The Secret Horsepower Race by Calum Douglas (and piston engine discussion)

[spicmart]

In Dan Sharp and Calum Douglas' great Me 309 book, a Major Petersen mentions that the Jumo 213 was smaller than the DB 603 when both engines weighed virtually the same. Further is said that the 213 requires a smaller radiator than the 603.

Looking at the Fw 190D and Ta 152, the early Doras' radiator wasn't sufficient so the DB 603-powered D-14/15 obtained
the Kühlerkopf of the Ta 152C.
Apart from the oil cooler the drum rads of the Ta 152 subtypes C and H look the same. The absence of an oil cooler means more of the radiator matrix could be used for cooling of Jumo 213E/F which is said to need less cooling than the DB 603 anyway?

My conclusion is that the Jumo 213 simply got more cooling although it needed less than its counterpart.
Combined with the higher exhaust thrust it provided greater propulsion.

Anyone enlighten me on this one?

 

[Nicknick]

Having just one exhaust valve reduces the heat flow in the exhaust port conciderable. During the 90th, Mercedes used three valve heads for their V engines (cars) and truck engines, mainly because the 3V configuration enabled higher exhaust temperatures and faster light off for the cat. In case of the Jumo, this also totally explaines the higher exhaust trust

Note, that most of the heat flow into the cooling system ist not comming from the cylinders but from the exhaust ports and the valve seats.

 

[Pasoleati]

Having just one exhaust valve reduces the heat flow in the exhaust port conciderable. During the 90th, Mercedes used three valve heads for their V engines (cars) and truck engines, mainly because the 3V configuration enabled higher exhaust temperatures and faster light off for the cat. In case of the Jumo, this also totally explaines the higher exhaust trust

Note, that most of the heat flow into the cooling system ist not comming from the cylinders but from the exhaust ports and the valve seats.

Any source for that claim?

 

[Nicknick]

That's more than one "claim", which one do you mean?

 

[Pasoleati]

That's more than one "claim", which one do you mean?

The last one.

 

[Nicknick]

Ok, I have it ob my PC at home, you get it tomorrow despite youre question could have been more polite....

 

[Scott Kenny]

The last one.

All engine builders will tell you that.

 

[Nicknick]

Actually, I was searching a nice graphic vom Curtiss-Wright but couldn't find it... This here will do the job too (https://core.ac.uk/download/pdf/289945175.pdf ):

 

[Scott Kenny]

Actually, I was searching a nice graphic vom Curtiss-Wright but couldn't find it... This here will do the job too (https://core.ac.uk/download/pdf/289945175.pdf ):

By that, 49.4% of all heat loss comes out of the cylinder heads as a complete unit. Cylinder is taking more thermal load than I expected, guess I need to add oil squirters to cool the underside of the piston.

 

[Nicknick]

It is about 68 %, don't forgett the valves. The terminus "head" is misleading, he surly ment the flame deck with that.

 

[Scott Kenny]

It is about 68 %, don't forgett the valves. The terminus "head" is misleading, he surly ment the flame deck with that.

Head = combustion chamber
Port = Exhaust Port (intake port is not particularly hot)
Valves = Exhaust valve(s), (intake valves are not particularly hot)
Liner = cylinder bore
Piston = crown of piston exposed to combustion temps

 

[Calum Douglas]

The 213 does not have a fluid drive supercharger coupling, which can transfer a vast amount of heat to oil at altitudes below rated, in addition its generally better designed with higher coolant pressure and generally higher coolant temps than contemporary German engines which obviously lowers heat to fluid. The 3 / 4 valve discussion is hard to evaluate, as the valve is of course a lot larger and then in the port itself of course opens out into a fairly familiar cross section. I would strongly suspect that the lack of a fluid SC drive, high pressure coolant system and integrated oil/water HX are the primary drivers here. The 3 valve head was probably valid in 1935 when rpm`s were capped by mechanical limits but it really wasnt a great idea long term, its a shame for jumo that the didnt fix that until the "J", which was a dramatically technically superior engine to anything the Allies had, just far too late.

