how to measure your port timings

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rosscla
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Sun Dec 01, 2013 11:19 pm

Cheers, Darrell. I ran my figures back into the calc to check I had that right. eden's one does take a negative figure for piston out the top.
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Darrell Taylor
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Sun Dec 01, 2013 11:26 pm

ok ross,
i never checked your info, is yours correct?
was a general reply to tavs question
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rosscla
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Mon Dec 02, 2013 12:06 am

I think those were the figures from the final build, certainly the transfers match the original port map I took.

If I recall you took a little of the bottom face to drop the barrel and raised the exhaust by 2.4mm and lowered the inlet by 1.3mm.

:oops: still not run it yet tho' :oops:

Will let you know when I get it going...
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tavspeed
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Mon Dec 02, 2013 8:17 pm

Evening chaps,taken some measurements of the ports with digital verniers and have the following measurements.

no packer plate piston protrudes 0.9mm

ex =180.73
in=128.51 blowdown =26.11

0.5mm packer plate piston protrudes 0.4mm


ex=182.63
in=130.91 blowdown =25.86

1.0mm packer plate piston 0.1mm below barrell top.

ex =184.53
in =133.28 blowdown =25.625

going to use pm25 exhaust and sx200 gearbox 4.9 final drive ratio,
any advice on which way to go,dont want a too peaky engine with narrow power band.
strange the blowdown alters,although the port heights are the same ,anyone know why ?cheers all.

Darrell Taylor
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Mon Dec 02, 2013 8:40 pm

run it as low as possible(no base) for best results that your looking for
blowdown changes as a result of the stroke increasing/decreasing transfer duration at a greater rate than it does ex duration
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tavspeed
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Mon Dec 02, 2013 8:55 pm

thanks darrell,will go with your recommendation.

Darrell Taylor
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Mon Dec 02, 2013 9:19 pm

do check the piston skirt clears and the cylinder spigot as mentioned before ,a 2mm head gasket will give u approx 1.1sq making it more torquey on the comp ratio ,u might want to burette the head though to check its safe enough
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tavspeed
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Mon Dec 02, 2013 9:31 pm

hi,darrell,i did take 1mm off the piston skirt,but must admit havent checked the spigot bottoming out in the crankcase yet,
a 2mm head gasket will take the squish out to 1.9mm,will this be ok,
i will check the head volume and work some figures out,cheers.

tavspeed
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Mon Dec 02, 2013 10:24 pm

right have measured the head volume with my daughters calpol syringe,and near as dammit, it measures 40cm3
piston protrudes .9mm
head gasket 1.5mm
add .6mm height in volume,so head volume =42.3 cm3

height from ex port =33.2 +.9mm piston protrusion =40.1mm
vol= pi x rad 2 x h = 154.3cm2, shared by 42.3 =3.64 : 1 corrected

i also get 5.54 : 1 uncorrected
piston dome has'nt been allowed for which will raise them,but they seem a bit low,my heads hurting now :D cheers all.

Darrell Taylor
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Mon Dec 02, 2013 11:24 pm

didnt know head had a rebate thought piston was +.9 out top on a std head

best to either grease top ring and tdc it, fill to top of plug thread then deduct thread volume 2.3cc
or grease piston to squish band fill to top of plug deduct 2.3cc and add the squish volume eg 1mm vol
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