mk1-forum.net

using my tiny pea brain ,iv been conteplating a theory ,and thought i'd stick it on here ..

theres been a lot written about charge robbing and the imbalance between inner and outer cylinder mixture ,and the problems that creates .

general thinking appears to be ,that the inner cylinder pulls in a charge of air fuel mix ,and then just before in closes ,the other cylinder in the pair opens up and asks for its share .the fuel ,being heavy ,wont change direction so easily ,and so the outer cyl gets a bit more air than fuel ,and so runs lean .

my thought was ,if you run a tube full of gas (eg , inlet tract) at a certain speed ,and close it ,theres a continuing ram of gas compacting on the closure point,for a moment .

now , imagine if almost concurrently another opening occurs , in this case the outer cylinder inlet valve ., its now opening on a higher pressure gas column ,carrying with it the inertia it built up feeding no3 . so its volumetric efficiency is raised artificially compared to no 3 .its fuel delivery may be similar to no3 , but its air delivery is way higher ...in effect , its been supercharged by no 3 initiating the flow speed ,and resulting inertia.

this would tend to explain the 100 bhp/litre + outputs of some 5 ports ,where on the face of it theoretical modelling such engines with a ve of 85 % simply doesnt replicate reality .

if this theory holds water ,then its a feature non siamese port engines dont share .and maybe the only type of engine with a built in supercharger ,if only on 2 of the 4 cylinders .

ps, im sure this must have been written about ages ago .or its total nonsense lol.

regards
robert .

Don't know. But the effect would only be short lived as the valve opens. So an supercharging would only take affect at small valve openings and for a short period.

It may be matematically calculatable, but the numbers would be so small to have zero affect in the real world, IMO.

i think it could be making the difference between a 85% ve inner cylinders ,and 105 % ve outers ,so making an average of 95%ve...a big effect ..the way i imagine it is like this ,,

the inner ports open first ,so get a clean shot .the outer ports get the inertia of the inner ports column of air as they open ,so get a substantial increase in flow , over what a single port would .

imagine a single port opening , it has to accelerate a stalled mass of air in a tube ,up to speed ,then maintian that speed then close .

now imagine that same valve opening ,but the air allready doing umpteen fps in its direction ,so it flow faster much sooner ,so the average port speed is way higher in a port when the piston speed is quite low ,this would give a very high percentage increase in flow on that first 50 odd degrees of lift ,and mean that port speed maximum is reached far sooner ..

its a bit like drag racing from a 30 mph speed ,rather than a standing start ,,, it would affect the whole run in a cumulative way ,,not just the launch .