Hot Cams

[SovereignDragon]

So I'm reading on here that the 78 XS11 cams are a bit hotter than the stock cams in my 80 XS11. I'm wondering why they are considered this, I can't seem to find any specs. Are the lobe profiles higher, do they scavange better, do they lope a little more? What are the pro's and con's? I was thinking these cams, slipping on some fat boy mufflers, and running a k&n stock style filter replacement or the one that is only two required because it slips over two carbs instead of the single pods. I already know I'll have to rejet with the dual carb pods and exhaust but what about the cams?

[crazy steve]

So I'm reading on here that the 78 XS11 cams are a bit hotter than the stock cams in my 80 XS11. I'm wondering why they are considered this, I can't seem to find any specs. Are the lobe profiles higher, do they scavange better, do they lope a little more?

The '78-79 standard cams have more duration; i.e. they open the valve sooner and keep it open later. This also increases overlap (the time during which both the intake and exhaust valve are open). These are common characteristics to any 'hi-performance' cam, whether it's for a XS or your small-block chevy. The advantage is better cylinder fill at higher rpm, with slightly lower power at low speed. The late exhaust cam has been reported to have slightly greater lift (.2mm), so some have used only the early intake cam. The early cam motors regain some of that lost low-end power by using a more agressive timing curve.

As to the specs, only the FSM manuals has any; they show lift. The duration numbers were gotten by a few guys actually checking with degree wheels, etc.

[James England]

Have PM'd you re camshafts//

[DiverRay]

ANY mods to the engine will require you to re-jet the carbs. With that said, the cams on the '78/'79 are a LITTLE more aggressive than the later cams. The biggest difference is in the advance system. the '78 has about 5 degree more movement than the rest of the models. My "seat of the pants" dyno tells me I get a little more bottom end, and it does pull a little higher as well.
If you want hot cams, they ARE available as reground. Do a web search, or try a search in here. I know I have posted a site who did re-grinds, but I don't have it handy. For the intake, I find the stock airbox with a K&N and six 1/2" holes drilled in the PROPER PLACE works very well. My "hot rod" engine is still in boxes, so I can't say too much more about the things to really get some power out of an XS11
Welcome to the site, and have fun with the project!

[81xsproject]

The '78-79 standard cams have more duration...

Steve, I am pretty sure 70's cams are 70's cams, special or standard. All 70's bikes have 2H7 cams and all 80's have 3H5. As far as engine and associated components, the are only 2 differences (that I can remember) between a 78 and a 79; The starter jets in the 78 are larger and the mechanical advance unit has more advance. But, I feel as though I am forgetting something (other that obvious cosmetic differences).

Dragon, try out the 70 cams on your 80. If you like winding the piss out of it, as I do , you will really enjoy the 70 cams. You will suffer some low end power loss, though. If you can't commit to just 80's or 70's, you might like the blend of just a 70's intake cam. That is what I am currently running. It's a nice blend with a little gain on top and less loss down low. However, I will be going back to both 70's due to the ability to overcome some of the associated low end power loss with the fuel injection.

[crazy steve]

Steve, I am pretty sure 70's cams are 70's cams, special or standard. All 70's bikes have 2H7 cams and all 80's have 3H5. As far as engine and associated components, the are only 2 differences (that I can remember) between a 78 and a 79; The starter jets in the 78 are larger and the mechanical advance unit has more advance...

You may be right on the cams; I'm getting less and less trusting of the UK parts fiche accuracy, as I keep finding more 'wrong' parts identification. But even the 'official' Yamaha site has discrepancies, so actual checking of the part may be your best option. But the best available info I can find all shows that the '78 and '79 standards both have the 'better' mechanical advance unit and the '79 special has a different unit with less advance.

