Bonneville America Forums Forums Technical Forums Performance Mods First Impression after Advancing Exhaust Cam

There's been alot of discussion on the various forums about advancing the exhaust cam in order to reduce valve overlap, and shift the torque curve towards the low end. Since I figured out that my cam profiles gave me 41 degrees of overlap, I had the room to spare to take out 15 of those degrees, and reduce my overlap to 26 degrees around TDC. So anyways, I had friday off, and after replacing my countershaft oil seal, I went ahead and advanced the exhaust cam one tooth. I don't have any dyno results, other than the butt dyno, but I think I can validate every benefit that's been said about this mod. The idle is smoother, less lopey, and the grunt definitely comes on earlier than before. While accelerating, the exhaust had a deeper tone, and the bike just pulled with more authority than before the mod. So FWIW, I was very happy with doing this mod. I realize that I'd probably lose some of the grunt in the very top-end, but I rarely push the tach over 6000 rpm, so I was willing to make that trade-off.

means 1
tooth forward??

Cool, keep us posted as to how it is working out for ya.
There is a lot of talk about this over in the "other" forums and I have yet to hear of anyone I know doing it.
I may try it with the MegaCycle cams too. You have different cams too if I member corectly? Can't spell, but you get the point.

Well, have over 150 miles on the new set-up, with no negative side effects to speak of. As a side note about the idle, even with the reduced overlap, the idle is much better with the manifold jumpering trick, than without. When I pulled the jumper off yesterday to check the carb sync, the idle was noticeably rougher than before.

Greg, yes, one tooth forward (clockwise)

have you got standard cams??

No, these are regrinds, based on the original camshafts, so the standard timing marks are applicable, but the lift, duration, and overlap values are different than stock. Advancing my exhaust cam actually reduced the overlap to near what the stock 790 grinds have already from the factory.

what about stock cams??

Any chance you can post some instructions on how to do this. Seems not to difficult

this is just like doing a valve lash check, except that you're not necessarily concerned with checking the shims; line up the camshafts to the timing marks in accordance with the Service Manual, pull the oil feed pipe (Taking GREAT care not to drop one of the washers down the cam chain gallery), pull the exhaust cam bearing caps, and then remove and reinstall the exhaust cam advanced one tooth against it's timing mark. Put everything back together in accordance with the manual, and that's really it.

i retarded my exhaust cam 1 tooth to increase valve overlap.
it changed the idle and the sound of the exhaust.
i havent gone wide open yet but so far i am happy with it.
snow time is here in carson so may not get to really check it out till next season.
will let you all know how it worksout when i do.

stv

This exhaust cam mod is for Americas only, right?

trboam, how are you liking the retarded exhaust cam? Lose anything on the bottom end?

thanks

Pure-Triumph in Fort Lauderdale has been doing the big bore kits. Ian of the dealership says moving a tooth on the exhaust is the same as putting in the high end cams. They are, acording to them, getting great results in the cam mod with the big bores and the new high output ignitors along with bigger carbs.

by moving a tooth do you mean advancing or retarding the exhaust cam? I would think most speedmasters would benefit by retarding the exhaust as would my T100, but the 790 motors are better off advancing the cam.

RETARDING THE EXH. CAM INCREASES THE VALVE OVERLAP WHICH HELPS OUT IN THE POWER IN THE MID TO HI RPM'S

IF ANY HAS CHECKED THE HI OUTPUT CAMS INCREASE VALVE OVERLAP AMONGST OTHER THINGS.

I BELIEVE THE OVERLAP HELPS TO PULL THE INTAKE CHARGE INTO THE COMBUSTION CHAMBER TO GIVE A BIGGER BANG.

BETWEEN BEING VERY SICK FOR 3 WEEKS THEN GOING TO AZ. TO VIST MY ILL FATHER I HAVE NOT BEEN ABLE TO RIDE MY BIKE .

IF WEATHER STAYS DECENT WILL TAKE HER OUT FOR A TEST RIDE OF GREATER MAGNITUDE.

THIS CAM JOB WORKS ON BOTH THE AMERICAS AND SPEEDMASTERS.

IM STILL NOT WELL BUT MAYBEE I CAM OPEN HER UP THIS WEEKEND.

THE BIG KAHUNA WILLING AND THE CREEK DONT RISE.

FOR THE APPROX. 100 MILES IVE RIDDEN SINCE THE CHANGE I DO LIKE THE DIFFERENCE.

STV

ONE MORE THING ABOUT THE EXHAUST MOD.

WHEN LOOKING AT THE CAM TIMING MARKS,

TO ADVANCE THE EXH. CAM THE CAM TIMING MARK WOULD BE 1 TOOTH BELOW THE MARK ON THE CAM DRIVE GEAR AND TO RETARD THE EXHAUST THE TIMING MARK WOULD ONE TOOTH ABOVE IT.

STV