Advanced French Fighters vs 1942/1943 contemporaries (1 Viewer)

[TM06]

There was zero chance of the HS 12B showing up in WW II.

Forget the 12B, that is a unicorn.
The whole H-S engine is problem, H-S was promising more power from less weight than anybody else. And the two other Hispano derived families (Swiss and Soviet) never came close to the power/weight ratio that H-S trying for. And they both had trouble with reliability/durability.

Why? If Hispano recognize the fundamental flaws with the 12Z engine - which they almost certainly would by around 1941 - then their attempts to fix it would likely result in the 12B or something similar. Looking at the images provided earlier in the thread paints it as just a solid engine rather than anything groundbreaking. The specs of the engine also place it quite squarely within the late-war inline V12's (DB 603, Jumo 213, Griffon VI / 61 / 65, Merlin 66, VK-107, AM-42, certain V-1710's) without being ridiculous. Given that the engine started development in 1945 and was ready for production in 1948, it being developed in 1941 would result in it being ready for production in 1944 - which also lines up with the previously mentioned V12's.

 

[Shortround6]

There is a real problem or rather a host of them trying to compare post WW II engine development to 1940-43 engine development.
For everything that makes development easier there is something that makes it harder. A 1945 design team has most of the knowledge that several other design teams spent 4-5 years acquiring. A lot of that covers materials and manufacturing techniques and processes. But the budgets and manpower are lower. In war time there are external constraints, like access to machine tools and materials regardless of cost/funding.

And an awful lot does depend on funding.

There seem to be two 12B power plants if not Three. There was a design study of a 12 -Z-B conducted in Barcelona which may have been the first. Double compressor with intercooler.
The French version/s of the 12B seems to have rivaled the Napier Nomad for complexity. Finding information on the "bare" engine is difficult and the ultimate version for power at 10,000 meters wound up with a 2190kg power plant. However that included the exhaust driven turbine/s that powered not only the 1st stage of the supercharger but also the 'fan' that provided the air flow through the radiators and then this air from the radiators was blended into mix of the exhaust gases (turbo waste gates?) the radiator air, and main exhaust from the turbo unit. Main exhaust and 2 concentric rings (?) around the main turbo exhaust nozzle. I have no idea how they handled the intercooler (liquid cooling tied to the radiators?)
Date of this contraption is a little iffy. 5 prototypes were built, it was never flown. Some information was published in the 1950 and 1951 editions of Jane's for basic engine but it was never marketed. The 12-B engine is supposed to have received it's approval tests in 1951 as a simple engine and the 1951/52 Jane's says the integral propulsion version was "under development"
This is from pages 368-370 of Hispano Suiza in Aeronautics by Manuel Lage.

I have no idea what was supposed to be ready for production in 1948.

 

[Bretoal2]

There is a real problem or rather a host of them trying to compare post WW II engine development to 1940-43 engine development.
For everything that makes development easier there is something that makes it harder. A 1945 design team has most of the knowledge that several other design teams spent 4-5 years acquiring. A lot of that covers materials and manufacturing techniques and processes. But the budgets and manpower are lower. In war time there are external constraints, like access to machine tools and materials regardless of cost/funding.

And an awful lot does depend on funding.

There seem to be two 12B power plants if not Three. There was a design study of a 12 -Z-B conducted in Barcelona which may have been the first. Double compressor with intercooler.
The French version/s of the 12B seems to have rivaled the Napier Nomad for complexity. Finding information on the "bare" engine is difficult and the ultimate version for power at 10,000 meters wound up with a 2190kg power plant. However that included the exhaust driven turbine/s that powered not only the 1st stage of the supercharger but also the 'fan' that provided the air flow through the radiators and then this air from the radiators was blended into mix of the exhaust gases (turbo waste gates?) the radiator air, and main exhaust from the turbo unit. Main exhaust and 2 concentric rings (?) around the main turbo exhaust nozzle. I have no idea how they handled the intercooler (liquid cooling tied to the radiators?)
Date of this contraption is a little iffy. 5 prototypes were built, it was never flown. Some information was published in the 1950 and 1951 editions of Jane's for basic engine but it was never marketed. The 12-B engine is supposed to have received it's approval tests in 1951 as a simple engine and the 1951/52 Jane's says the integral propulsion version was "under development"
This is from pages 368-370 of Hispano Suiza in Aeronautics by Manuel Lage.

I have no idea what was supposed to be ready for production in 1948.

The Hispano-Suiza 12B was designed by Jacques Blanc, former chief engineer of Gnome-Rhône who took refuge in the unoccupied zone, while the management of G&R remained in Paris.

