Bonneville America Forums Forums Technical Forums Performance Mods Question about cams.

I'm about to order the Wiseco kit...thinking I should do cams too whilst I have it apart...anyone have any experience with British Customs' Stage 1 or 2 cams? or any others?

Might be worth the wait to see what Thunderbike comes up with on their cams. In fact, I think they should be coming out with something soon for the 790cc motors from their past posts. They first went with cams for the 865cc motors, and said they'd do the 790cc motors next. Anyone checked on this lately?

I think for the money better carbs might produce about the same results in increased horsepower for less money. If you can wait, it'd probably be worth it to see what Pat and Matt end up with on their dyno runs to see what direction you might want to go. I believe Pat said he was going to dyno his bike after the Georgia Rally in May. Matt has the Amal carbs that Brent will be selling soon.

I have a set of the MegaCycle cams I am going to put in my bike too. I would really like to dyno it first though, maybe this or next Wednesday if it's dry enough to get to the Hawg Barn. I really want a comparrison to see if they really do add what I am looking to add.
By the way, the MC cams come with a complete timing sheet with every possible spec you would ever need to know about the cams timing, even lobe center º's. Cool stuff.

Pat, what are you doing about valve springs with the Megacycle cams?? Keeping stock, or have you found replacements somewhere?

The stock springs are fine. These cams are supposed to be a simple bolt on replacement, no springs or valve work required. Maybe just a shim here or there to readjust the clearances, but that's supposed to be all there is to it. I was told that they are the farthest you can take a cam on these bikes without reworking something. And they are made special for a 904 Speedmaster. How convenient! We'll see.

Oh, and let me add this too, I have been talking with some of the other racing bonneville guys and have been told that we can simply put another intake cam in the exhaust cam spot and gain a good deal of HP. Seems simple enough, and the price of a stock cam is a lot less than custom grinding cams.
Don't say I never told ya any of my secrets now.

cool...and it makes sense, too...stock 790 intake cam is .380 lift and .248 duration and exhaust is .366 lift and.247 duration...so using an intake cam for exhaust will give some decent lift increase and just a tad duration...

Sal, wait for the thunderbike guys to post their dyno run with their new cams. Graeme at Thunderbike has been e-mailing me whenever he gets updated on their progress........Angelis

From what Pat is saying in his second cam posting, it would seem that the 835cc engine guys could install two 790cc engine intake cams and be way ahead in the game, both in performance and cost!

NOTE: Remember that 270º and 360º engines take different cams because of the firing order difference.

I'm wondering if the timing alignment mark on the intake cam being used on the exhaust side, should be used, or re-positioned?

Just cause a different cam can open more and for longer does not mean the stock head can flow it.Also, on the street it's all about flow velocity, not volume, unless ya want a dead dog til you really get rolling. Racers use the throttle different than steet people do. It's either all the way open or all the way closed, totally different than street driving.Careful or ya will turn your street bike into a dog, it's a very fine line.What works for racing real well seldom works very well on the street. Vegas

PapaDean, I was wondering the same thing about the timing mark on the intake cam. Let me know if you find out any info on this........Angelis

What Vegas is alluding to is that in a street motor, making mods to increase the volume of intake flow could possibly kill the lower rpm port velocity. That would mean less cylinder filling, thus lower HP readings at lower rpms, though higher rpm power should be better. (And, lower port velocity mucks up the carb's ability to meter fuel properly. That's why "real" carbs have accelerator pumps!)

Add to that a "bigger" cam (longer duration and more overlap) and the problem of loss of low end power is exaccerbated.

Shades of those 10,000+ rpm crotch rocket 600 cc 4 bangers.

As for cams, though, IMHO, any custom grind for a Hinckley twin, which can get away with using stock valve springs, is not too big for the street.

One other note: Overall gearing of one's bike makes a big difference in what one can do for mods to his engine, and get away with. That is to say, if you're trying to pull an 18 t. sprocket, you're going to need more bottom end power. But, if you "gear down" to a 16 t. sprocket, bottom end power (lack of, actually) becomes less of a problem.

This whole area is a lot more complicated than I care to address here, but suffice to say, a nice mild custom cam, some port work and bigger intake valves, increased displacement, opened up exhaust system, and better ignition output won't kill one's street performance.

This comment deserves a separate post. What's really needed for these bike engines is what is being done with smaller auto engines these days: variable valve timing.

You get the best of both worlds with this: better bottom end power and throttle response of a "smaller" cam, AND, better top end power of a "larger" cam.

Or heck, even what Honda's got going on the VFR. Not a true VTEC, but still, keeps only two valves operating below 6400 RPM to get that high gas velocity for torque, then above 6400 lets all 4 valves operate to give mass air flow for top-end power. There were two or three good articles on motorcycledaily.com about this.

By looking at the cams, there are actually both timing marks on the cams. One side is labeled E with the little lines and the other side is labelled with the two dots. I may have that reversed but you get the idea.
I was told to just line them up with the marks as before, just using the backside as a reference. Does that make sense? If you had it apart and in front of you, you would easily see what I mean. I am going to take another one apart tonight and will flip the cam and post a picture if I can hold off on too many brews and remember to do this. I will also fit the MC cams in and try to get a picture for reference of the fit on them too.

This will be a very interesting post, Pat. Thanks!

I'm guessing you had too many beers?

Naw, my stupid camera got all the shots, but wouldn't let me download them at first, but now it did. I also got some others that are pretty weird (big surprise there eh?).
I will try to get them posted tonight, i've been busy after work.
By the way, we got Jaymo's top end off his bike and ready for the machine shop in less than two hours. We're getting good at this. I can just sit back and point and my assistant, Matt and biker, do all the work. Jaymo opens beers and tells stories. Fun for all. i have a great picture of these guys hard at "work". I'll be sure to post that one too.