Pratt vs Wright

[tomo pauk]

Can you please explain this chart to me?

Why does the R-1830 have less horsepower at 8,000 feet that 10,000 feet? In both cases the blower is on low, and at 8,000 feet the atmosphere is denser.

Exactly because the atmosphere is denser.
When the auxiliary S/C is in 'low' gear on the R-1830-86, the rated altitude (a.k.a. critical altitude) is at about 12000 ft. Rated altitude is the altitude above where the throttle can be fully opened; under that rated altitude the throttle is partially closed in order for the boost to be kept constant, or the engine might suffer detonation due to over-boosting. Lower we go under the rated altitude, the more throttling is needed to keep the boost in check; more throttling = more losses = less power. Obviously, if we go at even lower altitude, the supercharger need to start using a lower gear (if present - there was a lot of engines that have had just one S/C speed) so the throttle can be fully opened now (= less losses = more power) and the S/C will be drawing less power (= again more power). When in 'neutral' gear (as found on P&W 2-stage supercharged engines), the auxiliary S/C stage is de-clutched, or disengaged, meaning it draws no power from engine, meaning again there is more power left to turn the prop; the aux-stage is bypassed by the 'plumbing' and all supercharging is done by engine-stage supercharger.
Note that less dense atmosphere at 12000 ft than it is on, say, 8000 ft, will also mean that the exhaust backpressure is lower, and the air entering the cylinders is cooler a bit - those two things might add slightly to the engine power.

Please note that the graph is not very accurate when it is about lines under the rated altitudes, the power loss due to throttling is/was a lot less severe. Graph was not made by engine companies, but it was done by F. Dean by using the known power vs. altitude values. I'll attach the manufacturer's graph for the engine of FM-2.



The engines with swirl throttle managed to avoid a lot of throttling losses (Mikulin AM-35A and later, Jumo 213 series), so did the engines with hydraulically-driven supercharger (DB 601 and later engines, the V-1710 versions with hydraulically-driven auxiliary stage, as installed on P-63 and P-82 - they still have had throttle plates). The turboed engines were also not suffering much due to throttling losses, if at all, they used waste gates as means of avoiding not-certified over-boosting.

 

[kitplane01]

Exactly because the atmosphere is denser.
When the auxiliary S/C is in 'low' gear on the R-1830-86, the rated altitude (a.k.a. critical altitude) is at about 12000 ft. Rated altitude is the altitude above where the throttle can be fully opened; under that rated altitude the throttle is partially closed in order for the boost to be kept constant, or the engine might suffer detonation due to over-boosting. Lower we go under the rated altitude, the more throttling is needed to keep the boost in check; more throttling = more losses = less power. Obviously, if we go at even lower altitude, the supercharger need to start using a lower gear (if present - there was a lot of engines that have had just one S/C speed) so the throttle can be fully opened now (= less losses = more power) and the S/C will be drawing less power (= again more power). When in 'neutral' gear (as found on P&W 2-stage supercharged engines), the auxiliary S/C stage is de-clutched, or disengaged, meaning it draws no power from engine, meaning again there is more power left to turn the prop; the aux-stage is bypassed by the 'plumbing' and all supercharging is done by engine-stage supercharger.
Note that less dense atmosphere at 12000 ft than it is on, say, 8000 ft, will also mean that the exhaust backpressure is lower, and the air entering the cylinders is cooler a bit - those two things might add slightly to the engine power.

Please note that the graph is not very accurate when it is about lines under the rated altitudes, the power loss due to throttling is/was a lot less severe. Graph was not made by engine companies, but it was done by F. Dean by using the known power vs. altitude values. I'll attach the manufacturer's graph for the engine of FM-2.



The engines with swirl throttle managed to avoid a lot of throttling losses (Mikulin AM-35A and later, Jumo 213 series), so did the engines with hydraulically-driven supercharger (DB 601 and later engines, the V-1710 versions with hydraulically-driven auxiliary stage, as installed on P-63 and P-82 - they still have had throttle plates). The turboed engines were also not suffering much due to throttling losses, if at all, they used waste gates as means of avoiding not-certified over-boosting.

Questions:

1) Is the pressure reaching the cylinders at 12,000 and 8,000 feet the same?

2) The less-hp-at-8000 is because of extra pumping losses in the supercharger, pushing air through a partially closed throttle?

3) If this is a supercharger-using-extra-power problem, did turbosupercharged engines have the same shape curve?