 

[Nicknick]

Each head has a different geometry, so there is no exact percentage of heat losses for the mentioned components.

I'm not saying, three valve heads are superior, but they tend to have lower heat losses, which is confirmed by several puplications from MB (I can't quote them, but I read them...). It is also quite obvious, that a singe big pipe has less surface that two smaller pipes with the same cross section.

In modern designs, the four valve pent rouf heads enable a central spark plug whereas the three valve heads often have two plugs out of the center. Unlike in modern designs, (As said before) the plug position in the Jumo 213 is superior to the four valve aero engines of its days, because the parallel four valve heads had their plugs on the perimeter of the combustion chamber.

Despite that, one singe exhaust valve is harder to cool and the gas exchange work ist surly lower for the four valve configuration.

 

[spicmart]

Were the Germans ever able to catch up with the higher efficiency of Allied radiator?
Those of the Spitfire were of only 55 % the size of German rads on the Me 109F/G.

 

[Nicknick]

I think it had more to do with the cooling temperature. The bad casting quality prevented the Germans from using higher cooling pressures if I remeber it right. I believe Behr builded the first modern aluminum cooler during WW2, so the cooler itself wasn't the problem.

 

[spicmart]

I think it had more to do with the cooling temperature. The bad casting quality prevented the Germans from using higher cooling pressures if I remeber it right. I believe Behr builded the first modern aluminum cooler during WW2, so the cooler itself wasn't the problem.

And the casting quality wouldn't improve until the end? Was that a question of inferior materials, too?

 

[Calum Douglas]

You will find that the cooler itself WAS a catastrophic part of the problem...

The tubes were squashed flat from round, and deeply unsurprisingly when you put pressure inside they turn back into tubes again.

109 rads expand like bicycle tyres when you try running high pressure>

View: https://youtu.be/ImEpk1s-Vk0?si=-lxleQhH_rGQh8-g&t=2975

 

[Nicknick]

Something about the German cooler development during the war, here the same design (to the very right side and at the bottom) is praised for beeing more effective and pressure resistant...

(Kyrill von Gersdorf et al: Flugmotoren und Strahltriebwerke)

 

[Calum Douglas]

Something about the German cooler development during the war, here the same design (to the very right side and at the bottom) is praised for beeing more effective and pressure resistant...

(Kyrill von Gersdorf et al: Flugmotoren und Strahltriebwerke)

I`m sure thats what the sales brochure said, but its more or less impossible to imagine a less suitable design for resisting internal
pressure, a very significant part of that is that not only is there nothing stopping the inside faces of the flattened "O" from moving apart internally, the tubes are not even brazed together externally. The whole lot is a floppy mess. Unsurprisingly, the idea for making tubes this way appears to have utterly vanished, never to be seen again.

Its a hopeless idea for making pressure resistant matrixes, and I suspect was only ever used because copper was in such sort supply that some sort of very quick and easy method was needed in a hurry in the late 30`s to make aluminium coolers.

 

[Nicknick]

It definately looks better as a drawing....
These type of cooler was developed around 1930 (according to my sorce above), at a time when copper wasn't really rare in Germany. I guess it was lighter an cheaper back than and the shortage of copper and brazzing materials made it an obvious choise later in the war. I guess,, pressurized cooling systems apeared later than this cooler design, so it became outdated during the war but couldn't be replaced with something better...

 

[Calum Douglas]

It definately looks better as a drawing....
These type of cooler was developed around 1930 (according to my sorce above), at a time when copper wasn't really rare in Germany. I guess it was lighter an cheaper back than and the shortage of copper and brazzing materials made it an obvious choise later in the war. I guess,, pressurized cooling systems apeared later than this cooler design, so it became outdated during the war but couldn't be replaced with something better...

