Can the 150R be a 125?

[Rich Rohrich]

Given what looks to be a change in the AMA rules that would push the 150R up a class, 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, and this is no exception. :banghead:

 

[nikki]

If the new "rule" might be a class for 100-144cc, 2-stroke and 4-stroke, why can't Honda just change the motor to a 144cc 4-stroke for 2008? I don't think it needs to be a 125cc, just a 144cc?

 

[Rich Rohrich]

If they dropped it to 144cc for a race version of the bike they would only have to shorten the stroke 1.6mm and raise the power peak about 500 rpm to 13,000. that is much more workable, and fairly simple to engineer. That's assuming they care about it as a general race bike.

Given how few CRs and CRFs ever see a race track it's possible that Honda won't care if it's a SuperMini only race bike. I think they'll still sell a zillion of them. Afterall, Yamaha sells more TTR125s than KTM sells motorcycles, so the market for fun little four-strokes seems established regardless of what happens on the race track.

 

[robwbright]

I've seen the talk of cc based classes, but it actually looks like the AMA is going to do it?

 

[Rich Rohrich]

Wardy is the District 17 President/ AMA Competition rep and he said the following was voted on and passed by the AMA .

Classes:

86-144 A,B,C 2 and 4-stroke
145-250 A,B,C 2 and 4-stroke
251-Open A,B,C 2 and 4-stroke


Supermini - 112cc 2-stroke, 150cc 4-stroke B

CRF150R would be legal in SuperMini and Schoolboy (but only the big wheel version)

It's unclear if this will go into effect in 2007 or 2008.

Once it's all locked in we'll get Wardy to sum it all up.

Things are about to get VERY interesting in the dirtbike world.

 

[lwsmithjr]

Other sites (other AMA reps) are reporting changes will go into effect in '07. (??)

As for the 150R dropping to a 144, the problem lies in the fact that it is a minicycle, not a motorcycle (by AMA definition). The 86-144cc class is for "motorcycles". Minis aren't allowed in a motorcycle class. They never have been. Schoolboy and Women are the only two classes that allow "motorcycles" and "minicycles" to compete head to head.

 

[robwbright]

Classes:

86-144 A,B,C 2 and 4-stroke
145-250 A,B,C 2 and 4-stroke
251-Open A,B,C 2 and 4-stroke

So if I understand, the AMA has now decided to get rid of the displacement advantage in many amateur classes?

Darn, I was seriously thinking of taking advantage of the advantage next season. . . if I keep the 144 does that mean I can't have fun beating up on 250f's anymore? ;)

Seriously, though - if this rule change takes effect in 2007, it would give me a reason to go one more season on the 144. Perhaps I'll get the suspension done over the winter and thrash it for one more year before trying out a thumper.

 

[wardy]

November 18th is the rules meeting overview by the ama board. they should pass the rules as placed to them since congress had little "against" on this issue of cc classes. IN fact it was within one or two votes a total FOR this rule vote.

see what happens on the 18th, so you guys know, AmA Trustees/directors most generally do NOT change a congress rule unless it doens't meet legal department needs, these rule changes do not have any legal implications.

wardy......

ps i submitted the rule change along with a few others.

 

[bclapham]

if the rule goes through, i am gonna buy the card and drag my two bikes to the races again.

 

[Moose]

Being AMA, these rules are not being passed over in Canada, correct? Are they even going into consideration?

 

[jboomer]

Is there a plan to change the rules for the Pro's too? Just curious if they're going to have to abide by the new displacement rules in the future as well.

 

[XRpredator]

Is there a plan to change the rules for the Pro's too?

doubt it

 

[highmileage]

Interesting note...Got the BooKoo ArenaCross pamphlet and they list the following:

85cc = 66-85cc 2 stk or 75-150cc 4 stk

85cc Super Mini = 80-105cc 2 stk (big wheel) or 150cc 4 stk

Go figure...it also appears that many off road series are going to allow 85cc 2 stk and 150cc 4 stk in same class

 

[XRpredator]

BooKoo AX isn't AMA, nor is GNCC

 

[lwsmithjr]

This rule is for AMA amateur racing only. AMA Pro is not affected by the rules change. It will still be SX and SX Lites, MX and MX Lites....

 

[nikki]

This rule is for AMA amateur racing only. AMA Pro is not affected by the rules change. It will still be SX and SX Lites, MX and MX Lites....

But.... will Lites now be 250cc 2-stroke and 4-stroke? I thought I had read that might be the new Pro format. And MX/SX would be 251cc and up. I could be wrong.

 

[highmileage]

It is interesting how this is lining out. Some non-AMA series are aligning 85cc vs 150cc and some are not.

