have just got around to trying my mugello after fettling it with my dremmel following advice from here previous problem that it was flat as hell above 6000 rpm
have increased inlet & exhaust timing and reprofiled head which wasnt the same profile as piston.
new timings are exh 179 widened to 44.3mm inlet 153 tran 124 ign varitronic set to 17 deg at 7000
the combustion chamber is 20cc squish 1.2 to 1.3 mm
jetting av266, mj128 ,slide 40, pilot 50 ,needle x13 2nd clip
it runs fantastic reaches 7000 rpm easy and not flat low down. but now the problem plug colour is a bit light at anything over 1/2 throttle no evidence of pinking, what i am worried about is because the compression ratio has increased will the heat build up over distance and hole the piston I ran for about 1mile at 1/2 & 3/4 throttle before plug chops.
the scooter is used for rallies so needs to be able to cover distance not just a quick blast about so should I increase the combustion camber volume or use .5mm head gasket to reduce comp ratio or just rejet to suit?
what is a safe comp ratio in either geometric or corrected?
when calculating comp ratio do I include squish volume ie.
cylinder + squish + combustion camber /combustion chamber + squish
your help is much appreciated
paul
mugello 225
For road tuned engines I have always kept compression to 9.5 or below, using a 1.2mm squish clearance, on an off set squish head..... This works for me....
If using a center plug, center squish head, 11.5-1 or less compression ratio (geometric)
If using a center plug, center squish head, 11.5-1 or less compression ratio (geometric)
do use the squish volume in your calc's in my case
cylinder 223+ squish 4.6+ head vol 20 divide by squish 4.6 + head 20 247.6/24.6 = 10.06 :1
or would you use
223+20/20 = 12.15:1
cylinder 223+ squish 4.6+ head vol 20 divide by squish 4.6 + head 20 247.6/24.6 = 10.06 :1
or would you use
223+20/20 = 12.15:1
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sean brady scooters
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i would try bigger main jets..........
go up in increments of two.............at a time........
from 128.....to 130......to 132 etc........and keep trying until you know you have reached the point of having a main that is just too big...........then back down to the best previous......
as far as measuring comp ratios.........i still prefer to do it on a built up motor
set piston at TDC ,and fill with oil from a measured syringe etc...............
go up in increments of two.............at a time........
from 128.....to 130......to 132 etc........and keep trying until you know you have reached the point of having a main that is just too big...........then back down to the best previous......
as far as measuring comp ratios.........i still prefer to do it on a built up motor
set piston at TDC ,and fill with oil from a measured syringe etc...............
Sean Brady Scooters - 01765 690 698
Going by your calc's cylinder volume plus head volume plus squish clearance volume. all divded by head plus squish volume...10.06-1
but the way I get to that, is to measure the combustion volume contained in the head and squish clearance as one ( Head Volume = HV) measurement using a Burette or syringe with the piston at TDC. then use this figure HV in the formula (HV+SV) divided by SV..... where SV = swept volume of the cylinder...I never calculate the head volume without the engine built as this eliminates errors in calculations which become more of a guestamate...and small differances in head volumes can make a big differance to actual compression ratios...
but the way I get to that, is to measure the combustion volume contained in the head and squish clearance as one ( Head Volume = HV) measurement using a Burette or syringe with the piston at TDC. then use this figure HV in the formula (HV+SV) divided by SV..... where SV = swept volume of the cylinder...I never calculate the head volume without the engine built as this eliminates errors in calculations which become more of a guestamate...and small differances in head volumes can make a big differance to actual compression ratios...
If the comp ratio is there abouts wont I have to alter needle and or atomiser to richen it at 1/2 throttle or will just the main do it ,oh by the way its a phbh 30mm with ram air, and is it better to get the main right before needle /atomiser ?