Could we go back to 125’s and 250’s?

We could do 200/350 4 strokes

I think the displacements are about perfect and shouldn't be changed.  A common debate is how to keep racing fair.  Today we have 450 4 stroke engines that can basically be competitive in stock form.

MX is a dangerous sport and always will be.  Safer track designs, IMO, would be the best way to mitigate the risks of injury.  It would help, but it can never completely eliminate it.

The reason why riders are getting hurt more today than ever before is because of speed.  The bikes are faster and the riders are pushing the limits.  It's incredible what these guys are doing and they keep getting better and better.  It isn't just MX but all action sports.  Look at what they are doing on skateboards and bicycles.  Did the basic performance of a skateboard change? No, it's just a competitive sport that keeps pushing the limits and raising the bar.  Think about all actions sports.  Every single one has the same problems that MX does.  These athletes are doing shit that 20 years ago would have seemed impossible.   

Honda has a 150cc engine, if they're confident stuff it into a 250f chassis and let it rip. 150cc's and 250cc's. Who cares about stroke. That is the perfect displacement for today chassis/suspension combos.

i sure as hell miss the 125cc pro class more than any other type of racing. cheaper for riders to run the complete circuit. speed limiting, lighter bike that doesn't jackhammer riders into the ground. would love to see mx1 go 2504t and mx2 go 125cc 2t also make an easier transition from amature to pro-am etc..

I didn’t have the money to keep my dam 2 stroke running. Had to sell :/

Just curious what makes smaller displacement 4 strokes more expensive?

RPM's to make horsepower

If they are to make comparable hp to 125 2 strokes they need to be revved a lot higher.

Depending on how well the particular engine makes torque it could be 60 to 80% higher.

This will mean to get your power up around 35 hp required to be on a par with smokers you will be looking at 20000 rpm from very short stroke, big bore engines, that will place high demands on the reciprocating parts, and on the cylinder head development.

At the moment, race engines that run to those rpms are few and far between and those that do, and have, need pneumatic valve springs, special materials for pistons and meticulous care and feeding of short life parts.

You could always throw out the single cylinder rule and spend some real money on engines 

No