Just remember that the specifications for future military aero engines (called "large" aero engines) at the time, were laid down in 1928, which included a stipulation that high pressure high temperature cooling ought to be developed (why this didnt happen is still not entirely clear, (I suspect they just ran out of time to develop ALL the features stipulated). Whilst with the existing trade arrangements Copper may have been "available" in 1930, the fact there was very little (if any) actual ore in Germany, would have been well known, as would the fact that once hostilities started, such "externally" available materials would be likely to vanish would also have been appreciated, preparations along these lines are clear from the synthetic fuel programme, which was being built at this approximate time. So I would not underestimate the degree of forward planning even a decade before the war in Germany.

 

[Elan Vital]

About halfway through the book (done with the chapter for 1941). I really like how citations regarding certain technical developments or problems are followed by comments from the author to explain what is happening. The chapters about 1940 and 1941 in particular are really good at showing the progression in engine and supercharger design as the belligerents try to deal with ever greater combat altitudes.

The comment about how a swirl throttle could have helped the Merlin 45 is interesting. In a very uchronistic way, I wonder what wartime exchanges between the French and British (if the Entente had held the line at the Franco-Belgian border) could have achieved. The swirl throttle from the Szydlowski-Planiol supercharger would be a useful addition to British supercharging arrangements, while the French could possibly leverage Rolls-Royce's efforts in superchargers to extract the most out of their Hispano-Suiza 12Y pending the arrival of the 12Z. The 12Y-51's 1000hp were probably the most that could be obtained from the problematic 12Y's design without requiring changes comparable in importance to the 12Z, but if this power could be maintained over a greater altitude range that would have been nice.

Some kind of progression like that:
Radial swirl throttle+single-speed single-stage S-P supercharger-->axial swirl throttle-->2-speed single-stage S-P supercharger (as experimented by the Americans in late 1940)-->2-speed 2-stage supercharger.

The long-nose versions of French fighters (Dewoitine 551, Arsenal VG-39) would probably have been better-suited to the longer arrangements required by an axial swirl throttle and 2-stage SC.​

 

[Elan Vital]

I have finally finished the Secret Horsepower Race after a couple weeks at a more regular pace.

This has been a very enjoyable read. I am not a mechanical engineer but the technical information was conveyed in a very understandable manner and the addition of the historical/behind-the-scenes context helps a lot.

It is interesting how wartime aircraft engine developments eventually made it to the civilian sector decades later, especially in racing. Calum, would you say that the long delay between the application of WW2 military research to civilian racing was caused by technical or financial limitations on the ground, or just that the automobile engine world had to rediscover this research much later on as it had not been spread very wildly?

 

[pathology_doc]

I'm re-reading this at the moment, and several things come foremost to the mind (again):

1) Germany's problems with alloy materials for engine steels and availability of high-octane petrol started VERY early in the war. Much more so than was apparent on first reading.

2) Germany's laughable (pun intended) stupidity regarding its codename for Nitrous Oxide injection ("HAHA process") was matched only by Britain's inexplicable stupidity in not realizing immediately what it meant (if only just ONE anaesthetist had been in the loop...).

3) It seems inexplicable that Supermarine struggled with trying to fit the single-stage, two-speed Merlin XX into the Spitfire III then just went right on ahead and lengthened the nose - seemingly without blinking - when it came time to put the two-stage, two-speed Merlin 61 in. Why so much fuss and hand-wringing over the one and not the other? This especially when several other significant changes were being planned for the airframe in general. MOST especially when RR at least were already thinking about putting a two-stage engine in the Spit and knew they would have to make room for it eventually.

ON A MORE GENERAL NOTE:
Is there a rule of thumb for how much power you have to lose to a geared, engine-driven supercharger in order to keep a full-throttle height of X thousand feet? Also, with respect to the following graph taken off the War Thunder forums, can Calum or some other knowledgeable person please explain why the higher boost pressure results in a lower altitude for maximum speed (and if I am right a lower full-throttle height) in a given supercharger gear? The way all three boost levels meet for the same Vmax at 12,000ft appears to be a neat coincidence.