I like learning.

 

[tomo pauk]

Questions:
1) Is the pressure reaching the cylinders at 12,000 and 8,000 feet the same?
2) The less-hp-at-8000 is because of extra pumping losses in the supercharger, pushing air through a partially closed throttle?
3) If this is a supercharger-using-extra-power problem, did turbosupercharged engines have the same shape curve?

1 - Yes.
2 - Yes.
3 - Turbosupercharged engines, at least the US ones back in ww2, have had almost flat power curves, from the SL up to the (one and only) rated altitude, that was usually at 25000 ft. The US turboed engines used the turbo to 'convince' the engine that is still at sea level, so to speak, even if it was at 25000 ft, by providing a bit over the sea-level pressure at carburetor. The engine-stage supercharger took over after the carb, pressuring the air further. Capacity of the turbo to provide extra boost was used up via the water-injection kit on P-47D, so the engine that was making 2000 HP in military rating was able to provide ~2300 HP in the 1st iteration of the water-injection kit, ~2600 HP shortly after, and ~2800 HP when water-injection was used in conjunction with 150 grade fuel. The P-47N used an improved turbo, that was also allowed for greater RPM, that
Note that engine-stage superchager on US turboed engines were using 1-speed 'low' gearing. The German and Japanese engines that gained turbocharger were still using 2-speed drives, meaning an increase of power above 25000-30000 ft.

I like learning.

Stick around.

 

[kitplane01]

1 - Yes.
2 - Yes.
3 - Turbosupercharged engines, at least the US ones back in ww2, have had almost flat power curves, from the SL up to the (one and only) rated altitude, that was usually at 25000 ft. The US turboed engines used the turbo to 'convince' the engine that is still at sea level, so to speak, even if it was at 25000 ft, by providing a bit over the sea-level pressure at carburetor. The engine-stage supercharger took over after the carb, pressuring the air further. Capacity of the turbo to provide extra boost was used up via the water-injection kit on P-47D, so the engine that was making 2000 HP in military rating was able to provide ~2300 HP in the 1st iteration of the water-injection kit, ~2600 HP shortly after, and ~2800 HP when water-injection was used in conjunction with 150 grade fuel. The P-47N used an improved turbo, that was also allowed for greater RPM, that
Note that engine-stage superchager on US turboed engines were using 1-speed 'low' gearing. The German and Japanese engines that gained turbocharger were still using 2-speed drives, meaning an increase of power above 25000-30000 ft.



Stick around.

So maybe one answer to my question would be this:

In 1944 is was possible to make a turbo-supercharger, eliminate the engine driven supercharger, and use that for large radials. Doing so would have saved a few hundred horsepower, along with better fuel economy and more power at certain altitudes.

That would be about a 10% increase in horsepower (more at certain altitudes), and a 10% increase in fuel economy. I don't think it would make the engine weigh less or be more reliable.

By "more at certain altitudes" I mean those altitudes that have dips in the horsepower/altitude chart.

Why was this not done?

 

[tomo pauk]

So maybe one answer to my question would be this:

In 1944 is was possible to make a turbo-supercharger, eliminate the engine driven supercharger, and use that for large radials. Doing so would have saved a few hundred horsepower, along with better fuel economy and more power at certain altitudes.

That would be about a 10% increase in horsepower (more at certain altitudes), and a 10% increase in fuel economy. I don't think it would make the engine weigh less or be more reliable.

By "more at certain altitudes" I mean those altitudes that have dips in the horsepower/altitude chart.

That idea was not limited just for large radials. Yes, getting rid of engine-driven supercharger means a gain in BHP since the engine does not need to drive that supercharger, just like it is done in most of the modern cars' engines last decades.
On the other hand, not everyone knew how to make reliable and powerful turbocharged engines, and not everyone was good in fuel injection.

Why was this not done?

Want my opinion on design & production choices made back then, or a justification from the engineers from 1940s?

 

[Reluctant Poster]

That idea was not limited just for large radials. Yes, getting rid of engine-driven supercharger means a gain in BHP since the engine does not need to drive that supercharger, just like it is done in most of the modern cars' engines last decades.
On the other hand, not everyone knew how to make reliable and powerful turbocharged engines, and not everyone was good in fuel injection.



Want my opinion on design & production choices made back then, or a justification from the engineers from 1940s?

The engine driven supercharger improved distribution of air to the cylinders. This was the primary function of the early superchargers which did not have high pressure ratios. There were actually some surprisingly intelligent people back in the day so they likely had good reasons to do what they did. Knowledge builds on knowledge.

