bore, stroke, rod length, port durations, gas temperature, and tuned RPM — 50cc kart engines through big-bore sleds and everything between. The physics doesn't care about the badge on the cases.
What does the Pro license unlock?
The free version shows the pipe shape and the wave dynamics. Pro unlocks the exact buildable dimensions — every cone's start diameter, end diameter, and length — so you can take the design straight to sheet metal.
Is this a subscription?
No. One payment, one license, updates included.
Who's behind it?
Grand River Racing — a competition powersports engine building shop with 30+ years across drag racing, motocross, hill climb, and sled racing, and decades of two-stroke porting and pipe work. The app exists because we wanted it on our own bench first.