Different cams for fuel injection vs carb?

casper

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San Diego, CA, USA

casper 2/9/2014 - 7:43pm

2/9/2014 - 7:43pm Edited Date/Time 2/10/2014 10:52am

I have a 2009 kx450 and my friend gave me a hotcams stage 2 intake cam from his '08. The box said it was for 2006-2009 kx450 so I put the intake cam in with the stock exhaust cam. The bike ran fine, and I finally decided to get the stage 2 exhaust cam so the 2 hotcams would match. Hotcams usually has consecutive last part numbers for matching cams i.e. 2074 goes with 2075. When I went to check to make sure I had matching cams, I noticed the numbers were off and my intake for the 2008 was not the same as the intake for 2009. The big difference between the 2 bikes is the '09 was the first year of the fuel injection.

I checked on the Hotcams website and the 2 model years have slightly different cam profiles.

----------- 2009 -------- 2008
intake
Duration 250 -------- 255.5
Lift--------9.91 --------- 10.16
Center --106 -------- 114
exhaust
Duration --259 ------246.5
Lift ------- 10.16 ----- 9.40
Center ----103.5 -----94.5

I'm not an engine builder, so I was wondering why the cam profiles are different for FI vs carb engine?

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Cola22

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Brooklyn, NY, USA

Cola22 2/9/2014 8:11pm

2/9/2014 8:11pm

Fuel inject is run by electronics, as carb is run by purely straight throttle if im not mistaken. The timing for both things are different, there is a lot more that goes into f.i as opposed to carb.

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Jakes Dad

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Brooksville, FL, USA

Jakes Dad 2/10/2014 3:56am

2/10/2014 3:56am

High lift short duration is for bottom to mid power. Longer duration more mid to top. FI bike will have better low to mid and can work more peak power by longer duration profile. Go to any aftermarket cam company Crane, Comp etc. and look in their catalog you'll see where mileage and towing cams have the higher lift shorter duration for that bottom end torque. Drag race with stall converters or circle track where motor doesn't go down to lower rpm, they'll have the higher duration profile's.