User:MinorProphet/Draft subpages/Engine power

From a (translated) technical overview of Maybach engines:

"In order to achieve good combustion (a fairly general description of very complex processes!), the combustion chamber has a spherical design (spherical section) so that the flame front spreading from the centrally located spark plug can ignite (erfassen) the mixture quickly and evenly. This in turn enables high compression ratios (6.3 to 7), one of the prerequisites for good efficiency, without the engines being prone to knocking when using the commercially available gasoline fuels (octane number 74 to 78)."^[1]

An official directive stated that from 1 October 1938, all engines used by the Wehrmacht had to be capable of using gasoline with an octane rating (German:Oktanzahl) of OZ 74.^[2] Previously, OZ 78 (often called 'Super' or similar) was generally available. In the UK during the war, pool petrol for civilian motorists was around 70 octane.^[3]

It appears that the original Maybach HL108 and HL120 engines (first produced in 1936^[4]) were intended to run on the higher-quality OZ 78 fuel: see Dienstvorschrift D. 653/25 Panzerkampfwagen IV (Sd.Kfz. 161), Ausführung A bis E, vom 15.9.44 - Pflegeheft [Service booklet].^[5] This covers all early models of the Panzer IV.

"For OZ 74 and 78, the ignition settings (Zündeinstellungen) are the same." (p. 12)
"The carburettor settings for OZ 74 and 78 are: (p. 13)
1st Stage:  Main jet  170, Idle jet 55, Choke tube 30
2nd Stage:  Main jet  165, Idle jet 55, Choke tube 30 

• Just because the requirement to run on OZ 74 dated from 1st October 1938, it doesn't necessarily mean that this fuel should be instantly and exclusively available all over the country. There would have been variable amounts of stocks/reserves of existing eg OZ 78 which would have taken some time to be replaced. It is possible that OZ 78 continued to be available to civilian motorists, at least until the start of the war.^{[citation needed]}

As the following sections hope to show, the rated power of Maybach engines (usually stated in the manufacturer's own engine manuals, or official Dienstvorschriften 'Army service regulations') was considerably reduced between 1936 and 1939 due to the requirement to run on lower-quality fuel. For example, the difference between 300 PS and 230 PS is a reduction of very approximately 20%. This may be the one reason why engines of different capacity have the same claimed power.

Basically, these two engines appear to have developed the same power of 100 PS, despite the difference in cylinder capacity.

• Treue & Zima 2021, p. 375, From Tab. 20.4, listing many engines which reached series production:

Engine Year  Bore x stroke  Power   RPM

NL 38  1936  90*100 mm      100 PS @3000
HL 42  1939  90*110 mm      100 PS @3000

But there were differences between various models of the NL38.

• Maybach manual Ersatzteilliste: Maybach NL38 HL42 12.43 [Parts list] lists 7 variants of the NL38 and 6 for the HL42 (but no power figures.)^[6]

• The manual D.606/4 m.Zgkw. 5t (Sd.Kfz. 6) Bauart L5 und L7, dated 1.4.1938, p. 6 states for the NL35 Spezial 90 PS and 100 PS for the NL38 Spezial.^[7]

• Manual D.606/3 Mittlerer Zugkraftwagen (Sd.Kfz. 6) Typ BNL 7: Ersatzteilliste zum Fahrgestell und Aufbau ['Parts list of chassis and body'] dated 3.2.40, The NL38 Spezial developed 100 PS @ 3000 rpm and 25 mkg of torque @1700 rpm, stated in Tafel 1, p. 9 [pdf 7], quoting Maybach number 91950/1 dated 1.4.36.^[8] Complete and detailed description of the ZF G45 v gearbox, ausreichend [sufficient] fur 100 PS Maybach NL38 (p. 13)

• Maybach-Motorenbau GmbH Friedrichshafen: Maybach 6-Zylinder-Vergasermotor Bauart NL 38 TUKRM-TUKRRM und HL 42 TUKRM-TUKRRM, Beschreibung und Behandlungs-Vorschrift, (October 1938) Dated Nm. 164/138.  10.38.  25.^[9] Includes engine nos. from 500 001, made by Nordbau. Tech specs, p. 7^[10]