 

[Shortround6]

In 1944 is was possible to make a turbo-supercharger, eliminate the engine driven supercharger, and use that for large radials. Doing so would have saved a few hundred horsepower, along with better fuel economy and more power at certain altitudes.

The engine driven supercharger improved distribution of air to the cylinders. This was the primary function of the early superchargers which did not have high pressure ratios.

In fact in the 1920s the rotating impeller between the carb/s and the intake tubes was sometimes called a "mixing fan". Making sure that the top cylinders got somewhat the same mixture as the bottom cylinders did. If V-12s have problems getting the same mixture to different cylinders then radials had a real problem. Having individual tubes coming right off the supercharger diffuser helped quite a bit.
Maybe you could get the idea to work using modern turbos and flow knowledge. GE turbos in WW II were actually pretty lousy superchargers. The compressor sections were low efficiency. You got a hotter intake charge temperature for the same amount of pressure. Which means the air is actually less dense.
By eliminating the two stage set up you now have a low altitude engine. A P & W R-1830 engine of 1200hp take-off rating was using 48in (9lbs boost) at take off. Most GE turbos could provide sea level pressure (30in) at 25,000ft for a pressure ratio of 2.7. The turbo engine may very well give you the same or more power between sea level and 12-13,000ft but above that it may only tie or fall slightly behind the single stage, two speed mechanical supercharger. altitude performance is gone. You used up about 25% of your supercharger capacity(pressure ratio) just getting to normal take-off power.
There may have been a very good reason that the turbos were always (on production aircraft) mounted a number of feet away from the engine in that the turbine section could only handle exhaust gases of a certain temperature and a close mounted turbo might be overheated. There is little doubt such an installation would be bulkier.

I would also note that by 1944 on the R-2800s they were using different exhaust systems than earlier planes and getting some exhaust thrust. This varied on individual aircraft.
F8F

from Texas Flying Legends Museum Bearcat Restoration

 

[XBe02Drvr]

In 1944 is was possible to make a turbo-supercharger, eliminate the engine driven supercharger, and use that for large radials

In A&P mechanic school we took apart and reassembled several radial engines of various sizes (W670 Continental, Pratt R985, Wright R1820) and had an electrically driven rotating cutaway of a Wright R3350. They all had their engine driven superchargers built right into the nose case, integral to the reduction gearing and the induction plumbing. The class wise-ass spouted off to our instructor that seemed like a stupid idea, and we got an assignment to think up an impeller-less intake manifold design for a twin row radial that would guarantee even mixture distribution to all cylinders, not obstruct cooling airflow, and fit into a tight cowling. "Huh? Hey boss, we're not engineers!"
"No, but you aren't stupid either, and have access to a library. Go figure it out if you can. Anyone comes up with a workable solution, I'll find him a scholarship to engineering school. He'd be wasting his time here!"
No workable solutions, but several entertaining plumbing nightmares. And Mr Hamm, not an engineer, had an amazing grasp of flow dynamics.
Cheers,
Wes

 

[Admiral Beez]

The USSR, Germany, and Britain had just one large displacement air-cooled radial manufacturer; Shvetsov, BMW and bit parts from Armstrong-Siddeley aside, Bristol.

Like the USA, Japan and France had two large displacement air-cooled radial suppliers; Mitsubishi and Nakajima, and Gnome-Rhône and Hispano-Suiza (licence-built Wright Cyclone). Only Italy had three major radial suppliers, Fiat, Alfa Romeo and Piaggio.

Did the US consider giving all radial production to P&W or Wright? Or did the Pentagon recognize the advantages of two competing firms striving for their best? Perhaps the first option was considered, but risks to supply were deemed too great.

 

[gjs238]

In A&P mechanic school we took apart and reassembled several radial engines of various sizes (W670 Continental, Pratt R985, Wright R1820) and had an electrically driven rotating cutaway of a Wright R3350. They all had their engine driven superchargers built right into the nose case, integral to the reduction gearing and the induction plumbing. The class wise-ass spouted off to our instructor that seemed like a stupid idea, and we got an assignment to think up an impeller-less intake manifold design for a twin row radial that would guarantee even mixture distribution to all cylinders, not obstruct cooling airflow, and fit into a tight cowling. "Huh? Hey boss, we're not engineers!"
"No, but you aren't stupid either, and have access to a library. Go figure it out if you can. Anyone comes up with a workable solution, I'll find him a scholarship to engineering school. He'd be wasting his time here!"
No workable solutions, but several entertaining plumbing nightmares. And Mr Hamm, not an engineer, had an amazing grasp of flow dynamics.
Cheers,
Wes

Direct fuel injection?

