Can the Auto Decomp Cam on an 02 426 Cause a Slight Power Loss

[srhines67]

I had the HotCams auto decomp exhaust cam put in my 02 426. It still runs great but it doesn't seem to have the snap that it did before. The work and valve adjustment was done by a pro so no problems there.

Has anyone experienced this?

[FriscoKLR]

If its very noticable it could have been installed with a 13 pin\chain gap that would retard it to WR timing instead of the 14 pin YZ timing gap.

[srhines67]

Hmmm. No way to tell for me. I'm not ripping into it. However, would using the HotCams exhaust with the stock intake cause this to happen. No that I think of it, it does ride more like my WR used to. Good torque off the bottom but way flatter power. More like an XR on roids.

[Fastest1]

The cam is probably ground to lessen the hit. It still puts out the same Hp or higher just not as explosive in the middle. I could be wrong, but that is what they did to the early 450's

[jmckinney]

I noticed the same thing with my 2000...You lose a lot on the bottom but the hot cam makes up for it at the top end. Throw a fly wheel weight on it and that will help.

[YZ426F Rider]

If its very noticable it could have been installed with a 13 pin\chain gap that would retard it to WR timing instead of the 14 pin YZ timing gap.

Oh man, I don't want to hear about problems! I just ordered the Hotcam exhaust cam for my '02 426 yesterday...

Please enlighten me about the pin/chain gap ?

[grayracer513]

The cam is probably ground to lessen the hit. It still puts out the same Hp or higher just not as explosive in the middle. I could be wrong, but that is what they did to the early 450's

This is correct, to the best of my knowledge. The Hot Cams Stage 1 AD exhaust cam is very likely ground more like the YZ450 than the stock YZ426 cams. When using an OEM 450 cam in a 426, the bottom end and mid range is improved with no sacrifice on the top end. the result is that the "hit" in the mid range never happens (because the power is there sooner, and comes on more like a four-stroke) and the false impression may be taken that the engine has less power. The truth is that it actually gains some.

Auto Decompression by itself has no effect on power either way, since it does nothing at all once the engine is running.

Auto Decompression cams CANNOT be moved around as the old ones could in order to switch between YZ and WR timing, because doing so will also affect the timing of the compression release. If srhines67 had installed his cam incorrectly as a WR, it would not have generated enough compression to start. With a Hot Cams cam made for use in a 426, you use the marks on the cam as if it were a stock YZ426, and not the pin count between the cams.

Also, Frisco, you have the procedure for re-timing a YZ backwards. Rotating the exhaust cam clockwise relative to the exhaust cam retards the cam, which is how you go from WR timing to YZ timing. Take a Look

[srhines67]

Grayracer, you cease to amaze me. I see your stuff all over the place. At some point you must have worked on a factory team or something. Anyways, what you described is exactly what I am encountering. I seem to have better low end and mid but it is all very smooth with almost no hit at all. It is actually very comfortable to ride trails with.

The question originally came up after I drag raced my brother on his KDX 220. His 220 is piped and jetted so its not stock. But, after a few races it was obvious that I could only get him by a bike length at about 50 mph. Now, my 02 426 only has about 60 hours on it and runs like a top so it's not like it is slow due to mechanical issues. Then I began to think about the fact that I had a stock intake cam and a HotCams 426 exhaust cam and began to wonder if I had lost acceleration due to this. I mean, it seems like I should have blown the KDX off of the map. But, it was not so. ?

Now, what's going to happen if I drag race someone on a YZ 250? I'm going to get killed.

Interesting note: I called HotCams and they said that if I bought their intake cam I would see a 10% increase in power and that their cams were designed to give more mid and high end. That's like 5 HP more. I find that hard to believe. It's also not consistent with what I experenced after having the exhaust cam installed which of course could yeild a different result due to the stock intake cam.