NL38 TUKRM/TUKRRM
Power			95 PS @3000 rpm
Max torque		25 mkg
bore x stroke		90 * 100 mm
capacity		3,970 cc
CR			1 : 6.7

NL42 TUKRM/TUKRRM
Power			100 PS @2800 rpm
Max torque		27 mkg
bore x stroke		90 * 110 mm
capacity		4,170 cc
CR			1 : 6.7

• By November 1938 Demag had completed its contract to produce the 60 vehicles of the 0.Serie D6 model (+ 8 Versuchs-Serie) of the new Sd.Kfz. 10 half-track. Demag installed Maybach's NL38 TRK engine developing 90 PS (Pferdestärke, metric horsepower) with engine nos. 50001 to 50068.^[2] Maybach-Motoren were obviously aware of the requirement to use OZ 74 from October 1938, and they modified the NL38 with a "new cylinder head and shorter pistons". The result was the NL38 TKRM, starting with engine serial no. 50069, installed in the 1.Serie mass production Sd.Kfz. 10 type D7. It wasn't until May 1940 that Oberkommando des Heeres (OKH) reported that the NL38 TRK had pistons which created compression too high for OZ 74. ^[2] Maybach later switched production of the NL38 TRKM to the HL42 TRKM.

• Manual D.672/3 l.Zgkw. 1 t (Sd.Kfz. 10) Typ D7 — Gerätbeschreibung und Bedienungsanweisung zum Fahrgestell [Device description and operating instruction for chassis], dated 1.3.39, states for the NL 38 TRKM: 90 * 100 mm, 3790 cm3, 90 PS @2800 rpm^[12], and for the HL42 TRKM: 90 * 110 mm, 4710 cm3, 100 PS @2800 rpm.^[13]

• J&D, Panzer Tracts 22-1, quote a post-war BAOR report on the Sd.Kfz. 10, saying the D6 had a NL38 TU of 83 PS, and the HL42 gave out 100 PS, but they say the report is unreliable.^[14]

• Datenblätter ^[15] states 90 PS for the NL38 TRKM and 100 PS for the HL42 in the 1-ton (Sd.Kfz. 10); and the same latter figure for the 3-ton (Sd.Kfz. 11) halftracks. Also, 115 PS for the HL54 TUKRM in the 5t Sd.Kfz. 6.

• Panzer Tracts 15-2 - Sd.Kfz. 251 1939-42 says that NL38 TUKRR and NL38 TUKRRM were fitted to 120 unarmoured Sd.Kfz. 251 Ausf. A (m.M.T.W., mittlerer Mannschaft-Transport-Wagen) "instead of the more powerful HL42 TUKRRM engines." You would tend to think so, BUT the data sheet states exactly the same power output for both engines, 100 PS @3000 rpm for the NL38 and 100 PS @ 2800 for the HL42...! ^[16] I wonder where they got this figure, since only the original NL38 Spezial made 100 PS @ 3000 rpm? Most other sources give 90 PS for the NL38 TUKRRM.
  • Was this the only time the NL38 was fitted to the 251? Possibly.

• An August 1944 report made by Vauxhall Motors, Luton, on an Sd.Kfz. 251 chassis (Description of German Three Quarter Track Armoured Troop Carrier, Chassis Type ZgKW 3t) includes a comprehensive report the HL42 engine from a Bussing-NAG 1-ton halftrack. Bore x stroke 90 * 110 mm, approx. compression ratio of 6.43 : 1.(p. 15) Pool petrol of 69 octane was used, and also pool petrol doped with ethyl fluid to 75 octane (similar to the recommended OZ 74.) "The only gain with the doped fuel was a slight decrease in the detonation." (p. 32 [pdf 36]) ^[a] The test results show torque and power curves in a graph on [pdf p. 40]. The graph indicates power of 100 HP @2800 rpm, and max. torque of 195 Lb·ft @2200 rpm, closely equivalent to 27 mkp. Vauxhall's engineers tested the motor right up 4000 rpm, with maximum power of 112 HP reached @ approximately 3600 rpm. Torque dropped to c. 188 Lb·ft (26 mkp) @2800, and fell off, unsurprisingly, to c. 145 Lb·ft (20 mkp) @4000.

