Some time ago as I was surreptitiously lurking on the subaruvanagon list
(before being caught and excised by Warren as an unwelcome alien) I perused a
minimalist tome penned by pensioner that waxed enthusiastically about the
modern design of the Subaru engines and their great efficiency as compared to
the VW ilk. Well, as some of you might imagine, this stimulated my seating
area, and I'm moved to respond. Numbers are good. Measurements are good.
Mechanical (careful here) feelings are often not real. The theory of the
nonlinear tail desperately sensing the positive improvement stimulated by the
most recent and stunning infusion of cash into the bottomless cash consumer.

So, anyway, I decided to prepare an table that could compare the mechanical
efficiency (and therefore engineering prowess) of the various engines that
could power these bricks through the ether. The quantity of comparison I have
chosen is the brake mean effective pressure developed in the combustion
chamber while doing work on the piston. The number is derived from the peak
torque developed at the flywheel per unit engine displacement. These numbers
are readily calculated from the meager engineering data provided by the
reclusive Subaru personnel, and are readily expanded by the addition of your
favorite heat pump. I have arranged the values in ascending order of higher
pressure (means higher efficiency). Pressure expressed in units of psi. In
essence, the torque maximum represents the peak volumetric efficiency of the
pump as well as the maximum efficiency of completely consuming the available
fuel for air heating. This number is a function of the combustion chamber
design, the intake and exhaust manifold flow dynamics, cam and ignition
timing, etc.,etc. Bigger is better. (Also often newer.)

Engine  Displacement    Torque      BMEP
             (liters)       (ft.lb.)        (psi)

Vanagon 2.0L A/C          101@3000      126.9
VW GX       1.8L I4        96@3000      132.8
VW MZ       1.8L I4        98@3250      135.6
Vanagon 1.9L WB       106@2600      136.6
Subie 2.5   2.5L WB (<96)     144@2800      136.6
Vanagon 2.1L WB       117@3200      136.7
VW 9A       1.8L I4       113@4400      140.8
VW HT       1.8L I4       105@3000      145.3
AUDI 2.3    2.3L I5       140@4500      149.7
VW RV       1.8L I4       109@3800      150.8
Audi 3A 2.0L I4       121@3200      150.8
VW ACC      1.8L I4       107@3500      150.8
VW AAZ      1.9L I4 TD        107@2500      150.8
Subie 2.5   2.5L WB (>97)     162@2800      150.8
Subie SVX   3.3L WB       228@4400      150.8
VW ABA      2.0L I4       122@3200      152.0
VW RD       1.8L I4       110@3200      152.2
VW AAA      2.8L I4       173@4200      152.6
Subie 2.2   2.2L WB       137@4400      153.0
Subie 2.5   2.5L WB P II      166@2800      157.4
VW PF       1.8L I4       114@3800      157.7
SAAB 2.0    2.0L I4       128@3000      159.5
TIICO (SA)2.0L I4         132@3500      164.5
Subie 2.2   2.2L WB P II      149@3600      166.4
VW AHY      1.9L I4 TD  i     149@1900      193.7
VW 1.9 TDi1.9L I4 TDi     155@1900      201.5
Subie 2.2T2.2L WB T       181@2800      202.2
VW 1.8T 1.8L I4 T         162@2200      224.1
SAAB 2.0T   2.0L I4       188@3000      234.3

Some comments:

1. The table is in 12 point Monaco Font.
2. The engine longest in the tooth is the old Type 4, followed closely by the
old low compression I4 CIS engines, and Vanagon WB engines.
3. Note that the pre 96 Subie 2.5L engine is just as inefficient as the
Vanagon WB's.
4. The 1.8L Digifant engines (RV, RD and PF) are much stronger than the VW
waterboxers as well as the 1.8L CIS and CIS-E engines.
5. The Subie SVX and the late 2.5 engines are no more efficient than the post
1988 VW engines.
6. The ABA cross-flow head (2.0L) and the VR6 are at the same generation and
are very good.
7. The SAAB 2.0L (very similar to the chipped Digifant or Bosch LH-Jetronic
driven Audi 3A or RV/PF engines) is a very efficient design.
8. If the TIICo numbers are to be believed, this 8 Valve head with Motronic
management outperforms the ABA crossflow head with Motronic.
9. The latest phase II engine design of the Subie 2.2 is a competitive WB, as
is the phase II 2.5L Subie.
10. The 1.9L and TDi engines are very efficient in this comparison.
11. The turbocharged gas engines lead the pack, with the highest efficiency.
The volumetric efficiency achieved by the pressurized inlet far exceeds
pumping losses due to inserting the turbo in the exhaust stream.
12. So, the VW WB's and the old A/C engine are really from an elder time, as
are the same vintage Subies. The I4 engines are right there with the
strongest. Only the turbos do better. Go to the turbo if you can.

Frank Grunthaner