Bonneville America Forums Forums Technical Forums Performance Mods MegaCycle Cams installed - Review

Me to
Nick

Hey Dinqua do you know the specs for the 900 Thunderbike Speedmaster/Scrambler cams?
T-Bike thinks it's a big secret, that they will not share with the forums, unless you buy a set, but are willing to advertise their impending availability and performance on this and the TriumphRat forums.

Cheers.............Agro

Agro, I've followed your dialog with RCV on the rat.net with no small amount of amusement. For what it's worth, my bike came with reground camshafts already installed, so in effect, I HAD already paid for the cams, and even then the dealership wouldn't tell me the specs on the cams! The speaker's opinion was that as soon as the specs were out on the street, people would be flocking to make their own cams like that. Since I can't exactly hold a gun to their head to extract the specs, I just hung up on them so that I wouldn't say anything that I'd regret.

Update on the Thunderbike 904cc big bore cams is that they tested grind-A, and found that they didn't have the desired results. So they will be testing grind-B & grind-C in the next week hopefully, these have more lift, duration and different timing.

Hey Dinqua, when are you dynoing this combo?

I will try to get it in this week. I need to get it done before I put on the Mikunis.

Ok, finally got around to dyno the megacycle cams.
The verdict is: Not worth the $$.
I have a printout, but the torque didn't print the curve (the printer he uses is old and only prints in one color now) and my scanner and digicamera are both dead. I will eventually post a shot of it.

I went from 76hp up to 77.9 hp. The torque went from 59ft/lbs to 57.6 ft/lbs. A slight loss of torque.
The dyno curve is still very nice and properly shaped, but the torque did drop off a little bit. And for the price, 2 hp ain't worth the big bucks.
Just my opinion though.
But at this point I will leave them in, unless one of you want to give me $550 for them??

So ya gonna try the Tbike vcams then?

Dinqua,
A quick and easy fix to get back your torque and more power with these megacycle cams you have installed, is to advance the megacycle exhaust cam 1 tooth, thereby opening & closing the exhaust earlier, reducing the overlap from 42 degrees to 27 degrees.
I advanced the Bonneville exhaust cam by 1 tooth that I had fitted to my Thruxton engine.
Trust me it works, got my bottom and midrange back and more.
I have a dyno simulation program and inputed the 790 SM cam specs, 790 SM intake retarded only & 790 SM exhaust, megacycle cam specs, megacycle intake & advanced megacycle exhaust.
The megacycle cams make about the same hp as the 790 SM cams but with a loss of torque. The adv. intake 790 SM, 790 SM exhaust makes similar torque and hp as the megacycle cams with the exhaust advanced.

Cheers..........Agro

I've read the thread over at the Delphi forum with your simulation program, and I was just wondering...in order to advance the exhaust cam one tooth, do you rotate it clockwise or counter-clockwise?

Good question!

You would rotate in direction it turns to open later, the other way for sooner. So you'd rotate it back a tooth to advance, right? Would this help with stock cams or would you just burn valves?

To advance the ex cam, should turn 1 tooth clockwise when looking at the timing marks from the l/h side of the bike. This works well on the 790 America/SM, with boost in torque in the low and mid range. This reduces overlap from 24 deg to 9 degrees.

Will not work on the 865 Speedmaster because their is no overlap, in fact both valves are closed for 7 degrees of crank rotation at TDC!! A side benefit of overlap is that cool intake charge flowing over an open exhaust valve assist in cooling the exhaust valve as well as scavenging the cylinder of exhaust gases.

Cheers...........Agro

So you're saying that anyone would benefit from a one tooth rotation?

Only the 790 would benefit and cams with lots of overlap like the megacycle grinds Dinqua and Roundslide posted, not the 865, it is a free mod if you do it yourself, if you dont like it, you can always return to stock timing.

But I mean anyone with the 790 would be cool with it. So weird the wussed out on the 865 cams...

Would this mod be similar to people who put an exhaust cam on their intake, or visa versa?

Well SCCTrim over on the rat.net tried this last night, he's got a 790cc bonnie out to 904 with some headwork. He said that bike felt alot more responsive in the mid-range up to about 6000 rpm or so. I want to get my bike back on a dyno, with the exhaust cam in the standard position, then advance the cam, and adjust the jetting as necessary, and then back on the dyno for a comparo.

That would be sweet! I can't see myslef finding time to do this anytime soon, but maybe for a spring project. I know it won't take long, but I rarely have two solid hours together lately, and I have a lot on my plate right now...

790 Exhaust Cam Mod Thread @ the RAT.net

Benny here is a link for intake, intake simulations.\

http://forums.delphiforums.com/acecafe/messages?msg=1240.16

So you guys are also considering an intake cam in the exhaust position then. Not just the exhaust cam advanced one?

From what I have read, installing a intake cam on the exhuast side ...( rotated 90* )...is purely a topend deal.

Something that would be far more suited for the track rather than the street.