just going back to 60mm stroke cranks ,and if they fit or not and hence require the casings machining/channel out to accomodate ..
I by far prefer to grind/machine off the con rod rather than alter the casings which are very thin in that area to start with ...but if you really want to go down that way its best to weld the casings up all around that area ...more important and needed if going for even longer strokes tho
Right, I've had a rummage in the garage and found an old SIL GP crank. I know these are meant to be good for a rod conversion, what rod is a good rod? who is good to build one/how much should i expect to pay (how much would you charge shaun?)?
As mentioned, the reduced variation in piston/rod angle over the dead centres with a longer rod will reduce side thrust, which is good, the reduced piston rock should also help reduce vibration. The ring pack gets an easier time too.
Another benefit is that the piston "dwells" longer about TDC, giving the burn more time to take place, so you can possibly reduce ignition advance. Of course the time to complete each revolution is the same so get from TDC to BDC the piston has to accelerate faster and peak piston speed is greater. This may be advantageous in a two stroke as a stronger pulse will appear because ports are opening more rapidly.
GM did a lot of research on rod length/rod ratios for their "non works supported" racing (both NASCAR and drag racing) in the 50's and early 60's.
Afs will soon (I hope!) have a 62 mm crank that fits in the casing with no machining required and less than £200, made for them suitable for big rbs. should be available in next few weeks. But dont quote me on that
After a bit of lookign around, is the RD400 rod the one to go for. I have found this rod, and is meant to be very high quality and used in many race engines from two stroke forums i have read.