(I am aware that Spitfire performance for a given mark is contentious at best, especially given how many different engine types could be put into the same Mark of Spitfire without the designation changing one lick - and that's even before we get to the low-blown, cropped-impeller models - while for some others, a simple engine switch brought a whole new Mark number. A change like that in an American fighter would get a new Block number at least, and definitely a new number suffix to the model letter in Germany. I know the internal Supermarine model numbers would and did change.)

 

[HoHun]

Hi,

ON A MORE GENERAL NOTE:
Is there a rule of thumb for how much power you have to lose to a geared, engine-driven supercharger in order to keep a full-throttle height of X thousand feet? Also, with respect to the following graph taken off the War Thunder forums, can Calum or some other knowledgeable person please explain why the higher boost pressure results in a lower altitude for maximum speed (and if I am right a lower full-throttle height) in a given supercharger gear? The way all three boost levels meet for the same Vmax at 12,000ft appears to be a neat coincidence.

I'm not quite sure which values you'd like to consider constant for your rule of thumb, but generally, the response will not be linear if you use the same basic engine and only increase supercharger capacity. Higher supercharger compression ratios will raise the charge temperature, which will lower the charge mass at the same boost pressure. Aftercooling can reduce the temperatures, but will increase overall drag, and lower the efficiency of the flow through the intake drag.

Higher boost pressure while keeping supercharger, supercharger rpm, and engine rpm constant (as well as the physical parameters of the engine) results in a reduced altitude for maximum speed since the supercharger compresses the air by an approximately constant ratio under these conditions.

Accordingly, if you need a higher boost pressure, you need a higher ambient pressure, which means a lower altitude.

The altitude for maximum speed is also called "full throttle height", because the throttle can be fully opened at that altitude (and above) without exceeding the maximum permissable boost pressure.

As the intake pressure with a forward-facing ("ram") air intake is not really the ambient pressure, but increased by the dynamic pressure caused by the relative motion between ambient air and aircraft. the values for full throttle height are slightly different between "static", climb and high-speed conditions. The more efficient the intake, the greater the difference.

That in the Spitfire graph, the three boost levels meet at 12000 ft is not just a coincedence, but the result of a falling ambient pressure. With the supercharger in low gear (probably called "moderate" or something in British terminology), at 12000 ft all the supercharger can deliver is +18 lbs/sqin boost pressure with the throttle wide open.

If your Spitfire XIV is cleared for +18 lbs/sqin, you'll have to close the throttle when you descend below 12000 ft. If it's cleared for +25 lbs/sqin, you can leave it wide open until you get down to about 6500 ft and thus gain a bit of speed at lower altitudes, as indicated in your graph. If you'd fail to close the throttle below 6500 ft, the engine would run at greater boost than +25 lbs/sqin ...

As usually, the limits in wartime were defined to avoid engine failures, you'd want to avoid over-boosting. The vast majority of WW2 aviation engines were fitted with automatic boost regulators to help the pilots with that, as excessive boost had the potential to destroy an engine within a very short period of time.

Boost pressure was only a coarse approximation for the parameters that decided if the engine was going to run OK, with charge temperature being another important parameter, so the method was not perfect. (Jumo at least managed to come up with sort of an analog engine control computer that accounted for charge temperature, giving them a better way to optimize engine power of the late-war Jumo 213, but that was a pretty complex solution.)

Regards,

Henning (HoHun)

 

[pathology_doc]

Thanks, Henning; that explains it.

 

[Calum Douglas]

I have finally finished the Secret Horsepower Race after a couple weeks at a more regular pace.

This has been a very enjoyable read. I am not a mechanical engineer but the technical information was conveyed in a very understandable manner and the addition of the historical/behind-the-scenes context helps a lot.