• Manual D.672/5, Sd.Kfz. 250, Sd.Kfz. 252 and Sd.Kfz. 253, dated 8.8.40, p. 7 states HL42 TRKM, 100 PS @2800 rpm for all three vehicles.^[17]

• Spielberger in Halbkettenfahrzeuge gives the HL42 as the only engine for the 250, 251, and 252 ammo carrier: all at 100 PS @2800, compression ratio of 6.7 : 1^[18]

Summary

Despite having nearly 1/2 litre greater capacity, the HL42 (first made in 1939)^[19] produced exactly the same power as the NL38 (first made in 1936). Was the lack of difference being due to the requirement to run on OZ 74 rather than OZ 78 from 1 October 1938?

Well, there seems to have been a certain spread of power output from various versions of the NL38, listed in chronological order.

The Sd.Kfz. 6 was the second half-track to be produced in early 1936, with the NL38 Spezial of 100 PS. (The Sd.Kfz. 7 was the first half-track to be made, in 1934, with the HL52 TU, later HL62 TU.) The run of the 8 + 60 Sd.Kfz. 10 D6 with the NL38 TRK was completed during the OZ 74 changeover, finishing in November 1938, only made 90 PS, and failed at the Army inspection. The follow-up NL38 TRKM (D.672/3), installed in the production D7 Sd.Kfz. 10 also only made 90 PS. Maybach's own manual (October 1938) states 95 PS for the NL38 TUKRRM, and J&D PZ 15-2 gives 100 PS for the same engine in the 251.

So what was the point of the HL42, first produced in 1938/39, which made no more power at 100 PS @2800 rpm? Well, it actually produced 100 PS, compared to the later NL38 TRKM of 90 PS. Only the NL 38 Spezial of 1936 made 100 PS with high-compression pistons and decent fuel.

• D. 652/6, Panzer III Ausf. B, Teil 1: Vorläufige Gerätbeschreibung und Bedienungsanweisung zum Fahrgestell, 7.2.1938 (p. 4) ^[20]

Bauart                              Maybach HL108 TR
Leistung bei n=2800 U/min           300 PS
Höchstdrehmoment bei n=2000 U/min    75 mkg

Schaltgetriebe:                     5-Gang-Aphon-Getriebe [ZF SFG 75 5+1] (p. 10)

• Jentz & Doyle, Panzer Tracts 3-1, Panzerkampfwagen III Ausf. A, B, C & D. In their text p. 3-32, they state the figures for power and torque of the HL108 as fitted in the Panzer III Ausf. A as 300 PS and 75 mkg, and give the max torque of the ZF SFG 75 5+1 gearbox as 75 mkg.^[21] However, on the data sheet on p. 3-39 they state 250 HP @2800 rpm^[22] and erroneously state that the gearbox was an SSG 75 (Synchronisierter Sechsgang Getriebe), although they correctly give only the five gear ratios of the SFG 75 (Synchronisierter Fünfgang Getriebe).^[23]
  • As regards the gearboxes: Since OZ 74 (Oktanzahl, 'Octane rating'} wasn't mandated until 1 October 1938,^[2], then all the SFG/SSG 75/76 gearboxes in the Panzer III and IV Ausf. A were in fact properly matched to the higher torque of around 75 mkg developed by the original HL108. See User:MinorProphet/Draft subpages/WW2 ZF gearboxes#Nomenclature of ZF gearboxes. All the Panzer III Ausf. A-D had been manufactured by the end of 1938.
  • The Panzer III Ausf. E (first examples appeared at the end of December 1938) used the HL120 TR and the Maybach SRG 32 8 145 semi-auto gearbox,^[24] whose numbering implies it was designed for an engine of 320 PS and 80~89 mkg (in fact, 82 mkg, see figures immediately below, and at #Maybach HL120.) This was intended to match with the original HL120 TR with high-compression pistons and using decent fuel, e.g. OZ 78. But this never happened because of the mandated OZ 74. Thus the modified HL120 TRM only made around 265 PS and (according to my calcs, 67 mkg) with the lowered compression ratio. Instead of making a theoretical SRG 26 6 145 (265 PS, 67 mkg) Maybach carried on making the SRG 32 8 145, which nevertheless turned to out be a complete disaster. The very first Pz III Ausf. E didn't appear until December 1938.

