Bonneville America Forums Forums Technical Forums Performance Mods How far can I go??

How far can a 790 be pushed? Curious about opinions on how much hp and torque can be squeezed out of these fine motors without making the jump to a 904 or beyond, or without getting into internal engine stuff. Although not disappointed with the stock output, it seems like from 'day 1' of ownership I've been spending a lot of time and $$ trying to reach the apex of what can be done. Have not dyno'd but may do so this year. My current setup so far is below. Not sure what else can be done to tweak performance, and at this point I'm way happy with the way my bike propels my 250#'s down the road. But have I gotten all there is to get?? The quest continues…

- open pod filters, airbox removed
- specialty spares short slash cuts
- 150 mains
- 42 pilots
- 1 shim
- drilled slides
- billet aluminum intake manifolds
- lots of chrome (no performance boost, but dang it looks good!!)

Possibly TBS needles, with 150 main if you are not now rich you should have upped the pilot to 45 probably, these 2 changes may require you adjust the main again. Blue print the ports and smooth them.Maybe the hotter coils and wires available although I have not tried those personally so don't know what kind of effect they have.

What about upping comperssion. I know you said you didnt want to get internal BUT removing the head doesnt seem so internal to me. Having bigger valves installed and possibly decking the head might be a way to go. Of course that is only if clearance will allow.
While the head is off you can also have it flow tested and tuned.
Then of course youd probably cross the line to getting bigger carbs. That might help now even without the above mods. Some discussion on the ratnet site has been going on about bigger carbs. At $1300 plus its costly but if you want to squeeze all the power out of it it seems a necessity.

only problem with skimming the head for compression is now its done and you cant go back. not sure how much headwork will get you on a stock motor but for the money you could do the 904 and get better pistons and i bet more power. guess it depends on your goal and how much you want or are willing to spend

Frank

Carbs with cable operated slides as opposed to the vacume we have now will give you better response but not effect HP. I don't think you would benefit from larger carbs on the stock motor but jetting is important.

I wouldn't deck the head on the stock engine either. If you wanted more compression I would check into stock bore forged pistons. Used to do that in the old 650s with forged Wiseco.

how about ditchin the chrome an anythin else ya dont need, mudgaurds,chainguard speedo ha ha.rats forever

And let's not forget, ride downhill as much as possible!

What do you want to make it faster than? Short of several thousand bucks you will not get it into the 11s in a 1/4. Just faster than itself you are already off track. You would need stock Dyno and stock 1/4 mile times. At this point you may be in the high to mid 13s.

Depending on what you want to do it will still be a slow motorcycle just not as slow.

Power is speed, speed is measured in time. 1/4 times are what its all about. What was the 1/4 time stock and what is it now? Then, where do you want it to be?

How many hundreds of dollars per .1 seconds are you willing to pay?

Just use your seat of the pants dyno and play around with it. I think your pilots should be 45s then you can twist in a bit on air fuel. They run all the time not just on decel.

You are pretty much done. Cams, heads, and/or big bore are all internal and you already discounted that.

In the day skimming the head to raise compression was always a cheap performance booster and to de-skim they just used two head gaskets. dont know if this is possible on the new bikes though
Blessings

It is possible to bore and stroke the engine to around 1100 CC, but it requires an aftermarket barrel casting and machining the crankcase. There is a guy in Sweden that is getting well over 100 HP from one that he races, but I doubt it would be much fun as a daily rider.

And remember, less weight = free HP.

Soooo, Greybeard, I reckon you're saying I will speed up if I drop a few dozen lbs!!

I've added Freak, and done carby mods to free up the engine so it breathes and performs as it should.... And I keep telling myself "It's a Cruiser"
"I BOUGHT A CRUISER"

What do I do on a cruiser, well, um, well, er, CRUISE!!!!

Well said Michael, I agree entirely. Mind you I now have my speedie pretty close to where I want it ie: Tors, K&N pods, drilled slides, 150 mains, stock needles with one shim and to be perfectly honest she has never run so well or strong.

Ok so now that I am happy with the "performance" so to speak, I too like to cruise around BUT at the same time I can get her to GO when I want to. It's just nice to know I have got what feels like those few more ponies when overtaking on the highway for instance or to get myself out of trouble if required. Of course now and again I'm not averse to letting her go from the lights just because I can