First some specifications;
lifts are gross valve lift off of the seat. Rocker ratios were 1.347:1 for XV700s to 1100s, and the XVS1100;
durations are taken from the point that the valve exceeds .040" (1mm) lift off of its seat until the point at which it falls
Note that 1) lifts and durations for Yamaha cams are tentative and hearsay; as I get time I shall cobble together a partial
engine and some soft springs, and -- with a degree wheel and some micrometers -- come up with some trustable numbers. 2)
The cams prefixed with "BT" are those we offer.
There was a 10L cam pair used on the '82 - '83 920 Virago. These sometimes show up on eBay still in their Yamaha wrappers. They are never cheap. I believe
that these were identical to the 42H that they supercede to, except that they were a degree or so retarded - giving them a trifle more top-end.
I remember at the time that the Virago would beat the RH/RJ in the quarter mile by a couple of tenths and a few miles per hour.
- Valve Lift:
- .383" - .401"?
- .379" - .391'?
- @ .050":
- @ .020":
- Lobe Centers:
- Intake Open
- 15° BTDC
- ??° BTDC
- ??° BTDC
- ??° BTDC
- 32.5° BTDC
- 18° BTDC
- 23° BTDC
- 43° BTDC
- Exhaust Open
- 51° BBDC
- ??° BBDC
- ??° BBDC
- ??° BBDC
- 64.5° BBDC
- 50° BBDC
- 47° ABDC
- 77° BBDC
BT-C01; These cams have .492" lift
and 270 degrees duration. They have 292 degrees duration at .020". Note: if you use Yamaha factory service manuals to find cam specs, you will find truly
astonishing road-race-sounding durations;
reputable after-market cam vendors quote duration beginning and ending when the valve is .050" off of its seat;
Yamaha appears to count duration as including any time the valves experience any lift at all, including the longish "acceleration" ramps.
The stock springs coil-bind at .440" lift and float at 8000rpm.
I've run a similar combination up to 8900: where the rev limiter closed things down.
These are not a drop-in. You must at least notch the pistons for valve clearance, unless you are running after-market pistons like our 1004cc kits.
These are road race cams (although I had no problem running a set on the street). They are made to rev.
To fully benefit from these cams, you should run 11:1 pistons, a free-flowing exhaust, and carbs with accelerator pumps.
It wouldn't hurt to open the ports a little. A multi-angle valve job would help.
Keep in mind that raising compression means more stress on your starter and related parts;
you should stake the ring (sun) gear inside the starter motor to the housing so it does not just spin without turning the engine.
Note well: although the BT-C01 will fit in 700s and 750s, I don't recommend them for the smaller engines. If you don't run rather high compression pistons (12:1?), you will have essentially NO low-end power and will find yourself down-shifting a lot more.
I also recommend against using them in the V Star; I simply feel that the whole bike had design problems. Compare the number of parts on eBay to those of the 1100 Virago. It's astonishing.
BT-C04: some cams that don't require spring kits.
At last: more power without having to pull the engine. These cams can be swapped-in in your driveway in under an hour. They have .432" lift and 264 degrees duration.
A real punch in the mid-range (think passing power) and finally the ability to rev a little.
These cams are meant to be used in an otherwise stock engine -- although they would benefit from pipes and carbs (and compression).
They push the stock springs pretty hard, so try to stay under eight grand.
Nothing NEEDS to be changed, but you may want to put some washers under your jet needles.
These work in ALL adult-sized Viragos: 700, 750, 920, 1000, 1100, the 1100 V-Star, the 920R, and the TR1.
They are about as much cam as the smaller engines can take without going further into the motor.
These cams have over a quarter inch more lift than any stock Virago. See my listing for rockers.
If you have the hole-in-the-pad unhardened rockers keep plenty of fresh oil in your motor. Change it frequently. Run an oil that contains zinc.
Your beast will finally take the deep breaths that a big twin with big valves should.
BT-C05: a somewhat more spirited profile.
Same lift (.432") as the BT-C04, but with a trifle more duration -- 272 degrees.
A good cam for the smaller bikes (700, 750) if you're looking to make them into café racers. Pipes a must, carbs recommended.
For the bigger bikes, look for a greater willingness to rev -- you'll think your twin has "gone Italian."
As with any longish duration cam, a little of the bottom goes away, but gobs of power are to be found from thirty five hundred on up past red line.
Again, pipes needed.
BT-C06: These are too much cam for any stock displacement XV.
are our cam of choice for the TR1 with the 1065cc kit. These are based on flat-track profiles.