Conclusion: no French collapse in 1940 = no Hispano 12B.

 

[TM06]

There is a real problem or rather a host of them trying to compare post WW II engine development to 1940-43 engine development.
For everything that makes development easier there is something that makes it harder. A 1945 design team has most of the knowledge that several other design teams spent 4-5 years acquiring. A lot of that covers materials and manufacturing techniques and processes. But the budgets and manpower are lower. In war time there are external constraints, like access to machine tools and materials regardless of cost/funding.

And an awful lot does depend on funding.

There seem to be two 12B power plants if not Three. There was a design study of a 12 -Z-B conducted in Barcelona which may have been the first. Double compressor with intercooler.
The French version/s of the 12B seems to have rivaled the Napier Nomad for complexity. Finding information on the "bare" engine is difficult and the ultimate version for power at 10,000 meters wound up with a 2190kg power plant. However that included the exhaust driven turbine/s that powered not only the 1st stage of the supercharger but also the 'fan' that provided the air flow through the radiators and then this air from the radiators was blended into mix of the exhaust gases (turbo waste gates?) the radiator air, and main exhaust from the turbo unit. Main exhaust and 2 concentric rings (?) around the main turbo exhaust nozzle. I have no idea how they handled the intercooler (liquid cooling tied to the radiators?)
Date of this contraption is a little iffy. 5 prototypes were built, it was never flown. Some information was published in the 1950 and 1951 editions of Jane's for basic engine but it was never marketed. The 12-B engine is supposed to have received it's approval tests in 1951 as a simple engine and the 1951/52 Jane's says the integral propulsion version was "under development"
This is from pages 368-370 of Hispano Suiza in Aeronautics by Manuel Lage.

I have no idea what was supposed to be ready for production in 1948.

Let me ask this then; using the specifications B Bretoal2 shared earlier from Flight, how long would it take for Hispano to make either a beefed-up variant of the 12Z or a new engine to match the ~1,750 hp SL / 2,200 hp TO at ~930 kg given for the 12B Type 20 - assuming they started around late 1940 or early 1941?
Most of the V12's in this similar range started showing up in bulk around mid 1943 to early 1944, so perhaps a similar timeline for this theoretical Hispano?

 

[Shortround6]

Let me ask this then; using the specifications B Bretoal2 shared earlier from Flight, how long would it take for Hispano to make either a beefed-up variant of the 12Z or a new engine to match the ~1,750 hp SL / 2,200 hp TO at ~930 kg given for the 12B Type 20 - assuming they started around late 1940 or early 1941?
Most of the V12's in this similar range started showing up in bulk around mid 1943 to early 1944, so perhaps a similar timeline for this theoretical Hispano?

You need to go to a new engine.
Trying to beef up an existing engine (even a tenuous one like the 12Z) by close to 50% pretty much means you are changing everything. You might as well start with a clean sheet rather than keep beefing up a few parts here and few parts there and sometimes going back to on of the first modified parts.
It generally took 3-4 years to get a new engine into production. A lot depends on how much of a new engine you are building and how much was based off an existing engine, even if scaling up. Also depends on what else you are doing. P&W took about 3 years to build the R-2800 C, they started in 1940. But getting the R-2800 B into production, and helping several other companies build new factories and working on the R-4360 (which used the same cylinders) may have slowed things up a bit.
France had screwed themselves with partial take over of the Hispano company in France and Marc Birkigt stopping work on aircraft engines. SO they needed either new designers/engineers or promotion of existing personnel. Birkigt and also designed a lot of the tooling to make the existing HS engines so you need people to do that.
And you need to build, in large numbers, the HS 12Y in several different models.
It took Junkers quite a while to get the 213 into production, they may have started in 1939/40 (?) They took the option of keeping the existing bore-stroke and increasing the rpm.
Daimler Benz took the larger cylinder size option with the 603.
This is part of the reason that trying to go back in time and saying "well, it took only 3 years in the late 40s when they were at peace so they could have done it quicker in war".
I have no idea of what the guys working on the 12B used for late war technology in relation to alloys, bearings, lubrication and so on. P&W did a lot of work in the early part of WW II on bearings. But in 1944-46 when they were working on the post war R-2800s and R-4360 they already had a lot bearing knowledge built up. And a lot of other "stuff".

We also have to figure what we want the engine to do. Some of the late war 1750hp / 2200hp engines were 'sprint' engines. With the proper fuel and/or W/A they would do it. but they didn't increase the 30 min climb or longer cruise settings much. A late war DB 605 with a 1800hp rating does NOT make a good replacement for a DB 603 or Jumo 213 as a bomber engine. Please note that the P&W R-2800 at 2000hp T-O would never had worked in the B-29 as a replacement for the R-3350. The R-3350 was only rated at 200mp more for take-off but it was rated at 300hp or more for the long periods of time it took to get a B-29 up to operating altitude.

