OzVMX Forum

Clubroom => Tech Talk => Topic started by: Expat on September 11, 2008, 07:55:53 pm

Title: Horsepower and 250's
Post by: Expat on September 11, 2008, 07:55:53 pm

What were the likely correct/true horsepower of the last pre powervalve 250's??.....early 1980's

Title: Re: Horsepower and 250's
Post by: Hoony on September 11, 2008, 10:42:45 pm

hard to say but i would be thinking somewhere around the 42-45hp mark at a wild guess

Title: Re: Horsepower and 250's
Post by: asasin on September 12, 2008, 07:03:38 am

Why Expat ,do you want to join the pre 86 men?Pre 75 too slow for ya?, Ask Shane at the weekend his 250 cr leaves the rest of us in a straight line like we have put the brakes on!!! ??? :o

Title: Re: Horsepower and 250's
Post by: JC on September 12, 2008, 08:51:52 am

Expat,

Lozza would probably have a fair idea.
My guess would be a bit below Hooney's, but I'm only guessing too.

Title: Re: Horsepower and 250's
Post by: mx250 on September 12, 2008, 09:49:13 am

Showed Lozza my 9 port reed valve Monty barrel recently....

(http://i323.photobucket.com/albums/nn458/mx250syd/barrel.jpg)

...and he reckoned 50hp ;D. Probably 'at the crank' ::). Whatcha reckon, 40-45 at the back wheel.

And that would everthing being spot on; best ign, best fuel, best carb, best tune, best chamber  ;). But not bad, a 50% improvement in 10 years, early 70's to early 80's.

I might have to put it together and find out.

Title: Re: Horsepower and 250's
Post by: JC on September 12, 2008, 10:06:40 am

Graeme,

Ain't there 10 ports in that Monty barrell? 3 ex, 4 tr, 1 in, 2 boost.

Title: Re: Horsepower and 250's
Post by: Lozza on September 12, 2008, 05:37:45 pm

With water cooling around the 35HP mark.

Title: Re: Horsepower and 250's
Post by: Rossvickicampbell on September 12, 2008, 09:18:04 pm

according to Mugen my 1980 CR had 36 HP and the kit added another 4 to take it to 40.

cheers

Rossco

Title: Re: Horsepower and 250's
Post by: JC on September 13, 2008, 09:16:44 am

I'm w Loz. I think the other claims are overly optimistic. Factory claims are notoriously optimistic.

A Graham Bell (in his 2stroke tuning book) put a 79/80 CR250R on the pump & got 29.8hp stock, but he upped that to 32.4hp w a three satge diffuser/tapered header pipe, tho its not exactly a fatty pipe.

Seems to me the exh valve was the quatum leap in obtaining hi power outputs in the mid-hi 40s.

Title: Re: Horsepower and 250's
Post by: Lozza on September 13, 2008, 11:10:09 am

Ignitions and carburetors went ahead also.Not to mention Nikasil barrels..............but todays 250 pump big torque numbers which is where it's at.