Best 928 to Turbocharge?

The question of which of the model years of 928 are best to turbocharge is often asked.  While on the surface it may seem like all 928s are equal lfor adding manifold pressure to, the reality is there are many differences which make some cars very cood candidates and other cars very poor candidates.

The 928 is a wonderful car that went through many variations throughout its production history.  It has a loyal following and represents a great bargain in today's used Porsche market.

For starters, if we were to make a wish list of features our 928 should have to make it easy for adding turbo power it would look like this:

  • Ability for stock internals to handle a lot of manifold pressure
  • A strong base HP engine
  • A stock fuel and ignition system that can be used to feed the engine on boost
  • Ample suspension and brakes for the added power
  • A tall rear end gear to make the best use of the turbocharged engine's torque
  • The base car must be reasonably priced

The best 928s for turbocharging are the 1987 and 1988 5-spd cars and this is for the following reasons:

  • Strong, thick ring lands
  • 316 HP stock
  • LH can handle 72 lb/hr injectors and LH and EZK can be massaged with Shark Tuner
  • Dual knock sensors and timing retard by cylinder is present
  • Car comes stock with 4-piston brakes
  • 2.20:1 rear end gear allows for nice wide powerband and can make use of bigger turbos
  • Cars can be purchased for around $10,000-$15,000 in excellent condition

While most of the positives above apply to all 32V 928s, the 85-86.5 models are severely limited in their engine management by only allowing about a 36 lb/hr injector set and in addition they don't have knock control which makes wringing the last bit of power out of the engine significantly more risky.  The intake manifold is also somewhat more difficult to get around.  You only get the S4 suspension and brakes on the 86.5.

The GT models are very good candidates for turbocharging, however they are somewhat more expensive and have a deeper reduction in the rear end making it more difficult to get traction under boost.  We rate these as 2nd best on the list of 928s to turbocharge. 

The GTS models are very pricey and some have been known to have a weaker set of connecting rods that bend under boost.  Their only real benefit is being able to fit a wider set of rear tires and to be able to say one owns a GTS.  Not remotely worth the extra money in our opinion.  For the price of a nice GTS, you can buy a nice S4 and turbocharge it.

While there are many 16V variants out there, most US cars are severely limited on power production because of the low starting power of 220 HP.  The CIS fuel injection on early cars is limited and problematic and in addition there is no knock control on these systems.  In addition, the early 16V cars have a very weak set of piston ring lands that easily break under any detonation.  Some of the Euro cars are far more powerful, but then you have the same limitations on fuel and spark management. 

With nearly a solid decade of modifying and building turbocharged Porsche 928s we can stand firmly on our assessment above.

© 2011 Kuhn Performance Technologies.