This is the eighth 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 installed a ported cylinder head.  The Stage II head flowed a lot better than the stock head.  More airflow equals more power.  It was an eye opener.   You can find Part 7 here.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1627891507


Part 8 will bump up compression.  The stock compression ratio (CR) is only 8.2:1.  That’s great if you want to run low-octane fuel, but if you want more power, crisper acceleration, better fuel economy, and a tire twistin cruiser, you’ll be needin more squeeze.  Getting that CR up around 10:1 or better makes a huge difference in performance and efficiency.

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 pop-top has a compression height that is only .025” taller than the stock piston.  The boost in compression ratio comes predominantly from the raised pop-top that sticks up about .060” above the basic top of the piston.

Here you see the stock and pop-top pistons sharing a wrist pin.  They have almost identical compression heights, but the pop top has an area that sticks up about .06”.

The flat-top is a different story.  Here’s the flat-top sharing the same wrist pin with the stock piston.

Rather than give you a blow-by-blow on piston installation, I am going to provide links to old posts.  I just didn’t have it in me to tear it down and do all the associated work and testing for the two high compression pistons.  I had already done it once for each piston and the posts were decent, so I figured they would be good enough.

This post provides a good summary of the pop-top installation and testing.  The test regimen is not the same as the regimen I have been using on this project, but it will give you a good idea of what’s involved and what to expect.   You will notice that when I did the post, I was worried about cranking pressure.  At the time, I felt that the pop-top was better suited for street applications.  It kept cranking pressure below 200 psi.  You can disregard those comments.  I have since learned through personal experience that the Savage will tolerate cranking pressures well over 200 psi.  You can expect about 155 psi from the stocker, 195 psi from the pop-top, and about 235 psi from the flat-top.  

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1585106199

 

If you read both of those old posts, you will see that the flat-top piston performs a lot better than the pop-top.  It vibrates less, runs cooler, gets better fuel economy, and is significantly faster.  The boost in compression combined with the tight quench work together to improve combustion and thermal efficiency.  The flat-top is way better.  The only advantage the pop-top has is ease of installation.

Let’s look at the acceleration test results.

This was the setup for the 94mm flat-top engine.  Stage II ported head, Web 340b cam, 3” flywheel, stock bore & stroke, increased compression ratio (10.4:1 for flat-top), modified airbox with K&N RD-0710 cylindrical filter element, PWK40 carb (actually 38mm), Mac 1.79” exhaust header with LCGP high flow muffler.   Except for the high compression piston and Web cam, everything is the same as it was for the Part 7 ported head test.

Here are the results for the Wiseco flat-top.  It’s killer fast.

Second Gear 4K to 7K: 2.41 seconds            0.27 seconds faster than stock piston

Third Gear 4K to 6.5K: 4.19 seconds            0.63 seconds faster than stock piston

Third Gear 4K to 7K: 5.61 seconds            0.99 seconds faster than stock piston

Fifth Gear 3.5K to 5K:       4.10 seconds            0.66 seconds faster than stock piston

Fifth Gear 3.5K to 5.5K: 6.45  seconds      0.74 seconds faster than stock piston

Operating Temperatures

Cylinder head temperature (CHT) was always higher on the engines with the stock piston or the Wiseco pop-top.  With both pistons, CHT ran around 310°and would routinely approach 330°-340° CHT.   The flat-top piston always ran around 280°-300° CHT.   We’re talkin cruise, not stuck in traffic.
 
Oil temperature followed the trend.  The stock piston and pop-top would motor along with oil temp around 200°-220°.  The flat-top runs around 180°-200°oil temp.

Durability

All three pistons held up well.  There was no evidence of wear or distress.   Oil consumption throughout all the testing with all the pistons was zero.  I never had to add oil on any of the projects.  My breather catch can never collected more than a drop or two of oil (it was usually bone dry).

The stock piston was a used eBay special.  I have no idea how many miles were on it when I installed it.  For this project, I logged 2917 miles and at least 180 WOT test pulls.  Visually it looked exactly the same as when I installed it.