New for 2008: 450cc Four Stroke Spec Class

[roadracer162]

Name the weapon and I'll build it...!!  Who would like to see a FZR400 take down the SV..??  Just let me know..  

I would love to see it. You got a motor? I would love to put one in my FZR400. Are we talking 560? But man will it last?

I do like the electric start as oppoesd to bump starting.

Mark

[BadBoyRR]

At this point the attached poll now shows 19 that would enter such a class vs. two lonely souls who need hp and $$$ to mask lack of ability. (JOKING!!!)

In any case, its been fun debating the topic and I suspect I'll be back out next year on either my KTM or CRF450, just because they are the most fun I've had on track since the old Norton. Too bad it couldnt keep its gear box together....

Don Allen

[Ducati23]

If you thought these newer MX 450 motors take a lot to maintain in MX trim where they are rarely held WFO for long periods of time wait until they are rev'd to death for awhile without wheel spin and a nice cushion of dirt. Even in these conditions they come apart and drop valves regularly.

These things will be exploding in a grotesque manner on a regular basis as they vibrate themselves apart starve for oil and break valve parts. Most of the members here weren't around back when thumpers were relatively popular. Those things rattled themselves apart regularly due to vibration. These new 450's are much lighter and more highly strung. 

[Super Dave]

Highly hung?

[resurection]

If you thought these newer MX 450 motors take a lot to maintain in MX trim where they are rarely held WFO for long periods of time wait until they are rev'd to death for awhile without wheel spin and a nice cushion of dirt. Even in these conditions they come apart and drop valves regularly.

These things will be exploding in a grotesque manner on a regular basis as they vibrate themselves apart starve for oil and break valve parts. Most of the members here weren't around back when thumpers were relatively popular. Those things rattled themselves apart regularly due to vibration. These new 450's are much lighter and more highly strung. 

Sounds familiar
I n one regard I disagree there are alot of old thumpers running just fine.

[Super Dave]

I think Clayton is saying that the new thumper MX motors aren't the one's of old.  As for vibration, yeah, even my SV1000 vibrates some things off more so than all the four cylinder bikes I had.  Old and new singles still do this.

Regardless, the new MX singles are stressed race motors spinning high RPM's with big cams.

There is no comparison to my XT500 to a YZ450F other than they are single cylinder engines and they are made by Yamaha.  One can probably expect to see XT/TT/SR500's over a length of time.  Four stroke MX bikes will be consumed.

[Knedragon]

Hey Mike,
Watch out for that crafty Mark,hes one fast dude!!

[Headdog122]

Over 90hp from FZR400  !!
Boy your talking big .This is not a challenge to your skills I don't even know you but have you built a bike that's competitive in it's own class let alone out of it's class

Brotha,

If you have to ask, you surely don't know me.  BTW....  "Betta Ask Somebody!!"  he,he,he...  And any bike I'm on is competitive..!!  Let me straddle my XR80....   

[Headdog122]

I would love to see it. You got a motor? I would love to put one in my FZR400. Are we talking 560? But man will it last?

I do like the electric start as oppoesd to bump starting.

Mark

It will last..  And, I'll leave the electric start on for those less motivated..!!  he,he,he... 

[resurection]

Brotha,

If you have to ask, you surely don't know me.  BTW....  "Betta Ask Somebody!!"  he,he,he...  And any bike I'm on is competitive..!!  Let me straddle my XR80....  

Cool in your next bike building project please consider our services.I'd like to meet you !

[resurection]

I think Clayton is saying that the new thumper MX motors aren't the one's of old.  As for vibration, yeah, even my SV1000 vibrates some things off more so than all the four cylinder bikes I had.  Old and new singles still do this.

Regardless, the new MX singles are stressed race motors spinning high RPM's with big cams.

There is no comparison to my XT500 to a YZ450F other than they are single cylinder engines and they are made by Yamaha.  One can probably expect to see XT/TT/SR500's over a length of time.  Four stroke MX bikes will be consumed.

Any carbs for old yam?

[tzracer]

One of the USGPRU regulars has friends in Japan running the 250 4 stroke class. The engines are based on the 250 motocross singles. I am not sure how modified the engines are, but they are slower than 125s and the pistons of the 250s are replaced every race weekend.