well i am looking to get a hmf slip on for my 420 rancher i was wondering if i could get away with just the pipe/slip on and no box thing if i can will it hurt anything

 

Box thing???? You mean air box? A CDI box? Remap for the fuel injection?

You might as well put on a higher flowing air filter as well. I recommend UNI, and I do NOT recommend K&N.

I would also look to see what headers are available out there, along with a muffler.

While fuel injection will compensate for small changes in the air intake, with major changes you are going to want to do a remap.

 

Because of the lean condition when adding the HMF Slip On I'd strongly suggest you use the HMF Optimizer. ...This will aid in adding more fuel which will keep internal exhaust temperatures at safe levels.
The HMF OPtimizer is a MUST in regions where ambient temperatures drop below 45 degrees.
If not...You WILL run the risk of extremely high internal exhaust temperatures which WILL burn out the packing in the muffler.
MUFFLER FAILURES ARE POSSIBLE.