This is the fifth in a series of reports intended to document the results of progressive modifications to the LS650 engine.

Part 1 outlined the project, set the rules, and established the baseline performance values for a box-stock LS650.  You can find Part 1 here.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1620523526


Part 2 examined the airbox.  We improved performance dramatically with a few simple and inexpensive modifications.  It was a lot of bang for the bucks.  You can find Part 2 here.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1621150483


Part 3 took a hard look at the exhaust system.   We tried a Dyna muffler and a hybrid muffler that I manufactured.  We also tried the larger Mac header pipe.  The exhaust modifications provided significant improvements in acceleration and fuel economy.   You can find Part 3 here.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1623048749


Part 4 installed a performance carburetor and revisited the air filter.  You can find Part 4 here.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1625732492


Part 5 installs a new camshaft with higher lift and duration.  The results were gratifying and informative.  With some valve overlap, the exhaust header takes on a new role.

What I am about to describe worked good for me.  If you decide to try this stuff on your own, you assume responsibility for the outcome.  If you don’t have the skills, don’t do it.  If you don’t understand something, STOP and get help.  Get a manual.  Read up.  Comply with ALL the safety requirements outlined in the manual.  Make sure you know what you are doing before attempting any of these modifications.

Let’s get started.

The DR650 cam is a good choice for several reasons.

1. It’s an off the shelf part available at the local Suzuki dealer or any of the on-line parts suppliers (Partzilla, Babbitt’s Suzuki Parts House, Ron Ayers, BikeBandit, etc.).

2. It’s a bolt-in cam.  It doesn’t require a special set of springs, machining valve guides, notching the piston, etc.  It simply bolts right in, a direct replacement for the stock LS cam.

3.  It provides more duration, more lift, and some valve overlap.  Valve timing is close to the Stage 3 cam Lancer sells.

4.  It’s a brand-new cam, not a refurbished cam, so no core charge is involved.  The journals are pristine, and you keep your original stock cam.

The stock LS650 camshaft works OK considering it is a short-duration low-lift bumpstick.  It has zero valve overlap.  Overlap comes in handy.  It provides an avenue for inertia developed in the moving gasses to scavenge and fill the cylinder.  On a naturally aspirated engine, valve overlap makes it possible to achieve volumetric efficiency approaching, and sometimes exceeding, 100%.  Without valve overlap, you would need a turbocharger or supercharger to exceed 100% volumetric efficiency.
 
The table below provides timing and lift data that I took on a stock cam.  You can see that at any of the usual arbitrary lobe lifts (.020”, .040” or .050”) there is zero overlap.  If you look at the valve lift at top dead center (TDC), you can see the valves are barely open (.018” intake, .032” exhaust).  Not much air is gonna squeeze past a valve that’s only open .018”.

This is a graph of the intake curves for the two cams.  You can see that the DR cam opens the valve sooner and lifts it higher but closes the valve just a bit earlier than the stock cam.  Closing the intake valve a bit sooner can improve low speed torque, but it can also cause problems with detonation.  The DR cam has significantly more area under the curve than the stock cam has.

A visual comparison of the intake lobes should give you an idea how the two cams achieve different valve timing and lift.  The stock cam is on the left, the DR cam is on the right.

It appears that the lion’s share of lubrication is derived from the lobe dipping into the oil trough just below the cam.  As the cam rotates, the lobes dip into the reservoir of oil.

Changing the camshaft is not too difficult, but it does require an understanding of how to correctly set the timing.  If you don’t correctly time the cam, you run a good chance of wrecking your engine.  Get the manual.  Read up.  Understand what you are doing.  This post just hits on the highlights.

To get to the cam, you have to remove the head cover.  Rotate the engine to top dead center on the compression stroke.  Verify it’s on the compression stroke by checking that the intake and exhaust rocker arms have play.

Remove the fuel tank, decompression solenoid, breather hose, top engine mounts, carburetor, etc.  It should look like this, as much room as possible over the top of the head cover.

If you are working on an older LS with the “old style” rocker arms, I suggest you upgrade to the newer style rocker arms (12840-24B10 Intake, 12850-24B10 Exhaust).  You really don’t want to run your brand-new cam with a set of old, chewed-up rockers.  Replacement will require removal of the intake rocker shaft plug.  Best break it loose now while the head cover is anchored to the engine.