• Engine manual: Maybach 12-Zylinder Vergasermotor / Bauart HL 108/120 TR, Beischreibung und Vorhandlungsvorschrift.
  (Cited in Koch 2000, pp. 18, 24): Front cover, p. 18, tech specs for HL108 (HL120), p. 24.

Leistung               300 (320) PS bei 2800 U/min.
Maximale Drehmoment    79 (82) mkg
Bohrung und Hub        100 Ø x 115 (105 Ø x 115)
Zylinderinhalt         1080 (1190)
Verdichtungsverhältnis 1 : 7
Gewicht                920 kg

• Geheimer Kommandosache! Merkblatt Anhaltewerte für Pz.Kpfw. und Pz.BefWg. Aufgestellt am 1.6.1938 p. 22 [pdf 24], cols. 5 and 6.^[25]

Panzer III and Panzer IV

PS   230 n=2600  (HL108)
PS   265 n=2600  (HL120)

• Datenblätter für Heeres-Waffen, Fahrzeuge, Gerät, p. 228 [pdf 115], Blatt G 402 VII, the 18t Sd.Kfz. 9 (the only other vehicle that used the HL108).^[26]

Motor:   Maybach HL108 TUKRM   230 PS

• Jentz & Doyle (1997a) confirm in Panzer Tracts 4 that the HL108 used in the Panzer IV Ausf. A only developed 230 PS.^[27]

• Engine manual: Maybach 12-Zylinder Vergasermotor / Bauart HL 108/120 TR, Beischreibung und Vorhandlungsvorschrift.
  (Cited in Koch 2000, pp. 18, 24): Front cover, p. 18, tech specs for HL108 (HL120), p. 24.

Leistung               300 (320) PS bei 2800 U/min.
Maximale Drehmoment    79 (82) mkg
Bohrung und Hub        100 Ø x 115 (105 Ø x 115)
Zylinderinhalt         1080 (1190)
Verdichtungsverhältnis 1 : 7
Gewicht                920 kg

• Maybach 12-Zylinder Vergasermotor / Bauart HL 120 TRM / Nm. 212/179   2.41.   80., p. 7 (NB Note date "2.41", website text says 1939)^[28]

Power              300 PS @3000 rpm
Max. torque        80 mkg
Bore x stroke      105 * 115
Capacity           11 900 cc
Compression ratio  1 : 6.5  [NB p. 5 states 1 : 6.45]
Fuel               Oktanwert von 74 CFR-Research oder mehr[29]
Magneto (p. 34)    Bosch JO 12 L 14

• A later edition of the same manual, dated on the front cover 2.44 (February 1944), gives exactly the same technical data: and it is difficult to avoid the idea that Maybach-Motoren were simply reprinting old data and avoiding the reality of considerably reduced power.^[30] For example, the Army manual D.653/39 for the Jagdpanzer IV Ausf. F dated 15.9.44, p. 6 states the 265 PS that most sources confirm.^[31]

• Dienstvorschrift D.653/1+ Panzer IV Ausf. A-D Gerätbeschreibung und Bedienungsanweisung zum Fahrgestell, 26.9.38^[32] This early secret (Geheim), red-covered manual refers to Vskfz. 622 (Versuchs-Kraftfahrzeug, 'Experimental [or Trial] Vehicle'), before the Panzer IV was designated Sd.Kfz. 161. The power figures given below are less than the highest ones quoted in Koch above,^[33] but greater than the usually-quoted figures of 230 and 265 PS for this engine. It seems possible these downwards-revised figures were released after Maybach had tested the engines again, possibly using lower compression pistons but with OZ 78 gasoline.

