Recently picked up a 400ex,has stage 2 hot cam and flat top piston and is jetted for the mods. Previous owner also hollowed out stock exhaust. Does not seem to have the back pressure that it needs now. So, I am looking to put and exhaust on it now. I have heard that putting a full system on a stock 400ex motor has minimal difference vs a slip on and isn't worth the extra money. But my motor is not stock. With the mods that are in my engine, should I do full system or stick with a slip on? Would like to save a little money if possible. Also, will I need to rejet again? Unfortunately I do not know the jetting specs on it, was only told that it was rejected. Also should I run with airborne lid off? I plan on hitting dunes with this and sometime I do run into a little water in the trails but never encountered anything too deep yet. Thanks in advance!

 

I'm thinking a slip on would be good. I have the same mods and just did a slip on & she runs out great.