piston info required to use in port timing calculator

[tea5ive]

i need to know the crown hight on an asso 70mm piston for a rapido. i also need to know on the inlet duration calculator what the piston hight is on inlet side, our where this measurment is taken from. cheers simon

[byron]

the crown height is standard 39mm
the inlet skirt is nominally 71mm

[Minority]

the inlet skirt is nominally 71mm

unless it's for a Rapido race and has had the skirt trimmed!

[tea5ive]

piston is in standard form as i have checked against byrons figures. i will now feed this info into the calculator with my port measurements. cheers for the info. simon

the crown height is standard 39mm
the inlet skirt is nominally 71mm

[tea5ive]

here are the results,

exhaust duration 184.9

transfers duration 130.91

inlet duration 139.


this was geusing the crown hight at tdc (1mm) as i have not had the top end built up yet. and this cylinder was a 200 clasic that was taken out to 225 due to a sieze. i have done nothing to the cylinder yet and was wanting to have a go at some more home tuning. so what can be done or are these numbers ok ? here are some more numbers if it helps

exhaust width is 42mm

inlet width is 44mm

will be using a masive carb ( why ?, because i have a nice 37mm and a 39mm )and the cylinder came with a masive inlet manifold and use a clubman of some sort rm,mb,rs etc

cheers simon

[Minority]

Sounds to me like you have a Rapido Race not a Classic with those port timings. The only difference is the inlet timing, but that is most likely because of the 71mm full length piston.
You can certainly match your casing to the transfers and match ports to the manifolds. You will most likely want to extend your inlet timing by either cutting the piston skirt or lowering the port.

This may interest you:

http://www.lambrettaspares.com/info/lam ... rs+50.html

Good luck!

[tea5ive]

just done some cyber tuning , if my theory is correct and i had 1mm crown hight at tdc and reduced this to 0 by either removing the base gasket or thiner gaskets or have the cylinder bottom skimmed it would make the port timings more like the clasic cylinder baring the exhaust acording to the info on the mb site . giving these figures

exh 181.11
trans 126. 06
inlet 143.62

this would then make the transfers more usable and still leave scope for triming the skirt to increase inlet duration ?.

Use the calculator to work out how much you need to cut the inlet skirt to get your prefered inlet timing.

sent from my phone via tapatalk

[Muppet]

Wont da rapido have more area for the same port timing makin it a different fish when it's swimmin

muppet,

[tea5ive]

is there any gains to be had by widening the inlet and exhaust ports ?. if so how much wider can i go. also when looking from the base of the cylinder up the bore with the piston in and at tdc the two smaller transfers are obscured by the piston skirt, is it worth trimming back the skirt ?. here is few pics

[Muppet]

:wtf: trim skirt where for what?