Only downside seems to be removal and replacement.  The stock screws can be replaced without removing the head cover.  These Cagiva screws require removal of the head cover.  They fit the rocker arms perfectly.

Tip contact was centralized on all four valves.  Should be OK.

This Stage II head incorporates a jack bolt to buck-up the rear chain guide and restore tensioner plunger engagement.  When I started the head swap, the plunger was at 16.5mm.  During reassembly, I adjusted the jack bolt to reposition the plunger to 12mm.  With the jack bolt feature, periodic adjustments are possible.  Now when I remove the clutch cover, I can inspect the tensioner and set it back to 12mm.  It’s a nice feature.

The jack bolt is just a piece of continuously threaded 5/16” rod.  The cylinder head must be spot-faced, and then drilled & tapped.  Of course, you do that when the head is off the engine

Once adjusted to the desired position, the jack bolt is locked in place with this special cap.

Removal and replacement of the cylinder head is straightforward.  It’s like doing a cam swap (plus a few more steps).  Part 5 of this series has good info on cam replacement.  While the head is off, modify the ports as discussed in the links I provided.   If you have an extra head, you can do the port work, then install it when convenient.

Set valve clearance to .005” and fill the crankcase with oil.  I must confess that I switched oil.  It was getting a bit too expensive.  I’m into this thing every week or two and I usually don’t re-use oil.  The Rotella T4 costs half of what Castrol V-Twin oil costs, and probably only one-fourth of what Mobile 1 V-Twin oil costs.  The Rotella will do for now.

A quick compression test pumped 160 psi.  No change.  Makes sense.  Same cam.  Same 56cc combustion chamber.  Same piston…..  Didn’t really do anything that would affect the compression ratio.   Ready for test.

How does it run?  Just fine.  Starts right up, idles smooth, revs quick.  It will absolutely bury the 8K tach.  No oil leaks.  No unusual noise.  The Cagiva valve adjusters survived a few laps around the block.  It’s always encouraging when your trick parts don’t fail in the first five-minutes of operation.

It was time for WOT acceleration tests.

Let’s review the setup.  Stage II ported head, DR 650 cam, 3” flywheel, stock piston, stock bore & stroke, stock compression ratio (8.5:1), modified airbox with K&N RD-0710 cylindrical filter element, PWK38 carb, stock exhaust header, LCGP high flow muffler.   Except for the ported head, everything is the same as it was for the Part 6 flywheel test.

I left the jetting as-is, a #35 pilot jet, #145 main jet, and the needle clip in the fourth groove (rich).

Second Gear 4K to 7K: 2.73 seconds            0.19 seconds faster than stock head

Third Gear 4K to 6.5K: 4.87 seconds            0.26 seconds faster than stock head

Third Gear 4K to 7K: 6.95 seconds            0.58 seconds faster than stock head

Fifth Gear 3.5K to 5K: 4.58 seconds            0.46 seconds faster than stock head

Fifth Gear 3.5K to 5.5K: 6.96 seconds      1.00 seconds faster than stock head

Wow!  That’s one sweet modification.  Nice fat improvements across the board.  Fifth gear pull to 5500 rpm is killer.  In addition, maximum rpm in third gear has increased by 100 (7550 vs 7450) and maximum rpm in fifth gear has increased by 400 (6450 vs 6050).  The porting doesn’t hurt the low end at all, and it extends the top end a bunch.  

What will happen when we throw on the Mac header?

Oil temperature and cylinder head temperature remain about the same (210/310), as does oil pressure.  Fuel economy is also about the same (55.4 mpg).  There’s no discernible change in audible noise.  Tha Cagiva adjuster screws are quiet (always a good sign).

This completes the cylinder head portion of the project.  The Stage II ported head was a huge success.  Performance has improved everywhere.  The biggest improvement was fifth gear acceleration (IMO, the most important test, passing power).

It is a relatively easy and inexpensive modification that will provide significant measurable improvements in performance, regardless of the cam or the compression ratio.  It demands free-flowing induction and exhaust systems.  It ain’t gonna work if you choke it off.

At this point, I have done 180 WOT acceleration pulls to dial in the different combinations.  There’s a little over 2600 miles on the engine since we started the project.  The old girl is still holdin up good.  No leaks.  No ugly noises.  Not using any oil.  Just a bit of oil accumulating in the catch-can.  It’s still a solid motor.

Next stop on the Power Train?  Compression.  Let’s see what happens when we bump up the squeeze.  Part 8 will install a Wiseco piston.

I hope some of you find this project informative and can use the data I collect to help make decisions on your own project.  If you have suggestions or comments on my test methods, post a reply so we can discuss.   As mentioned earlier, if you have a particular component or modification that you would like to see included, let me know and we can collaborate.
 
Best regards, Mike    

I'm glad you asked that question Ruttly.  I consider the epoxy buildup the most beneficial feature of the Stage II head.  Raising the floor of the intake port allows you to increase the short-side radius.  The column of air tends to lift off the bottom of the port as it makes the tight turn just before the valve seat.  That causes the air to pile up on the top side of the port.  You can see from this sketch that the short side radius is much larger (red line).