WORCS is an example of not:

super mini = 85-105cc 2 stk or 150cc 4 stk

open mini = big wheel 85-105 cc 2stk vs 150 cc 4stk

Needless to say that after this year there will definetaly be some re-arranging of classes in reference to this matter, as there will be several series running 85cc vs 150cc and several running super's against 150cc.

My opinion is that eventually there will be changes, especially if KTM gets on board with a small four stroke. They would be one that sells the 125cc 4 stk MXer with a 150cc top end in the crate or available through KTM hard parts. They seem to meet the market niches. Modified 85 SX chassis with the motor???

 

[wardy]

GNCC is ama, if that is the offroad series.

these rules do not affect pro in any way. it is only amatuer rules.

non ama events some have let the 150 in and others have not. I think the people in the committee didn't want to "jump" off that cliff the first year. Hence 150 minicyle was placed like it was. after 07 lets see how it really competes and how "fair" it is in what ever class.

wardy

 

[jboomer]

If that's the case, I thought it was confusing before..but now look at it! Imagine from the amateur stand point.

 

[lwsmithjr]

Wardy can correct me here if I'm wrong, but I 'm pretty sure that most other disciplines of AMA Motorcycle Racing have adhered to displacement sized classes (meaning 4 strokes have no size advantage) for some time. Motocross is just following suit.

As for the 150F, I'm guessing local promoters are going to end up making the final call for their individual tracks. Unless it is a large Amateur Race, the local guy just wants to please his customers. This was not a surprise to the AMA -- there have been rumors of a mini YZ thumper for two years. Best guesses back then were that Yamaha was waiting on this decision to produce the bike so they would know whether it should be a 125 or a 150. It probably would have been easier to accept if the ruling had been made before the 150 hit the market. I'm with Rich though. I think Honda will sell every one it can produce, regardless of whether or not it's legal in the 85 class....

 

[steve125]

wardy......

ps i submitted the rule change along with a few others.

Thanks Wardy, I hope the rule change goes though, this should have been done years ago. :cool:

This brings back the 125 classes
Makes the 250 class a real 250 class
Allows racing to be more affordable for those on a budget(2 smokes)
And defines the 450's as open bikes

It will be interesting to watch the mix of 4 vs 2 strokes in the 250 class.

 

[cancanman]

so what class would a 2 stroke 125 be in?

 

[lwsmithjr]

Wardy is the District 17 President/ AMA Competition rep and he said the following was voted on and passed by the AMA .

Classes:

86-144 A,B,C 2 and 4-stroke
145-250 A,B,C 2 and 4-stroke
251-Open A,B,C 2 and 4-stroke


Supermini - 112cc 2-stroke, 150cc 4-stroke B

CRF150R would be legal in SuperMini and Schoolboy (but only the big wheel version) .

86 - 144cc 2 or 4 stroke

 

[motodawg]

Posted October 25, 2006

AMA clarifies proposed Youth racing rule changes for 2007
The AMA is clarifying two proposed rules changes that could affect motocross and other Youth racing classes for 2007.

Many youth racers and their parents have contacted the AMA recently about proposals approved in early October by the AMA Congress, the Association's rules-making body for amateur racing and road-riding events. Two proposals have drawn the most questions and comments:

A change in displacement limits in certain classes in motocross only, which would eliminate different displacement limits between four-stroke and two-stroke machines.
Changes to Youth regulations that would allow four-stroke motorcycles up to 150cc (such as the newly introduced Honda CRF150R) to compete in Super Mini and "schoolboy" 12-15 classes.
All competitors should remember that rules changes proposed by the AMA Congress do not take effect until or unless they are approved by the AMA Board of Directors. The AMA Board will next meet on November 18-19 to consider proposals from Congress, among other business. Unless otherwise stated, rules approved by the AMA Board will take effect February 15, 2007.

The final decision made by the AMA Board on these rules will be posted on this website.

Proposed changes

Here is a summary of the two rules changes proposed by AMA Congress that have drawn the most questions:

-In motocross only, new displacement limits would be applied to class 2 (100cc-144cc), class 3 (145cc-250cc) and class 4 (251cc and up). This means that both two-stroke and four-stroke motorcycles would be limited to the same maximum displacement and the limits would apply to A, B and C classes.
-In Youth racing, the displacement limits would be changed in the Super Mini (12-15) and Class 16 (86cc-125cc age 12-15) classes to allow 75cc-150cc four-stroke motorcycles (such as the Honda CRF150R), in addition to the current two-stroke limits. In Super Mini, the maximum displacement for two-strokes would be increased to 112cc.
AMA members can best influence future rules-making processed by contacting their representatives in the AMA Congress. You can find your Congress representative online. Comments may also be sent to AMA staff, who will present Congress' proposals to the Board, by using the contact form on this website.
http://www.amadirectlink.com/email.asp