84 250r vs 1978-80 cr250

[bebeav]

i just found that in 1978-80 the CR250 dirtbike used to have a similar engine to our 84 250r. both having a bore & stroke of 70mm x 64.4mm.

i also found that the engine in the cr250 pushed aproxx. 39hp at 8500rpm, but they were running 38mm keihin carb.

my question is how can this engine push this amount of power?

ALP
Beav

[EvilMooseofDoom]

Having built a 1979 CR250 for my brother...I did one hell of a port/polish job on his head, and I had trouble keeping the front wheel on the ground through 4th while riding on the street in front of my house(it ripped off the center row of knobs on the rear tire the first time he went riding), and I weigh 315 lbs.....he has also been keeping up with a few later model CR500's and KX500's (and dusted a YZ490) at a local riding area..39 hp, though? I don't know. These bikes had a wicked 3000-3500 rpm HIT stock from the factory, it just got worse with my head porting, lol. He has a new pro-form pipe coming for it, though, to mellow it out, absolutely insane for trail riding with the stock expansion chamber.

It also HAD a stock 34mm keihin carb on it, but I ditched it for a 38mm mikuni, and Unifilter.

[bebeav]

so they maybe just upgraded for the 38mm carb in 1980. by your tought i think the bike really got his 39hp stock. anyone here know if there any compagny that still make 78-80 cr250 expansion chamber??? is the head has a better design? diferent port size? different base? any information would be good.

ALP
Beav

[EvilMooseofDoom]

So far as the expansion pipe goes, there are two companies that still make pipes for the CR250, ProForm and DG....DG, however, uses the original 1979 design(ancient, lol), while the proform pipe was only put out just a year or two ago, using modern pipe tech....the proform pipe is what my brother is picking up.

Am I to understand that you are going to try to utilize a 1978-1980 CR250 engine in a 1984 ATC250R frame?

[bebeav]

no more trying to use performance part from the bike to put it on the Air R. i know the expansion chamber doesnt attach like the one on the trike but with some custom modification of the angle of the expansion chamber i think i could fit this exhaust system on my trike. in europe i found a place where they still sell the proform complete exhaust system for 450 euro, so approx 700cnd buck.

horever do you have any pic of the cylinder of the cr250??

ALP
Beav

[MTS]

this is very intrstin... i know where an air coold bike in pieces is and a 250r dirtbike motor....will have to try and get my hands on it...heh

[bebeav]

at least try to know if the cylinder is the same as our 250r.

ALP
Beav