This is the seventh 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 (home-built).  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.  The larger carb and filter extended the upper rpm limit.  Overall performance was improved.  You can find Part 4 here.

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


Part 5 installed a new camshaft with higher lift and duration.  The results were gratifying and informative.  Big power gains were evident.  Now, with some valve overlap, the exhaust header took on a new role.  You can find Part 5 here.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1626391255


Part 6 installed a lighter flywheel.   The results were surprising.  Acceleration in the lower gears was improved, while top speed suffered a bit.  You can find Part 6 here.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1626921647


Part 7 installs a ported cylinder head.  The Stage II head flows significantly better than the stock head.  More airflow equals more power.  It’s an eye opener.


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.

About three years ago, Fast650 turned me on to an article about a home-built flow bench.  It was a simple device.  I decided to build one using the concepts discussed in the article.  Mine isn’t nearly as nice, but it’s perfect for our LS650 cylinder heads.  The bench is not calibrated, but it will verify an improvement in flow, and it quantifies the improvement as a percentage.  It’s a tool that can measure flow and provide consistent, repeatable data.
 
Once I had a tool to measure flow, I started experimenting with various port modifications.  The Stage II and Stage III heads were developed using the little flow bench.  We will be installing a Stage II head.  I have a well-used specimen.  It’s perfect for this project.

The head has a set of DR650 valves (33mm/28mm), RD valve spring kit, and shortened valve guides (all to accommodate the additional lift of a Web 340b cam).  The DR valves, RD spring kit, and shortened valve guides have absolutely no affect on flow, they simply accommodate the higher lift cam.

The Stage II modifications include:

-Raised intake port floor

-Widened intake port runners

-Exhaust port outlet enlarged to 1.5”

-Exhaust port guide bosses radiused

-Blended valve seats and bowls

-Back-cut valves

In this post, I’m not going into all the details of the port modifications.  If you review these old posts, you will see that the stuff I summarized above is very easy to accomplish.  You don’t need to change the valves, valve springs, or retainers.  The stock components work fine with the DR650 cam.  The old posts provide port maps, dimensions, required materials, and most of the how-to.  The Stage II head is essentially the same as the Stage III except for the 34mm intake valves and the 1.79” exhaust port outlet.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1554362214

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1595224521/0

This graph shows the exhaust flow of a stock head compared to a Stage II ported head and a Stage III ported head.  At max flow, the Stage II has a 19% advantage over the stock exhaust port.

I think the Stage III exhaust port should be reserved for larger displacement applications (97mm bore) with the larger Mac header (1.79”).   The Stage II port (1.5”) works good on smaller displacement applications (94mm bore) with the stock header.

I use epoxy to raise the intake port.  You can see from this picture that the epoxy is stained, but it’s still in good condition.  It’s hangin in there.  The intake port doesn’t get very hot.  The intake valves are a little crusty, but it wasn’t worth the trouble to disassemble and clean.  Ain’t gonna win no beauty contests, but she’s solid.

Another part of the exhaust port that responds well to grinding is the left runner.  It has a straight vertical wall that can be rounded out with a carbide burr.  The yellow line shows where to grind.  Don’t get carried away, just make it round and blend it in.  My old post regarding the Stage III head provides good details.

The intake valve stems looked OK, round wear patterns centralized in each stem.  The retainers & cotters looked good too.  As mentioned previously, the stock valves, retainers, cotters and springs work perfectly with the DR650 cam, the RD spring kit is not necessary.  I didn’t want to change these parts.  They shouldn’t have any effect on the acceleration tests and I didn’t want to tamper with the head.

Back in April, during a routine inspection I found a chunk missing from an adjuster.  It was on the intake rocker arm.  I attributed the fracture to edge loading.  The 340b cam has a lot more lift.  The extra lift appeared to swing the adjuster screw far enough to cause the sharp edge of the screw to contact the valve tip.

Then polished it up.  It came out good, so I did the same thing to the other three screws.