Still more hot air

[JHertzman@domain.elided]

Keith Hyndes correctly says "The 13% increase or so is on the mark if 
comparing a turbo charged non-intercooled engine, with an intercooled turbo 
engine. When Saab introduced intercooler on the 900, they went from 145 to 
175 HP, albeit with an extra 8 valves" but it does not follow that 
intercooling in itself contributed to the horsepower increase, and I assume 
that was not what he meant. A blown engine (whether centrifugal, rootes, vane 
or whatever, and whether driven by exhaust, gears, belts or whatever) does 
not generally need (or get) an intercooler if the boost pressure is modest; 
if the boost pressure and consequent temperature rise is substantial an 
intercooler allows more boost, but it is the "more boost" and not the 
intercooling which deserves the credit for the power gain. It is hard for me 
to see much relevance of intercooling in a discussion of naturally aspirated 
engines.

On the general question whether Alfas would benefit from breathing air which 
had not been preheated by the radiator, I believe the last multi-carb Alfa 
engine which breathed the general underhood atmosphere was the 6C 2500 SS 
which went out of production in 1951. The base single-carb 1900 and the 
single-carb Giulietta used the underhood air, but I believe that the 1900 TI, 
Giulietta Veloce, 2600 Sprint and Spider, the single-carb 105 Giulia, and all 
of the twin-carburetor (or injected) variants of the 1600-1750-2000 engines 
had either ducted air or an air-cleaner "snorkel" drawing from a suitable 
hole off to the side of the radiator bulkhead, as do all of the V-6s. I 
believe this is the case with all of the boxer engines also, although I have 
no personal experience with them.

Graham comes back to the question of how great is the power increase 
attributable to cool air induction? The difference in power between a 
Giulietta and a Giulietta Veloce was 10 hp, 12.5%, which is attributable to a 
combination of the cold ducted air, two Webers in place of the single Solex, 
7% higher compression (9.1 vs 8.5), 5% greater valve lift and about 5% longer 
duration. I would think that the Webers, the camshafts, and the compression 
ratio would get the lion's share of the credit.

John H.

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