 

[XBe02Drvr]

Direct fuel injection?

Even that doesn't work well unless air distribution is perfectly equal, or you're going to get into individual tuning of injectors, and you're going to be running in mostly steady state conditions. Maybe OK for bombers and transports, but not for fighters.

 

[swampyankee]

The USSR, Germany, and Britain had just one large displacement air-cooled radial manufacturer; Shvetsov, BMW and bit parts from Armstrong-Siddeley aside, Bristol.

Like the USA, Japan and France had two large displacement air-cooled radial suppliers; Mitsubishi and Nakajima, and Gnome-Rhône and Hispano-Suiza (licence-built Wright Cyclone). Only Italy had three major radial suppliers, Fiat, Alfa Romeo and Piaggio.

Did the US consider giving all radial production to P&W or Wright? Or did the Pentagon recognize the advantages of two competing firms striving for their best? Perhaps the first option was considered, but risks to supply were deemed too great.

I think a major difference between the US and the other nations' makers of large radial engine makers is that the US had a much more robust commercial air transport sector*: it could support two makers of large radial engines; none of the European* countries had much of a commercial air transport industry**, so there was a limited non-governmental market for engines.

---------

* The USSR, due to its vast size, may have been able to build one, but Russia was probably the least industrialized of the pre-WW1 great powers (and the urbanization necessary for industrialization was considered dangerous to the ideology of autocracy, orthodoxy, and social order held by Nicholas II and his supporters), and the Revolution and subsequent civil wars were very damaging to the national infrastructure and killed large numbers of people. Further, even post-Revolution, the soviet government was not particularly willing to permit workers' mobility.

** Western Europe is densely populated, geographically small, and quite well-connected by efficient rail lines.

 

[Shortround6]

Did the US consider giving all radial production to P&W or Wright? Or did the Pentagon recognize the advantages of two competing firms striving for their best? Perhaps the first option was considered, but risks to supply were deemed too great.

You forgot the smaller engine makers, Lycoming, Continental, Jacobs, and Kinner. A few more of even smaller engines. The US had, by far, the largest, most robust, civilian aviation market in the world in the late 20s and 30s. The US market may have been as large as all of Europe put together.
It wasn't up to the US Government to decide who made what. It was up to the Market place. The US market place was big enough for multiple engine makers even without government support. By the late 30s (1938 and after) it was too late to try to shut a company out, they needed all the production they could get.
Wright in the early/mid 30s was making 3 different sized 9 cylinder radials, plus experimenting with a few others. P&W had the R-1340 Wasp, the R-995 Wasp Junior, the R-1690 Hornet, the R-1860 Hornet (less said the better) and the R-1830 14 cylinder. It actually came before the R-1535.

 

[kitplane01]

That idea was not limited just for large radials. Yes, getting rid of engine-driven supercharger means a gain in BHP since the engine does not need to drive that supercharger, just like it is done in most of the modern cars' engines last decades.
On the other hand, not everyone knew how to make reliable and powerful turbocharged engines, and not everyone was good in fuel injection.



Want my opinion on design & production choices made back then, or a justification from the engineers from 1940s?

Yes, both please.

 

[kitplane01]

In A&P mechanic school we took apart and reassembled several radial engines of various sizes (W670 Continental, Pratt R985, Wright R1820) and had an electrically driven rotating cutaway of a Wright R3350. They all had their engine driven superchargers built right into the nose case, integral to the reduction gearing and the induction plumbing. The class wise-ass spouted off to our instructor that seemed like a stupid idea, and we got an assignment to think up an impeller-less intake manifold design for a twin row radial that would guarantee even mixture distribution to all cylinders, not obstruct cooling airflow, and fit into a tight cowling. "Huh? Hey boss, we're not engineers!"
"No, but you aren't stupid either, and have access to a library. Go figure it out if you can. Anyone comes up with a workable solution, I'll find him a scholarship to engineering school. He'd be wasting his time here!"
No workable solutions, but several entertaining plumbing nightmares. And Mr Hamm, not an engineer, had an amazing grasp of flow dynamics.
Cheers,
Wes

That's interesting, but
1) Surely a mixing fan does not need several hundred horsepower
2) Modern engines don't need this, and the question was about modern knowledge.
3) I was under the very strong impression one could make a reasonable radial engine without a supercharger of any kind.

