Bonneville America Forums Forums Technical Forums Performance Mods Cam Talk

Hi all, for some time now I've been intrigued with the discussions regarding cams. For instance I have read and it appears many agree the 790 cams are better than those on the 865's. The thing is, why did Triumph change them if they had it right in the first place?

Like, what makes the 790's a better cam?

Personally I prefer to ride with more mid range torque and when I need it, or just because of the thrill factor, a blip on the throttle to get up and go is always brilliant.

Anyway, can anyone tell me why the 790's are better and how do they effect performance? Also, is there any down sides to changing cams as I'm only looking for improvement.

I also read the TBike cams are similar to the 790 cam profile, is that true? Then there are the other makes where there seems to be some doubt on exactly how much better they are etc etc. Certainly, I wouldn't want to fork out the bickies unless I was absolutely certain the investment in extra "fun factor" was worht it.

My reason for asking is, there have been comments that suggest boring out an 865cc motor isn't really worth the extra money and time however, different cams and some head work, and particularly increasing the compression ratio is worth every cent. It makes sense to me as 39cc's extra really isn't big time now is it?

I know all these factors have probably been covered in other threads over the years but sometimes it's a matter of reading between the lines to understand the answers I'm after.

The other area I'm interested in is, the use of some kits with needles that have the circlips to raise or lower them much like a shim.

At the moment I couldn't be happier with how my bike is running but much like being a drug, getting the tweak factor to optimum is always in the back of my mind and considering my last dyno had me running just a tad rich, I was thinking maybe there was merit in it as an option. So any experience on this one would be great also.

Thanks to anyone who can pitch in here and clarify these two queries which I must admit I've been meaning to ask for some time.

cheers

stacka

ps: to any pommie cricket lovers out there, "go the Aussies" )

I can only speculate on why triumph changed the cams on the 865 motors, but I would suspect that emissions were part of it. On the 865 cams the lift is substantualy less and there is no overlap.
While the 790 cams are superior to the 865s, The t-bike cams are not the same as 790s. somewhere, I think on the ratnet the 790 cam spec are posted. I measured up my t-bike cams before installing them and they are not the same as the 790.

that covers half your question (sort of)

I believe I read somewhere that when the displacement was bumped up to 865cc they had to put milder cams in for emission compliance. the Thunderbike cams are also a new set of cams where as the other companies regrind your stock cams.

Staffo,
I'll toss in a few of my observations here.
I am currently running with the Megacycle Medium Street grind cams in my 904cc, 2003 Speedmaster. These were purchased from a vendor that got them in some trade or whatever from another member that no longer has his bike. Don't know the whole story, but the deal was too good to pass up.
I have run dynos before and after and it seems that the torque is a mere 2 ft/lb higher and more consistent, but with a drop, again a mere 2hp, but a drop none the less in the max hp. I personally love the way it feels when I get into it with the throttle. It seems to pick up speed a little quicker and keeps pulling all the way to the red-line in any gear. No hesitation or stumbling at all in any gear at any throttle position. The big question would then be..."Is the US$800+ cost to swap your cams out with MegaCycle worth it?" eeh Not at the regular price I would say. But, I got mine for less then half that so Yes, then it was a good deal and worth it. Besides, i also sold my stock cams and that basically covered the cost of the MC cams.
I have no experience with the T'Bike cams, but I would assume that they are worth every dollar as T'Bike is some pretty smart mofos and they deserve the respect and $$ they ask for their products. (Boy I wish they made their pipes in Stainless though...another time another thread)

The needle jets with the c-clips..I have a set of them and I will send them off to ya to play with if you want. I am not sure exactly what brand they are, maybe the DynaJet ones. Not sure since someone took them out of their 02 America and gave them to me and I don't really have a need for them. I figure that once you get the needles and shims right, what difference does having an adjustable needle position make? Anyway, send me your address and I will look around in the garage and send them off to ya, play with them to your hearts content. Buy me a nice cold VB and drink it for me since it will get warm before I get there to enjoy it.
Cheers!

Stacka, most of the value in a 904 kit comes from the better pistons, rather than the 39cc displacement bump.

If I had to rank the cams, it would go:

1. TPUSA 813
2. T-bike
3. 790
100. 865

If you do any of the top 3 cams you're going to be very pleased with the performance, fair dinkum!

Well, what great comments guys and Starting with Mags, it looks like the other blokes agree with you buddy about Triumph changing the cams for emission control reasons and you know what, it makes perfect sense. IMHO, the euro zone has taken up the mantle as being one of the toughest regions on emissions so it doesnt surprise me one bit this was the motive for change. It's also music to my ears as now I have an excellent reason to use this option in the future. So thanks Mag Man, you've helped to convince me this is a good way to go down the track.

Thanks for your reply Jay, you've helped to reinforce the opinion they were changed for emissions reasons. Also I wasn't aware how T-bike did there own instead of exchanging. This is important to me as my cousins over the ditch in Kiwi Land have a favorable exchange rate compared to the Aussis. Certainly means a considerable difference in cost vs the $AUD. cheers

Hey Pat, that's certainly one of your longer replies and I appreciate your opinions. Seems other than cost I can't really go wrong with after market cams can I, particularly how you explain it increased your torque by 2 ft-lbs and the steady and consistent acceleration. I wonder what diff there would be between the 865 and the 790 cams???