I suspect that the parts fiche problems may be due to Yamaha 'updating' them as time passed, substituting functionally 'close enough' parts for some items that had model/year differences that they felt weren't important, or more likely, to reflect current parts inventory. By the time these were archived, the earlier fiche versions had disappeared. And Yamaha started selling not-quite-duplicate parts fairly early; I ordered a new '78 'macho maroon' tail cone in '80, and what showed up had the correct color but lacked the OEM striping... I wasn't very happy.

[SovereignDragon]

So I got offered a set of cams pretty cheap from a fellow member in the u.k. but the numbers are 2H9 instead of 2H7. Anyone know the differencess?

[TADracer]

Consider this

I have the early cams with slotted sprockets and notice that moving the intake cam causes a change in performance you can feel (either for better or worse) while moving the exhaust cam does not really cause anything noticable. The change in performance is not really more power but is more just moving the power curve either up or down in the RPM range and either flattening it out or making it more of a peak curve at higher RPMs.

The early/late cams are so close in grind and use the same stock 101 degree lobe center, fixed by the non-adjustable stock sprockets that I feel no large, noticable performance gain will be had by simply changing the camshaft. I think one can probably get the particular results they are looking for with either type camshaft by properly 'degreeing' in their cams to adjust lobe centerlines. This will change overall duration and position the valve opening, closing and overlap events to give the type of power curve best suited to their style of riding. Thats just my two cents, tough.

The late exhaust cam has been reported to have slightly greater lift (.2mm), so some have used only the early intake cam.

Probably the reason many guys have only used the early intake cam on later motors is because the exhaust cam will usually not make any real difference in performance compared to even a slight movement of the intake cam lobe center.

[crazy steve]

..I think one can probably get the particular results they are looking for with either type camshaft by properly 'degreeing' in their cams to adjust lobe centerlines. This will change overall duration and position the valve opening, closing and overlap events to give the type of power curve best suited to their style of riding. Thats just my two cents, though...

I'll agree with most of this, but will point out that duration can't be changed as that's dependent on the cam lobe; the only way to change it is to re-grind the cam. If you have two sets of cams with the same lobe centerlines, the set with more duration will have more overlap. Degreeing the cams (changing the centerline) to change overlap will change the power curve; the more overlap you have, the more the power moves to the upper rpm range.

But there's a lot of voodoo involved with lobe shape/duration numbers too. You can have two cams with the same lift numbers and different durations that will both flow the same amount of air, depending on how 'fast' the opening/closing 'ramps' are. A 'fast' ramp can open the valve later but faster, giving the same flow. The downside is increased stress on the valvetrain and shorter cam life. This is why roller cams have become popular; the reduction in friction at the lobe allows faster valve action.

[TADracer]

I love discussion

I'll agree with most of this, but will point out that duration can't be changed as that's dependent on the cam lobe; the only way to change it is to re-grind the cam.

Very true for an individual cam but I do not think so for a pair together. That is why I said 'overall duration' for lack of a better term for the combined events from exhaust opening through intake closing. The beauty of dual overhead cams is you can lengthen or shorten this 'overall duration' of the two cams by adjusting the lobe centerlines. But that also has an effect on the length of the overlap too and decreases the piston to intake valve clearance alot. It is all still a bunch of trial and error and what works for one machine might not work the same for another that is exactly identical. I find these vintage machines to have different personalities, unlike all the computer controlled, fuel injected cookie cutter crotch rockets turned out today.

My machine is a naked 79 SF and I do very little cruiseing on the highway but ride more on the backroads where I like rapid acceleration and braking to manage the curves. So I have hit on the best combination (for me) with the exhaust cam advanced 2 degrees and the intake advanced 6 degrees. This advanced both centerlines but also widens the lobe seperation angle which builds more low end torque, broadens the power band and shifts the low end torque effect up about 500 RPM to around 3500. So most of my power comes on quick at 3500 and pulls steady through about 7500 and then begins to trail off significantly. Puts that power band right where I like it but would kind of suck for a drag racer who will be up around redline alot or someone in constant stop and go city traffic.