It is interesting how wartime aircraft engine developments eventually made it to the civilian sector decades later, especially in racing. Calum, would you say that the long delay between the application of WW2 military research to civilian racing was caused by technical or financial limitations on the ground, or just that the automobile engine world had to rediscover this research much later on as it had not been spread very wildly?

Currency conversions from wartime Germany to today, are hideously imprecise.

However, using a very conservative estimate from an online source suggesting that in 1940 £1 Sterling was 11.5 RM,
that would put the price of a Jumo 213 (assuming the rates did not alter between 1940 and 1944) in todays money
at £200,000 Sterling per unit (there are less conservative ways of doing the calculation based on purchasing power and
not exchange rates which put the unit cost at nearer £600,000 a unit).

This cost is if you are mass producing thousands of engines, the cost of making a couple of prototypes might be imagined (
add a couple of zeros).

Imagine its 1946 and your devastated economy has some racers riding old bikes around deserted airfields in England, and
you can start to see why tech from these engines was not very appealing. The advances put in were so far ahead of automotive
that asking why it was not used is very much like asking why your lawnmower doesn't have self-sharpening blades
maintained by a swarm of AI nano-bots. (I exaggerate a little, but not THAT much).

I would say cost was the primary barrier to the technology entering commercial use, although unfamiliarity is also a factor
as these are aero-engines, and aero engineers gave up on piston engines for cutting edge use at this same point due to the
advent of the turbojet. So it was also the "wrong" group of engineers to apply it to automotive as well.

 

[Nicknick]

I'm re-reading this at the moment, and several things come foremost to the mind (again):

1) Germany's problems with alloy materials for engine steels and availability of high-octane petrol started VERY early in the war. Much more so than was apparent on first reading.

2) Germany's laughable (pun intended) stupidity regarding its codename for Nitrous Oxide injection ("HAHA process") was matched only by Britain's inexplicable stupidity in not realizing immediately what it meant (if only just ONE anaesthetist had been in the loop...).

3) It seems inexplicable that Supermarine struggled with trying to fit the single-stage, two-speed Merlin XX into the Spitfire III then just went right on ahead and lengthened the nose - seemingly without blinking - when it came time to put the two-stage, two-speed Merlin 61 in. Why so much fuss and hand-wringing over the one and not the other? This especially when several other significant changes were being planned for the airframe in general. MOST especially when RR at least were already thinking about putting a two-stage engine in the Spit and knew they would have to make room for it eventually.

ON A MORE GENERAL NOTE:
Is there a rule of thumb for how much power you have to lose to a geared, engine-driven supercharger in order to keep a full-throttle height of X thousand feet? Also, with respect to the following graph taken off the War Thunder forums, can Calum or some other knowledgeable person please explain why the higher boost pressure results in a lower altitude for maximum speed (and if I am right a lower full-throttle height) in a given supercharger gear? The way all three boost levels meet for the same Vmax at 12,000ft appears to be a neat coincidence.

View attachment 741843

(I am aware that Spitfire performance for a given mark is contentious at best, especially given how many different engine types could be put into the same Mark of Spitfire without the designation changing one lick - and that's even before we get to the low-blown, cropped-impeller models - while for some others, a simple engine switch brought a whole new Mark number. A change like that in an American fighter would get a new Block number at least, and definitely a new number suffix to the model letter in Germany. I know the internal Supermarine model numbers would and did change.)

I doubt that this graph is correct, with a faster running supercharger, more throtteling is needed for low rpm, so the engine would have less power at sea level than a variant with slower supercharger speed (if eveything else is the same). With climbing up, it would start becomming faster than the slow SC variant, until this needs to shift into 2 gear. This will go on until the engine with the faster superchager also needs to shift in the second gear.

During the next phase, both engine run with maximum boost, but the one with the slower SC runs again more efficient until it can't keep the maximum boost. Shortly after, the engine with the faster supercharger will become faster and remain so till the max. flight height. Of course, the engine with the faster SC Speed will also be able to fly higher.

