Motorcycle News (UK) - - Garage -

Smart fu­elling

At par­tial throt­tle set­tings, which is where a lot of trail rid­ing is done, carbs run rel­a­tively rich, but our TPI bikes are 30-40% more ef­fi­cient. On a wide-open throt­tle, it’s 3-5% bet­ter than a carb’d ma­chine.

Less oil

Oil con­sump­tion is way down too, re­duced by 50% to ra­tios of 70:1 to 100:1, and with a 700cc oil tank that means eight tanks of fuel are cov­ered, use­ful in com­pe­ti­tion events in re­mote ar­eas.

Trans­fer ports

Al­though you’d strug­gle to see the changes to the con­fig­u­ra­tion of the trans­fer ports and ther­mo­dy­namic ar­range­ments from the 2007-spec en­gines, we had to work hard at get­ting the stream and di­rec­tion of the in­com­ing charge right with the in­jec­tor po­si­tion­ing.


Like a four-stroke engine there are five sen­sors de­tect­ing engine speed, throt­tle po­si­tion, crank­case pres­sure, coolant tem­per­a­ture and in­take air tem­per­a­ture sen­sor. We had to po­si­tion those sen­sors smartly and work in col­lab­o­ra­tion with Syn­er­ject, a French Engine Man­age­ment com­pany. It took al­most ten years to painstak­ingly learn what each com­bi­na­tion of data meant in the combustion cham­ber so that we could de­velop the per­fect con­trol strategy.

Ex­pan­sion pipe

Al­though we call them two-stroke en­gines, there are some so­phis­ti­cated ther­mo­dy­nam­ics hap­pen­ing through each cy­cle of the pis­ton with vary­ing ex­haust pipe pres­sure waves mean­ing you need com­pletely dif­fer­ent charge com­po­si­tions. If that’s not de­tected you can have a 6-8 stroke engine as some charge goes into the ex­haust un­burnt or it ig­nites be­fore the op­ti­mum point and the engine needs 50 cy­cles to come back from flame-out to a steady flame cy­cle.

No fuel flows through this 39mm Dell’orto – just air You only have to fill up the oil once ev­ery eight tanks of fuel

Ex­pan­sion pipe re­turns un­burned fuel to the cylin­der

In­jec­tors spray pre­mixed fuel di­rectly into the trans­fer ports

Slight tweaks to the cylin­der trans­fer ports were needed

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