I just visited DMC's Website and they claim that they gain 9.9 peak horse on the YFZ, and they didn’t rejet at all. They are saying to run this system, take off your airbox lid, and never touch the carb….umm? Survey says….how does the thing even run without rejetting for that much hp??

 

yeah, I bet it runs ... but VERY hot. Mine was pretty lean from the factory. I cant imagine running it without the lid and free flowing exhaust. thats just asking for a meltdown ... I wonder if there factory and dyno are at 10000 feet. LOL

 

Most pipes are advertising 10 hp gain in general for the yfz, I don't know if they are re-jetting/removing box lid etc....but I'm running no lid no baffle w/ stock jetting and I''m rich...I'm 4500 ft elevation....and I've talked to other yfz owners here running stock jetting w/ pipes saying it runs great......So I guess it depends on what elevation they dyno'd the dmc.

 

how much horse power does a YFZ 450 stock have ?

 

39 hp give or take a few, due to elevation

 

You wont read on a dyno more HP from elavation.

I think that when they say peak they add the bottom mid and top together unstead of dividing them together. Plus you would be running so rich ince they come like that from factory