Scooterotica

hi chaps,on with a engine,its a suzuki ts250 piston ,monza barrel,with inlet modified for a atomic reed valve,60mm crank with a110mm rod,the ex port is 32mm from top of barrell,and transfers are 42.6mm,piston is as near as dam it flush,putting these figures in the lambretta port timing calculator ,i am getting ex 189 deg and transfers 147 deg,blowdown 21 deg,these seem very high,but does the deck height of the suzuki piston need to be accounted for ?,cheers all

tavspeed wrote:piston is as near as dam it flush

Flush?
With top of barrel?
Or.
Bottom of transfers/exhaust?
Or.
Both?


If all of the above I can't see that the compresssion height comes into it.
But what do I know!

SF

hi,yes piston is nicely flush with bottom of exhaust and transfer ports,and top of barrel ,it has a reed valve so inlet timing is 360 deg,the port timings are coming out very wild,i think the suzuki piston deck height is 36mm and a lambretta piston is 39mm,so not sure if this affects the readings,anyone know ?,cheers

I assume you are using Eden's calculator so he is best qualified to comment.
However, just thinking it through, if you were to substitute the Suzuki piston for an imaginary lambretta one you would need an imaginary 3mm packer to bring things back into line and end up with exactly the same port timings! I think.

SF

aahh,but i have a 110mm rod,which is 3mm longer than a standard 107mm rod,have been using eden's port timing calculator,the only measurement you can't put in is the deck height of the piston,had a search on the internet for another port timing calculator but couldn't find anything,

Port timings would be different with packer and different crown height but I don't know in which direction.

to get the port timings to something more acceptable for a road engine,i would need to machine 2mm off the base of the cylinder and run with a thick head gasket to get a good squish,the 2mm would be inputted as -2 0n the calculator,was wondering if the 3mm difference in deck height would be inputted as -3 on the calculator,

There's an app from Stage 6 for port timings.

You mention that you cant input compression height into the calculator; Well your deck height accounts for this.

107 plus 39 equals 146 (standard set up)

110 plus 32 equals 142 (your set up)

your rod is too short to get anywhere close without altering the barrel. so rod change, or barrel re-work, or piston change.

Id say the cheapest wins!

best of luck

cheers,that's starting to make sense