What is the lift and duration of the xr400 versus 400ex cam? How does the xr cam compare to the White Bro's cam? Is WB selling xr cams packaged in their name? That is what they did with the rev boxes.

 

some told me that with the following a 400 can do 88 mph
-slip on pipe
-K&N filter
-correct jetting
-porting
-3 angle valve work
-xr 400 cam
-Polishing the inside of where the exhaust somes out both in the headpipes and in the engine to match exactly
-and with correct gearing


BS or not?

 

For both 400EX and XR400 stock cam spec are as follows: Intake Exhaust
Valve Lift .327 .320
Duration@.040" 236° 234°
Lobe Centers 107° 108°

Ref: Megacycle Cams
90 Mitchell Blvd
San Rafael, CA 94903
415.472.3195

 

So, what you are saying is that the xr and ex cam are the same? Why are all these guys saying to use the xr cam? IF they are the same, they are wasting their money. What is the deal?

 

Hmm, the XR cam is differnt as Honda even stated so when the EX came out. I vividly rember honda stating that only the pistion, Head and cylinder are XR copys and everything else is beefed up for the EX. I know my friends EX has alot more torque than my XR400R does.

 

Well, according to my 400ex service manual, the valve timing at 1mm lift (.040", where on most car cams it's measured at .050") in intake opens at 5°BTDC, closes 40°ABDC, and the exhaust opens at 40°BBDC, closes 5°ATDC. This gives a duration of 225 intake and 225 exhaust at .040" lift (add 180 + opening + closing time). I can't find the valve lift ANYWHERE in the manual, but if your specs are correct for the XR cam, then it is indeed a little bigger cam (more duration) than the 400EX has.

 

Also, if you want specs on the WB cams, check out this web page (stated valve timings are at .040" lift on there as well):
http://www.motojoe.com/atv_pages/whi...engine_atv.htm

 

UPDATE ON THE CAM QUESTION!!!! Through my own research I have found that the XR and EX cams are different. The duration of the EX cam is 225 degrees on intake and exhaust. The duration of the XR cam is 232.5 degrees on intake and 232 degrees on the exhaust. I will find out about the lift tomorrow. So, to all of you who were wondering about this, here is the answer.

 

All I can say is that it made a big difference on mine, but I also put in a JE 416 piston, too.

 

What compression on that JE Piston? Do you run race fuel?

My mods are going to be exactly like yours