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Discussion Starter · #1 ·
I've got a speedmaster as a spare bike and totally dig it but find its underpowered for what I'd like.

Its a great bike to ride and feels very "surefooted" which I also dig, though I might get some different rear shocks.

Theres gotta be some way to pull another 20 or so horses out of the motor, can anyone out there offer me any advise or clues on how to go about it ? I 've heard as well as bigger bore kits theres a few carby jetting tricks - the bike still has 1 year warranty left its only travelled 1500 klms but I'm ready to modify for the extra horses regardless.

...trumpee99...
 

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Discussion Starter · #3 ·
speedmaster motor mod

Thanks for that - can you tell me, what other bigger bore kits are available and who makes 'em.

904 is only 45 odd cc larger - maybe a kit is around at approx 950 ?

Is there a cam mod that can be done or any aftermarket mild cam available that gives it go without making it run too lumpy or is it better to just give it more cc's and better carbs...

trumpee99
 

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IMO the best bang for the buck is to ditch the airbox and replace the exhaust, & tune the carbs. I consider that to be mandatory. But that won't get you another 20. Then cams. Then headwork. Beyond that your talking relatively big money, & if you do a big bore, you still need the cams, headwork, & maybe new carbs. 904? That seems too much work on a 865 for too little displacement.
 

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I'll weigh in here because I have actual experience with this...

my bike was a 865cc and now it is 904cc w/ a Wiseco kit, and I'm using the HSR 42mm carb kit from Bonneville Performance, along with some head work. It runs great, the compression is higher than stock so even though the displacement gains aren't that much, the compression is where the benefit is. Plus, the Wiseco pistons have bigger valve pockets that allow for the larger valves that I have installed.

I'm still running the stock 865cc cams, and it doesn't feel lacking in any way. I'm sure there are benefits to be had w/ different cams, but I'm still waiting on that purchase. Too much uncertainty and secrecy w/ cam specs.

The thing runs like a banshee! I wouldn't go back if I could.
 

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Discussion Starter · #7 ·
speedmaster motor mod 2

Thanks for the info - heading in the right direction.

Thats a seriously cool looking black bonnie you got there - anyone in Australia got one like it ?

trumpee99... heading for a blat attack...
 

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Like stated before, ditch the airbox, put pod filters on there(individual K&N) and put some good pipes on there, then jet it to run right. You may want to port match the head and swap cams in after that.
 

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...I'm still running the stock 865cc cams...
All other things equal, a bump in displacement has the effect of taming cam specs. The stock 865 cams are incredibly mild. I think proper cams would take your bike to a 'nother level. Right now from my perspective that's your limiting factor.

I would wonder what your opinion would be if you did the 904 kit & nothing else (although that would be foolish) how it would compare to a stock 865, but we'll never know that because other variables are in the mix.
 

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Take it to a place like this...

http://www.cylinderheadshop.co.uk/

The cylinder head/valvetrain is the heart and brains of the engine, intake and exhaust being supporting members.

No matter what you do performance wise, this cylinder head work - Multi angle valve and seat grind, porting, valve shrouding, combustion chamber shaping and flow, and so on, is an absolute must, and an obvious start-point.

Without a proper lift, proper duration performance camshaft, you will never see the full potential of the engine.

Think of your engine as an air pump. Draw the maximum and precise atomised air/fuel mix in, compress it as much as reasonably possible, ignite it thoroughly, experience the benefits of maximum/efficient power, then exhaust the spent gases quickly and efficiently. Repeat as necessary.

The above cannot be done efficiently without cylinder head work, and proper gas flow testing and results.

Once you know the precise gas flow results of the headwork, you can size the required carburetion, re-jet, and have a custom, properly engineered and shaped exhaust system manufactured by experts in such fields.

Also remember that unless a properly balanced program of performance enhancement is considered, you may end up with an unreliable, dangerous, and tempermental bike. Think of yin/yang - and the old adage...to every action, there is an equal and opposite reaction.

Suspension, brakes, low end strength, transmission strength - all must be carefully considered and calculated before starting in with any major performance enhancements.

You also need to consider what YOU want. Loud and rude? Efficient? Better handling? Better reliability? Strictly Street riding? Long Range Touring? Weekend track racing? Dragster?

All have different approaches, different results, different methodology. The first step is always the toughest - Decide on what YOU really want as an end product! Then devise a reasonable plan on how to get there.
 

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Discussion Starter · #12 ·
speedmaster motor mod 3

yeah should've mentioned earlier its had the mandatory airfilter madaz pipes and carby tune done by the dealership since new. This was sposed to give it another 6 or 7 hp - glad I got at least that done or I would've had to consider goin' back to wearin' tweed.

