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Port & polish????

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I have a CRF450R '05.... I love the power! However I find myself looking for 6th gear all the time. I had a 13 tooth front and 48 rear. I recently purchased a 14 tooth front knowing this will drop 3 teeth in the rear. While ripping my bike down I figured it would be a good time to do some motor work. I was told that port and polishing would take some bottom end away. Does anyone know if this is true? What are the pros and cons?

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I have a CRF450R '05.... I love the power! However I find myself looking for 6th gear all the time. I had a 13 tooth front and 48 rear. I recently purchased a 14 tooth front knowing this will drop 3 teeth in the rear. While ripping my bike down I figured it would be a good time to do some motor work. I was told that port and polishing would take some bottom end away. Does anyone know if this is true? What are the pros and cons?

If you get someone who knows what they're are doing, they can give you more power without loosing your bottom end... My head is flowed on my 09 and I still have plenty down low with way more over rev up top... :lol::thumbsup:

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there is more too it then simply grinding the metal away as Jason indicated above. the basics are not only to open it up but to polish the exhaust side and leave the intake rough. the rough surface creates eddies that helps keep the fuel vaporized. you could complement the higher flow by boring your carb as well.

since your rebuilding the motor consider adding a BB kit. i have an 06 450 with a Thumper Racing 390 kit in it and with the BB kit you can gear taller and the motor actually feels more manageable/controllable than compared to stock. Travis also does porting work if you feel more comfortable having him do it than yourself.

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The loss of bottom end is generally due to the loss of cylinder pressure. Installing a cam with more duration and / or more overlap will take away from bottom end more that porting the head. Many times when people port the head they add a cam, and that may be why you were told this.

http://www.bigborethumpers.com/porting.html

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good port work will add power every where in the curve .compression ratio does not always make more hp the cam and piston as well as porting should be a package.there are some fuels that simply do not like compression say over 13.5-1 on a 450 .

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good port work will add power every where in the curve .compression ratio does not always make more hp the cam and piston as well as porting should be a package.there are some fuels that simply do not like compression say over 13.5-1 on a 450 .

Is this mostly due to increasing the port cross section at the smallest point and filling in the dead zones? From what I understand increasing the X-section will reduce intake velocity and at some point power has to be lost someplace due to the varying port speed at X RPM. Isn't going above or below mach .5 reduce VE and thus power?

Ok, give it up, HOW DO YOU DO IT :smirk::bonk:

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i have that mach index sae papers some where i remember years ago when you could by just about any sae paper for $13.00 .port cross section vs displacement vs aplication dont try to over diagnose it .

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i have that mach index sae papers some where i remember years ago when you could by just about any sae paper for $13.00 .port cross section vs displacement vs aplication dont try to over diagnose it .

so if you blend the bowls and clean up the hallways, a good valve job, would it do much?

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yes. cleaning up the casting lines, sharpen the intake splitter, open the exhaust up a little, shine it up and get rid of those atrocious valve guide casting steps.

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Sharpening the splitter is debatable. Round like the leading edge of an airplane wing is better. Sharp will chase seperation and turbulence directing it away from the wall. Send it for a good valve job to someone who has a flow bench and has done w 450 head at least there's alllllot to it. Also I hat the term port and polish I like port better.

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countoring the divider and making it stream lined not only makes the air follow it better but also the fuel its great on the flow bench but fuel runs right out the exhaust i still sharpen the divider just to get maximum cross section in that area .blunting the divider reduces flow slightly but disperses the fuel in the combustion chamber better when wet flowed .its debatable if it helps but the test engines that i did never showed a loss of power .i need more sofisticated test equipment to determine if its of value.

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Well rons the expert. But I know a streamline is a tear drop. A wing is a tear drop. I sure killed some 2 strokes with knife edging. To me a rounded edge should create less pressure drop. I'm actually supprised that works for you Ron.

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i have that mach index sae papers some where i remember years ago when you could by just about any sae paper for $13.00 .port cross section vs displacement vs aplication dont try to over diagnose it .

Ron,

You have been diagnosing heads for years :bonk: Can it really be over diagnosed or is your idea of over diagnosing more than 50 years disgnosing? :smirk:

Porting is a black art that is difficult to get clear answers on. Practice practice practice!

Have you used Power Lynz grooves with any sucess?

Years and years ago the boaters used to wax the bottoms of boats because they thought it would make the bottoms "slicker" and hence faster.

Then started seeing boats with stepped hulls to create tiny bubbles on the bottom of the hulls.

It would seem logical that when fuel and air are mixed the fuel is heavier and can fall out of suspension when changing speeds. If a false boundry layer is created beneath the surface the air above it will be faster. After all, anything wet that touches the surface is traveling at zero speed.

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i had good results contouring dividers in 2 strokes also i flow tested and it worked its a diferent situation in a four stroke no time for fuel and air to mix .a 2 stroke requires much less ignition advance which indicates a more homogenous mixture

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