Bonneville America Forums Forums Technical Forums Performance Mods Explain performance results

I see where members have installed the big bore kits and posted the dyno results. Yes, there is an increase in h.p. and torque, but how does this translate onto the street?
Has anyone seen elapse time results of 0-60mph and the 1/4 mile between stock and modified? Those results would better serve in my decision on wether to add the big bore kit or not.

Stock motor = nice ride, reasonably quick. 0-60 in about 6 seconds.
Wiseco 904cc = nice ride, mucho quicker, more torque for big butts, 0-60 in about 4 seconds, arms stretch more as well.

The biggest difference I felt was going up hills, it is now effortless even with all my "weight". No more downshifting either, just crack throttle and vrooooooooooom up the hills.

The bike is faster, but the torque is the main advantage to the 904 kit. There are a lot of us with them in now and more everyday. maybe someone would let you take theirs for a quick spin so you could actually feel the difference.
Ask Phil, he rode mine and went out and had his done. Once you ride one with the BB kit, you will be taking yours apart .

Pat, do you get most of the benefits of the big bore kit, with stock carbs, cams, etc. on the 790? I'm kinda waiting to see if Triumph comes out with a larger twin cruiser. If the new bike doesn't do it for me, the big bore kit moves to number one on the list. I love my bike, but who wouldn't want more torque, not to mention a little more hp.

The difference is huge when compared to stock...when I had my motor work done and picked up the bike it felt like a different machine...I rode like this for a while.


When I added the hsr carbs...it was the same feeling all over again.

I've also been thinking of what it would be like to do the BB but as I've got an 865, and I see a lot of blokes doing the work on their 790's, where does that leave us with the 865's. For instance we are only really talking about 40cc not 115cc difference. So my question is, is it worth it for me to do the BB? Also, what are the other options that can be done once the motor is apart, like bigger ports etc. I reckon we also may be able add to the mix, mikuni carbs when Pat has time to sort them out thereby having another option for more power and torque. For me then, being able to milk all the performance out of my sm using safe and well researched options to give maximum output, would be a great goal to look forward to but I'm just not sure yet what those options are. Is there anyone who can give me a bit more info on what they would do in my situation to get the best performance? I'm not planning on doing it now but I would like to know what my options were for the future.

it is not all about cc's, it raises the compression with is always worth power, you also get a super strong forged piston which you dont have to worrie about. there are a ton of people with these kits and i never heard anything bad about them, only good things. if you want maximum power with reliability iw ould go this route. head work and carbs will help, and also if you get a better exhaust

Frank

Frank

Thanks Dinque. I talked to a guy at a rally who had the BB kit. He said it cost about $2k to have it done (parts, labor, machining etc). That seems a bit high. Did I misunderstand him?

thanks Frank, I thought as much. I'm now really interested in how Pat goes with the mikuni's because having both the BB and better carbs sounds really impressive. Certainly something to dream about and one day.....

I thought that price was out of line. But the again, having owned Harleys in the past, that sounded about right.

why not do the 1100cc kit that wisco is putting out
now, they already have the sleeves in production and
are working on the pistons now should be ready by the
last of march or the first of april for more info on this
check out the 100hp project posted at 2001+ modified
triumph bonnevilles on the delphi forums

What impresses me about this discussion is the added torque and horsepower these guys are getting without the added pounds and bulk you would get if you bought this kind of power in a new bike.

Hopefully Triumph will bring out a new Speedmaster in the 1200 range with the same weight and handling.

Somewhere along the line my other reply to this post got lost. As said above this mod isnt about the additional cc's gained, it's the increased compression ratio that makes the power. Anytime you go from 9:1.1 to 10:5.1 your going to see gains. The small increase in cc's is meaningless.

If you want a increase in cc's to make a difference, wait for the 1100 and 1200 stroker kit's to be available that are currently in development.

1200cc bonnie.........imagine that.

I'm really considering doing this. Questions my bike is brand new and has a two year warrenty.

1: What happens to the warrenty if you do it yourself ?

