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boyesen port what to expect?

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Hi,

Iv got 2 cr250s 2001 that i bought last year.

Iv talked to terrobelone about these and recently hijacked another thread but decided to make my own thread so that i can expand the truth about these supposed "stock" cylinders of different previous owners.

stock cylinder?

100_5016.jpg

ported cylinder

100_4898.jpg

100_4889.jpg

And here is what they look like from the reed cage view.

100_4687.jpg

100_4688.jpg

My question is, what was intended for this port job?

what should i expect from this powerwise, as iv never ridden 01 without these ports?

Could othe rTT members care to post a pic of their 01 cylinders?

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I've never seen those added to a 250, but they're seen fairly often in highly prepped CR500 jugs. It doesn't change your port timing at all, but it does give the intake path more window space when the piston is down in the stroke. The only comment I've ever heard from a professional engine builder who installs these ports is to the effect that they restore some lost low end to a bike that has had the exhaust duration modified for higher rpm power. I can't verify that of course, and I also can't give an explanation as to why the new ports would add low end.

I doubt if they will change anything at all in your seat of the pants dyno unless the engine has other significant mods, including carb, reeds, exhaust porting and pipe change. I also wouldn't be concerned about reliability, because it looks like the port edges are chamfered fine, and these small windows shouldn't have any effect on ring life.

That's my 2 cents, and I'm glad to be educated by anyone who knows more.

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from my readings i have found that

lowering port hight will add low end and raising will add top end

The clearer the intake path for the fuel air charge the better, this makes the scavenging effect of the crankcase more efficient as it can breath a little better

so again here you're adding flow the reason this boosts the low end throttle response is the mod done to your cylinder allows the fuel/air charge to bypass the crankcase and go straight into the combustion chamber with out going through the transfers so this has a similar effect as lowering your transfers in the sense that there is more fuel/air charge available lower in the stroke

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I must edit this thread by theway.

i looked into my cylinder pictures and both cylinders are different.

iv noticed that the "stock" cylinder has no added port like the one i said "ported".

i must appologize for the confusion of having 2 cylinders and thinking both are stock. when i jumed into the other thread previously, i was concered that why my other cylinder has tooling marks on the ports and the other did not.

i then thought that i had both identical cylinders when infact, the so called "stock" didnt actually have that port. and terrrobelone was right that my other cylinder had an extra port drilled in, from comparing both my jugs based on the pictures.

so now i have a reall stock and a modified one.

lets all just conectrate on the modified one and leave the stock alone for awhile.

does this slow the intake velocity? does this add CCV of the whole package?

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It doesn't change your port timing at all, but it does give the intake path more window space when the piston is UP IN THE STROKE.

I also wouldn't be concerned about reliability, because it looks like the port edges are chamfered fine, and these small windows shouldn't have any effect on ring life--BECAUSE THE RINGS NEVER TOUCH THESE PORTS.

That's my 2 cents, and I'm glad to be educated by anyone who knows more.

Looks like I get to educate myself on my own stupidity. Corrections made to my own post.:smirk:

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Boyesen would never do a port job that looks like that, it is a backyard port job from what i can tell.

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Boyesen would never do a port job that looks like that, it is a backyard port job from what i can tell.

boyesen invented the port thats were the name comes from :smirk:

that is a back yard job i don't see that adding much power

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send that to me. ill make that port job all purdy for you.

Absolutely do NOT send it to Chopper for port work :bonk: he'll put the dremel right threw the cylinder and butcher it all up :smirk:

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haha im not sending this to anybody. from what it felt. its really has a great bottom end and mid ranges. for some reason, it doesnt sign off the highs either.

it has more bottom end than my 250sx.

i describe the KTM to have an "artificial" bottom end coz of the change of exhaust system.

but this particular CR with port job. it seems to have that natural "biff" on the bottom end. i seem to get tired pretty quickly with this bike than the orange one.

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