what is the advantage of Dual cams over a single cam?? It makes no sense to me. i don't see how 2 cams can be better than 1. one cam gets the job done fine. is 2 cams just a marketing gimmick or what? any answeres will be welcome

 

DOHC places the camshafts closer to the valves, eliminating some of the rocker arm assemblies & reciprocating mass, supports higher RPMs with more valve timing accuracy...

Also allows the exhaust valve timing to be changed independantly of the intake valve timing.

 

DOHC on the Mojave is 1986 technology. I don't mean to bad mouth it, but when you compare the DOHC system on the new Yamaha's to the Mojave's you will find the Mojave system is dated. I own a Mojave and recently adjusted the valves so I got a chance to see how everything was assembled. The head was much larger than that used on a KLX 300 dirt bike or the new Yamahas. The YZ 400/426 and 250 use a DOHC that has the cams act directly upon the valves where the Mojave utilizes rocker arms to accomplish the same task. There is nothing wrong with the Mojave's valve train, it rev's freely and to a high RPM but simply isn't advanced as the Yamahas. The reason they both use a DOHC is to allow greater control over valve opening and closing. If you have two seperate cams you can control things to a closer tolerence than if you use one cam, ala Honda. The benefit of one cam is easier valve adjustment. I can attest to that having owned a 250X and a '01 Mojave. The Mojave's valves ar'nt difficult to adjust but it does take twice the time to remove all the plastic and you need to use two feeler gauges to do it right. I should add that the Yamahas and new Suzuki DRZ's require a shim and bucket valve adjustment which I am not familier with. My understanding is that you need to have the proper shims in you possession to adjust the valves while the Mojave's system does not require you to spend any money. Even if it is old, I like that aspect.

 

Excellent post, Gabe!

Double OHC setups are found in elite racing engines, reducing reciprocating valvetrain mass (as you say), permitting higher rpms and consequent higher power peaks. DOHC geometry can permit more practical latitude in combustion chamber design optimizattion, also.

Does the new Kawasaki 650 has two sets (four total) of DOHC; one set for each cylinder? Or, does the 650 have one cam per cylinder?

Diogenes

 

also you have more valves so the engine can "breath" better.

 

2000MOJAVE,


More valves? you have an extra cam not an extra valve.

 

Not true, the MAIN reason for multiple cams is to open multiple valves. Nobody is gonna put two cams in an engine to open two valves.(as in one per each cam) Most use one cam to operate two exhaust valves and one cam to operate two intake valves.(although Yamaha I believe uses 3intake and 2exhaust on the Raptor). Variable valve timing is just another advantage of being able to control the intake and exhaust valves individually in a DOHC engine design.

 

To answer your question we need to go back to some basics. If you want more performance from your engine you need to get in more air and fuel and exhaust more spent gases. For the engine manufacturer there are two choices, first bigger valves, second a more radical camshaft. The drawback to the camshaft is that as the duration and lift increase dramatically, driveability decreases. The drawback with bigger valves is that as the valve gets larger the flow of the gases around the valves decreases driveability. A good solution to this problem is to have more small diameter valves, this lets more gases flow without poor flow characteristics and it eliminates the need for an aggressive (poor driveability) camshaft. Due to space limitations in engines two camshafts are needed, one for both intake valves and one for both exhaust valves.

There is no advantage to two cams versus one, the desire for more power via 4 valves dictates the need for 2 cams.