500 valves on 350 heads?

[Tom]

Morinisti,

I am rebuilding a 1974 Strada at the moment, i will have to replace the heads anyway, and now thinking of using a set of 350 heads adjusted with bigger valves from a 500. Will this make a point performance wise?
And even more important, will this work on standard 350 cilinders? Maybe the bigger valves will hit the side of the cilinder or the surroundings of the piston, or maybe other problems will occur?

Has somebody done this before, or is it just plain stupid...

Thx!

[EVguru]

This used to be done for racing and you do indeed need to relieve the top of the cylinder liner to clear the valve. Without flow testing it's questionable as to how much advantage there is given the shrouding of the valve by the cylinder wall.

Go up to a 400cc bore and the 500 heads will fit and I think even the 501 heads which have the valve guides further apart for even bigger valves.

Lambertini really knew his gas flow and unless you're upping the capacity and/or fitting a camshaft with much longer duration then you may just give up low and mid range torque without gaining much top end power.

[Tom]

Thank you Paul, this is of much help. First I will get rid of the plan doing this.. and second use these heads on an other bike where i will try to shorten an old 500 piston to get the bore of a 500 and stroke of a 350 = 390cc

Tom

[EVguru]

Your maths is way off. With the 69mm bore of the 500 combined with the 57mm stroke of the 350, you get 426cc.

The 500 uses a 20mm gudgeon pin, whilst the 350 is 17mm. You used to be able to buy 69mm pistons with the 17mm pin bore especially for this conversion.

[boris tarpit]

I have a bike with a 426 motor (501 top end on a 350 bottom end) and it goes very well indeed, great fun to ride, gutsy and direct tho a bit highly strung. It revs like a two stroke and feels faster than the 501 Excalibur I have although that is still in restricted form. I have a 375 with old style 478 heads but haven't had that one running yet.
The 426 is the engine that Morini should have made - a worthy up grade while keeping the spirit of the original 350 sport.

[Tom]

Hmmm jummy, sounds great!

[solviken]

PM sent

[huub]

I have a bike with a 426 motor (501 top end on a 350 bottom end) and it goes very well indeed, great fun to ride, gutsy and direct tho a bit highly strung. It revs like a two stroke and feels faster than the 501 Excalibur I have although that is still in restricted form. I have a 375 with old style 478 heads but haven't had that one running yet.
The 426 is the engine that Morini should have made - a worthy up grade while keeping the spirit of the original 350 sport.

how does that work? shortened 501 cylinders?
or longer conrods?
i cant get my head around how you compensate for the difference in stroke ..