Bonneville America Forums Forums Technical Forums Performance Mods Air Box mod

Just installed the "Fake Freak", aka performed an Air Box Modification. Removed the bottom cap of my Uni filter, then cut same oval hole in bottom air box. Installed some fine mesh screen to keep large debris out. Then I removed part of the wall between the two intake holes. I ran around town for a little while, seems to add some pep to the mid range. Will have to wait for a true test of top end gains and mileage change. My mileage was low to begin with. Originally the mechanic who performed the AI removal, Carb sync/balance and other misc. adjustments rejetted the bike "for performance". I had just installed my long TOR pipes prior to his rejetting. I'll see how it runs, do a plug check and see where I need to go from here.
I need to check the setup file to see what jets others with similar mod are running. Any ideas?

Bigsteve

Thats basically what i did......drilled the bottom of the airbox/uni/snorkel removal. I didn't cut or remove the restrictor tho.I think you'll find you can now rejet and get considerably more power. When i first started messing with the airbox i found that when increasing the airflow it either got just a bit more performance but considerably more once rejetted FOR the incresed flow, or it started running ragged and cutting out which meant it was in dire need of rejetting and was way too lean. You're in the middle where you can now rejet and get more gains, but it's not so lean it's developed problems like cutting out. When i was at the stage you are i found it was the needles and shims where all the power was waiting to be released after incresing the intake. I would consider more tapered needles, tho i don't know what bike you have so i can't say which. You could add shims at least and that should get you more power. But if you really want a good sized boost, try some thruxton or TBS needles. Which you choose will depend on the bike. If it's a 790 i'd try the TBS needles. then if you noticed little to no gains, shim them. Try one, then 2, etc, till you find the point where it stops responding with further gains, then remove one shim. (assuming the last shim you added gained nothing) The needles affect the largets range of throttle opening and really boosted my power in a sizable way. Mains on the other hand mad little difference all the way to 130's. I would suggest tho that you up the mains after doing those mods if the WOT position was close to correct before. Especially if it pops on decel after WOT bursts in top gears. At least thats what i found. YMMV.