Design the chamber. Command the burn.
Grand River Racing Pro Head is a two-stroke cylinder head designer that takes your chamber from shop measurements to machining coordinates — with engineer-level squish and combustion simulation checking every decision. Live, in your browser, on any device you own.
THIS IS NOT A VIDEO. A 66.5 × 54 methanol top end with a two-stage bathtub chamber — piston, gap, jets, and the MSV number are computed live by the same equations the app uses.
The head isn't a lid. It's a mixing machine.
In the last degrees before top dead center, the squish band slams the trapped charge out of a closing gap at tens of meters per second — and that jet decides how fast, how clean, and how safely your engine burns. Get it right and you gain power and detonation margin. Get it wrong and you're one lean pass from a hole in the piston. The app shows you all three acts:
Compression
Bore, stroke, gasket, deck, dome, bowl — the app integrates the real chamber to give you true volumes and compression ratios, geometric and trapped, from your exhaust timing. No burette needed until the verify cc.
Squish
As the gap closes, charge escapes the band at a velocity the app solves every quarter degree. Maximum Squish Velocity is the number that sets turbulence and burn speed — and Pro Head tracks it against RPM, with rod stretch and piston-to-head clash warnings built in.
Ignition
A Wiebe combustion model burns your actual fuel — methanol, gasoline, or any E-blend — in your actual chamber, solves MBT timing, watches the endgas for detonation, and prints an advance curve you can hand to your ignition.
Your chamber doesn't burn alone. The pipe decides what's in it.
On a two-stroke, the expansion chamber's pressure waves set what the cylinder actually traps when the plug fires — how much charge, how hot, and how diluted with exhaust. Pro Head is the only head tool that feeds live pipe pressure data into the burn model, so the fuel charge, the burn rate, and the ignition timing all respond to the pipe, at every RPM.
The four numbers the pipe hands the combustion model, interpolated at every RPM across your band.
Slow burn, big advance
Below the band the pipe isn't helping: low trapped pressure, heavy exhaust dilution. The charge burns slow, so the engine wants more advance — and can safely take it, because cylinder pressure is low. Pro Head's solver gives it that advance, inside your safety tiers.
Fast burn, less advance
At tuned RPM the plugging wave stuffs the cylinder: high pressure, hot returned charge, low dilution. The burn goes fast, the engine needs the timing pulled out — and this is exactly where detonation margin is thinnest. The advance curve dips right where your pistons need it to.
That's why a one-number ignition setting is always wrong somewhere in the band — and why Pro Head's printed advance curve breathes with your powerband instead of averaging across it. Run Weeks Pro Pipe? Export your pipe and import it straight into Pro Head — your actual pipe's pressure waves drive the burn. No pipe file yet? A parametric pipe model (tuned RPM, peak charge, powerband width) stands in until you have one.
Shop measurements in. Machining coordinates out.
Every input is something you can measure at the bench — depth gauge, flat width, wall radius — and every output is something you can act on: a cc, a timing number, a warning, or a coordinate table for the mill.
Bowls the way you actually cut them
Hemisphere, bathtub, and two-stage bowls defined by depth, flat width, and wall radius — the numbers off your depth gauge, not abstract curve constraints. Squish gap, band size, band angle, and fillet all under your control, auto or manual.
The squish number that matters
Maximum Squish Velocity solved every quarter degree through the compression stroke, plotted against RPM — with dynamic rod-stretch correction and a hard warning when the effective gap closes toward piston-to-head contact.
Dial the band to a target
Tell it the MSV window you want and the optimizer sweeps the squish geometry to land inside it — instead of you iterating cut after cut on real metal.
Timing from combustion physics
Wiebe burn model, MBT solver, endgas detonation watch by fuel octane, and safety-tiered advance limits — for methanol, gasoline, and E-blends with a slider from E0 to E85. Prints a full advance chart for your ignition box.
From screen to spindle
The finished chamber exports as an X / Y coordinate table — radius and depth from the split line — ready to program the cut. Design it, verify it, machine it. One tool, whole job.
Browser-based, no install
Laptop at the mill, tablet at the bench, phone at the track. No Windows requirement, no license tied to one hard drive. Your license follows you, not your computer.
Head math has been stuck in the '90s
The established tools are Windows-era calculators — static numbers out of static formulas, no combustion model, nothing you can watch, and nothing you can hand to a mill. Pro Head simulates the chamber like an engineer and speaks to you like a machinist.
| GRAND RIVER RACING PRO HEAD | WINDOWS HEAD CALCULATORS | SPREADSHEETS & RULES OF THUMB | |
|---|---|---|---|
| PLATFORM | Any browser — laptop, tablet, phone | Windows install | Wherever the file lives |
| SQUISH ANALYSIS | MSV solved vs crank angle and RPM, animated live | Single static MSV number | "About 25 m/s is good" |
| MECHANICAL REALITY | Rod-stretch correction + piston-to-head clash warning | Not modeled | Not modeled |
| COMBUSTION & TIMING | Wiebe burn, MBT solver, detonation watch, printable advance curve | None | None |
| PIPE COUPLING | Pipe pressure data drives charge, burn rate & timing — imports Weeks Pro Pipe designs | None — head treated in isolation | None |
| FUEL MODELS | Methanol, gasoline, E-blend slider to E85 | Limited or none | None |
| MACHINING OUTPUT | Chamber coordinate table for the mill | Varies — often dimensions only | None |
| UPDATES | Instant — it's the web | Versioned installs | — |
Comparison reflects the typical feature set of established Windows-based two-stroke head calculation tools as published by their vendors. Verify current versions before purchase.
Built for engineers. Priced for builders.
Design the chamber on screen, verify the cc and the squish before you touch the mill, then cut from the coordinate table. Re-cuts cost time and castings — simulation costs nothing.
Compression, squish, and timing are one system — change fuel or altitude and Pro Head shows what the chamber and the advance curve should do about it. Stop tuning the head by folklore.
Pair the ported cylinder with the chamber it deserves and hand the customer a printed spec — volumes, MSV, advance curve. That's what engineer-level work looks like on paper. We're a shop too; that's why it exists.
One license. Every head you'll ever cut.
Less than one scrapped billet head. Less than one detonated piston and a bore job. Yours forever.
- Full chamber designer — every bowl type, every input
- MSV solver with strain correction and clash warnings
- Squish band optimizer
- Ignition module — Wiebe burn, MBT, printable advance curve
- Machining coordinate output for the mill
- 3D chamber view, live volumes and compression ratios
- Runs on laptop, tablet, and phone — all updates included
Instant license by email. Questions first? Call the shop — (616) 755-3101.
Straight answers
What does the simulation actually model?
The chamber geometry is integrated numerically for true volumes and compression ratios. Squish velocity is solved from the real piston motion and chamber shape every quarter degree of crank, including dynamic gap loss from mechanical stretch at RPM. Combustion uses a Wiebe burn model with fuel-specific properties to solve MBT timing and watch the endgas for detonation. It's the engineering treatment — presented in shop language.
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 a machined or machinable head, yes — kart, motocross, snowmobile, drag, vintage, watercraft. Enter your bore, stroke, rod, gasket, piston crown, and exhaust timing; the physics does the rest.
I measure with a depth gauge, not CAD. Can I use this?
That's exactly who it was built for. Bowls are defined by depth, flat width, and wall radius — the numbers you already take off the head with a depth gauge and radius gauges. No spline handles, no CAD experience required.
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 head work. The app exists because we wanted it on our own bench first.