Hotcam vs. OEM 450 Cam for 426

[Traction12]

I've been reading a bunch of posts about the auto decomp upgrade for the 426 but am finding some conflicting information concerning the difference in power output between the hotcams 426 cam and the OEM 450 cam. I've read that:

A: they both increase horsepower

B: the hotcams exhaust cam has to be matched with the hotcams intake to have an increase in power

C: the 450 cam increases power without changing the intake cam

Thanks!

...you know, if I would quit crashing so much during races I wouldn't have to worry about this upgrade so much.

[MattyH]

dollar for dollar the best way out of your cam dilemma would be to get a set of cams as opposed to mixing and matching 426/450/hotcams. either the hotcams or the 450 cams as a set will deliver more power.

as far as my understanding of cams goes i'm inclined to think that if you install an exhaust cam with more duration the charge will simply get blown out your exhaust and it will cost you in terms of power.

in reference to your points A and B, they are both true. point C however to me seems dubious because the differences in lobe centres and cam duration may cause problems.

i'll probably get pulled up by the moderators (hi guys!) but i'll slip in a shameless plug for the set of stock '04 450 wr cams that i have for sale, they are a slightl;y retarded version of the yzf cam but a press and a degree wheel will soon sort them out

[grayracer513]

Point C is far from dubious; it's an established fact, gleaned from actual experiences of those who have tried it. The OEM 450 cam works extremely well in harmony with the OEM 426 intake, and in fact, it not only increases peak power slightly, it also extends the power curve, particularly the lower middle. The result is a very wide, smooth power curve that almost everyone likes.

While matching cams in pairs intended to be used together is perfectly logical and sound mechanical theory, these two cams work so well together that they may as well have been produced as a pair.

So, given the fact that a Hot Cams exhaust is more expensive, and doesn't really provide its full potential unless matched with a second $100+ camshaft, I have to disagree; the OEM is clearly the best buy of the two.

Here's an added note on the '04 WR cam: You can't re-time the auto-decompression cams to change between WR and YZF timing as you could with the '02 and earlier models. The reason is that to do so will cause the decompression pin to be moved out of position. If you re-time a WR to YZ, you will end up with so little cranking compression that the engine may not start. Re-timing an auto-decomp YZF to WR will significantly reduce the auto-decomp functionality.

[Chills]

In regards to your question...

I dont know if you are getting conflicting information. This topic has been a subject that has been floating around for quite sometime. When it comes down to it, you ultimately have 3 options, all with slightly different results.

1. Keep the existing 426 Cams = Pain in the @ss to start, no performance gain, stuck going through the drill to get it fired.

2. Updating the 426 cam with a newer 450 Automatic Decompression Exhaust Cam = Cheap, Easy to start, Smoother Power throughout the curve, with slightly increased performance.

3. Updating the 426 cam with a HOT CAMS 426 Automatic Decompression Exhaust Cam= Pay higher cost, Easy to start, NO Performance Gain

a. Updating the 426 with a HOT CAMS 426 Intake Cam= Increased Performance, 2x the cost

Ultimately if you have an extra $200+ plus to toss away, then by all means, go for the complete 426 HOT CAMS with Automatic Decompression. Most of us have gone the 450 Exhaust cam route and save the extra $200 bucks to spend on something else. I personally love my 450 Cam in my 426. It completely smoothed out the entire power curve. If I had the chance to do it again with another 426, I would do it in a heartbeat...

Just my .02 Cents

[Lukejt]

YZ450 exhaust cam, nuff said.

Lukejt

[Traction12]

You guys are awesome. Really, I'm honored to have gotten responses from riders who are so informed and passionate about the sport and the machines. OEM 450 exhaust cam it is! This is the first time I will be attempting an engine upgrade and am extremely excited about it. I'll keep you guys posted. Thanks again! ??

[MattyH]

the auto decomp function on the OEM 450 cam is in effect at low rpm, i.e kick starting speeds until the revs rise enough to enable the hammer component to take effect and disengage the auto decomp so rotating the cam gear would have little if any effect on its ability to function, if anything it will engage a little later but you only need to crack the valve open slightly for it to decompress in any case.

i've probably opened a pandoras box in regard to the interchangability and suitability of the cams in this case but if everyone throws their 2 cents in odds are we'll all learn something

[grayracer513]

the auto decomp function on the OEM 450 cam is in effect at low rpm, i.e kick starting speeds until the revs rise enough to enable the hammer component to take effect and disengage the auto decomp so rotating the cam gear would have little if any effect on its ability to function, if anything it will engage a little later but you only need to crack the valve open slightly for it to decompress in any case.

