Bonneville America Forums Forums Technical Forums Performance Mods 904 TPUSA BB kit

I seen posts on the various triumph forums about the TPUSA 904 kit adding 16hp and 8tq. Does anyone know if these numbers are the 790 or 865?

I have a 865 and would be interested in this mod.

1087 can you step in and list the numbers?

doesn't matter if its an 865 or 790....your increasing it to a 904.
The only part that would make any diff might be the cams but it wouldn't be that big of a deal.

I guess it only matters if you care about the cc/$ net increase...

Perhaps I wasn't clear in my question.

What I am after is the net HP and Torque increase of the 904 TPUSA BB kit when installed on a 865 Carb motor.

Previous post's quote 16 BHP and 8 LB TQ increase but, they never clarify whether it is a 790 or 865 (Carb or EFI).

Using the numbers listed from Triumph Twin Power, one can easily see that each motor has a different starting point. If you where only adding 39cc (865 to 904), basic engineering fundamentals would indicate you were not adding as much as 114cc (790 to 904).

790 61bhp @ 7,400rpm 44.3ft.lbf @ 3,500rpm
865 54bhp @ 6,750rpm 51ft.lbf @ 4,800rpm
865 EFI 61bhp @ 6,800rpm 55ft.lbf @ 3,300rpm

Right Zmilin,
That is the post I was referring too.

The best bang for the buck is the 904 kit. But are those numbers starting from a 790 or a 865 (carb or efi)?

I was hopping to get 1087 to jump in here and clear that up...

Zmilin - I get a 404 error on your link.

sorry....heres the link again: http://www.bonnevilleamerica.com/forums/...true#Post385477

Zmilin - where did your research end up for you, TPUSA 865 HP kit or 904 BB kit?

After doing all my research and taking into consideration my needs vs wants....
I need more Tq (Im 300# so passing usually requires a downshift).

After talking to Carlos about the best plan of attack here is where Im headed:

I concluded the HC (High compression) kit was not what I needed or wanted. The amount of work for both 865 HC and 904 is the same (heads off, jugs off, pistons off, etc...)

Step one will be cams. I am well past my valve adjustment so I need to do that. Since Im going to be in there cams seem to make sense. I should pick up up to 3-5 ft lbs of Tq. BTW...Im going with the 813 cams for the 904 upgrade. Im hoping to have these shortly.

Step two will be carbs. IF I didn't need to do my valve adjustment carbs would be first. Carbs will give me another estimated 5 ft lbs. This is the biggest bang for the buck with the least amount of work....its a simple bolt on that will give you a Tq gain. If funds are available I might do these at the same time as the cams.

Step three will be the 904 kit. This is where it becomes night and day especially if I already have carbs and cams in place. Yes, I could go bigger BUT that requires cracking the cases. Maybe if I blow the motor or something. 904 is the least invasive biggest gains you will get period! This wont happen till after the riding season but it is happening.

Somewhere in there Ill do the ignitor mod as well.

I have considered a few other aspect of this sort of mod as well.....
I dont know of a local machinist that can do the work I would need with a cheaper Wiseco kit. I could look one up BUT its worth it for me to pay a few more bucks to be 100% sure that the items Im buying/installing are set to go from the get go with no hassle. Hence the TPUSA 904 kit.
The support I have received from this vendor before ever spending a penny with them has been stellar so that goes a long way in my book.
The history/reputation of this vendor in the performance arena is second to none. Yes there are other vendors that others will back BUT I am on the west coast so I will stick with a west coast vendor.
Cheaper shipping, reputation, service, etc... its all there.

I've got 2 questions...
1. Has anybody tried ot fit a set of these?
http://cgi.ebay.com/ebaymotors/ws/eBayIS...RK%3AMEWAX%3AIT

& 2. Why hasn't TPUSA/Newbonneville etc. came out with a bigger bolt-on BB kit for the 865 motor? 790 - 904; = 114cc

why no 981???

dont know about teh carbs but regarding anything bigger than a 904...they do have kits that go up to 1087 BUT they are not "bolt on". Anything bigger than a 904 requires removal of the motor, opening it up and machining the cases for clearance.

