questions on a big bore kit??

[natemoen]

My understanding is that cams don't make any more HP, they just move around the HP the motor already makes?

If you can make the fuel air mix flow better and get more in the cylinders it will make more power and more lift and duration can do that but not always.

[BA80]

If you can make the fuel air mix flow better and get more in the cylinders it will make more power and more lift and duration can do that but not always.

But that moves the horspower up the RPM scale because the longer the valve is open the less vacuum there is until there is enough RPM to bring the vacuum back up.

[natemoen]

I am not disputing that it moves the curve, I am just say cams can increase HP.

[BA80]

Yes, as long as there is carb CFM enough to feed it and exhaust thats able to get rid of it.

[natemoen]

I used the word CAN not the word WILL. Most any engine mod require other variables to be considered.

What else are you going to throw in here Greg?

[BA80]

Well, I could start talking about playing with timing curves to get max output too.

[natemoen]

Most any engine mod require other variables to be considered.

What else are you going to throw in here Greg?

I will just keep quoting myself.

[BA80]

I will just keep quoting myself.

Ouoting or repeating?

How's you bike running Nate?

[natemoen]

Ouoting or repeating?

How's you bike running Nate?

It was to insightful to be called repeating, quoting though is more fitting

Haven't reallt had any free time the last couple weeks and I don't feel like freezing on the way to work so I haven't messed with it.

[BA80]

Been nice down here. My bike is running great as always.

Got some new tires on him last week. Looking forward to a trip sometime soon.

[trbig]

Back to the cams, after Greg changed the subject..


Can you buy just a slotted sprocket for these OEM cams, or do you have to order the whole cam? I realize a machinist can get'er done with what I have, but didn't know if there was a reasonably priced option to just order one.

[BA80]

You can slot the gears yourself Tod. A dremmel with a good cutting bit would do it. Your not going more than about 3º in any direction and that ain't much.

[crazy steve]

I got to believe the durability of the cam isn't compromised and awful lot. I understand it places more stress/strain and wear on the components but the street cam probably would drastically decrease the overall life of the engine...would it? I would be more concerned about the longevity of the bearing surface on the head and bearing caps. It would have been nice if they originally designed the head with with removable bearing sleeves.

Everyone always seems to be looking for a little extra cheap performance, why wouldn't cams fall into that category? Does anyone know what the cost is? Seems like it would be plug and play in addition to some carb tuning...

Great discussion, thanks for the info.

Camshafts and valvetrain are still in that 'black art' catagory of engine design, with so many variables involved that it's impossible to say that any one design is 'best'; that's why you still see so many different types used on modern engines. All of them have advantages/disadvantages, it's up to the engine designer to determine which 'fits' the application best.

The shim-and-bucket design is popular on motorcycles for a couple of reasons; one, it's simple and compact. Two, due to low valvetrain mass high rpms are easier to attain without valve 'float' or excessive valve spring pressures. The major downside is limited lift while controlling wear.

The issue I have with welded cams is they're known for poor wear; 'back in the day' welded cams were common as many cam grinders couldn't afford new cam 'blanks' so most were reground on welded OEM cams. But lobe failures were common because of incompatability between the weld metal and the surface it was acting against, whether it was a shim or lifter. The metallurgy involved in selecting cam and shim/lifter material is critical to good wear, and this was specifically mentioned in period reviews of the XS that Yamaha had carefully selected these so that wear would be at a minimum. Lobe/shims failures are extremely rare, so I'd have to say they did a very good job.

But with a welded lobe, did they use a weld metal identical to the original? How about the heat-treat? Not to mention the effects of the welding on the parent metal? These are all reasons that welded lobes have pretty much gone away, being limited to applications where the cost/availability of new cam blanks makes this an affordable method of restoring a rare OEM cam or producing a hi-po cam for a non-popular motor. It's virtually unknown these days in the main performance market as durability is compromised to a degree no matter what. The question is how much....

Keep in mind that in auto racing classes where they're limited to flat-tappet cams (non-roller cams, pretty much the same type of wear you'll see in the shim-and-bucket on the XS), lifts over .600" are rare and rapid cam wear is expected. Here you have the advantage of rocker arms multiplying the lobe lift to the valve, so actual lobe lift will only be .400" with a 1.5 ratio rocker. Typical 'street' cams will be in the low .500" range, so lobe lift is only .350", or about the same lift as the OEM XS cam. The cams I'm running in my Sportster are .555" lift at the valve, but actual lobe lift is only .336", less than the XS.

And as far as how much power you can make with a cam change and where it appears in the power curve, that's pretty much controlled by the limitations of the cam/valvetrain design. Generally speaking, more lift will add power all across the curve, duration will move the power up or down in the curve.

[motoman]

Well, I could start talking about playing with timing curves to get max output too.

Now, there's a member that KNOWS how to squeeze any lost potential out of a motor! Used to use the SUN ditributor machine to re-curve our muscle car distributors to better match what they were wanting and when.

[WMarshy]

Cool stuff, except for Greg the pessimist lol. I just called Megacycle and price the cams. Both street/road racing cams that dont require race pistons cost the same... $415 for the set of cams (254-00 and 254-70). To be able to use the 254-70 (which has more lift and duration than 254-00) you have to use their race springs that adds $70. So, this doesnt exactly fall into the "cheap performance" section..

We did have a talk about durability and the manufacturing process. I didnt exactly write it down or try to memorize the materials they are welding on the cam lobe but she told me they have a "1 year warranty" and the durability issues from the past are no longer an issue today for the most part. She did add they recommend a high zinc content oil to reduce wear so, none of that Mobil, Castrol, Rotella junk.