 

[sienar]

Some papers on post war engines from the time;

Postwar Internal–Combustion Engines and Their Fuels

https://www.jstor.org/stable/44467821

Lessons from Aircraft Engines Applied to Heavy-Duty Ground Vehicle Engines

https://www.jstor.org/stable/44467753

 

[pathology_doc]

Here's a question that my mind was mulling over last night.

We know that by the end of the war, the British had the Merlin engine operating at +25lb boost, mostly (as I understand it) by means of increasing the knock resistance of the fuels they were using. But how far can you continue to push this, assuming you had the fuels to let you push it higher? (We'll ignore the logistics for now.)

In fact, let's cast a magic spell over the engine components themselves such that they won't be destroyed by detonation when it starts to happen. What's the limit condition as you drive a Merlin two-stage supercharger harder and harder?

It seems to me that there have to be two. The first is of course the choke condition as you get the flow to sonic heading out of the compressor, in which case my understanding is that you just get a higher and higher pressure and temperature behind the normal shock until everything comes apart.

But the second... if you handwave things so that the mechanism does NOT fly apart, doesn't that have to be a temperature rise to the point where the fuel-air mixture ignites?

 

[Nicknick]

Are we talking about the production supercharger, hypothetical superchargers in their time or hyphothetical modern 2-stage superchargers?

A single radial compressor can archieve a pressure ratio of about five (very large ones in marine engines go up to seven!).

I do a little calculation with realistic compressore efficiencies

With a pressure ratio of five for the first stage , the air in an ideal compressor would heat up according to :

T2=T1*5^(k-1/k)

I assume kappe would be about 1.25 for a rich air fuel misture with dropplets. With a starting temperature of 300 K at sea level:

T2 = 1.4287 * T1 = 428 K =155° C

Assuming an isentropic compressor efficiency of 75 %

T2 = T1*((1,4287 -1)/0,75) + 1) = 1.57 * T1 = 471 K = 198° C (still far below self ignition of gazoline)

lets assume an intercooler between the first and second stage which cools the air down to 330 K. The second stage should have a lower pressure ratio of 3, to avoid weekening of the aluminum compressor wheel. All fuel will be evaporated after the first compression and even after the CAC. The estimated Kappa will be 1.35. With the same kind of calculation it would end up with

T3= 475 K = 202° C

The pressure would be 15 bar abs. which would blast every Merlin...

Of course, at hih altitude a pressure ratio of 15:1 can very well be used and the absolute presser will totally be in the usable range. This example should just demonstrate, that the max. pressure at sea level will not be limited by the compressor system.

 

[sienar]

Reno Unlimited Merlins are running at 135-140 inches, ie +54 psi. They are typically using Allison conrods though.

 

[Foo Fighter]

I read an article somewhere that suggested some pretty exotic fuels in use at Reno and other races/speed record events.

Now of course, I am wary of articles like this because I better understand the fact that a lot of people like to talk brown porridge about anything and be considered 'experts'. Yes, drips under pressure.

No, not peanut butter.

 

[F119Doctor]

Reno Unlimited Merlins are running at 135-140 inches, ie +54 psi. They are typically using Allison conrods though.

Most of the serious Reno Merlins have the aftercooler removed to eliminate the flow restriction and run a ton of water injection to cool the supercharger discharge air to suppress detonation at those extreme boost levels.

 

[tomo pauk]

Eh, pretty close.

All British engines were hand assembled by a person called a "Fitter". The Fitter would take parts as they came off the line and would measure, mix and match until they got a set of parts that all fit together with tight clearances. No torque specs, the Fitter tightened the bolts "enough." The Brits had not heard of a Torque Wrench in 1940!

You see, the various parts as they came off the British lines had very wide tolerances that were "acceptable". So wide that it was possible to have a piston larger in diameter than the bore of a given sleeve.

But that Fitter would go through a stack of parts until he found a bore sleeve that a given piston would fit in, or would chuck the piston in a lathe to turn down to a size that would fit. That took a lot of time to assemble one engine.