The way the auto decomp works differs significantly from the manual set up. The purpose is not to release pressure throughout the entire compression stroke, but rather, to reduce it to a level that an electric starter can deal with. At speeds lower than idle, the spring overcomes the flyweight and retracts it, which in turn extends a pin from the camshaft. This pin is positioned so that it passes over the left exhaust lifter as the compression stroke begins and raises the valve off the seat, releasing compression. The pin rolls off of the valve and lets it seat at a point roughly 3/5 of the way up the compression stroke, far enough before the spark event to allow the engine to generate about 90-100 psi of compression, and to assure that the valve is closed when ignition occurs.

When you re-time the Auto-Decomp WR camshaft to YZF specs, you retard the cam 22.5 crankshaft degrees (the sprocket has 32 teeth; 360/32=11.25 degrees at the cam; crank rotation is 2:1 that of camshaft; 11.25x2=22.5). This means, since the decomp pin is in a fixed location within the cam, that the left exhaust valve will be reseated 22.5 degrees later in the compression stroke than it's supposed to, and cranking compression will be reduced. Timing an AD YZF as a WR has the opposite effect.

Some have proposed ginding the decomp pin down to restore the proper timing of the valve reseat, but this is not a good plan.

See: https://www.thumpertalk.com/forum/showthread.php?t=265839&highlight=grind+pin

Auto-Decomp cams should be timed as they intended to be, and the best bet if you want to change an AD equipped WR to YZF timing is to buy a YZF cam for it.

[BergRyder]

3. Updating the 426 cam with a HOT CAMS 426 Automatic Decompression Exhaust Cam= Pay higher cost, Easy to start, NO Performance Gain

I disagree with that the HotCam exhaust cam provides no performance gain. I race Supermoto where HP is far more important than on the MX track. My bike was stock except for a Yoshi pipe it had about 43 hp. I had it dyno'd after installing the HotCam and K and N filter, 47.4 hp - no way that's just the filter. It sounds different - more aggressive, revs more freely, remember in Supermoto we have these things pinned (wfo). I bought the HotCam after reading posts on this site and liked the idea of adding the intake cam later.

[MattyH]

BergRider, what make of dyno was it out of interest?

[srhines67]

Hey Berg, I just did the same thing. But I'm thinking I got a decrease in power. Did you make any jetting changes or ever install the intake cam?

[stillsun]

Or do what I did (doing), get the HotCams exhaust (non-auto decompressor, $75) and intake cam (about $125)....so for both it was about $200, and I don't need a stinking auto-decompessor on my bike, I have no problem starting it and I actually like being able to manually open the exhaust valve if need be.

J

[srhines67]

What was the difference in performance?

[GreenKLX]

Okay, so I have a similar question. I don't understand the effect of lift and duration on the power curve, but I purchased a Hot Cam exhaust cam for a '03-'05 YZ450. I just got it today and was wondering if anyone can decipher how it will change the power by the cam's specs. The cam is going into a 2001 YZ426.

Specs:

Lift: 8.67mm

Lobe Center: 103

Duration @ 1mm: 265

Valve lash: .20mm

I don't know the stock specs, but any input from someone that has more knowledge of how cams effect power would be appreciated. ?

[srhines67]

I just talked to Hotcams and they have dyno tested the 426 exhaust cam with the stock intake cam. There is absolutely no difference in overall power according to them. However, the power curve could have changed. They are going to call me back and give me the info on that. With both cams they predict a 9% increase in power.

You should give them a ring. I talked to Mike but Tim is the guy who tests the stuff.

[stillsun]

Okay, so I have a similar question. I don't understand the effect of lift and duration on the power curve, but I purchased a Hot Cam exhaust cam for a '03-'05 YZ450. I just got it today and was wondering if anyone can decipher how it will change the power by the cam's specs. The cam is going into a 2001 YZ426.

Specs:

Lift: 8.67mm

Lobe Center: 103

Duration @ 1mm: 265

Valve lash: .20mm

I don't know the stock specs, but any input from someone that has more knowledge of how cams effect power would be appreciated.

Why did you buy a 450 cam? ? HotCams makes a 426 cam with auto-decompressor...

[mxgene]

Personally, I went the Hot Cams route.

Main reason being the chain fitment not matching on the '03+ cam.

I didn't want to install something that may, or may not, cause me to lose a cam chain.

[stillsun]

What was the difference in performance?

I wrote "doing" because I'm in the middle of setting the whole bike up right now... don't have any experience as for the performance gain yet, but I am doing the big bore at the same time so it will be hard to say exactly what the cams did and exactly what the big bore did.

J

[GreenKLX]

Why did you buy a 450 cam? ? HotCams makes a 426 cam with auto-decompressor...

It was on ebay and I was told on here that it would work.

[stillsun]

Yeah I can understand the people who buy the OEM 450 cam.... but when HotCams actually makes one specifically for the 426 with the correct gear I just never understood the reason, but hey if you got a good deal and it will work then so be it.

J