Bonneville America Forums Forums Technical Forums Performance Mods what gains from 904 big bore kit

hi
can anyone tell me what gains I can expect from fitting a 904 big bore kit to my 05 america (790).
can I realy expect the gains of 40 or 50% bhp and torque.
thanks

hi steve, i recommend you chat with fasteddy or dinqua they are two of the best guys on the big bore kit.

A bigger fuel bill

just do it. depending on where your power is now, yes, 40-50% increase.

The 904 kit will transform the bike into a completely different machine. There is a huge and very noticable increase in the performance. The HP and torque both go up substantially. it is well worth the money to do to a 790 motor, not so much with the 865 though. Another thing to be sure to do is to have the intake and exhaust cleaned up while it is apart. getting the rough spots ground away helps the fuel flow much better giving a smoother response. This is just a bit more $$ but in my opinion it is s must do if you're already into the motor. Just don't make it too smooth, it needs some turbulence to get the air and fuel mixed properly. Any decent engine shop can do this for you.

Steve, my mates going to USA in August and bringing me back a 904.. when are you planning on doing it? I plan on mine about November when the weather turns, got lots to do to the bike.

If you do end up fitting one let me know, we can compare notes and maybe help each other out? not physically but note sharing etc.

Cheers, TrOjAn

thanks to everyone for the replys, I have mailed fast eddie to see how much it will cost to ship one over to me, hopefully less than the over 600 pounds I have been quoted here in the uk.

Don't forget the import duties and VAT that will be added and also the £8 you'll have to pay Parcel Force. That and shipping which is quite expensive for heavy items, could add quite a bit to what your quoted for the 904 kit from the US.

Absolutely the best money I ever spent on my bike. I also have an 05 America. HUGE difference. It didn't make any significant mileage difference but I did end up going from mid-grade to premium fuel. The bike seemed to run better on it.

With airbox and UNI, I'm getting 66 ft. lbs. of torque at the rear wheel. The torque is what you will notice the most. Go for it!

let me break it down for you...

pre 904 with Scepter pipes and airbox removed




post 904 with same stuff and ported head and 1mm oversized valves



even more to give with new carbs and intakes




bottom line is, the motor will make great power bored out and with some tweaking here and there

day and night difference,go for it you won't be disapointed.

I cant wait, Im in the middle of fitting my big bore now.. jugs go off tomorrow for sleeving.. its exciting YeeeHaaaa

You're exited? That's nothin'...I'm jealous!!! I Hope it turns out perfect for you. It will be a while for me.

This will just make me keep my speedy.. the extra bang will make it even better to whizz about on, should be able to keep up with the harleys now

I'll concur. The 904 kit is far and away the best thing I've done for the bike -- totally different machine now. Pulls like a freight train up to red line in every gear.

Make sure you upgrade the clutch too or you'll get slippage on hard acceleration.

--Jaeger

I did the clutch a while back, so ots upgraded, good choice I thought at the time taking a while to get my barrels back. In case anyones comparing prices I have been quoted £75 PLUS the dreaded VAT so about £90 for the barrels.

While Im waiting on them Im re jetting carbs and redesigning the airbox.

Had a few interesting conversations regarding "laping" the valves in while the heads off.

Haynes manual says you can,
Triumph dealer says you shouldnt unless its NEEDED
My mate the Triumph mechanic of 30 years says leave them alone.

So I left them, there not letting by so saved myself some work