RB250 SCOOTER SHOOTOUT MOTOR

Post your Lambretta dyno graphs here! But graphs & spec info only, keep the chat in the 'dyno chat' section ;o)
martints1
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Darrell Taylor wrote:Heres an update on the shootout motor,Eric who owns the bike has continued running around on it doing his wed night ride outs as well as a run up to cadwell park but has been a little lost as to why its so tractable and felt more could be had as he reckons a std ts1 is more peaky
so he stripped the motor out and sent me the top end over for a rework whilst he gave it a once over following its torture at elvington doing over 55 runs up the strip
he found the chain stretched and in need of adjustment and thought he would try it with a close ratio box,he found the clutch had started to slip so fitted new plates and heavier springs along with some new gearbox bearings that showed some wear
i set about the barrell based on the high bmep figures ive seen on the 225ts1 at 39bhp it led me to believe that although this 250 was powerful it still wasnt as efficient so had more power potential left in it,making some changes to port durations to help improve blow down and trimmed the piston cut outs to match the cylinder better
the straight line ignition has been swapped for a varitronic and just thrown on to be fine tuned on the dyno to find best results
collected it today and eric took it for a quick spin and reports no loss in tractability :? but feels a lot quicker so see what the dyno says

i dynoed it on same jetting as a previous dyno run on a middle of the road jet and have yet to fine tune the varitronic timing to find best results which i hope to do tomorrow

so heres the graph before and after ,didnt think id find this much more especially with no major low down losses so still leaves more to try
i need to dial the ignition in then revert back to old ignition to see if this is where part of the improvement has come from

b4 40.64 bhp
after 45.52 bhp
Image
great result...please could you post some engine specs (carb, exhaust, port-timings,...) ? Thanks
Darrell Taylor
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std case with no welding to crankcases was matched to cylinder
machined for stroke/rod clearance
rb225 kit bored to 72mm (not advised skirt is too thin)
long rod 116mm
38mm keihin carb
lth or std inlet
franspeed race
varitronic or electrex ignition
std rb reed block
std rb piston with skirt/cutout mods
ron moss blank head and cowling i cut to my own spec cr/squish design

cylinder porting started with welding up the triple ex port back to a single port and welding up the 2 boost transfer ports to a single small boost port leaving it a very simple 1 exhaust port 5 transfer port design
i did resist welding the boyessen feeds up as development is approaching bmep figures that will start to need them soon and prefer to do it as a seperate test with a couple of balls of filler stuffed in either side ,i think people thought it was a wind up when i said weld up all the ports on the rb in a previous post,seen as a backward development step but u can see now i was serious.

the durations/widths/angles are to my own tuning specs and as the motor is also used in sprint events and the results are from months of hard development work and testing and weeks of lost wages and my personal time and money spent on testing various parts as well as eric the scooters owner time/money and effort spent
so im sure youll understand these elements of my trade will remain private
Last edited by Darrell Taylor on Wed Nov 14, 2012 2:22 pm, edited 1 time in total.
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martints1
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Darrell Taylor wrote:std no welding crankcases matched to cylinder
rb225 kit bored to 72mm (not advised skirt is too thin)
long rod 116mm
38mm keihin carb
lth or std inlet
franspeed race
varitronic or electrex ignition
std rb reed block
std rb piston with skirt/cutout mods
ron moss blank head and cowling i cut to my own spec cr/squish design

cylinder porting started with welding up the triple ex port back to a single port and welding up the 2 boost transfer ports to a single small boost port leaving it a very simple 1 exhaust port 5 transfer port design
i did resist welding the boyessen feeds up as development is approaching bmep figures that will start to need them soon and prefer to do it as a seperate test with a couple of balls of filler stuffed in either side ,i think people thought it was a wind up when i said weld up all the ports on the rb in a previous post,seen as a backward development step but u can see now i was serious.

....thanks for all the information - for the R&D-work I really understand you well - no problem ! what crank do you use ? Which stroke ? Thanks Martin
the durations/widths/angles are to my own tuning specs and as the motor is also used in sprint events and the results are from months of hard development work and testing and weeks of lost wages and my personal time and money spent on testing various parts as well as eric the scooters owner time/money and effort spent
so im sure youll understand these elements of my trade will remain private
Thanks for all the information ! Which stroke do you use ? Thanks Martin
WINTERMODEL150
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Great results again Darrell !!!
tonydevon
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holy crap!!!

thats the sort of motor I would like, even "just" 35ish bhp would do me, lob it in a ratty as hell old S2 and have some fun

that must be a beast to ride

they are very impressive figures

now then, just have to pick 6 magic numbers on Saturday :)

nice to see an engine tuner thats happy to explain and put the time into helping others, obviously not the "trade secrets" but thats to be expected, they are your earners

too many forums and various other "hobbies" etc, the specialists are just silent and act as if they are some sort of gods
heavy is good, heavy is reliable, and if it does fail, hit them with it!!!
Darrell Taylor
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thanks wintermodel
martin its 62

thanks tony,im not gonna suggest its a motor for daily use ,at these levels service intervals are very low to keep on top of component wear ,its a race motor that is being used on the road and is displaying good manners in terms of rideability ,eric uses this scoot regularly its a toy for him and he loves it but doesnt intend to use it for rallys,its not what this motor is about he pops into town/blasts round the villages and does local wed night ride outs a bit like a kit car compared to a daily driver
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martints1
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...thanks for the information, Darrell ! do you have a "ft-lbs-dynorun" also ?
Darrell Taylor
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i hope to do one later when i retest the electrex ignition
the varitronic picks up wrong on the rpm so cannot do an rpm /torque run from it
it did 25 ft/lb tq before so i guess 26/26.5 now
feel free to use this link to contact me on facebook and like it(if u like it)
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warts
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Lovely.
martints1
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...perfect....thanks....
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