malossi 210 HSTR 12·1:1 head

[ssteam177]

I have just installed the malossi 210 kit with their hstr head to my 200 engine. The uncorrected ratio of the head is 12·5: 1.
Malossi's installation instructions say to use a head with 10·5: 1 compresssion what i would like to know is if the head as a 18cc combustion chamber for 12·5: 1 how many cc's does it need to be opened up to to achieve the 10·5: 1 so i stop the pinging @ W O T?
Thankyou in advance for any replies!!

[ricalnic]

if 210 (swept volume)+18cc head = 228
228/18 = 12.5 - what you've got
if 210 (swept volume)+20cc head = 230
230/20 = 11.5
if 210 (swept volume)+22cc head = 232
232/22 = 10.5

so by my reckoning I would estimate 22cc head ?

I'm no expert by any means but just my thoughts and maths

[ricalnic]

for what its worth, I've just ordered the SIP 11.5/1 head as I too experienced slight and occasional detonation no matter what jetting or timing on mine.
once its warmer in the garage I'll have it fitted for the better weather, but just got another 4 inch of snow last night !

[ssteam177]

Cheers for the that info . I dont understand why Malossi's would even do a 12·5 :1 head when the instructions say to use 10·5 :1. Changes to my timing and jetting didnt stop the pinging on mine either i also tried octane booster of 7 points to no avail. As for the weather here atm every day is 30° to 35° c which is not good for an aircooled 2T that ha denotation issues

[ricalnic]

ok, so have been using my p210 last few weeks basically the same spec as end last year. I had had to slot the stator last year and retard ignition to stop the detonation. So last week I whipped of the Malossi HSTR cylinder head and fitted the SIP head I obtained during the winter. I also returned the ignition to 18deg, from what was nearer 14-15 deg.
Thottle response is bettered and performance retained (indicated 75mph), running prolonged WOT shows no sign of detonation - so am well chuffed.

whilst I had both heads off to compare, I must admit if I was asked to select one to fit it would be the SIP head, The Malossi HSTR head seemed to mask the end of the plug slightly, IMO the plug fitted the SIP head far better and more as you would expect to see or be familiar with.