                                A. Technische Angaben[32]
Motor                     Ausführung A       Ausführung B und C

Bauart                    Maybach HL108 TR   Maybach HL120 TR bzw. Maybach HL120 TRM
Leistung bei 2800 U/min   250 PS             285 PS

• Datenblätter fur Heeres-Waffen, Fahrzeuge, Gerät, p. 145 [pdf 73], Blatt G' 317, Flakpanzer IV 2cm, Pz.Fahrgest. IV/3 (basis for the Wirbelwind, Ostwind, Möbelwagen etc.) ^[34]

   Flakpanzer IV 2cm, Pz.Fahrgest. IV/3

Motor HL 120 TR 112, 272 PS bis 2800 U/min

The name of this semi-mythical engine, variously described as HL120 TR 112 or TRM 112, seems to stem from this specific Datenblatt, and has been repeated in a number of reliable sources (HL120 TR112 for the Wirbelwind only (Panzer Tracts 12 - Flakpanzer & Flak Selbstfahrlafetten, p. 12-37); Spielberger Panzer IV and Variants, Wirbelwind and Ostwind (272 PS @ 2800)^[36]; and Chamberlain & Doyle, Encyclopedia of German Tanks ^[37]). Jentz & Doyle corrected this in their Panzer Tracts 12-1 to a plain HL120 TRM, but retain the higher power output (272 PS) except for the Kugelblitz.^[38] The nomenclature of HL120 TR 112 is wholly untypical of any other Maybach engine, and is almost certainly some sort of error going back several decades if not to contemporary wartime documents. Nevertheless, its power of 272 PS doesn't seem to appear in any yet identified official manual, although it seems unlikely to be an error of transcription.

• Walter Spielberger, in the appendix to his Panzer IV & its variants (p. 154) gives some figures for power and revs of the HL108 and HL120, but he may have confused things somewhat, or at least silently conflated different sets of figures.^[39] WP:OR?

Vehicle                Panzer IV                  Panzer IV
Ausf.                  A                          B
Years built            1937–1938                  1938
Information source     D. 635/1, 1 Nov 42         D. 635/1, 1 Nov 42[32] 

Engine                 Maybach HL108 TR           Maybach HL120 TR
CR                     6.5 : 1                    6.5 : 1
RPM Normal/Maximum     2600/3000                  2600/3000
Horsepower             230/250                    265/300

Note that the D-manual D.635/1 referenced just above is dated 26.9.38, just a few days before the OZ 74 directive came into effect on 1 October 1938, and states the partially-reduced power figures of 250 and 285 PS: but the version that Spielberger used may well have stated 230 and 265 PS. However, the row heading is named "RPM Normal/Maximum", and it seems possible that Spielberger may have been familiar with another set of figures, for example from a Maybach manual such as shown at the start of this section, stating 300 PS @3000 rpm. Essentially his somwhat confusing idea of "Normal/Maximum" appears to refer to two incarnations of the same engine: the original HL108/120 TR with high-compression pistons, and the later de-rated HL120 TR/TRM. WP:OR?

Summary

Thus we can see from figures in official contemporary publications dating from around 1936, that:

• The HL108 has been rated at 230 PS @2600, 250 PS @2800, and 300 PS @2800 rpm:
• The HL120 could apparently produce anything from 265 PS @2600 rpm, via 272 PS and 285 PS@ 2800 rpm, 300 PS @3000 rpm and 320 PS @ 2800 rpm
• Compression ratios are variously stated as 6.2 : 1,^[40] 6.3:1,^[1] 6.5 : 1 (^[32] to 7.0 : 1^[41]

Initial source:^[4]

Nothing

The notes below the row work if there is a lot of text, eg, List of early color films, but the main point of the table is to be sortable, and the intervening text interferes with the legibility.

|- | HL | 1935 | I-6 | b*s | PS | rpm | mkg | cast | app