Zmilin,
My point exactly; I'm well aware of the bigger kits on offer. I've been hoping for time that someone would come up with a bigger bolt on, to save spliting the cases & machining. i don't think there's anyone here in Australia that does that sort of work to these bikes, maybe someone can correct me... After much study of these pages & other forums, I'm just about to fit FCR's then maybe a cam...
I'd love to fit a big bore, but it doesn't seem worth it for only a small increase in cc's; When I should be able to pick-up 100cc's for the same time & money;

Hi Dinqua,
I've sent the guy with the carbs a message to get a centre to centre distance on the head side of the carbs... I'll let you know what they are when he answers

I dunno Zdenko. Over a little while now I've come to the conclusion that there are possibly better and easier ways to produce more of the ponies and torque than by upgrading carbs. Of course I'm no mechanic and can't even say my daddy taught me as a boy either.

The only info I base my opinion on is reading these and other forum posts and stealing other bloke's experiences over time.

Perhaps new carbs if an upgrade went beyond 904, but with the standard mods I've seen here based on the 904cc bore out, I'd be keeping the stock carbs and researching the benefit of the bigger intake manifolds and their higher cfm and velocity potential as an example (I think I've got the right terminology there, but as long as you know what I mean).

I'd actually be interested in what others who have more experience and technical smarts than myself and what they thought about the potential benefits of bigger carbs vs other less expensive mods that could achieve the same output.

Of course, I'm only talking about info in Reading what others have done to their bikes and seeing their dyno results to help back up their bum dyno claims but if I've missed something, I'm all ears and would love to hear about it. It's all learning.

In trying to put the various pieces of the "power puzzle" together for myself though, and even hearing some say installing bigger carbs was just a big waste of time and money, I'd certainly need more blokes on here praising them before I was convince they were one of my priorities.

I'm cerainly not trying to rain on anyone's parade here Zdenko. I'd just want more verification that's all.

Staffo

Staffo makes some valid points. I have had 4, count em 4 different sets of carbs on my bike to play with.
Read what you will into this.
1) Stock
2) Mikuni 42mm flatslides - big $$
3) Custom made Amals that leaked like an old man with prostate issues
4) Custom made Mikuni 36mm flatslides - a very decent response from these too.

Anyway, to make a long story short - I finally got tired of playing and just wanted to ride hassle free without always experimenting with the bike so now I have stock carbs back on and could not be happier. There is a lot of room to play with these too. I dyno'd every set of carbs except for the leaking Amals (pieces of cr*p for sure).

I have a 904 big bore (stock was 790 motor), ground intake and exhaust ports (not really "Ported" just cleaned up very nicely to improve fuel mixture and flow - gotta keep a certain bit of turbulance), megacycle medium street grind cams and Thunderbike pipes/freaked.
The 904 was by far the biggest bang I got out of these mods. But then again I went from 790 to 904 which was a nice jump vs 865 to 904 (which I would think is a waste of $$ and time - go with older cams instead)
Your mileage may vary, other's opinions are what they are.

By the way, this is the order I did my mods:

TOR pipes - jet stock carbs to 130
Freak - Gutted pipes - rejet stock carbs to 160
BB - 42mm carbs - Thunderpipes
Stock Carbs - rejet to 150
Cams - rejet to 145
Amal 36mm Carbs
Stock Carbs
36mm Mikuni Carbs
Stock Carbs jetted to 150/42/TBS needles

Well, I'd have to say I really appreciate listening to a bloke who says it the way he sees it from his own experiences and from what they have taught him. No better way to learn I reckon. In this instance, Pat laying it out there speaks volumes. IMHO

staffo

Dinqua,
Got a message this morning; carbs are 5" from centre to centre engine side...

Well what I am interested in, is not increasing BHP, but increasing the torque, as that is what we mostly use on our low revving bikes, and that is what I really want to improve. So is there a easy mod other that a re-bore that will increase Torque in particular?

Cams will improve your torque, as will a better set of carbs and intakes.

They're almost 6.5 inches...
Not sure what holds these carbs together... maybe able to make a spacer?