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Hamish

Camshafts

14 posts in this topic

I'm considering doing the cam mod on my 426. The auto decomp doesnt intrest me (at 210lbs and 6'3" I have no trouble starting the 426), but the extra power does :)

A few questions... is it worth it for the power increace?? and has any1 tried a hotcams Ex cam with the stock inlet cam?

thanks,

Hamish

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A few questions... is it worth it for the power increace?? and has any1 tried a hotcams Ex cam with the stock inlet cam?

There isn't enough to be gained from changing just the exhaust cam. If you only want to change one cam change the intake. They do work best as a set, but I guess that part is obvious. :)

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I just did the exhaust cam. There is a slight increase in the midrange, I didn't loose anyting on the bottom. I haven't had a chance to really get into the top end power yet. I did it to loose the starting routine. I could start it fine before but now it's even easier.

If you looking for more power your probably better off going with the intake and exhaust cams. I wouldn't recommend the intake by itself for more power.

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If you want the auto decompression cam so you can loose the auto deco lever then all you need to change is the exhaust cam. You can still run your stock intake cam.

It is possible and many people here have done it already to install a YZ450 intake cam on the 426 get the auto decompression feature. It will work and it's much cheaper then the Hot Camshafts auto deco cam. But the 450's cam sprocket size is just slightly different then the 426 cam Sprocket. Over time it's said it can lead to increased wear. But I have heard stories of people getting lots of trouble free miles out of them.

I went with the Hot Camshafts because it is a correct fit. It cost more but I just wanted the peace of mind.

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Hamish,

The exhaust cam is a great deal... I am 6' 6" and a bit over 240 at the moment, so I have no problem starting it either, except when I am tired, on the side of the hill, the sun is setting, the camel back is dry and you have to go UP the hill to get home, then I appreciate the 'kick it and go' deal...

The OEM 450 exhaust cam will increase your bottom end, and that helps to lessen the mid-range 'hit' - you will have more power from idle to WOT.

If you do the 450 DCM, and get your bike jetted right, and are still looking for more power then you will be in the market for a pipe... (PM me for a killer deal on carbon fibre and Titanium units)... I presume you have removed the air box lid?

Good luck,

David

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David,

air box lid was gone b4 i got the bike...already have DSP full system, which it too loud. So if u have a not so loud pipe for sale PM me the details. I'm up your way every few months when we go to Miriam Vale to visit the girlfriends kids. My 426 is easier to start than my 2 smoke , partially due to the 250's stuffed crank where the seal run. Even my GF can start the 426 :D

I wouldnt use the yamaha 450 cam based on the cam sprocket differences (unless I made a boss and fitted the 426 sprocket without the decomp). I know I am gonna get shot down for this comment, but it's just the way I feel on the subject. I know it works, I know that people have got thousands of miles out of it with no problem, but it's a risk I am not prepared to take. Those Ti valves arent real cheap. Besides, I don't wanna loose that midrange hit :)

I wouldnt use an Auto decom Hotcams either, due to the cost. I'm thinking about a set of 265/9mm hotcams. As my sis is in the states ATM I could get her to bring back a set. Anyone gone this way?

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My set of Hotcams should be here today, so I might have something to say by Friday. I lost my original intake cam due to the loss of all oil because my ignition sight plug fell out. Any choice of cams should be as a set IMO, they are designed as a set. From what I have seen, the yz450 cams are a little milder than the yz426 hence the reported loss of hit or smoother mid using the auto decompression 450 cam on a 426/400. The Hotcams for the 426 are slightly more aggressive than stock, higher lift maybe even some more duration. Cams don't make the power but more or less decide where it will come in. It is also a give and take,to make more power on top will come at the expence of low end.

With my cam change I am expecting a very slight increase in the mid and top with a little less bottom. I am changing the exhaust cam for a) the auto decompression and b)it is a matched to the intake. For me it doesn't make sense to not go for the auto decompression unless you need the adjustability of the exhaust timing gear (not availible on the auto decompression cam) I am getting killed on dead engine start races playing with the routine while the guy next to me has electric start.

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I have the Yamaha Tech CD for the YZ/WR450F and on it there are a bunch of specs for the YZ450 and the WR450. The cam specs listed for both the YZ450 an WR450 intake cams are identical, only the exhaust cam is different on the 450's.

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The lift and duration are the same on the factory cams its the lobe center degrees that differ between the YZ and WR.

The smaller the lobe center angle means more valve overlap (to an extent moving the power up the rpm scale). While a wider lobe center has the inverse affect of above. Given this information you can see the relation to the power band between the WR(strong low into mid) and YZ(strong mid with more on top).

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four years ago i bought a pair of camwheels from falicon cranks, clearwater, wherever that is and had them shipped to the UK.

i changed the cam timing 4d on the inlet and about 9d on the exhaust with a clearly 'feelable' heap load of torque increase. don't quote my numbers there but i did it all properly at the time.

having bought the gear my only regret was that I DIDN'T JUST REPOSITION THE CAMWHEELS AND I WOULDN'T HAVE PAID A PENNY!

depends how your minds work lads doesn't it-if you're a 'catalogue' racer this is balls and if you're a real racer it's 'yeh, i can save money and get the overdraught down'.

i put all the figures here somewhere but i was the only one that did it. i think they were lobe centred at 107-108 degrees.

Taffy :)

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the other things is, a lot of people know the 450DCM as the one that gets rid of the starting drill... howver, I think the real benefits comes from being able to clutch start the bike while it is rolling... sure, you can do it with the decomp lever and all that, but it is complicated... and you have to think about it... with the 450DCM, just pull in the clutch lever , knock it down a gear and pop the clutch... fires right up, rather than dragging it's sorry self to a stop with a berm of dirt piled up in front of your rear tyre... :)

I think that is the real sleeper aspect to the 450 cam mod...

David

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