Bf-109K-4 engine choice.

[David_4555]

Wanted to ask what engine do you all prefer to choose on the Bf-109K-4 when you can select either DB 605DB and DC. Simple curiosity. 

[I./JG53_BlackJaguar]

Personally, Bf 109 K-4 DB 605 using the DB spec as it designed perform better at higher altitude

[MDzmitry]

DB 605DC is a straight upgrade, pretty similar in nature to the Allies' 150-octane fuel. And both were, from what I understand, barely used on the actual frontline. One was an on-and-off occasion depending on what fuel was available (if any), and the other was tested, adopted and dropped depending on its necessity considering additional strain on the logistics.

So I personally tend to stick to the more "boots on the ground" version (however ironic it may sound in the context of a flight sim). But I'm primarily a singleplayer dweller, so the situation may be more "min-max every ounce of performance" online.

[LukeFF]

150-grade fuel was in common usage by the RAF on the continent by early 1945. It was the USAAF who deemed it an unnecessary strain on logistics, with units such as those of the 9th Air Force. 

[Kurfurst]

Its the same engine the designation simply stands for the new, increased DB 605 ratings promulgated at the start of December 1944 and the changed designation corresponded to the rating (and fuel used : B-4 or C-3). 

 

A become AB (with boost increased from 1,42 to 1,5 ata)

AS became ASB or ASC  (with boost increased from 1,7 to either 1,8 or 1,98 ata)

DM become DB or DC  (with boost increased from 1,75 to either 1,8 or 1,98 ata)

 

The altitude performance was unchanged in each case, although the C versions run poorer at low altitude when not using maximum boost, due to different supercharger slippage setup. 

[MaxPower]

Here is a chart depicting the difference in TAS between the K-4 with the DB engine (blue) and the K-4 with the DC engine (red).  The data was collected by community members doing flight tests in the sim.  The curves on the left (bright lines) are for combat power.  The curves on the left (dark) are for emergency power.  As we can see, there's no significant different above the supercharger critical altitude.  The difference in speed at 6000 meters looks like it's around 25 km/h.  There is probably also a noticeable difference in max climb rate, since there's an 8 percent difference in engine power (1850 vs. 2000 PS).

 

[David_4555]

Thanks for that data! It looks like the DC is a no brainer in almost every circumstance (if available)

[FeuerFliegen]

22 hours ago, MaxPower said:

Here is a chart depicting the difference in TAS between the K-4 with the DB engine (blue) and the K-4 with the DC engine (red).  The data was collected by community members doing flight tests in the sim.  The curves on the left (bright lines) are for combat power.  The curves on the left (dark) are for emergency power.  As we can see, there's no significant different above the supercharger critical altitude.  The difference in speed at 6000 meters looks like it's around 25 km/h.  There is probably also a noticeable difference in max climb rate, since there's an 8 percent difference in engine power (1850 vs. 2000 PS).

 

What is 100%?  Would that be 1.45ata?

 

I've always been under the impression that for the same manifold pressure, the DB will be faster (say if they're both at 1.35ata), which I assume is due to the additional power the supercharger requires to run on the DC;  but the DC has the ability to do a much higher manifold pressure at max power.  I also assume that the DC does not have a larger supercharger, because if it did, it would have a higher critical altitude, so I am not sure exactly why it would require more power to run.

 

The specifications are:

DB- Maximum true air speed at sea level, engine mode - Combat: 543 km/h - Power: 1430 HP

DC- Maximum true air speed at sea level, engine mode - Combat: 536 km/h - Power: 1370 HP

 

 

DB- Maximum true air speed at sea level, engine mode - Emergency: 599 km/h - Power: 1850 HP

DC- Maximum true air speed at sea level, engine mode - Emergency: 614 km/h - Power: 2000 HP

Edited July 31 by FeuerFliegen

[MaxPower]

The first line is 'combat power'.  The second line is 'emergency power'.  That's how the test was conducted, as recorded in the thread below.
 

Quote

Fw-190s = first line is combat, 2nd line is emergency (A8boost = boost on, A5U17 = boost on up to 1km , no bombs, G3 = boost on up to 1km, no bombs ). (default, 50%) 

If you want to know what the intake pressure is, I suppose you will have to fly the planes with tech chat on and look at the gauges.  The test procedure is also shown in that thread.  The actual gauge readings are not supplied.

[MaxPower]

12 hours ago, FeuerFliegen said:

What is 100%?  Would that be 1.45ata?

Oooh I was thinking more about your question and I understand it better now.

The question is more relating to the weird terminology.  The reason why the legend is "100%" and "MAX" is because this graphing program was developed for IL2 1946.  The developers for 1946 chose different terminology for levels of engine power output.  I think 100 percent analogous to 'max continuous' but I'm not totally sure.  On this graph, the lines that are called '100%' in the legend are actually Combat Power as tested by CountZero in IL2 BoX.