The Duke I got I had the original pipes modified and it growls real good, can't say the same for these madaz pipes I'm thinkin about pullin' them apart and chopping say for starters about a 1/3 of the baffle out so they don't sound so "corked"

Like I said earlier I really like the look and riding position of this bike, and for a cruiser it handles great in tighter round town riding - just gotta get it the more horses it deserves.
 

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All other things equal, a bump in displacement has the effect of taming cam specs. The stock 865 cams are incredibly mild. I think proper cams would take your bike to a 'nother level. Right now from my perspective that's your limiting factor.

I would wonder what your opinion would be if you did the 904 kit & nothing else (although that would be foolish) how it would compare to a stock 865, but we'll never know that because other variables are in the mix.
going from 9.2 to 1 comp. ratio to 10.5 makes alot of power by its self .pluss 865 has junk cast pistons.you gain alot more power then you think. more so then doing a cheap port job.The cams that are out there for these motors are kinda un proven .yea the older 790 cams are better. I would say the 904 kit if you do the work is more gain for $ than most of the other stuff left after air box and pipes.big carbs,and major head work with over sized valves cost big $.
If you have not done a 904 kit maybe you should try one and then you will know the true deal.
 

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Discussion Starter · #14 ·
Will these older 790 cams fit straight in, and are they suited to improve performance with the stock valves - maybe with a slight timing shift ? ?

I'm thinking 904 kit / 790 cams combo and maybe re jet the standard carbs = approx 20 hp maybe a tad more.

Further, modify the madaz pipes so they make enough noise for others to know you're in the neighbourhood.

Didn't say earlier that I find at 110 kmh or 65 mph as it goes now it lacks too much if you wanna overtake or give it grunt, especially when 2 up and no, my missus ain't fat - she couldn't dance like that if she was...
 

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a stock bonnie puts down ~50-55hp at the wheel, add some pipes etc and that number gets closer to 60-65hp. A 904'd bonnie should be around the 70 mark, and add some flatslide carbs, maybe some headwork, etc and it should be 75-80hp.

these are just ballpark numbers, some make more, some make less.
 

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...If you have not done a 904 kit maybe you should try one and then you will know the true deal.
Living large is on my to-do list. Don't get me wrong, I'm in favor of the 904, & I like higher compression, however if I'm going to go to the trouble of digging inside its gonna be a stroker.

I understand that initial feedback has been favorable with Thunderbike cams in the 865/270 motors. I'm thinking that might be my first internal mod.
 

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Living large is on my to-do list. Don't get me wrong, I'm in favor of the 904, & I like higher compression, however if I'm going to go to the trouble of digging inside its gonna be a stroker.

I understand that initial feedback has been favorable with Thunderbike cams in the 865/270 motors. I'm thinking that might be my first internal mod.
Looks excellent, very impressive gains across the board, low end power you can use on the street as well. See Dyno chart - hard to read, but if ya' squint a little you can see the straightforward improvement #'s, especially with the reworked heads, etc.

http://www.newspeedmaster.com/html/high_performance_cams.html
 

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Living large is on my to-do list. Don't get me wrong, I'm in favor of the 904, & I like higher compression, however if I'm going to go to the trouble of digging inside its gonna be a stroker.

I understand that initial feedback has been favorable with Thunderbike cams in the 865/270 motors. I'm thinking that might be my first internal mod.
Well the cams maybe be better but they wont tell you up front what the cam specs are ,are they any better then the older 270 790 cams? I do know the flat track boys run the the 790 cams.
If you go with a stroker you wont have to worry about ft/bs on low end they will be there even with the cam you have.below 5000rpm wont mater you wont be there long enough to worry about low end.6000RPM TO 8000+ RPM is where these bikes make the power.If i hit mine in 1st gear at 2000 rpm it bounces off the rev limit amost quicker then i can shift it and will not drop much under 7000 rpms till i get scared and let off in 5th gear.mine is a 360 989 with stock old 790 cams.
 

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Good question, I don't know yet. It could very well be that the 790/270 cams may be optimal!
Yea i dont know ether and it cost alot to find out.Wish we could find a cam grinder that wanted to sell cams for our bikes that would regrind them with out chargeing the crazy prices the guys sell ing these cams are getting.You can buy a new full blown race cam for a V8 car motor for what some of these guy charge for a reground stock cam for our bikes and you have to send them your cams.I think the tb cams are new cams arent they? but i think there way higher then the regrinds arent they?
 
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