Changing Power of CRF450R

[cthowards]

This past winter I replaced the valves and springs and also installed a 13.0 to 1 high compression piston on my 2005 CRF450R. In addition, I installed a White Brothers Carbon Pro pipe as my stock pipe was badly flattened at the cylinder. The bike runs great and has a ton of power, but the low end is missing and it has a hard hit from mid-range up. I get arm pump more this year than I did last year because it just wants to take off.

Anybody have any suggestions on how I could get more low end and generally mellow out the power throughout and make it more user friendly? I ride motorcross 2 - 3 times per week.

 

[Rich Rohrich]

Changing the cam phasing with an adjustable sprocket is the cheapest way to make the change. A complete cam change along with an adjustable sprocket to bias the intake valve close timing to towards low end power would be the next step. Before you do any thing I would look hard at the jetting. Jetting can have a huge influence on the way power is delivered big four-strokes. It's worht taking a close look at the size of the head pipe on your WB system. Most of the WB pipes I've seen have head pipes with way too large an inner diameter (too much area) for most riders. This will kill the low-mid range and put a big trough (hit) in the torque curve. For pros who can ride above 8000 rpm all the time that might work, but for most riders the pipe is too damn big and doesn't work as good as the OEM head pipe.

Engines are systems and a change in one area can have far reaching effects that may not always be immediately obvious. It's worth measuring your head pipe (primary length as well as diameter) and comparing it to an OEM before you make any significant changes.

 

[whenfoxforks-ruled]

Did you put a cam in it?

 

[cthowards]

As far as the jetting, I e-mailed Tom Morgan at White Brothers during the winter and he indicated that they do not recommend any jetting changes for the Carbon Pro on the 2005 CRF450R. However, he did indicate that on his race engines they do make some minor jetting changes. He gave me the sizes of the pilot and main jets but they are out in the garage at the moment. I adjust/check the fuel screw periodically and the bike never has any bog or never runs poorly.

I have the stock cam in it. Would a Hotcams Stage 1 provide more low end? Or is the White Brothers header just too big?

Perhaps my best bet would be to put a stock or similar to stock pipe back on or install a Hotcams Stage 1.

I let a friend who also has a 2005 CRF450R ride my bike and he is said is breaths way better than his bike and revs up very quickly. He was very surprised at the difference.

 

[Ol'89r]

for most riders the pipe is too damn big and doesn't work as good as the OEM head pipe.

Engines are systems and a change in one area can have far reaching effects that may not always be immediately obvious. It's worth measuring your head pipe (primary length as well as diameter) and comparing it to an OEM before you make any significant changes.

What you have done is change the dynamics of your engine. Like Rich said, "Engines are systems". You can't just buy a cam from one vender and a pipe from another and hope they will work together. These items along with pipe length and diameter, cam design and timing, and many other factors have to be designed to work together. Usually on a dyno.

Changing one item that is not compatable with another will usually cause your bike to run worse or not take the throttle properly.

I would take Rich's advice and go back to the stock pipe or at least the stock header. The smaller diameter header should give you better low end.

The higher compression piston will make your engine rev quicker.

Just my $ .02

 

[whenfoxforks-ruled]

Stage one for cleaner bottom. Stage 2 for more everywhere. Its almost like a 2t on steroids. But,it also had porting! Slapping the piston in it,and the WB pipe with different back pressure,bye bye get up and go! Get the stage 2 and the head ported for the mods,then have your friend ride it!

 

[cthowards]

I don't disagree with any of the advice provided above. In particular, Rich your technical expertise is very impressive and way over my head...I wouldn't know what to do with the header measurements if I had them! I went riding this afternoon with a couple of friends at the MX track I normally ride and am a member of. The track was just groomed and was perfecty flat. In any event, I had a blast and really focused on what I thought the bike was going to do and tried to exagerate or over compensate with my body positioning and it seemed to work. In short, the bike plain rips and I started to think that maybe I don't want to mellow it out. In particular, there was this one section on the track that had a double, then a double, then a triple, then a table top and then and left hand sweeper that lead to an up hill table top. I nornally can't clear the up hill table top (because the sweeper gets whooped out), but today since it was smooth, I would enter the sweeper and roll it on in 3rd gear until full throttle and I was clearing that table top no problem. I had a huge smile winding out that mutha! Also, in the corners, I was riding almost like a two stroke. I would enter the berm, rev it up and let the clutch out and then take off from there. :laugh:

 

[Rich Rohrich]

If the power compliments your riding style then you likely have the right mods for you. These bikes are so good stock it becomes apparent that unless you plan on making a living with the bike, mods are more to increase the enjoyment you get from the bike than anything else. It sounds like you have accomplished that , so your money seems like it was well spent. ;)