350 4stroke replace the 450?

[cnielse5]

Just thought I would get you guys thoughts on this one. AMA and FIM are looking to get the 450 downsized to a 350.

here is a link to the interview with steve whitlock head of the ama.
http://www.racerxill.com/articles/detail/1869/when-giuseppe-met-steve.aspx

 

[likelite]

i thought they tried this already.the manufacturers complained .

 

[JKoepsell]

My whole take on this is ....
I think, and I hope we all would agree, that there should always be two stroke and four stroke bikes on the market. There are so many die hard four stroke and two stroke fans that it makes no sense to upset that many people.
Firstly, although I do find the 250 class does need some attention, the 125 class is much more unfair. The 250 two stroke is at a disadvantage but I think that moving 450's down to 350's might be kind of an drastic. If this were the case, everyone would probably ride two stroke 250's again to be competitive and we would hear whining from the die hard four stroke fans. The manufacturers should do some testing on the dyno and at the track to see what the most fair engine displacement would be. This would solve all of these issues and people could ride what they want. Honestly, I think it would be exciting seeing both bikes on the track battling it out fairly.
I also think that the manufacturers wouldn't lose much money switching their bikes to 350's or whatever it will come to. I don't build engines but it seems quite simple, just sizing everything down a bit. I would be very excited to ride one of them and I am sure many of the four stroke fans would too.
I am also very excited to see (if this does really happen) what the manufacturers will come up with as far as two stroke engines and the tightening of emissions rules. Unlike some people, I do care a lot about the environment so I feel kind of guilty riding a two stroke. It would be great to see some new designs like the Honda EXP-2 or fuel injected two strokes. Sadly thought manufacturers aren’t really experimenting with FI 2 stroke MX bikes are they?

 

[XRpredator]

My whole take on this is ....
I think, and I hope we all would agree, that there should always be two stroke . . . bikes on the market.

I disagree. Punt 'em.

 

[2 strokes for life]

I think a slveeded down 400 would be the best.

 

[Rich Rohrich]

I think a slveeded down 400 would be the best.

Why is that?

I also think that the manufacturers wouldn't lose much money switching their bikes to 350's or whatever it will come to. I don't build engines but it seems quite simple, just sizing everything down a bit.

It's not that easy. The engine would have to be redesigned from the the bottom up. The R&D expenses would be significant.

A question came up a little while back about making a Honda CRF150R into a 125. A few people have asked if it would be possible to sleeve a 150R down and make it a 125. I gave it some thought and came up with the following.

As it sits today the CRF150R has intake valve area that represents 31.04% of the bore area, by comparison the 250R has 31.59% valve area and the 450R has 28.13% area. The 150R has pretty major valve area from a japanese design standpoint. Considering it's making around 160hp/liter it kinda makes sense.

Sleeving it down to a 125 would forced you to drop the bore size from 66mm to about 60.4mm. This would bring the valve area up to 37.06% of the bore.

Once you get above around 33% valve area you run into some real issues with valve shrouding, and combustion chamber shape, not to mention that much valve area forces a very real bias towards high rpm power.

Dropping the bore size 4.5 mm would wreak havoc with the quench area built into the original cylinderhead design and really shroud the valves in a major way. I'm tempted to make up a 60.5mm cylinder flow bench adapter just to see how bad it would be.

Shortening the stroke the 6mm or so it would take to bring it down to 125cc and lengthening the rod would seem the be the better way to do it but it would require an upgrade in valve gear and a change in the cam design. If you assume you want to keep the same mean piston speed of 3600 ft/min at the power peak that Honda is using, then you'll be making peak power at 15,000 rpm instead of 12,500, and redline would be flirting with the 17,000rpm range. Titanium valves and GOOD springs would be a must.

It's always tricky when you try to out-engineer Honda or any of the big japanese OEMs, and this is no exception.

 

[Bakemono]

i thought they tried this already.the manufacturers complained .

Not true. The manufacturers were in favor of it, but it was voted down by the AMA congress.
Im in favor of the move to 350Fs. We need to keep 2-strokes alive because it will keep the sport affordable the the average weekend warriors who are buying their own bikes and paying for bike repairs out of their own pocket.
4-strokes are great untill you have to rebuild them and thats when they rear their ugly head. :nod:

 

[2 strokes for life]

Rich Rohrich, i was just thinking it would be easyer and cheaper then going to a 350. But they could always make a 285 2 stroke to level it out.

 

[just_a_rider]

They might have done some studies and came up with this new displacement but dropping a 100cc's? Thats drastic. More along the lines of a 375 or a 380 4t would be more resonable. It's like the 150 4t, it should have been more along the lines of a 118 to 120 cc, instead they jumped the gun and over jumped the 85cc class to much.

 

[James]

In my opinion, they need to get the bikes down to 90 db or less.

That should reduce the power comparably to making them 350s