[srhines67]

YZ426F Rider, I don't think you will have problems. I really like the result I got. It's like there is no power band and lots of torque everywhere. There was a recent article about Chad's 06 and they said that the power was like having an electric motor on the bike. No power band at all. You just get what you twist. For what I do it's great. I was just thinking it was a hair slower acceleration wise. But, it's hard to tell really unless you timed it.

Now I just want to drag race a YZ 250 to see how fast the 2 smokers are.

[grayracer513]

Now, what's going to happen if I drag race someone on a YZ 250? I'm going to get killed.

Maybe, maybe not. Two things we often hear are that the '03 was the hardest hitting and meanest of all the 450's, and that the '06 just doesn't have that kind of power; that it's soft. The numbers run up on dynos don't bear that out, exactly, as a stock '06 put out 49.75 hp on Eddie Sisneros' dyno at 5000 ft., and the best running stock '03 I can recall seeing numbers on was more like 48.5.

Still, riding the two bikes, you would swear it was the other way around. One day, my son and I ran ours side by side and the net result was a dead even run, with the '03 pulling very slightly in the lower gears, but the '06 pulling away on top. In as much as a good YZ250 puts up about 45 hp vs. around 47 for a 426, I'd rather be a news reporter than a fortune teller on that one. The weight might decide it.

[srhines67]

OK. Great info. My bro's KDX 220 is really fast. It's also lighter. Anyways, the 426 is great. There's a great hill at Mammoth Bar in Auburn CA that the 426 just eats alive. The tractor power is great at Stonyford as well.

Greyracer, I have one more question for the road. I have head that Honda recommends a much shorter valve replacement interval if you are trail riding their race bikes. The reason given is that the engine just runs hotter overall which is hard on valves. I would assume the same for Yamaha's. Given all of this assuming I am wondering if my oversized Clarke tank, which covers the top of the motor on the sides, is causing my top end to run hotter than it would otherwise. Do the water cooled motors get much benefit from airflow around the cylinder and valve cover? If so, I'm thinking about using the Clarke tank only on long rides.

[srhines67]

Hey Gray, how about the question before. Have you every heard of a KDX that fast. Or do I maybe need to do some rejetting with the new cam?

thx

[srhines67]

Stock exhaust cams vs. the Hotcam

****** 426 Hotcam 450

lift**** 8.23 9 8.48

duration 256 265 252

[grayracer513]

I have head that Honda recommends a much shorter valve replacement interval if you are trail riding their race bikes. The reason given is that the engine just runs hotter overall which is hard on valves. I would assume the same for Yamaha's. Given all of this assuming I am wondering if my oversized Clarke tank, which covers the top of the motor on the sides, is causing my top end to run hotter than it would otherwise. Do the water cooled motors get much benefit from airflow around the cylinder and valve cover? If so, I'm thinking about using the Clarke tank only on long rides.

Oversized tanks are only a problem if they obstruct air flow over the radiators by getting in the way of air exiting them, which they could. (The Clarke doesn't that I know of). Insulating a water cooled engine from outside air doesn't have much effect on it (guess how hot it gets under the hood of your car), although running it out in the open is obviously better. It's just not that much better.

Heat is not the reason valves last longer on a trail bike. It may be a factor, but the fact is that a bike that's trail ridden is normally run at a lower average rpm compared to a race engine, which means the valves open and close fewer times per hour, and simply take longer to get worn to any particular level.

[02YZ426]

I ran the hotcam in my my YZ426 and the bike didn't lose any hit in the power range... not sure why yours did.

[FZ1426]

Be sure to take into account temperature and altitude as well as ground (soil) conditions when comparing power characteristics between modifications. There are a lot of factors that affect the feel of power. Drag racing in dirt is a very rough measure of performance comparison.

Trail riding can develop more heat than motocross because you don't stop in motocross. It's the low speeds and stopping in trail riding that requires trail bikes to have coolant catch tanks because of the (potential) low speed and lack of airflow through the radiators.