This data is correct, coming from various sources, edited over the years..

Standard Stude 289 - 8.5:1 compression, 4 bbl, 225 HP

(R-series engines horsepower ratings are low estimates)
 R-1 -  10.25:1 compression, unsupercharged 289 cu.in., 4 barrel Carter,  
dual point distributer, 260 deg cam. Only engine offered with Air 
Conditioning.  240HP

 R-2  - same engine with 9:1 compression with a supercharger blowing into 
the pressurized carb thru a cast cap bolted to the carb. 280HP

 R-3  - custom built by Paxton (Granitelli), 289 bored out to 304.5 cu.in.  
9.5:1 compression, 276 or 288 degree cam, dual valve springs, forged 
pistons, larger port heads, pistons, manifold. dual point distributer, 
Standard 276 deg cam. dual point/mechanical advance distributer.   Carb in 
a pressure box and equipped with factory headers. Suspension mods included 
steel upper inners. All were hand assembled and dyno tested.  9 were sold 
in the total production run.  Engine numbers started with 'B9" . -335HP 

R-4 -  dual 4 barrel version of the R-3 but without the blower and 
12:1 compression.  276 or 288 degree cam.  dual point/mechanical advance 
distributer dual valve springs, forged pistons, larger port heads, forged 
pistons, None sold in an Avanti and only one sold in a 64 Daytona.  280HP 


editors Note:  Granitelli built a Bonneville experimental car (Avanti) which had 
dual paxton superchargers and an intercooled fuel injection system 
created from a Bendix aircraft unit.  It was called the "Duo Cento" in 
pursuit of the 200 mph run he was looking for.  The car achieved 196 mph 
after trials and was never used again.  After a year or so, it was 
dismantled and the parts misplaced, never to be heard of again.  There are 
those who refer to this engine as the "R-5", but this has never been 
sanctioned officially.  EST 500 HP


Pics of the Duo Cento are at ( cut and paste) 
 http://patriot.net/~jonroq/Archive/exotic.html