Ways to make a big bore rev high.

[Honda 250r 001]

Im wondering if there is anything i can do to help my big bore rev way up there. I know like on the suzuki lt 250r they have thrust washers you can replace with billet ones for strength and weight.

But is there anything i can do to a 250r? I already have no head stay but i believe my jetting may be fat up top. I want a super long lasting top end, but if i would drop a jet would it maybe run a little better up high?

I have also heard that the cr 250 rod is titanium and will work on a trx 250r crank if you use a short rod crank, is this true? If so should i have this done next time i have my top end apart since i need a crank anyway? What years will work?

Thanks guys!

[250r grave yard]

get a billet crank
700 bucks but a bigger rod and dont have to worry bout the sheet metal around the crank coming apart on you they come balanced and trued with your piston

also heard people using a yz490 rod

[Honda 250r 001]

Originally posted by 250r grave yard
get a billet crank
700 bucks but a bigger rod and dont have to worry bout the sheet metal around the crank coming apart on you they come balanced and trued with your piston

also heard people using a yz490 rod

billet crank eh? Got a link.

are the yz 490 rods lighter or somehting? I only want a drop in deal i dont want some sitty set up.

Thanks

[Jason Hall]

Lighten the flywheel, lighten the counter balancer. Or buy a CR250 Ignition!!!

[Honda 250r 001]

would i be better off to get a ricky stator lightened flywheel? What im doing instead of getting a cr 250 ignition is wiring a 01 cr 250 cdi into my stock ignition.

[250r grave yard]

What im doing instead of getting a cr 250 ignition is wiring a 01 cr 250 cdi into my stock ignition. [/B][/QUOTE] how you do that ?

and for the yz 490 rod i heard of people using them dont know what has to be done to use it but for the billet crank call tim at titan racing 601-845-5399 . or any good motor builder can get them but like a said get ready to fork over $700 + for the crank

[2-330s]

make sure you have a top end port. buy a ftz drag ignition (4 oz aluminum flywheel) 44 mm or bigger carb.medium compression and a top end pipe. a ported rad valve,nitrous,supercharger or alcohol would help!!!!!

[Honda 250r 001]

Originally posted by 2-330s
make sure you have a top end port. buy a ftz drag ignition (4 oz aluminum flywheel) 44 mm or bigger carb.medium compression and a top end pipe. a ported rad valve,nitrous,supercharger or alcohol would help!!!!!

im not really lookin for a top end screamer, i would just like to have a little more to work with.

[hondamancbr03]

If you're not looking for a top end screamer why waste the money on expensive crank work, get an OEM and have it checked for balance before installing it (some cranks are not perfect from the factory), adjust the port timing and pipe.

[Honda 250r 001]

Thats my plan i guess, i think i heard that the short rod revs higher, im either gonna get a hotrods and have it trued and welded or get a used oem crank and have a cr 250 titanium rod put on it. Then wire the cr 250 ignition in it and hopefully i will have a little more to work with.

Once again...

Does the titanium cr 250 rod work?

[hondamancbr03]

I run Hot rods in my Banshee's and I highly recommend that you replace the bearings (if they come with it) with OEM Honda bearings....Hot rod cranks have gotten better over the years but they cut corners on bearings IMO.

The last 4mil Hot rods I installed was .009 out of true right out of the box......

Out of curiosity do you know what your current port timing is?

[Honda 250r 001]

nope, i havnt got time to get a degree wheel yet.

[86 Quad R]

Originally posted by Honda 250r 001
nope, i havnt got time to get a degree wheel yet.


got a cad program? you can make ur own and print it out. :cool:

[250r grave yard]

Originally posted by Honda 250r 001
Thats my plan i guess, i think i heard that the short rod revs higher, im either gonna get a hotrods and have it trued and welded or get a used oem crank and have a cr 250 titanium rod put on it. Then wire the cr 250 ignition in it and hopefully i will have a little more to work with. just build your self a 265 plenty of power for what it is .

86 style piston with the 88-89 long rod how cheap it is to build and get your compressoin up to 170+ psi

or get someone to deck your cylinder or cylinder head for what ever set up you would like to run they make some beast of motors when done right

[rsss396]

lighter flywheel will make the motor rev faster not higher.

Exhaust pipe design dictates the max rpm of the motor more than anything.

[250r grave yard]

Originally posted by rsss396
lighter flywheel will make the motor rev faster not higher.

Exhaust pipe design dictates the max rpm of the motor more than anything. x-2 what he said

[Honda 250r 001]

im not wanting a 265, not enough power. Is a forged or cast piston lighter. Right now im running a forged. Im going to get my crank trued and welded because if its off that will not let it rev as high. Then i guess i will see where im at.

[250r grave yard]

then get a sabertooth setup up if a 265 is not enough or build you a 270 sleeper motor 60 whp on pump gas just your on the 2nd to last bore

and i believe with the forged piston you have to let the bike warm up completly before riding it or there goes your piston

and a short rod wont rev higher but will rev quicker

[86 Quad R]

Originally posted by 250r grave yard then get a sabertooth setup up if a 265 is not enough or build you a 270 sleeper motor 60 whp on pump gas just your on the 2nd to last bore

and i believe with the forged piston you have to let the bike warm up completly before riding it or there goes your piston

and a short rod wont rev higher but will rev quicker

a short rod 310 thats built right with all matched components is a wrist stretcher for sure. :D

[Honda 250r 001]

i love the short rod i hated the long rod when i tried it. But the short rod will rev higher correct?

[86 Quad R]

quicker/faster.

[Honda 250r 001]

so do they claim that the long rod revs higher but slower?

[hondamancbr03]

Originally posted by Honda 250r 001
so do they claim that the long rod revs higher but slower?

