Confessions

[Uniflow]

Last 125 twostroke GP rotary valve 55 HP, not bad! But narrow power. Fit a vairable rotary valve housing and all the mid range you want!

[2T Institute]

IMHO a 125 could not compete with a 250F at the pro level. Ever. The peak power required out of the 125 would mean the spread would be very narrow. DI is not going to help this. DI and other electronic tricks has the possiblity ot taming the powerband of the 250 two stroke by snitching some of the top end HP and piling it lower in the range with shorter port timing and tricks done with timing, and electronic power valve but a 125 has nothing to spare.

Don't believe that. The RSA 125 had over 50 HP for more than 2000 rpm, if you can't keep a 125 in that wide a band . Then you need to improve as a rider. You have to realise no proper engine development has been applied to a 125 mx engine since probably the late 90's. With a variable disc valve and Aprilia GP style cylinder and maybe a variable length pipe/stinger size, a 45HP/20ft/lbs torque 125 would be realised having about 4000 rpm wide band of liquid power, which would be easily enough to blitz 250f's

[Jeram]

all we need to do this is a race prepped 125MX chassis and a 125 disc valve kart motor, then its just about developing the variable valve timing and the sliding header pipe.

Only big issue with a disc valves MX bike is that you'd need to put crash protectors on the bike for the carb side of the motor. This was enough of an issue on the aprilias road racers to redevelop the motor to have a rear disc valve so imagine the need for protecting the carb on an MX bike, but Im not sure us 'amateurs' would have the budget to develop a rear disc valve so stunt bike style protectors will have to suffice!

[Uniflow]

What I have in mind for the 350 disc valve engine will have the engine no wider than my YZ 250 engine. Using EFI ( no carb ) and a extra trick vairable valve housing ( also throttle ). Electric driven. It's only ideas at the moment.

[Jeram]

What I have in mind for the 350 disc valve engine will have the engine no wider than my YZ 250 engine. Using EFI ( no carb ) and a extra trick vairable valve housing ( also throttle ). Electric driven. It's only ideas at the moment.

sounds very interesting, however what happens when you crash on the right hand side?

[citabjockey]

All I can say is, I will believe it when I see it. Dyno charts, podium finishes and all. And if a variable stinger/header pipe and variable intake valve timing and DI are required for this then -- is it any less of a headache than a four stroke?

IMHO a 125 could not compete with a 250F at the pro level. Ever. The peak power required out of the 125 would mean the spread would be very narrow. DI is not going to help this. DI and other electronic tricks has the possiblity ot taming the powerband of the 250 two stroke by snitching some of the top end HP and piling it lower in the range with shorter port timing and tricks done with timing, and electronic power valve but a 125 has nothing to spare.

Don't believe that. The RSA 125 had over 50 HP for more than 2000 rpm, if you can't keep a 125 in that wide a band . Then you need to improve as a rider. You have to realise no proper engine development has been applied to a 125 mx engine since probably the late 90's. With a variable disc valve and Aprilia GP style cylinder and maybe a variable length pipe/stinger size, a 45HP/20ft/lbs torque 125 would be realised having about 4000 rpm wide band of liquid power, which would be easily enough to blitz 250f's

[Uniflow]

At least it can't eat valves!!!
 Opps in saying that I've got a valve ( rotary type ) hanging on my wall that looks like an orange peel after a piece of piston went through it. When I puled the carb off there it was like a big spring sticking out. Yes one of the problems with rotary valves is they don't suffer parts through them very well.

[citabjockey]

Rotary valve warning sticker -- keep fingers and toes away during normal operations!   LOL

[riffraff]

IMHO a 125 could not compete with a 250F at the pro level. Ever.

you meant ever again right? back in the early days the 125's regularly beat the 250f's

[citabjockey]

Yes, comparing a current state 250F bikes against the early 250F's its a whole new 14,000 rpm ballgame.

IMHO a 125 could not compete with a 250F at the pro level. Ever.

you meant ever again right? back in the early days the 125's regularly beat the 250f's

[dean100yz]

Yes, comparing a current state 250F bikes against the early 250F's its a whole new 14,000 rpm ballgame.

IMHO a 125 could not compete with a 250F at the pro level. Ever.

you meant ever again right? back in the early days the 125's regularly beat the 250f's

Yeh 4 bangers wernt arnt like they were. My modern CRF450 handles amazing and pulls like a train. Its all I use for racing in almost all conditions

I took out my RM250 tuesday on a very icy sandish track, 3 corners in and a kick of the smoker power had me highside off and dislocate my shoulder.

I know on the 450 it would have tracked better. I find the 250 smoker slower and more violent with its power but its great fun to ride, sounds a hoot and good fitness.

[2T Institute]

All I can say is, I will believe it when I see it. Dyno charts, podium finishes and all. And if a variable stinger/header pipe and variable intake valve timing and DI are required for this then -- is it any less of a headache than a four stroke?

If you want to win it's no headache, injection is not required, what is required is more torque and a wider spread of torque. All of the electronic can be controlled by ignitions anyone can buy right now.

[Uniflow]

My rotary valve housing is controlled by an off the shelf Ignitec. Just plug and play!

[citabjockey]

If its a reasonable project to make a 125 competative with a modern 250F then why have the manufacturers not done so? They clearly have the engineering staff on hand to put all this together -- given what that staff has been able to do with 250F technology of the past few years.

There are two possibilities:

1) There really is a conspiracy to have everyone on 4 strokes to keep the parts/service  dept profit up in the stratosphere

2) its not as easy as some posters seem to say it is here and/or the engineering dept does not have the resource to do it (I.E. its difficult) and continue with 450F development at the same time.

To say that a road race engine is a model for a MX engine probably is not valid. A 50 HP 125? It may make over 30 over a wide range but the curve is going to be steep never the less. It would not do well against a flat power curve 250F putting out only 35 HP.

The solution is easy. CC for CC racing (at least for the 125 and 250 classes -- yes, now I am convinced. We need all three classes).

[Uniflow]

You may be right, we are "farting against thunder" but I want to have a try anyway. I like the attitude of one of my workers, " How hard could it be" ? How many times that has got us in trouble!!!
Worst case, I've got an orphan bike only I like, good, no one else will want to ride it.