Why didn't Allison quickly develop a one-stage 2 speed Supercharger for the P-40

wuzak said:

Perhaps it is not necessary to read the whole thread, but the title instead:

Why didn't Allison quickly develop a one-stage 2 speed Supercharger for the P-40

In any case, the XP-40Qs were fitted with a 2 stage V-1710, and were based on P-40K or P-40N airframes. The engine was fitted by lengthening the fuselage ahead of the firewall.

Curtiss XP-40Q Fighter

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Some of the conversation spilled over into mentioning the Two Speed-Two Stage setup and that is what I was addressing.
Apologies for not being clearer on that.
As for the OP's question, I got into a discussion with someone here many years ago and they were quite knowledgeable about engines and blower systems.
One thing about single stage two speed systems is they are not as efficient as two stage-two speed systems.
It is better to re-pressurize the air going into an engine, rather than trying to increase the pressure put out by a single blower by simply increasing the speed of the impeller.
....then there's the whole intercooler/after-cooler idea...
However, from I did see so far, it seems we've touched on all that already.


Elvis

Schweik said:

And yet the V-1710-33 seems to have been producing 1580 hp routinely at low altitude in the actual field, not to mention the -73.... (at 60" Hg per the Allison memo) could a Merlin III do that?

Not suggesting Allisons were better than Merlins because I don't think they were - the altitude performance was very important, but low altitude performance also had some uses.

I also don't think the -33 was equivalent to a Merlin III frankly.

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I should have been more clear - the supercharger performance was similar to the Merlin III's supercharger.

The boost limits of the Merlin III was not limited by the supercharger, but the strength of the engine itself. The -33 was a later engine than the Merlin III, IIRC. Certainly the Merlin III didn't see widespread use beyond 1940.

Ok, found the book and did a bit of number crunching.
What I was looking for was the pressure ratio of the single stage superchargers. How many times the supercharger could multiply the pressure of the incoming air.

Engine................altitude................MAP...............pressure ratio
Allison -33..........13,200.................38.9in.................2.14
Allison -39..........11,700.................44.6in.................2.31
Allison -81..........15,500.................44.5in.................2.69
Merlin III............16,250.................42in....................2.69
Merlin X (HG)......17,750................41.5in.................2.74
Merlin 45.............18,000.................48in...................3.61
Merlin 45.............11,000.................62in...................3.13
Merlin XX.............18,500.................48......................3.23
Merlin 46..............23,000................48......................3.96
P&W R-1830.........14,500.................39.....................2.26
R-2600 B..............12,000.................44.5in................2.34
DB601..................14,750................39in...................2.29
DB605A................19,000................39in...................2.72
DB605A................18,700................42in...................2.88
DB605DB..............19,700................54in...................3.85

As can be seen from the pressure ratios the Allison was right in with the other American single stage superchargers.
There are at least 3 different early DB601 engines with critical altitudes from 3700 to 4500 meters, I used the highest one and figured 1.3 ATA as 39 in.
Some rounding off was done.
On the world stage the Allison was doing all right except when compared to the Merlin.