Fair enough (so you agree)drunkmunkey6969 wrote: Yes, we did it on an RB20 motor that a customer is running round on, and it worked for that application, as you know....having your own dyno gives you the luxury of testing whatever you want and PROVING what works and what doesn't.
so you have a dyno graph you can show us that would be great to see
On this motor, larger transfers were beneficial, we gained a small amount of power right across the rev range.
Darrell Taylor wrote: have you read my comment about transfer window size constantly changing
in my example a 20mm wide transfer at 1mm open is 20 sq mm the std duct entry is 600sqmm so the ducts entry is 30 times bigger !!
many modern race engines have larger transfer duct entrys but have you seen the ultimate 125 gp motors transfer ducts? approx 1 to 1 ratio
, but a Lambretta is not an ultimate gp motor is it, you have to compare like for like
(so why are you comparing lambretta engines to big motorcross motors and modern 125 engines).
And presumably the cylinder transfers on the ultimate gp are larger than a Lambretta cylinder, so at 1:1 the ultimate gp will make sense.....
(i cant see how that makes sense if the windows are bigger than a lambretta cylinder then your now saying the entry should be smaller????)
and if we are enlarging transfer ports on the lambretta cylinder wall, then we will want a large entry to match.(see what i mean not making sense??)
But i see what you mean, (are you sure ????)
although surely the crankcase window size/area should at least match the cylinder transfer area when they are fully cracked open and not just when they are 1mm open??
as per my post? i said at 1mm open the entry is 30 times bigger
and when they are fully cracked open the entrys are still bigger than the windows and the majority of the transfers work is done
Or can you offer further info on why this is not the case? Please explain why if so, i'm interested to learn.
upon first opening of the transfer,there is only a little transfer but a continuation of blow down spent charge is entering the transfer port contaminating the charge luckily the short circuiting of this first batch of contaminated charge is lost out of the ex port to be never seen again ,the remaining charge will exit via a small opening say 2mm at a greater velocity than when the port is fully open and if the transfer system is designed well will be put to good use
When the ex port is fully open and the transfers are fully open they are exposed to the adjacent exhaust port increasing the likelihood of lost charge this charge is the good stuff fresh/cool and has no contamination ,Now we dont want to lose that and fortunately at this point we have a lower velocity stream emerging that wont fire it straight out the exhaust
And lastly.......do you not find that when the piston is nearly at BDC that the transfer window in the crankcase is almost blocked/closed.....another reason why we modify pistons and transfers, let me know your experience in this case.
ive never bothered except for matching cutouts to the liner,i genarally do a simulation to find crank angle related flow data and match up at the angle thats most beneficial