Regarding the circlip type needles, I appreciate the offer to send them over but I have a pr myself I've never used. I was just picking the brains just in case. Looks like they'll stay unused but just wanted that one covered so I could move on one way or the other.

Now the important subject. How do you know about VB? Believe it or not it's my beer of choice and has been virtually since day dot. Personally whilst I don't mind the "Gucchi" type beer, IMHO ya can't go past the VB as a thirst quencher. So at least you have some taste

I didn't dog-pile on the emissions thing, however I would also add noise control to the list.

The 813's increased the noise a bit, both in valve train noise, & exhaust (when the throttle is opened up).

Glad to help out Staffo. I was hoping the Kiwis played nicer with you Aussies than we Yanks do on shipping and exchange rates. If cost is a concern you could also try to snag a set of 790 cams off Ebay or possibly from a member here who has set laying around. I would hate to see what it would cost to have to ship your cams here to the States and back.

Yeah I don't think the 813's are an option really. Probably be looking at the T-Bike's with the Kiwis only being across the ditch with a good exchange rate too.

I'm also a bit fussy about noisy cams, so thanks for the tip on that one Ken. Of course, if a cheap set of 790's were available, I'd probably have no probs there either.

I've virtually decided I'll be keeping my Ferdie now. Next to my missus He's my best mate, where we've had some great times together. He just does everything I want and more. Plus I've still got heaps of plans for more tinkering.

Thanks guys. I'm pretty sure I've got a direction on cams now. I'll be posting more questions on other performance questions soon too

Staffo,
VB was my favorite choice of cold brew when I spent some time in your beautiful country many years ago. I traveled the entire country for many weeks by rail pass, climbed Ayer's Rock, snorkled the barrier reef, cruised the reef out of Townsville, crossed the country on the India Pacific, laid low in Perth (My favorite city in the entire world), hung out in Sydney for a few weeks, hung with some other travellers in Melbourne as well, great city, drove all around the entire Tasmania island, followed Hunters and Collectors by coincidence and saw them about 6 times. Those guys sure could party.
Drank tons of VB. Didn't care much for the other local brews, too light for my tastebuds. You know why they call Castlemains XXXX? Queenslanders can't spell beer.

Gee Pat, you've seen more of Aus than I have, but at least I'm now working on that one

Anyway, I'm glad you enjoyed yourself over this way and hope we treated you well which I'm sure is true. It better have been.

My next major ride I'm planning is Tassie. In fact my most favourite image in the whole world just happens to be " The Map of Tassie"

I'm just not sure I'll be able to organise a riding buddy given how hard it is get all the moons aligned so I'm thinking I'll probably end up going by myself. In fact I really enjoy doing my own thing as I've been riding up to Queensland twice a year by myself for a few years now and have found the inland country people are salt of the earth folk where I never feet out of place or isolated. I guess by myself I'm not looked as a threat and in fact many times I've found it hard to get going again after stopping at milk bars for coffee etc.

I'm with you on the xxxx thing too. Perhaps it's an acquired taste but after living in Toowoomba for 6 yrs during my Army days, I still needed more acquiring time.

Btw, my son was recently posted to Townsville at the Army Barracks and I'm thinking besides riding up to north of Brisbane for my daughter's engagement party in January, I might just keep heading north after it to see him up there before he's deployed to Afghanistan mid year. It's a bit of a ride but I want to tick off as many boxes as I can before I'm too old to "Tick" anymore if you know what I mean.

Thanks for the yarn Pat. I like hearing of others exploits particularly when one of my favourite topics (VB) is mentioned.

Query:When you change 865cc stock cams over to a set of 790cc bump sticks, apart from the intake upgrades, are there timing, ignition changes that need to be made as well in order realize the performance gains? If you know, then by all means, chime in...thanks

You don't have to change the timing per se just because of a cam change. If you have or get a programmable CDI, you can play around with your timing, many on here have the programmable one from Procom and say there is power to be had just with the timing alone!!

Thanks Jay. As a matter of fact, my store of choice is FES. Eddy is fantastic and someone I consider a mate of mine. We haven't spoken for a while though but now with winter coming on he might have a few minutes spare etc.

I know Thunderbike have a good reputation over your way but I'm still trying to work out how much value for money they are. Btw, they wrote back and told me the shipping cost was incorrect and a glitch in their website.

Anyway, I'm sure there is someone near where I live who will be able to work on my head (what ), and do a good job.

I have plenty of time to decide what's good bang for my buck but gives me trouble free power.

As it stands it appears good cams are important, and a free flow head which maybe comes with different valves. To be honest I'm pretty confused at the moment and would just love someone to itemise all the things that would work well without being too much trouble.

For instance, boring out an 865cc doesn't seem to me to be good value, but who would consider +$1K good value for high compression pistons.

So yeah, lots of consideration in there, that's for sure. At the moment I'm a sponge though.

On the TPUSA 813 cams. I was wondering do the bikes run clean enough to pass emissions with carbs set up right of course? I live in the only state in the country(I believe) that makes bikes pass emissions each year after they are 5 years old.Also how long really does it take to get you cams back after sending them off to have them welded up and machined? I do not want to have the bike down for four or five months. I would really like to go for this mod when I get the money,but I got to be able to get it through emissions so I can ride it on the streets.

mag10 I may take you up on your offer. I have a couple of logs in the fire right now,so it may be a few months before I can actually do this. I do like your idea. I did not actually see an email address for you under your profile.