Kind of the reason that Avro went to the Griffons in the Shackleton's instead of high power Merlins.



It may mean that Hispano would have to shelve the 12Z while they work on the 12B and that leaves you with the 12Y-51 as the standard bearer for 1940-41-42 and into 1943.
That also may mean that they have to straighten out the 12Y-51 while working on the 12?? as the 12Y-51 had problems.
I have no idea of what the guys working on the 12B used for late war technology in relation to alloys, bearings, lubrication and so on.

 

[Shortround6]

A problem for me is that the French engine industry was operating at sub par levels during the 1930s.
H-S and G-R were the survivors with the other French companies operating on borrowed time. Maybe they were starved of contracts before the late 30s rush and then it was too late.
H-S 12Ys were having trouble with durability/reliability even in 1933/34 during the Soviet tests. The whole radial engine detour was a fiasco to put it politely. One book claims the 14 AA engine (45.2 liter) were getting pulled from the LeO 45 prototype after 18 hours of service. This threw the load for production onto the G-R 14N (38.7 Liters) . Likewise the failure of the 14 AB (26.1 Liters) necessitated the G-R 14M (19 Liters) being substituted in all of the planned aircraft that were slated to use the 14 AB.

Marc Birkigt had stopped production of motor cars in 1936 after nationalization and he also personally stopped work on the aero engines leaving his son Louis to oversee the Radial engine projects and other designers to work on the V-12s. How much the radial projects took resources from the V-12 side of things I don't know, radials were built in a new factory (?) but how much design staff was shared/borrowed at times?
Unfortunately the 12Y-31 engines in the MS. 406 have been described as fragile and wearing out quickly affecting it's combat performance in during the phony war. Worn engines means the planes won't perform up to "book" levels.
Using short lived engines works IF you can supply replacement engines and if you have a decent overhaul capability. Due the French efforts to build large numbers of new aircraft that may not have the been the case for France in 1939/40.
The 12Y-51 was known for having problems in Swiss service (the only large scale user, if Swiss service can be called large).
The French may have been able to solve some of the issues with the 12Y series and even build some of the lower powered 12Z versions in 1942/43. Which requires substantial re-tooling. Trying to build 1500-1600hp 12Z engines that are reliable enough for service use (even a much shorter lives than the Merlin) seems to be really pushing things.
The Problem is not with the fuel, it is getting the engines to hold together even at the lower power settings.

I don't know were the cross over point is from cheap/light disposable engines and expensive/heavy engines is. It may vary a lot depending on the Nation and the expected service.
But try to imagine the RAF trying to use H-S engines in the thousands of Lancaster's and Halifax's of bomber command the needing to replace them 3-4 times more often?

 

[Bretoal2]

A problem for me is that the French engine industry was operating at sub par levels during the 1930s.
H-S and G-R were the survivors with the other French companies operating on borrowed time. Maybe they were starved of contracts before the late 30s rush and then it was too late.
H-S 12Ys were having trouble with durability/reliability even in 1933/34 during the Soviet tests. The whole radial engine detour was a fiasco to put it politely. One book claims the 14 AA engine (45.2 liter) were getting pulled from the LeO 45 prototype after 18 hours of service. This threw the load for production onto the G-R 14N (38.7 Liters) . Likewise the failure of the 14 AB (26.1 Liters) necessitated the G-R 14M (19 Liters) being substituted in all of the planned aircraft that were slated to use the 14 AB.

Marc Birkigt had stopped production of motor cars in 1936 after nationalization and he also personally stopped work on the aero engines leaving his son Louis to oversee the Radial engine projects and other designers to work on the V-12s. How much the radial projects took resources from the V-12 side of things I don't know, radials were built in a new factory (?) but how much design staff was shared/borrowed at times?
Unfortunately the 12Y-31 engines in the MS. 406 have been described as fragile and wearing out quickly affecting it's combat performance in during the phony war. Worn engines means the planes won't perform up to "book" levels.
Using short lived engines works IF you can supply replacement engines and if you have a decent overhaul capability. Due the French efforts to build large numbers of new aircraft that may not have the been the case for France in 1939/40.
The 12Y-51 was known for having problems in Swiss service (the only large scale user, if Swiss service can be called large).
The French may have been able to solve some of the issues with the 12Y series and even build some of the lower powered 12Z versions in 1942/43. Which requires substantial re-tooling. Trying to build 1500-1600hp 12Z engines that are reliable enough for service use (even a much shorter lives than the Merlin) seems to be really pushing things.
The Problem is not with the fuel, it is getting the engines to hold together even at the lower power settings.

