With Larry Harris and Jim Mazzola Photos and engine by Jeff Pollock
Rotational Dynamics' Adjustable Camshaft Sprocket and Removable Timing Cover
The engine in the Samurai is notorious for its lack of power. The aftermarket was pretty quick with the common modifications. The larger Carburetor, header and cam have been around for years. There has even been high compression pistons on the market for the little engine that thought it could. Where to go next for more power? The engine transplants are getting more coming, but expensive. Until now there have not been many other options for gains in horse power. In addition to the most common modifications we now can modify our cam to crank timing just like the bigger engine owners. Only the new system from Rotational Dynamics' is better then the big engine system. You do not need to use offset keys to make the changes. With the new removable timing cover and adjustable cam sprocket you can experiment with your engine to gain the best power output. So you see size is not important 😉
Why is it a good thing to be able to adjust your crank and cam pulley separately. With the conventional system in general terms advancing the timing will generally gain on the lower end and lose a bit more on the upper end. Retarding the timing will cause you to loose power on the lower end but gain a bit more on the top end. As a general rule, you shouldn't retard more than 9* cam degree or 4 1/2* crank. On the other end I wouldn't advance more than 12* cam or 6* crank. You will always lose more than you gain. Remember this is not a perpetual energy machine. Whatever you gain you will lose more at the other end.
Advancing the actual cam timing relationship to the crankshaft actually changes the time in which the valves are open to allow air/fuel mixture to enter the cylinder. Depending on engine speed, and manifold runner length, it varies the Volumetric Efficiency or V/E of air / fuel mixture that is capable of getting into the cylinder each stroke. This can not be done with the stock system. You can't really get something for nothing. In reality, you actually gain up at one end you give up a little more at the other. A bit like a teeter totter. This is where experimentation comes in. You can change your timing cam to crank in a easily through the removable cam access plate.
Spark timing changes are pretty minor with cam timing, but advancing 3 to 5 is a pretty safe bet when going from regular to premium fuel. Advancing the camshaft will cause the engine to be more knock limited at low speed, while retarding the camshaft will allow more spark advance at low speed. Minimum spark timing which yields the Best Torque from the engine is called MBT. MBT spark at peak power will be pretty Consistent with camshaft timing, so too much spark advance might lead to an over advanced condition -- 5 should be safe, but do not go much more than that.
Remember with experimentation it is pretty tough to get real numbers unless you set up some actual test locations and times with a video camera. The other alternative is to use a G-Analyst. It a device manufactured by Valentine Research. It can record actual times and accelerations and forces. It uses an accelerometer to record the test number. The other alternative is to use the G.A. method. This method is used by many, perfected by few. Held in highest esteem by those who don't even have a clue. Well, give up......It's the Golden Ass.
So what does all this mean? The new kits are a great way to gain that additional HP you are after. It is easy to install and fun to tune 😉 Check out the access cover!
Contact Information Rotational Dynamics 4648 Runway St. Unit B Simi Valley, CA 93063 (805) 587-6262
*Update - Original manufacturer has discontinued production of this product.