Thanks Adam, I got a 4 mm base spacer and had the cylinder top skimmed 1 mm and transfer ports lowered 1 mm.Adam_Winstone wrote:Unless you dowel the head so that it aligns correctly every time, the squish will vary as the head is free to float a little, only being aligned by the cylinder studs. As such the difference of 1.5 to 1.3mm is perfectly in the typical 1.0 to 1.5mm range (I tend to aim for 1.5mm) and that's fine.
Whilst we're talking about the head, don't assume that the volume is correct for the compression ratio to suit your motor and/or run reliably on today's poor quality fuel. Many of the smallblock kits come with a head that started as a 150 head and have simply been opened up to suit the larger piston, whilst the combustion chamber is still the 150cc size (!). You should never assume that the head that comes with a kit is actually suitable, which is a shame, and you should measure the volume of the combustion chamber PLUS the volume of your 1.4mm (average) squish band, which combined will allow you to calculate the geometric compression ratio. You should be looking for a figure of about 8:1 geometric, which would then give you a reasonable correct compression ratio with your intended port timings.
Have a look on Lambretta Images website and you will see that Eden has kindly designed and shared a Lambretta Port Timing Calculator, which will allow you to calculate compression ratios (geometric and corrected) as well as check port timings.
Good luck,
Adam
At bdc piston sits level with bittom of transfers and top ring is beliw the bottom of exhaust.
This gives me port timing of
exhaust 171
transfer 135
blowdown 18.24
inlet 140
With no head gasket i get
squish .75 one side and 1.33 the other
compression ratio 8.75 uncorrected 5.74 corrected
With head gasket
squish 1.45 one side 1.95 the other
Compression ratio 8.05 uncorrected 5.32 corrected
Am thinking of going with the head gasket as best setup ir woukd it be ok and more powerfull without?
Cheers
Tippi
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