Supercharging vs. Turbocharging

TurboSystem Response Video #1

The differences between turbos and superchargers are subtle but important.  Both provide additional air into the engine for more power.  The most essential difference is the method of driving the turbo or supercharger.  Turbochargers are driven by exhaust energy which is usually otherwise wasted out of your tailpipe into the atmosphere.  Superchargers are driven by a belt which draws power from your engine's crankshaft.  The advantages of turbocharging over supercharging include:

1.  More power produced per pound of boost (intake pressure), since the turbo does not rob engine power from the crankshaft like a supercharger. 

2.  Variable power levels: a turbocharged engine can be set up to provide different power (boost) levels at the push of a button, while a supercharged engine requires changing pulleys and belts to change power levels.  This turbocharger versatility can be quite handy in many instances.

3.   No maintenance, adjustment or replacement of drive belts and pulleys is required for turbochargers, an aspect which frustrates some supercharger owners.

4.  Turbos offer much higher overall power potential, with the ability to be modified easily for higher power levels in the future.  Superchargers are more expensive to upgrade for more power, if upgrades exist at all.

5.  A supercharger's drive belt will stress the crankshaft and adjacent main bearing due to the additional strain of driving the supercharger, while turbochargers are widely regarded as being quite easy on engines.  It is not unusual to see stock type engine components surviving at power levels of two to three times their stock output when turbocharging is employed!

6.  The TurboSystem will usually be easier to install, especially on four cylinder engines.

EGT Monitoring

EGT (exhaust gas temperature) monitoring can be a very effective tool in tuning, but "ideal" EGT can vary from engine to engine dependant upon combination.  Usually, 1300 to 1500 degrees F is optimal for normally aspirated engines on gas, while gas turbos will run optimally @ 1500 to 1650.  An important note:  this is measured before the turbo, not after, as the turbo will reduce EGT by an average 200 degrees F.

Finding the optimal EGT signature for your engine is a trial and error (hopefully more trial than error!) procedure, and other factors such as power output, plug readings and air fuel ratio equipment should be used to corroborate the data.  Once you have ascertained this ideal EGT, it should be repeatable regardless of climatic conditions:  simply tune for the same previously determined optimal EGT, and your engine should perform at full available output under any ambient conditions.

Easy error for new users of EGT: high temps indicate lean condition.  Not always true!  Excessively rich conditions will result in "after burn", where the fuel, which was unable to completely combust due to insufficient oxygen in the cylinder, lights off in the exhaust system, causing an unusually high temp reading.  If all other indicators still suggest a rich mixture, try leaning in small steps, and you will likely see the EGT go down.  Just be sure that the power does not also go down from the changes.  If you are on the right track, power should go up noticeably as you lean towards optimal mixture while EGT drops.  As you approach and then pass the optimal mixture point, the EGT will begin to climb again.  STOP! Richen by one step and you are there!  Now, when climatic conditions worsen (i.e.: hotter temperature, more humidity, less air density), lean until you get that optimum EGT again.  If conditions improve (colder weather, lower altitude, less humidity), richen for optimal EGT.  Bear in mind: if EGT suddenly changes for no apparent reason, you may have an aggravating factor (ignition problem, fuel pressure wrong, clogged air inlet, etc.) which is unrelated to tuning.  Be observant, and the indicators should guide you to the right tuning decision. 

Another caveat:  Air fuel ratios, which are not optimal throughout the entire available RPM and manifold condition range, will mislead you.  In other words, an optimal EGT signature at high RPM may not show an incorrect condition at lower RPM or different manifold pressure.  Although perplexing, this problem is truly the difference between a happy, powerful and long-lived engine and one that is trying to destroy itself slowly but surely.  It is one reason why the precision of fuel injection is usually superior to carburetion in both power production and engine life.  Just watch ALL the indicators, and remember: lean is mean, and fuel is power.  Instead of continuously trying to lean it for maximum HP, try to find ways to get more air to the engine, and thusly support the combustion of more fuel.  There's only so many BTU's in a gallon of fuel, no matter how you burn it.  Just try to burn more fuel!