They spin up faster than the BT-C01. Running them with stock pistons would require notching the reliefs all the way through the piston crown.
The lift is enormous and the duration long in the extreme. They don't idle well with constant velocity carbs.
Even with flat-slides, a stable idle will be between 1200 and 1500RPM. The lift helps give back some of the low-end that the duration takes away.
NOT recommended for commuter bikes. They are meant to run with a minimum max rev of 10,000RPM.
It is not recommended to exceed ten five, as I believe that the tensioners are designed (not by intention) to grenade between
eleven and eleven five.
Also note well, cam prices are exchange elsewhere. Some vendors have as much as $300 core charge on these.
The BT-C01 and BT-C06 cams require spring kits, which requires pulling the heads -- on a Gen I, this means dropping the engine.
A good time to install a big bore kit
The combination of pistons and cams will have you looking for ways around the rev limiter cut-off. Look at Ignitech
(we'll add these, but not soon), or exercise some patience while we sort out our cam-driven single spark ignition.
There are some mighty gimmicky ("three sparks per ignition event") alternatives out there. They are pretty tidy,
but to buy everything needed for full tuability could easily run you a thousand - three times as much as the Ignitech.
Also, keep in mind that the cams have very little "flywheel" effect - they tend to move in-and-out and they self-retard under load - but not on a dyno!
Check out this page
There is some disagreement on how much lift the guides will allow without being modified (shortened). The spring manufacturer used to sell the same
kits listed below as good to .600" valve lift. Now in the instructions it says good to .450" valve lift. They had reports that the retainers were
contacting the guide seals at higher lifts. I personally ran a set of their aluminum-topped springs with .502" valve lift. There was clearance between the guide seals
and the retiners at full lift. It is possible that Yamaha's casual attitude toward tolerance makes them hit on some heads and not on others.
I suggest turning the cams through a whole revolution on the bench and if you don't have .060" clearance between the guide and the retainer at full lift,
that you shorten them accordingly. This will almost certainly be the case with -C06s. The guide seal flexing in-and-out is not a problem.
If you opt for complete heads, this adjustment will be made by us.
Note the prices below now obtain. I am out of cores and there are suddenly none to be got.
Titanium jumped very high. Use the contact button on the front page to tell me what you want and I'll send you an invoice.
Right now, if you want cams outright, I'll have to buy good cams and weld and grind them.
The cam and titanium spring kit combo would go for $975.
If you sent me your cams first and I found them useable, I'd invoice you $775.
Cams outright are now $695; send yours first, $495.
Titanium topped spring kits are now $285.
Queries from the contact button often proceed to dialogues that end in steep package discounts
$975 BT-C01 or BT-C06 Road Race Profile Camshafts (no exchange needed) with Titanium Spring Kit.
Note that if you get the kit above, you are already getting the spring kit listed below.
Note thgat the reciprocating parts (less valves) in a stock XV are 3.9 to 4.1 oz -- this is springs, retainers, and keepers.
The same parts in the following two kits weigh 2.9 to 3.0 oz. Less reciprrocating weight equals faster spin-up; less float likely.
$285 High Performance Valve Springs with Titanium Retainers - Good to .600" Valve Lift
$250 High Performance Valve Springs with Aluminum Retainers - Good to .600" Valve Lift
As durable as the titanium, but without the glamour of being to say that your bike contains titaniun.
I've been told by the distributor that these are back-ordered indefinitely - possibly discontinued.
Some thoughts on Springs.
$695 Hard-weld cams only -- no springs
If you opt for cams outright, you spend an extra $100 each per cam. If you send in your old cams after the receivng the new, I will reimburse you $100 - less than the cores cost you, as I
must srtip complete heads - a lot of work when one considers the rockers and valves.
I am very small. I can't always afford to keep cams in stock; I try to keep -C01 and -C05 kits on hand. When I order from my usual vendor, it takes up to a month for them to grind my cores.
Right now it is a week or two. If you are in a hurry, or want to explore other profiles, the cams on this page are
seventy five dollars more per set, but only have a maximum two week turn-around. Use the contact button on the welcome page to ask for an invoice.
Currently, I am OUT of cores most of the time. If your engine is apart, send them in and I'll have them brought up to performance spec and you'll pay less.
If you don't buy cams, but have some old, used units you no longer need, contact me and I'll pay thirty dollars a pair - or?
Regardless of condition - as long as the journals are round and the snout is not broken.
I may ask for pictures. If you have a lot of cams and want to buy better, I'll credit fifty dollars per pair toward newly ground units.