I don't know were the cross over point is from cheap/light disposable engines and expensive/heavy engines is. It may vary a lot depending on the Nation and the expected service.
But try to imagine the RAF trying to use H-S engines in the thousands of Lancaster's and Halifax's of bomber command the needing to replace them 3-4 times more often?

Some points:

Early days (or years...) of the LeO 451 are well known: 13 HS 14Aa engines in 50 flight hours in 18 monthes for the 451-01.

Hispano-Suiza had only one production site in Bois-Colombes; the "decentralized" factory in Tarbes (800 km from Paris), built with State funds, did not begin shipping engines before early 1940.

More generally, the inferiority of French engines in the late 1930s can be explained by the absence of the new generation of models: they were in gestation in 1935-1936, but the social and political troubles that lasted until the aftermath of the Munich crisis prevented their release and development. Marc Birkigt was completely demoralized because the "theft" of his French company occurred at a time when Spain was sinking into civil war, and Paul-Louis Weiller found himself embroiled in a thousand legal cases, and was also very poorly regarded by the most active of the Air Ministers, Guy La Chambre (one of the most long-lasting ones - two years and two monthes !).

The LeO 451, Amiot 350 and Bloch 174 should have received engines of the 1,200/1,300 hp class such as the HS 14Aa, G&R 14P or 14R, HS 12Z, but had to make do with 20 to 25% less HP because these engines were not ready (the 14P will be abandoned...).

Another problem was that of the homologation of the engines. This was only done by means of bench tests at 0m (admission through a vacuum box to simulate the altitude). Real flight tests only took place from the end of 1938 (Munich, again!), accompanied by longer and tougher tests for the bench tests - Paul-Louis Weiller dared to protest against the failure of the homologation of the 14P on the bench for that it had been designed "according to the old standards".

The result was that prototype engines were flown on prototype aircraft, considerably extending the development time; in addition, most prototypes were ordered for only one example, which might be catastrophic in the event of an accident!

That being said, I think that once the beginning of the war was over, and the errors of the mobilization were corrected (the engineers returned to their offices and not to the Maginot Line...), there was a real national upsurge and that enormous efforts were made to catch up on quality and quantity, engines and airframes. But no one knows what the French aeronautics industry would have become if Gamelin had not sent his troops to Belgium...

 

[Shortround6]

Thank you for corrections/new information.

Many things contribute to successful engines or to poor engines. The US had it's share of poor engines, fortunately for the US there enough good ones that the poor ones did not see service.

That being said, I think that once the beginning of the war was over, and the errors of the mobilization were corrected (the engineers returned to their offices and not to the Maginot Line...), there was a real national upsurge and that enormous efforts were made to catch up on quality and quantity, engines and airframes. But no one knows what the French aeronautics industry would have become if Gamelin had not sent his troops to Belgium...

It is hard to say what the French aeronautics industry would have become with several more years from 1940 on but they were several years behind some other countries in 1940 in some areas.
The era of single designers had come to an end. You needed a crap load of skilled, hard working assistants/employees to bring a modern high powered engine into service use.

A few numbers/dates from the R-2800 history.

March 31, 1937 design started.
Aug 15th 1938 1000 hours of run time (bench)
July 1st 1939, completion of military type tests.
3300 hours of run time to completion of type test. All ground testing.
325,000 engineering man-hours from start of design to completion of type test.
July 12th 1939, first flight (Vultee Y-19B test mule)
Feb 12th 1940 5000 hours of run time.
March 1940 5 engine accepted.
Dec 1940 19th engine accepted.
Jan 1941 13 engines accepted that month.
Nov 1941 371 engines accepted that month, including 1 each of two newer models and 99 engines from the Ford plant. 369 of the engines were the 1850hp version.

During the late 30s and 1940 P&W had told the government they wanted to discontinue both the R-1535 and R-2180 14 cylinder radials and all the liquid cooled sleeve valve projects. They wanted to concentrate on a few different models/lines rather than spread out their resources. And the US was not officially at war.

Enormous effort can only do so much and trying to cram 3-5 years of catching up into 2-3 years while keeping up with other countries improvements in 1941-43 is going to be very difficult indeed.