2: Is this a project my dealer will take on and if so would the warrenty still be valid ?

3: I have read Pat's detailed step's can any machine shop do the machine work or do I have to find one that specializes in Triumph's ?

4: In my limited knowledge of engines any time you increase the compression on the top end it will effect the lower end going from 9.1.1 to 10.5.1 with these engines would not have that great of an effect, but going from 9 to 11 or 12 I would think you would have to beef up the lower end to take the increased power.

I think if I'm going to do it I going Pat's route with the 904 BB from Brent's.

Big Poppy, I'm not sure but I'd imagine you pretty much kiss the warranty goodbye once you pop the top, at least the motor related warranty anyway. If a coil or brakes or anything else fails (not related to the big bore) I think it should still be covered though.

The dealer will probably do the work (at 60/hour +)

any automotive machine shop should be able to handle it

the bottom end on these motors is very solid, and is left alone when installing the 904 kits.

Is everyone that installs the BB kit going with oversize valves too. In order to understand the differences, I am curious about gains that would be made without installing the BB kit. In other words, how much of the total increase is each mod (head vs BB) delivering?

How much valve clearance there is on the stock 790 to allow for milling the head & improving the flow of the stock valves?

I've already got obvious stuff done, Freak, Pipes, etc. Is it not worth the effort to mess with if you don't go to the BB?

1. very few are doing oversized valves, as they aren't being produced for sale, only custom orders
2. oversized valves won't fit with stock pistons, the wiseco pistons have bigger valve pockets
3. milling the head will possibly interfere with the ability to install bigger valves

My valves were made by Manley, cost me $250 shipped, plus the machine shop is charging about $250-300 to install them.

Most people do the headwork at the same time as the big bore because it's convenient and you have to pull the head anyway, so why not?

just on the difference of opinion a couple of our fellow bonny owners have regarding "having the skills to BB", I understand Bonnyusa's preference to hire a shop to do his mods because I'm not entirely sure I have the confidence to tackle this one. When I had a look at Pat's instructions for instance, when I got to the

"WARNING! If you are not an experienced mechanic and have never pulled cylinders out of a motorcycle before, please re-consider doing anything else, refer the job to someone that knows what they are doing. If you mess these next parts up you may destroy your motor. Consider yourself warned"!

I too thought mmmm, how dumb would I feel if I got to a point during the re-build and I did something wrong just because "you don't know what you don't know". Yeah, if I could watch someone else do it first, brilliant says I cos now "i do know" sort of. Also I don't have a mate nearby who know's these motors to help me and anyway, there's nothing more satisfying than just plodding along doing it yourself right?

Which brings me to the next point. Say for instance I did embark on this somewhat unknown journey, in a take your time and if you get stuck, just ask your fellow bonny enthusiasts at the other end of the puter. Of course I'd have to have some sort of mechanical sense but as has been pointed out already, this is easy and anyone can do it can't they?

My point is, there are slightly different viewpoints on this one and given I would one day (say a year or 2) love to give it a shot just because I could, is there anyone who reckons someone like myself (just getting into mechanical stuff besides the basics) could do it assuming if there was problems, I could ask questions and then receive advice so as this thing could actually happen? That's what I would like to know but not if I was getting over my head and didn't actually know it, particularly after having "BEEN WARNED" from the guru. Nothing worse than someone getting there expectations mixed up with there capabilities is there?

Just one last thing, I am pretty much really interested in people's experiences in this one but would really prefer people respect others viewpoints even if you don't agree. Thanks guys.

Well I think its like anything. If your not 100% sure you can do it is it worth the risk?

Not to mention if it goes bad it costs a LOT more AND you lose out on riding time.

when i do mine i am going to have someone do it because i do not have the space to tear the bike down

Frank

This is the stuff I want to hear guys, both the yay's and the nay's and for whatever reason. Great to hear what other's thoughts are or were when contemplating the "BIG BB".Then I can sort of have a street map of what may lie ahead. Certainly so I'm not as confused anyway

My dealer (D & D Cycles - Pensacola, FL) has there own BB package. Rather than sleeves, they bore and re-nickel the cylinder heads. When assembled, it's just like stock but 904cc. No dissimilar metals and factory reliability. When I'm ready, I plan to have them do it. I guess I don't mind paying for the results. I do mind the headaches of tackling a job I don't feel qualified to do. This year I plan to either get the larger twin cruiser OR keep my bike and get the BB setup done at my dealer.