In the specs, we see that the manifold pressure for 'combat power' is the same for both engines, but on the chart we see that the DC engine is slightly faster.  Not sure if it puts out more power at that manifold pressure or there's something else going on with manifold pressure and how it relates to 'Combat Power' in the game, which is why I recommended you test it.

 

Quote

Engine modes:
Nominal (unlimited time): 2400 RPM, 1.35 ata
Combat power (up to 30 minutes): 2600 RPM, 1.45 ata
Emergency power (up to 10 minutes): 2800 RPM, 1.8 ata

Engine:
 

Engine modes:
Nominal (unlimited time): 2400 RPM, 1.35 ata
Combat power (up to 30 minutes): 2600 RPM, 1.45 ata
Emergency power (up to 10 minutes): 2800 RPM, 1.98 ata

 

Edited July 31 by MaxPower

[=MERCS=JenkemJunkie]

It's a quirk of the timer system. The game lets you go a varying amount over the spec page combat value until you cross over into using the WEP timer, and the DC engine got lucky and is able to go farther past 2600/1.45 until it crosses over into WEP than the DB.

[messermeister]

On 7/29/2025 at 10:16 PM, Kurfurst said:

Its the same engine the designation simply stands for the new, increased DB 605 ratings promulgated at the start of December 1944 and the changed designation corresponded to the rating (and fuel used : B-4 or C-3). 

 

A become AB (with boost increased from 1,42 to 1,5 ata)

AS became ASB or ASC  (with boost increased from 1,7 to either 1,8 or 1,98 ata)

DM become DB or DC  (with boost increased from 1,75 to either 1,8 or 1,98 ata)

 

The altitude performance was unchanged in each case, although the C versions run poorer at low altitude when not using maximum boost, due to different supercharger slippage setup. 

Small correction, AB was also 1,45/1,80 ata:

[FeuerFliegen]

9 hours ago, =MERCS=JenkemJunkie said:

It's a quirk of the timer system. The game lets you go a varying amount over the spec page combat value until you cross over into using the WEP timer, and the DC engine got lucky and is able to go farther past 2600/1.45 until it crosses over into WEP than the DB.

 

right, that's why I question if "100%" just meant the maximum you could go with technochat still reading "combat power", even though it would be well above 1.45, and less than 30 minutes timer.  Best way to test would just be to do both engines at 1.45ata.

[MDzmitry]

8 часов назад, messermeister сказал:

Small correction, AB was also 1,45/1,80 ata:

Hold on, according to this both DB's and DC's allowed "Sondernotleistung" is 5 minutes, while Il-2's K-4 is given 10 minutes on both engines.

Has anyone got sources stating otherwise for DB-605 DB/DC?

[=MERCS=JenkemJunkie]

5 hours ago, FeuerFliegen said:

 

right, that's why I question if "100%" just meant the maximum you could go with technochat still reading "combat power", even though it would be well above 1.45, and less than 30 minutes timer.  Best way to test would just be to do both engines at 1.45ata.

The context of those tests is min/maxing, so I'd say it's likely he was using the upper limit of combat power, not 1.45, but yeah a quick test at 1.45 for both would confirm.

[messermeister]

4 hours ago, MDzmitry said:

Hold on, according to this both DB's and DC's allowed "Sondernotleistung" is 5 minutes, while Il-2's K-4 is given 10 minutes on both engines.

Has anyone got sources stating otherwise for DB-605 DB/DC?

They went from 10 min on/5 min off to a more conservative 5 min on/10 min off. Page 2 from same directive, second to last paragraph section B::

[MDzmitry]

2 часа назад, messermeister сказал:

They went from 10 min on/5 min off to a more conservative 5 min on/10 min off. Page 2 from same directive, second to last paragraph section B::

Thanks for additional info

 

So, when it comes to Emergency timers the Kurfürst is somewhat similar to La-5FN. There's recently been a bit of a debate whether ASh-82FN was allowed 5 or 10 minutes of WEP, a similar case seems to be happening here.

[the_emperor]

6 hours ago, MDzmitry said:

There's recently been a bit of a debate whether ASh-82FN was allowed 5 or 10 minutes of WEP, a similar case seems to be happening here.

If any one is interested:

 

[Kurfurst]

21 hours ago, messermeister said:

They went from 10 min on/5 min off to a more conservative 5 min on/10 min off. Page 2 from same directive, second to last paragraph section B::

Yeah thats the TAGL I was referring to, but working from memory, and I mixed up the A and AB. AB was originally the  AM, not the A.

 

So the A remained A but it’s max. boost was increased to 1,5 ata (ca. 1550-1600 PS), and it was the AM that became AB with a slight max boost increase to 1,8 ata (1850-1900 PS?). But then of course the 1,8 ratings starting using retarded ignition from about late January due to fuel quality issues and with a loss of about 50 PS.

 

Its also noteworthy that the later WEP times of MW50 boosted engines has been reduced to 5 mins from 10 mins, and, that by late 1944 and before the base 605A had a 10 minute WEP rating even without MW50.