 

[Shortround6]

Some of the things going on with Allison may help shed light on things. In 1938 Allison ended the year with under 700 employees. During WW II at Allison's peak production they had over 23,000. In 1939-40 Allison was have a lot of difficulty getting the engine into mass production (and even building new factory space) but Allison was a division of General Motors
and General Motors management selected engineers and managers from GM auto plants to beef up Allison's efforts so that Allison could meet it's contracted delivery times and meet their export orders. There were some delays but this manpower transfer shortened them considerably and enabled further expansion. Once the US government shut down auto production a number of GM auto makers were used as sub-contactors for Allison. Cadillac made crankshafts and rods and other things. But Cadillac did not have aluminum casting facilities (Car engines were iron) so another GM division (Delco Remy ) did a lot of casting work. And so on.
For France it is not enough to get previous employees/workers back from the Army, they have to get a lot more engineers/draftsmen/machinists than they had in 1938 and they are competing with every other war industry. Britain had the same problem, they had not been graduating enough engineers/draftsmen/machinists from traditional schools or trade schools. It was this lack of engineers/draftsmen that slowed down the British rearmament even after Dunkirk. You can have a working prototype but if you can't make production drawings you are stuck.

 

[TM06]

You need to go to a new engine.
Trying to beef up an existing engine (even a tenuous one like the 12Z) by close to 50% pretty much means you are changing everything. You might as well start with a clean sheet rather than keep beefing up a few parts here and few parts there and sometimes going back to on of the first modified parts.
It generally took 3-4 years to get a new engine into production. A lot depends on how much of a new engine you are building and how much was based off an existing engine, even if scaling up. Also depends on what else you are doing. P&W took about 3 years to build the R-2800 C, they started in 1940. But getting the R-2800 B into production, and helping several other companies build new factories and working on the R-4360 (which used the same cylinders) may have slowed things up a bit.
France had screwed themselves with partial take over of the Hispano company in France and Marc Birkigt stopping work on aircraft engines. SO they needed either new designers/engineers or promotion of existing personnel. Birkigt and also designed a lot of the tooling to make the existing HS engines so you need people to do that.
And you need to build, in large numbers, the HS 12Y in several different models.
It took Junkers quite a while to get the 213 into production, they may have started in 1939/40 (?) They took the option of keeping the existing bore-stroke and increasing the rpm.
Daimler Benz took the larger cylinder size option with the 603.
This is part of the reason that trying to go back in time and saying "well, it took only 3 years in the late 40s when they were at peace so they could have done it quicker in war".
I have no idea of what the guys working on the 12B used for late war technology in relation to alloys, bearings, lubrication and so on. P&W did a lot of work in the early part of WW II on bearings. But in 1944-46 when they were working on the post war R-2800s and R-4360 they already had a lot bearing knowledge built up. And a lot of other "stuff".

We also have to figure what we want the engine to do. Some of the late war 1750hp / 2200hp engines were 'sprint' engines. With the proper fuel and/or W/A they would do it. but they didn't increase the 30 min climb or longer cruise settings much. A late war DB 605 with a 1800hp rating does NOT make a good replacement for a DB 603 or Jumo 213 as a bomber engine. Please note that the P&W R-2800 at 2000hp T-O would never had worked in the B-29 as a replacement for the R-3350. The R-3350 was only rated at 200mp more for take-off but it was rated at 300hp or more for the long periods of time it took to get a B-29 up to operating altitude.

Kind of the reason that Avro went to the Griffons in the Shackleton's instead of high power Merlins.



It may mean that Hispano would have to shelve the 12Z while they work on the 12B and that leaves you with the 12Y-51 as the standard bearer for 1940-41-42 and into 1943.
That also may mean that they have to straighten out the 12Y-51 while working on the 12?? as the 12Y-51 had problems.
I have no idea of what the guys working on the 12B used for late war technology in relation to alloys, bearings, lubrication and so on.

I don't think scrapping the 12Z in its entirety would be the best move, especially with how many aircraft France was planning on producing that were going to use it. A safer bet might be tuning the 12Z down for reliability (going from 1,400 hp to 1,250 hp or something - which would still be more than the 12Y could produce in a reasonable amount of time), mass producing it while not making more variants, and then basing this new 1,750 hp engine off of the 12Z to speed up development - I'll be referring to this engine as 12T (T for Theoretical) from now on for the sake of simplicity.
Phasing out the 12Y in favour of this tuned down 12Z would also possibly help, as there would be less stuff on Hispano's plate that could take resources away from the 12T's development. As far as I can tell, almost all of the important aircraft that used the 12Y had variants being worked on that replaced it with the 12Z, so it's unlikely that the 12Y would be used past 1941 anyways.

