pm tuning pro street

minor holding the two top racing cranks or is it pm cranks lol

map by minor :thumbsup:
the head has been used and cleaned up and the barrel has had something written on it then sanded out and 55 mm written over the top (not been used though)was the barrel intended for something else ,then had to be changed ?
i am sure they will come on and tell us lol

 

like to see rumplestiltskin wheelie a 70 up my 45 deg drive in the pissing rain :this:

 

Been playing with the software while i`ve got a minute to myself (dos`nt happen very often) and came up with some figures (OK boring to the un-initiated but very important as to how an engine will perform (theoretically :grin: ).

Going by the figures provided (the port map) the specs for the PM barrel are (and useing two different length rods as this spec wasnt given)

55 stroke 105mm rod ex. duration 189.6 trans duration 117.2 blowdown 72.4
"" 110mm rod " "" 188.8 "" "" 116.4

Both these durations are on the low side, the exhaust is`nt too bad and without further specs can only guess at the max power is aimed at the 8500rpm range approx however the transfer duration is extremely low and this engine will not breathe at all well in the upper rev range and is aimed at producing torque at the expense of max power.The blowdown is huge and aimed at a high revving engine, not a good combination?

A std malossi 172 with a std 52mm crank works out to:

52mm stroke 105 rod ex. duration 172.2 trans duration 115.8. blowdown 56.4

Exhaust duration is lower meaning a less revvy engine but notice how the transfer duration is within a degree of the PM barrel!Depending on the pipe and set-up most of these engines seem to produce max power at about 8000-8200rpm which bears out the figures, a good allround configeration.

Now it starts getting intresting :grin: (unless you`ve already fallen asleep).

For the sake of arguement lets asume that all the 55mm stroker cranks have a 105mm rod (if it is a 110mm rod just subtract a degree from these timings and your in the ballpark).

Slap a std Malossi (non-ported) on a 55mm stroke (1.5mm base spacer and 0.5mm gasket to correct stroke) and you get:

55mm 105 rod ex.duration 180.6 trans duration 129.8 blowdown 50.8.

The exhaust duration is better for revs but the transfer duration has gone too far the other way possibly compromising power at the lower end and there is not enough blowdown, not enough time for the ex gases to escape before compression starts.
It`ll run but it`ll get hot and be down on power as the fresh charge will mix with the burnt charge trying to escape as the door closes :eh:

So.... we raise the exhaust port to 28mm giving a duration of 193 degrees and lower the transfers (by any means you see fit or by useing Devcon/jb) by 0.5mm and the specs then read:

55mm 105 rod ex. duration 193.0 trans duration 128.0 blowdown 65.0

This is more like it, for a bit more finess you can lower the primary transfers by 0.5mm and the secondarys by 1.0mm (125 degree) this will give a slightly wider spread of power.
Raising the exhaust port a further 0.5 mm (27.5mm) will give you 195 degree and increase the blowdown to 67.0.
This configeration will be a rev hungry set-up (9200-9500rpm? possibly higher) and need the pipe etc to match but the figures look a lot more healthy :mrgreen:

To compare:

PM barrel ex.duration 189.6 trans. duration 117.2 blowdown 72.4.

Computer generated ex.duration 193/195 trans. duration 128/126.5 blowdown 65/67.


This is all of course going purely on durations! There is the not inconsiderable matter of Time and Angle/areas, direction of flow, roof angles,ex port area to stub exit area (1.05-1.5:1)stub matching and blending, widening and matching the transfer entrys and blending to the case, transfer entry area (base of cylinder)to actual transfer area (inside cylinder) ratio and a few other considerations


These are just my thoughts and I had an hour to kill anyway :grin:

 

This is more like it, for a bit more finess you can lower the primary transfers by 0.5mm and the secondarys by 1.0mm (125 degree) this will give a slightly wider spread of power.
Raising the exhaust port a further 0.5 mm (27.5mm) will give you 195 degree and increase the blowdown to 67.0.
This configeration will be a rev hungry set-up (9200-9500rpm? possibly higher) and need the pipe etc to match but the figures look a lot more healthy



would it be rude to though ?and then compare the two barrels on the same case :whistle:

 

hock:
My learning curve hit the roof

 

Not really Shiny, these are just the numbers I crunched and dont take into account the variations I listed (roof angles/angle area etc) and the million and one other subtle details that make a good spec, go for it and see what it does :mrgreen:

Oh opening the exhaust to 27.5mm from the top and blending the radii would mean an exhaust exit at the stub of about 36mm dia and a corresponding pipe with a stub/header of that diameter (std malossi exit is 29mm!).
Also the porting and high rpm would determine a pipe with a belly diameter of at least 114mm and a tuned length @ 9500 of 960mm measured from the piston face to the end of the reflection cone (various ways of measuring tuned length including the "correct" way of piston face to 2/3 of the way down the end cone) where the stinger joins.

Again just number crunching on a day off and these figures are basic and obviously not a design for a complete exhaust :grin:

 

love this thread,

makes my head hurt !

 

^^ indeed.
any one else here feel like their back in school in a science class.

scooter stuides with mr minor and mr blue dwarf,
and shiney the supply teacher.

sir can o go toilet? :lol: :mrgreen:

 

erm... :whistle: yeah thats what.. it... is ick:. you will have to explain all this shit in simple mans english when you next down

 

i can understand moast of that i think but got confused by blowdown can you explain for me as im a noob haha god i need to read up more

 

Same here on the blow down hock:

 

sounds like time between the exhaust closing and inlet opening !

EDIT: too slow but wasnt a million miles out lol

 

its shiny now lol