New Malossi MHR 77cc an 86cc kits
- Thread starter roost
- Start date
The highest score with 2fast over here is 27,4 BHP @ tovami.
The new malossi kits are verry interesting
Ok, but you guys use it only for drag racing. We do not dragrace, but use the scooter on the circuit, the usability is more important than a good ET!
We also need reliability!
http://www.bestpic.nl/output/1194638428.jpg
timing is 192/132
?????
I don't know if the figure is bad or the values!
If the cylinder deck = TDC than it has got very low port timing!
Correct me if I am wrong but if the stroke=44 mm the conrod=85 mm than 24 mm from the TDC is equivalent 88 degrees from TDC -> (180-88)*2=184 degree also if we see the exhaust port height = 44-24=20 mm= ~ 184 degrees.
Maybe the cylinder head penetrates into the cylinder so the TDC unknown. ???
I didn`t calculate it. I have the timings from the malossi site
Look at the 2fast portmap, it's more radical, and I know it's combustion chamber penetrates into the cylinder so the distances from the TDC is less than the Malossi:
http://www.scootertuning.net/showarticle.php?ID=47
Maybe!
Now I see you wrote the squish is 0,8 mm, if I substract the squish clearance it's 189 degrees so we are closer to the 193!
With some tricks maybe it's +-190 Another ~0,8-0,9 mm is necessary (the cylinder head penetration?)
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tiba_karotsu
OVERREV TUNING
most likely the combustion chamber's going to be recessed into the cilinder, to get to a 192 degree exhaust port the port height must be 22,6mm from roof of the exhaust to TDC, then we subtract 22,6 from 24 & we get a difference of 1,4mm then again we subtract the squish clearance of 0,80mm & we arrive at 0,60mm head intrusion.
if that is also the case then the ports would be fully open before the piston reaches BDC by the same amount (1,4mm), to me that's wasted area, we could grind down the floor to level with the piston at BDC.
if that is also the case then the ports would be fully open before the piston reaches BDC by the same amount (1,4mm), to me that's wasted area, we could grind down the floor to level with the piston at BDC.
Wieger
JS-TUNING
On the sign it says "vsht 28" Probably the carb lays behind the crankshaft-sign
50cczip racer
Well-Known Member
its probably been recast with the extra outer section on the base for the stroker kit but without extra added to the inner bore so it looks strange
glad to see the port timings are getting down to where the powers really at
tiba_karotsu
OVERREV TUNING
i see what you are pointing at, looks to me they still used the original mold for the 70cc 7T only they machined it with a different parameters for a 44mm stroke, they made the deck height taller for the longer stroke & conrod.
i see no problems with the skirt running short, it might even be beneficial for gas flow to the tunnels.
It's started me wondering if you could do away with the inner
wall of the boost port altogether... On a regular cylider (apologies
for straying from the subject), with the 2 windows on the piston,
replace the piston with one that has no holes, remove the
inner wall completely (making the boost port go all the way down
to the cylinder base), and the piston side would be the inner wall
of the boost port. The inner wall of a port duct should be curved,
but on a lot of cylinders the boost port is pointing up anyway,
so maybe the curved inner wall is not so important.
Areomyst
Scootin' America!
There are actually many pocketbikes that are done this way. Many lawncare 2 strokes don't even have a "wall" or "floor", but those are very very different from the engines we have.
I have seen a few scooter cylinders that have been modified the way you describe though, I just can't remember where. A. Graham Bell's book suggests that this style of boost port aides piston cooling. As long as the roof angle is where you want it, the floor angle (or it's existence period) is probably not going to be as important as the rest of it.Just my two off-topic cents.
~Josh
There are actually many pocketbikes that are done this way. Many lawncare 2 strokes don't even have a "wall" or "floor", but those are very very different from the engines we have.
Just my two off-topic cents.
~Josh
You are right chainsaws and other small engines use this method. Even the transfer ports haven't got cylinder wall.