 

[Shortround6]

I don't think scrapping the 12Z in its entirety would be the best move, especially with how many aircraft France was planning on producing that were going to use it. A safer bet might be tuning the 12Z down for reliability (going from 1,400 hp to 1,250 hp or something - which would still be more than the 12Y could produce in a reasonable amount of time), mass producing it while not making more variants, and then basing this new 1,750 hp engine off of the 12Z to speed up development - I'll be referring to this engine as 12T (T for Theoretical) from now on for the sake of simplicity.
Phasing out the 12Y in favour of this tuned down 12Z would also possibly help, as there would be less stuff on Hispano's plate that could take resources away from the 12T's development. As far as I can tell, almost all of the important aircraft that used the 12Y had variants being worked on that replaced it with the 12Z, so it's unlikely that the 12Y would be used past 1941 anyways.

You need a new engine to get to the 1750hp area.
Build the 12Z in some form but forget about using the 12Z as a base for the 1750hp engine. There are reasons that the RR Griffon weighed just over 800kg with a single stage supercharger. Almost 33% more than the 12Z. And it only made 1750hp at low altitude. The MK VI made 1630hp at 10,500ft using 15lbs of boost.

This is sort of what got H-S into trouble in the first place. They kept trying to use legacy parts and manufacturing tooling. Going to Allison (because they have the most details in one book/source), they went through several major redesigns/rebuilds between start in late 20s to 1942/43. It started as a 750hp ish engine but one designer (they had several during the 30s) pushed for a 1000hp goal in the early 30s. The Army also changed the certification requirements and insisted on a 150hr engine run. Allison redesigned the engine including a new crankshaft. Engines were rated at 1000hp at take-off and less at altitude. During the early to mid 30s US engines were rated at max continuous, not military (5 min) or 1-3 minute take0ff power so things get a bit confusing comparing them to later engines. Engine didn't pass the Army type test until April 1937200 and a lot of things had to be changed. However in 1940 the basic engine was having trouble with the new army test of 1090hp at 13,200ft. This required the engine to turn at 3000rpm instead of 2600rpm in order to make the power needed to drive the supercharger to make the desired power at altitude. Allison modified the crankcase and the crankshaft (and shotpeened the crankshaft) to make the new 150hr test. Modifications were needed to get the basic engine to next level of 1325hp for take-off in 1942. Nitrided crankshaft and new block casting techniques. You could drop the new parts into old engine blocks which helped repairs. It does show that it is not a matter of "tune". Allison had to change even more stuff when they tried for 3200rpm G series engines including 27lbs of counter weights on the crankshaft.

Now the Allison had a much longer "life" than a H-S engine did and that cost both money and weight.

The problem for H-S and the French is that they need to produce the hell out of the 12Y-51 and fix it in 1940-41 to get to the 12Z. And they need to set up to produce the hell out of the 12Z as soon as they could so perhaps some of the more trick ideas (like fuel injection) may not get put in the mix. They could make fuel injection, could they make hundreds of fuel injection units per month? Or do they have to wait a year or more.
It also interesting to look at Wright and the R-1820 radial. They were shipping a 1200hp (take-off) version in very early 1940. It took until the middle of 1943 to get the 1300hp version in numbers over 10 per month. It was a completely new engine that just shared the same bore and stroke. Granted they were busy with a few other engine in the mean time but sometimes you have to bite the bullet and start over. They were able to take stuff they learned from other engines and apply it to the R-1820, like a new way of making cylinder fins.

The 12T just seems way too ambitious for the French in 1943. There was more too it than the fuel. You need the bottom of the engine to stand up to the power being made by the better fuel. Jumo 213 A made 1776hp for take off, it made 1600hp at 18,000ft which beats the Griffon by over 7,000ft, but the 213 was about 100kg heavier than the Griffon.

France had lost a lot of time from 1936-40 and while lot could have been been made up (given allied cooperation) some could not.

 

[TM06]

You need a new engine to get to the 1750hp area.
Build the 12Z in some form but forget about using the 12Z as a base for the 1750hp engine. There are reasons that the RR Griffon weighed just over 800kg with a single stage supercharger. Almost 33% more than the 12Z. And it only made 1750hp at low altitude. The MK VI made 1630hp at 10,500ft using 15lbs of boost.

Functionally, the 12T would be a new engine. I say base it off the 12Z in the loosest sense possible - similar to how Group B Rally Cars were "based" on production cars (Lancia Delta S4 as my best example). The basic design of the 12Z absolutely has more potential than any of Hispano's other engines, so using it as a starting point could help speed up the development process. Doing that is the really the only way I can see them getting the engine done in any reasonable amount of time.

