Search tools & parts — exact eBay / site search (no Lambretta prefix). Handy for non-Lambretta tuners.
Port timing & Engine calculators
Same piston-crank geometry as the original Lambretta Images Archive calculators, with live results, shared engine specs, inverse height-from-duration, and a few extras tuners actually use on the bench. If you want anything else adding to this page please click the display comments button below and leave a comment.
Exhaust & transfer duration
Height over port = top of barrel down to the top of that port. Measure transfers at the centre of the roof if the port is radiused.
Blowdown
(Exhaust duration − transfer duration) ÷ 2. Touring often sits around the high 20s; big top-end numbers climb through the 30s.
Inlet duration (piston-port)
Skip this on reed engines (TS1, GT reed, etc.) — those are effectively 360° inlet. Piston height inlet side is crown edge to bottom of the inlet-side skirt, including cutouts that uncover the port.
Ignition — degrees ↔ mm BTDC
Dial-gauge method: zero at TDC, rotate the mag anti-clockwise until the gauge reads this drop, then mark the housing.
Compression ratio
Uncorrected uses full stroke. Corrected uses the trapped stroke from TDC down to exhaust opening (deck-aware). Enter the measured head cc, a target CR, or both — required chamber volume is trapped ÷ (CR − 1).
Does not include expansion-chamber stuffing. When the pipe comes on, effective CR rises — size the head with that in mind.
Capacity & bore/stroke
Mean piston speed
A quick sanity check on rev ceiling. Many road two-strokes live happily under ~20 m/s; race lumps push higher at the cost of ring and pin life.
Two-stroke oil mix
BMEP (2-stroke)
Brake mean effective pressure in psi, same convention as the original page. One power stroke per revolution.
Squish band (approx. peak velocity)
Rule-of-thumb only — useful for comparing two heads, not a lab number. Band width is radial width of the squish shelf.
Gearbox & sprocket calculator
Overall ratio = (loose ÷ cluster) × (crown ÷ front). Speeds use the rolling circumference you pick. Factory tooth counts below are the widely published Innocenti sets — swap them for your measured / house figures when you send them.
Carb size starting point
Choke diameter from a common two-stroke rule of thumb. Jetting, filter and manifold still decide whether it actually works.
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