When that $700 fell into my lap, it was like a sign from above John!

Bonneville Performance (aka, Bill Gately) did the machine work. He was gracious enough to ship an already machined/sleeved set of jugs down here with matching parts. I basically rode to Pure Triumph with my big bore kit and there were all the new parts waiting. I did that on a Saturday. If we had not gone up to Daytona for Janet's new Corbin, I could have picked it up the following Friday morning. No problem, I got it Saturday!

Could I have done it myself? Without a doubt. Would have taken longer, I'd have learned a thing or two, been very self-satisfied, and might have spent a few dollars less. Would I do it with the shop again? Absolutely. These guys did a great job on my bike and I am very happy. As I said elsewhere, not counting the big bore I got for Christmas, my total out of pocket was $169.

Big_Poppy,

You will void your warranty on the motor the moment you do the big bore. You may actually void transmission major work if Georgia ask the dealer anything that would show major mods to torque and the possibility of metal debris.

Doing this mod on a warranted bike would be very risky if you value the warranty for the motor and transmission. If the warranty is not a big issue to you in those areas then go for it.

They will still warrant the electrical stuff, master cylinders, ect.

Pat, to keep things in perspective. After the BB is the America faster than the Magna?

LOL not even close. Those things are fast...

Look, there is no doubt that paying the bucks to the professionals would be I guess a relief knowing great, now its done and the fun part begins, after breaking in of course. Where I am, my dealer's head mechanic has on a few times frowned at my purchasing needles for instance which gives me the sh#ts. It's like "who do you think you are doing stuff to the bike, that's OUR job". Makes me think I'd love to do it myself just to prove a point, not only to them but myself. Otherwise I've been toying with the idea of getting the Sydney mob where I bought it to do it.

Anyway I'm really happy to see 2 blokes who have been there and done that and are are proud to tell everyone of their great experience.

On a side note, the thought of getting rid of (blue) my bike for "The BIG cruiser" is not an issue (not really, but sort of if you know what I mean). Being a loyal soul, even if it was just the ants pants, I just couldn't ssssss, sssss, replace it. See, I can't even say it. The word isn't part of my vocabularly when it comes to it. Mind you, the rush of buying and then changing is just the best I reckon, and I've got some real plans ahead but just need the magic moolah.

Jane's Magna is fast!

I think the Magnas were rated at 90hp stock, right? We win the beauty contest though. I came REALLY close to getting a magna a while back, kinda regret not having it. They're kinda like a mini-Vmax. The same basic motor of the old VFR750.

Good thread though guys, keep it coming.
The guys that are anyway at all apprehensive - DON'T DO IT
Those that choose to pay someone to do it, spend about a 1000-1200 or so for total work, parts included.
And for the record, for what Fill paid to have bill Gately's crew do his, I would have jumped on that!
When I did mine, shops had not really done any and were charging $2000-3000 cause it was so new. Now that the price is way better, go for it with a REPUTABLE experienced shop, pay about a grand and change, and grin for years, and know that you have a unique machine. For the old timers, remember the twin 750 kits? Hmmmm? Even Trump switched to them after awhile. How hard to find are the original 650s that have not been converted over to 750s?
Another 2¢. WISECO is THE only way to go, nuff said.
Just my opinion guys, not anyway near gospel, there are tons of guys that know way more than I do, I just took pictures and shared my experiences. Sweatmachine is just as competent from our conversations we have had, and Bill Gately, well he's on a whole new plain. I be humbled by his expertise. I wish I knew half of what he has forgotten.

How long will a BB engine last before having to be re-built?

& fast! when that motor decides to come to life...whoa!