Now this isn't me saying that the 12T would even resemble the 12Z let alone be a development of it, but more that it might be prudent to take the actually good things about the 12Z and graft them onto a new and much more capable engine.

This is sort of what got H-S into trouble in the first place. They kept trying to use legacy parts and manufacturing tooling. Going to Allison (because they have the most details in one book/source), they went through several major redesigns/rebuilds between start in late 20s to 1942/43. It started as a 750hp ish engine but one designer (they had several during the 30s) pushed for a 1000hp goal in the early 30s. The Army also changed the certification requirements and insisted on a 150hr engine run. Allison redesigned the engine including a new crankshaft. Engines were rated at 1000hp at take-off and less at altitude. During the early to mid 30s US engines were rated at max continuous, not military (5 min) or 1-3 minute take0ff power so things get a bit confusing comparing them to later engines. Engine didn't pass the Army type test until April 1937200 and a lot of things had to be changed. However in 1940 the basic engine was having trouble with the new army test of 1090hp at 13,200ft. This required the engine to turn at 3000rpm instead of 2600rpm in order to make the power needed to drive the supercharger to make the desired power at altitude. Allison modified the crankcase and the crankshaft (and shotpeened the crankshaft) to make the new 150hr test. Modifications were needed to get the basic engine to next level of 1325hp for take-off in 1942. Nitrided crankshaft and new block casting techniques. You could drop the new parts into old engine blocks which helped repairs. It does show that it is not a matter of "tune". Allison had to change even more stuff when they tried for 3200rpm G series engines including 27lbs of counter weights on the crankshaft.

I think there's a miscommunication regarding my use of "tune" here. I meant de-rating the 12Z to produce less power in the interest of longevity and reliability - similar to what Russia did with a few of the Klimovs.
If the intended horsepower for the 12ZTer was 1,400 hp, reducing it to ~1,250 hp (perhaps by lowering the RPM?) should help lessen the strain on the engine along with possibly cutting away some of its development time, no?

The problem for H-S and the French is that they need to produce the hell out of the 12Y-51 and fix it in 1940-41 to get to the 12Z. And they need to set up to produce the hell out of the 12Z as soon as they could so perhaps some of the more trick ideas (like fuel injection) may not get put in the mix. They could make fuel injection, could they make hundreds of fuel injection units per month? Or do they have to wait a year or more.

Alright, but how would they fix the 12Y-50/51? How long would it take to do so? And even if they did fix it, would it stand up to the previously-mentioned de-rated 12Z that they could likely get up and running around the same timeframe? If Saurer is anything to go by, the limit of the basic 12Y is not exactly stratospheric without some serious and time consuming overhauls.

The 12T just seems way too ambitious for the French in 1943. There was more too it than the fuel. You need the bottom of the engine to stand up to the power being made by the better fuel. Jumo 213 A made 1776hp for take off, it made 1600hp at 18,000ft which beats the Griffon by over 7,000ft, but the 213 was about 100kg heavier than the Griffon.

France had lost a lot of time from 1936-40 and while lot could have been been made up (given allied cooperation) some could not.

Too ambitious for 1943? Probably. The optimist in me would hope for late 1943, but mid-to-late 1944 might be more reasonable. Although I should note that some of these engines could've gotten into large scale mass-production much earlier if not for some odd choices (Jumo 213 included).
It is also interesting to note that on either side of these theoreticals (France holds out or no embargo placed on Vichy France) would allow them to have hands-on experience with these heavier V12's - Griffon for the former, DB 603 and Jumo 213 for the latter.

 

[Shortround6]

Functionally, the 12T would be a new engine. I say base it off the 12Z in the loosest sense possible - similar to how Group B Rally Cars were "based" on production cars (Lancia Delta S4 as my best example). The basic design of the 12Z absolutely has more potential than any of Hispano's other engines, so using it as a starting point could help speed up the development process. Doing that is the really the only way I can see them getting the engine done in any reasonable amount of time.

Well, Right did base a lot of their engines off of early versions, They kept the same bore and stroke and engine mounts (at times) and changed everything else

Now this isn't me saying that the 12T would even resemble the 12Z let alone be a development of it, but more that it might be prudent to take the actually good things about the 12Z and graft them onto a new and much more capable engine.

Basically unbolt the cylinder heads and slide new cylinder blocks, crankcase/crankshaft, piston/rods and induction system?

I think there's a miscommunication regarding my use of "tune" here. I meant de-rating the 12Z to produce less power in the interest of longevity and reliability - similar to what Russia did with a few of the Klimovs.

Soviets also shortened the expected overhaul times. So did the Germans.

