Long stroke cranks

[jon]

Hi all,

I’ve a question on long stoke cranks. Specifically the +4mm.

If these are used with YPVS barrels or say an Athena 392cc do the ports need lowering to the floor of the new BDC?

Is it essential or recommended. If it’s done is it too much port timing?

Jon

[midlifecrisisrd]

I'd say it is highly preferred

If you look at how narrow the transfer ports are dropping them 2mm makes quite a difference to the port area

My next bit of info may of got confused a bit but I'm sure slinger said the 1ua barrels have slightly too much port duration and the +4 crank corrects this

Steve

[muttsnuts]

you need different pistons for a start, once you have those then you can measure your port timing and adjust to suit your requirements, flooring of the ports is generally required, you also need to factor in your base gasket thickness, ideally do a dry build with the gaskets you are going to use so that your measurements are correct