 

[kitplane01]

In fact in the 1920s the rotating impeller between the carb/s and the intake tubes was sometimes called a "mixing fan". Making sure that the top cylinders got somewhat the same mixture as the bottom cylinders did. If V-12s have problems getting the same mixture to different cylinders then radials had a real problem. Having individual tubes coming right off the supercharger diffuser helped quite a bit.
Maybe you could get the idea to work using modern turbos and flow knowledge. GE turbos in WW II were actually pretty lousy superchargers. The compressor sections were low efficiency. You got a hotter intake charge temperature for the same amount of pressure. Which means the air is actually less dense.
By eliminating the two stage set up you now have a low altitude engine. A P & W R-1830 engine of 1200hp take-off rating was using 48in (9lbs boost) at take off. Most GE turbos could provide sea level pressure (30in) at 25,000ft for a pressure ratio of 2.7. The turbo engine may very well give you the same or more power between sea level and 12-13,000ft but above that it may only tie or fall slightly behind the single stage, two speed mechanical supercharger. altitude performance is gone. You used up about 25% of your supercharger capacity(pressure ratio) just getting to normal take-off power.
There may have been a very good reason that the turbos were always (on production aircraft) mounted a number of feet away from the engine in that the turbine section could only handle exhaust gases of a certain temperature and a close mounted turbo might be overheated. There is little doubt such an installation would be bulkier.

I would also note that by 1944 on the R-2800s they were using different exhaust systems than earlier planes and getting some exhaust thrust. This varied on individual aircraft.
F8F
View attachment 579755 from Texas Flying Legends Museum Bearcat Restoration

Are you telling me that back in '44 they could not make an exhaust driven supercharger that could work well at 25,000 feet (without an engine driven supercharger too). If so, that sounds like a place one of them could have done better. It is a solvable problem given enogh time/money/talent. And if that's a 10% horsepower gain, and a 10% fuel savings ...

 

[tomo pauk]

Yes, both please.

Until the engine designers from 1940s chime in, I'll just toss in my opinion.
As noted by other members, the engine-stage supercharger was essential in providing a more or less uniform mixture to each cylinder. It was also providing boost, providing the pressure ratios of 2.5.1 to perhaps 3:1 (depending on how efficient the S/C was, how good the installation of the S/C was, capacity - weight/time - of S/C). The turbocharger (provided that it was installed) provided another means of rasining pressure ratio, thus making the S/C system a 2-stage.
Without the engine-stage supercharger, something else need to cater for uniform distribution of, now, fuel. Without direct fuel injection this is not possible. Unlike in Germany, there was no mass production of fuel injection systems for gasoline engines in the USA during the best part of ww2 (only the R-3350 has gotten it, since it have had fuel distribution problems despite the engine-stage S/C; production of such R-335s was drop in a bucket vs. what was produced in the USA back in ww2). The US production of carburetors was huge, on the other hand.
Then we have a thing that turbochargers were suffering if there were peak heat loads, meaning that best place for US superchargers was several feet to several yds away from engine itself, so the heat loads will not reach the turbine. Even so, the turbo needed cooling air to help with keeping the temperature within design limits. In the USA, 1st turbines with hollow blades (so the air stream can cool the blades) was suggested, to the best of my knowledge, by Ford for their V-1650 design (has nothing to do with Packard-Merlin V-1650). A reason for this is that they intended to get rid of engine-stage S/C indeed because it consumes the power, with turbo being installed close to the engine. They intended to outfit the engine with direct fuel injection. Ford patented the turbine with hollow blades some time in 1941, it will took some time for other company (Wright) to actually make such a turbine, and produce the turbo with hollow blades from 1944 (used on the Curtiss SC-1 floatplane fighter, about 1000 produced, none survives today).
Their turbo was of a 2-stage variety - the turbine was turning two impellers, the impellers and turbine sharing the shaft. This is another bone of contention - Genereal Electric, a company that produced 99% of turbochargers in ww2 was making only 1-stage turboes (so did the Wright company), and was mooting the 2-stage S/C by late ww2. Having just 1 stage of supercharging, even if it is turbo, will not cut it for altitudes above 20000 ft that good as the 2-stage supercharged engines will.
Then we have production issues - main, branch and license factories were making mostly 1 type of engine en masse.