If the intended horsepower for the 12ZTer was 1,400 hp, reducing it to ~1,250 hp (perhaps by lowering the RPM?) should help lessen the strain on the engine along with possibly cutting away some of its development time, no?

You could use 1250hp as a stepping stone, they are going to need 1400hp sometime, the next question is identifying at what altitude you want the rated power.
At the end of 1942 an Allison in a P-40K could give you 1580hp at 2500ft or 1490hp at 4300ft or 1150hp at 12,000ft.
At the end of 1942 a Merlin 45 in a Spitfire V could give you 1515hp at 11,000ft or 1230hp at 18,000ft. It would probably given 1150hp at just over 20,000ft.

Alright, but how would they fix the 12Y-50/51? How long would it take to do so? And even if they did fix it, would it stand up to the previously-mentioned de-rated 12Z that they could likely get up and running around the same timeframe? If Saurer is anything to go by, the limit of the basic 12Y is not exactly stratospheric without some serious and time consuming overhauls.

Well, they can't keep making 12Y-45/49s while they make the next generation. I am guessing the French could sort out the -51 quicker than the Swiss did but it may take sideling the 12Z development for a while. What they learn could be applied to the 12Z or perhaps a parallel development could see faster/ bigger improvements to the -51?
-51 used bigger intake valves in the existing heads for one thing so while not as good as 4 valves it is an improvement that can be made using some of the existing machinery. They also reinforced the upper and lower crankcases to handle the bigger loads of the increased RPM but only by about 10KG for all the improvements. H-S crankshafts employed dampers but not counter weights and while they may not have needed 30KG of extra crankshaft weight like the YS-2 got there is a lot of room between a no counter weight 50kg crankshaft and the YS-2 80kg crankshaft. If you are going to try for 2500rpm and especially for 2600rpm you need to counterweight the crankshafts.

It is also interesting to note that on either side of these theoreticals (France holds out or no embargo placed on Vichy France) would allow them to have hands-on experience with these heavier V12's - Griffon for the former, DB 603 and Jumo 213 for the latter.

The problem here is you need new airplanes. Yanking an 500kg Hispano out of a D.520Z (or a 600kg) and replacing it with a 920kg Jumo 213 is not going to go well. And you need all the "stuff" that goes with the bigger engine (large prop, larger radiators, more coolant and oil.)
I can have the best 1/2 ton truck in the world but if I load it with 3/4s of a ton every day I am going to break things. Just to get airplanes to fly you have to get the center of gravity right.

Something we have not addressed is fuel. The H-S and G-R engines are not going to get the full benefit from 100-130 fuel. But they could get something. A lot has been written about H-S engines and 100 octane fuel and raising the compression ratio from 5.8 to 7.0. How much is wishful thinking and how much is nonsense I don't know but but raising the manifold pressure may have been easier than turning more RPM?
Now I say nonsense because some accounts say that the H-S 12Y-21 of 1935 was rated for 100 octane fuel because it had a 7.0 compression ratio. In 1935 Howard Hughes set the world speed record using "100" octane fuel. It was 100 octane, he got laboratory grade 100 octane fuel that cost 10 times what normal aviation fuel cost per gallon. Every engine designer worth his drafting pencils knew 100 octane fuel existed, they new it was coming. What they didn't know was WHEN and what it would do in their engine/s and they wouldn't know that unless they bought a few barrels and tested it. And what they were testing in 1935 was pretty much 100% isooctane and not a blend. Or they were testing a batch of blended fuel doped with varying amounts of lead to "equal" 100% isooctane in the opinion of the lab or company that made that batch of fuel.
H-S may have gotten some 100 octane fuel and they may have test and rated their engines on it but nobody was getting 100 octane fuel in commercial aviation (or military) quantities until 1938/39 and then it was pretty rare stuff.
What the French did I don't know but the US went through an intermediate stage of fuel that the British did not. The US went from 80 octane to 87 octane then went to 90-92 octane for few years before going to 100 octane. And US was using 100/100 fuel. Some of the American radials never used very high boost numbers. The R-2600s used in B-25s and early TBMs and some other planes never went over 42-44in (6-7lbs boost) even with 100/130 fuel. The R-2600 engines that were rated at 1900hp used more boost but they were entirely new engines. Some American engines stayed at the same ratings with 100/100 and 100/130 fuel due to cooling issues or strength issues.
Some engines could see gains going from 87 octane to 92 octane, the difference is larger than it seems as the octane rating scale in not linier.
Perhaps a -51 engine would be better off with a little beefing up and running higher boost than running the higher RPM? Or something similar for the 12Z?
But somebody has got to beef up the bottom end of the H-S V-12 engine and accept the weight gain.