What Ford did (they were making the engines under contract in the UK) was greatly tighten up the tolerances on the "as made" parts, so that every piston would fit in every bore sleeve (etc). This meant that the clearances between the parts were wider than the RR hand fitted engines, but you never had to search for the right size parts or take them to a lathe/mill to be modified to fit.

And it was the Ford UK plans that got sent to Packard.

Example: the RR hand fitted engines kept about a 0.020" gap between crank and bearings, piston and bore, etc. The Packard assembly line engines kept more like a 0.040" gap between all their parts. So the RR engines made a little more power and could be pushed a little harder, but the Packard engines could just be thrown together and they'd work first time every time.

@Calum Douglas - would you care to comment?

 

[Calum Douglas]

@Calum Douglas - would you care to comment?

Scott has forgotten to inform Packard or Rolls-Royce, who published a Parts Interchange Manual, which tells you which Packard part number to use in a RR built merlin, and which RR part number to use in a Packard engine.

The only parts which were not interchangable were the ones which were just totally different (like the US made magnetos) or some small things like some shim sets were made in different graduated step sizes.

The entire "hand fitting" stuff is utter garbage and doesn't even need the parts interchange book to prove. How many times... *head in hands*.

Any aircraft operator today who deal with both types knows this.







Even the "not strictly interchangable" parts will fit with some small external dressing on a casing where it clashes with something etc.

 

[tomo pauk]

Thank you

 

[sienar]

I read an article somewhere that suggested some pretty exotic fuels in use at Reno and other races/speed record events.

Now of course, I am wary of articles like this because I better understand the fact that a lot of people like to talk brown porridge about anything and be considered 'experts'. Yes, drips under pressure.

No, not peanut butter.

The really exotic fuels were in the immediate post-war period of 47-49.

Sohio produced a 130/170 with 4.34ml lead putting out 19100 btu/lb.

Shell made a Shell Methyl Triptane-1 with a claimed 200/300 octane. Cook Cleland unsuccessful tried to combine this fuel with hydrogen-peroxide in place of the normal ADI. Bill Odom and Anson Johnson both ran this fuel with added lead, with Johnson winning the Thompson while flying with a Sohio sticker on the side of his plane.

Most of the serious Reno Merlins have the aftercooler removed to eliminate the flow restriction and run a ton of water injection to cool the supercharger discharge air to suppress detonation at those extreme boost levels.

How could I forget about the tube Merlins.

This is a chart from a Pete Law presentation available on, though I forgot which presentation this is from; https://www.enginehistory.org/members/Convention.php

There is quite a bit of info on the various racing mods in the other articles, as well as this good overview; https://www.supercoolprops.com/articles/gwhitegearheads.php

 

[Scott Kenny]

Scott has forgotten to inform Packard or Rolls-Royce, who published a Parts Interchange Manual, which tells you which Packard part number to use in a RR built merlin, and which RR part number to use in a Packard engine.

The only parts which were not interchangable were the ones which were just totally different (like the US made magnetos) or some small things like some shim sets were made in different graduated step sizes.

The entire "hand fitting" stuff is utter garbage and doesn't even need the parts interchange book to prove. How many times... *head in hands*.

Any aircraft operator today who deal with both types knows this.

And that was done by the Ford plant in the UK, who slapped RR upside the head and said "we cannot make an engine like this".

Do you have a copy of the letter from Ford US or Packard asking what the torque specifications were? That Rolls literally didn't have because they didn't use torque wrenches but a highly trained fitter to hand assemble all this stuff to "tight enough"?!?

 

[Nicknick]

Most of the serious Reno Merlins have the aftercooler removed to eliminate the flow restriction and run a ton of water injection to cool the supercharger discharge air to suppress detonation at those extreme boost levels.

Are you sure about that? This would mean plenty of steam in the intake air and a problematic homogenisation of that. I guess, it is more likely that the water is sprayed on the outside of the charge air cooler to increase the effectivness.