So all in all - yes, by 1944 there was enough of knowledge to make the engine in layout you propose, like eg. it was the case with jet engines. Just that is not needed. The mass and quality of US (and other Allied) gear is crushing the Axis completely. Post-war will see the turbo-compound R-3350s in service. P&W will suggest the R-4360 without engine-stage S/C, but jets and turbo-props have already there.

....
2) Modern engines don't need this, and the question was about modern knowledge.
3) I was under the very strong impression one could make a reasonable radial engine without a supercharger of any kind.

If I may:
2 - Wrong thread?
3 - For military purposes of ww2, engine needs to have a S/C. Let's recall that radial engines used on US tanks have had superchargers, the tank operating where there is plenty of air.

 

[XBe02Drvr]

Surely a mixing fan does not need several hundred horsepower.

No it doesn't, if it's only a mixing fan. It's when you try to get more boost out of it that the horsepower demand increases. If you're going to try for 40 or 42 inches MAP at seal level, you have to design more compression into it and spin it faster, making it suck up more horsepower.

Modern engines don't need this, and the question was about modern knowledge.

Modern engines aren't radials and don't have the vertical distribution between upper and lower cylinders and the circular distribution of mixture to the cylinders. A lot of the detailed understanding of fluid flow dynamics that goes into today's engines was derived with the aid of CAD and powerful computers that didn't exist in WWII.

I was under the very strong impression one could make a reasonable radial engine without a supercharger of any kind.

You probably could, but what's the use? It would have to be a smallish single row low altitude engine, as mixture (or air, if FI) distribution issues get sticky real fast when you get into multiple cylinder rows without some sort of radial impulsion in the induction system. Such an engine would have an unfavorable power to weight ratio and be relatively inefficient vis a vis modern opposed cylinder engines. A number of modern opposed type air cooled engines are now being offered in liquid cooled form, which are more efficient due to the tighter tolerances allowed by the narrower temperature range of liquid cooling. This would be awkward and heavy to apply to a radial.
Cheers,
Wes

 

[kitplane01]

Here's my concern (and I'm willing to be educated).

If one could make an exhaust driven supercharger, one might get an engine with a few hundred more horsepower, while flying farther due to lower fuel consumption. There were smart people in WWII, but this was not done. So why ...

1) Getting a good fuel/air mixture to all cylinders? That honestly seems like it could be done without consuming a few hundred horsepower. A much lower powered fan, or fuel injection tuned to each port, or tolerate the inefficiency assuming it's less than a 10% horsepower reduction.

2) Inability to make an exhaust driven supercharger that could provide enough compression. Maybe. I'm not educated enough to know if that's possible in 1944, but it's possible now.

3) Industrial stuff. They had working production lines using working technology, and didn't want to take any delays.

4) Tradition. Sometimes people do things because thats how it's done. But if an amateur behind a keyboard can think of it, I'm sure they could too.

Did anyone make a large radial without an engine driven supercharger? I cannot find any over 500 hp.

If everyone does something (and it seems that way) then there is a reason. But it's awfully hard to grasp that 10% of all horsepower for these engines was required for mixture distribution!

 

[pinsog]

Here's my concern (and I'm willing to be educated).

If one could make an exhaust driven supercharger, one might get an engine with a few hundred more horsepower, while flying farther due to lower fuel consumption. There were smart people in WWII, but this was not done. So why ...

1) Getting a good fuel/air mixture to all cylinders? That honestly seems like it could be done without consuming a few hundred horsepower. A much lower powered fan, or fuel injection tuned to each port, or tolerate the inefficiency assuming it's less than a 10% horsepower reduction.

2) Inability to make an exhaust driven supercharger that could provide enough compression. Maybe. I'm not educated enough to know if that's possible in 1944, but it's possible now.

3) Industrial stuff. They had working production lines using working technology, and didn't want to take any delays.

4) Tradition. Sometimes people do things because thats how it's done. But if an amateur behind a keyboard can think of it, I'm sure they could too.

Did anyone make a large radial without an engine driven supercharger? I cannot find any over 500 hp.

If everyone does something (and it seems that way) then there is a reason. But it's awfully hard to grasp that 10% of all horsepower for these engines was required for mixture distribution!

Sir, I am a bit confused, a turbocharger IS an exhaust driven supercharger. The P43, P47, B17, B24 and B29 were all powered by turbocharged engines.