The length of the rod does not determine the peak RPM's....Compression, pipe, port timing, balanced crank etc etc.

As mentioned, the shorter rod does reach peak HP sooner but puts more side load on the piston which a lot believe causes the piston to wear out sooner....Lot's of opinions on this subject.

[Honda 250r 001]

Originally posted by hondamancbr03
The length of the rod does not determine the peak RPM's....Compression, pipe, port timing, balanced crank etc etc.

As mentioned, the shorter rod does reach peak HP sooner but puts more side load on the piston which a lot believe causes the piston to wear out sooner....Lot's of opinions on this subject.

Ok so obviously theres no way other than having your crank balanced and removing the head stay.

[250r grave yard]

what would benifit from removing the head stay

[rsss396]

it doesn't change anything removing the head stay except help with head gasket problems if you have them.
and balancing a crank will not help either, it will just make the crank stay together longer at higher rpms.

[hondamancbr03]

Originally posted by rsss396
and balancing a crank will not help either, it will just make the crank stay together longer at higher rpms.

I would have to disagree with this comment....Balancing the crank in conjunction with lowering the compression and several other components will allow the engine to rev higher (pipe/port timing etc)......Try and put a crank that's .009 or further out of true in an engine and see how that vibration affects the motor. The vibration fights against the rotation of the crank causing it to not rev as high.

[rsss396]

trueing a crank is not balancing a crank.

balancing is done by adding weight (tungsten) opposite the crank pin to help offset the downward and upward thrusts of the piston and rod.

trueing puts the crank halves inline with each other

trueing and welding is a excellant thing to do to the crank to help keep vibrations down, but unless its way out of wack I don't believe it would limit rpms.

And singles have less of a problem than twins when it comes to the crank not being true

[Honda 250r 001]

Well im going to call a shop and see if they can have it balanced and trued for my 310 pistons because they are heavier than the stockers.

[hondamancbr03]

Originally posted by rsss396
trueing a crank is not balancing a crank.

balancing is done by adding weight (tungsten) opposite the crank pin to help offset the downward and upward thrusts of the piston and rod.

trueing puts the crank halves inline with each other

trueing and welding is a excellant thing to do to the crank to help keep vibrations down, but unless its way out of wack I don't believe it would limit rpms.

And singles have less of a problem than twins when it comes to the crank not being true

I agree that the true term for balancing is adding weight or a full circle as some call it.

But I still disagree that vibration doesn't limit RPM's.....How can you actually say that a crank that vibrates from being out of true would not fight against itself? I've been in the machine shop when the crank was spun on a dial caliper showing .009 out riding on the crank bearing (Hot rod crank new out of the box), that .009 out would cause the crank lobe to swing .009 out.

Yes, single do not have as much problem with being trued as twins, and they are easier to get spot on....But I witnessed with my own eyes a hot rod crank being .009 out.

Best thing about a forum is most everything is based on opinions....The machine shop I use has the opinion that truing a crank gives you a higher/smoother running engine.

[Honda 250r 001]

Originally posted by rsss396
trueing a crank is not balancing a crank.

balancing is done by adding weight (tungsten) opposite the crank pin to help offset the downward and upward thrusts of the piston and rod.

trueing puts the crank halves inline with each other

trueing and welding is a excellant thing to do to the crank to help keep vibrations down, but unless its way out of wack I don't believe it would limit rpms.

And singles have less of a problem than twins when it comes to the crank not being true

i think im going to have to agree with these guys, with the piston going up and down at 133 times per SECOND at 8,000 rpm. any little part thats off balance will rattle like a sum *****, and that makes the crank harder to turn up in the higher rpm's

[rsss396]

Originally posted by hondamancbr03
I agree that the true term for balancing is adding weight or a full circle as some call it.

But I still disagree that vibration doesn't limit RPM's.....How can you actually say that a crank that vibrates from being out of true would not fight against itself? I've been in the machine shop when the crank was spun on a dial caliper showing .009 out riding on the crank bearing (Hot rod crank new out of the box), that .009 out would cause the crank lobe to swing .009 out.

Yes, single do not have as much problem with being trued as twins, and they are easier to get spot on....But I witnessed with my own eyes a hot rod crank being .009 out.

Best thing about a forum is most everything is based on opinions....The machine shop I use has the opinion that truing a crank gives you a higher/smoother running engine.

I agree with you more than I may be coming across:)
hot rod cranks and even rods are hit or miss for sure so having them checked is a must.
And for the record my stuff is trued-heavy balanced&welded for high rpm racing!

[hondamancbr03]

Originally posted by rsss396
my stuff is trued-heavy balanced&welded for high rpm racing!

What kind of compression are you running for top end power?

[rsss396]

Originally posted by hondamancbr03
What kind of compression are you running for top end power?

I run alcohol with a 15-1 compression ratio

This is a cr500 motor stroked 6mm (553cc)
with a Shearer drag pipe

[2-330s]

if the motor is built to rev it will with high compresion. i've seen some ftz motors 260 comp making peak hp at 10,500-11,000 rpm

[Honda 250r 001]

wow, i would be ****less to hit 10 grand.

[hondamancbr03]

Originally posted by rsss396
I run alcohol with a 15-1 compression ratio
This is a cr500 motor stroked 6mm (553cc)
with a Shearer drag pipe

I have a buddy running about the same motor in a 250R Lager framed three wheeler....He gives Banshee's running 10mil Cheetah cubs a fight.
That's a hell of a motor to kick start.......

[rsss396]

Originally posted by hondamancbr03
I have a buddy running about the same motor in a 250R Lager framed three wheeler....He gives Banshee's running 10mil Cheetah cubs a fight.
That's a hell of a motor to kick start.......

yes it is :D
but I have put a compression release in the head and I have a hand held remote starter if kicking it doesn't work