[brentce]

Actually the 605D/C2-C3 fuel was first fitted to preproduction prototypes for the 109K, was adapted for MW50 (DM motor) then evolved firstly into the D-2 using either B4 or C3 and finally into the DB and DC variants which entered production (MW50 standardised for both). No "DM motor" entered production, but the D and D-2 entered production for development purposes.

Here is the specifics for analoguous comparison between AS/A motor, and ASB/DB or ASC/DC motor.

Climing condition (standard 30min setting, no MW50 use)
AS 1275PS with 1150PS @ 7.8km
ASM 1250PS with 1150PS @ 7.8km
AM 1275PS with 1250PS @ 5.8km

ASB 1430PS with 1285PS @ 6.9km
DB 1430PS with 1285PS @ 6.8km

ASC 1400PS with 1285PS @ 6.8km
DC 1370PS with 1285PS @ 6.8km

Full Throttle Height performance/MW50 use
ASM 1500PS @ 6.4km
AM 1700PS @ 4km

ASB 1600PS @ 6km
DB 1600PS @ 6km

ASC 1800PS @ 6km
DC 1800PS @ 6km

Rated altitude
AS/ASM 7.8km

A/AM 5.8km

DB/DC 6.8km

ASB/ASC 6.8-6.9km


So the figures clearly stipulate the AS motor is a supercharger alteration to the A motor. Whilst the ASB/ASC motor is a supercharger alteration to the DB/DC motor.
Documentation says the AS was developed by mounting the 603 supercharger to the 605A. One can reliably infer the ASB/ASC was this same method applied to the 605D which was done in 1945, using the figures provided for engine performance between the 605 series in full.

It also makes a great deal of sense, considering the reliability and serviceability issues when applying MW50 boost to the A motor, which were not a problem with the D motor.

But again I must ask, what are your sources for holding such reservations about D motors using 1.98ata?
And a new question, what leads you to think the ASB/ASC are constructed from an A motor base like the AS, rather than the D motor base in current production in 1945? It would seem a rather backwards step would it not?

edit.
I should add for prosperity the stipulation of 603 supercharger fitment lay in the cruising conditon of the ASB/ASC compared to the DB/DC, which is a kilometre higher for the same output.
The D series obviously had a larger supercharger casing than the A series to begin with, which blurs the line between it and the AS, combined with increased flow dynamics through the cylinder heads which can alter performance outputs at altitude as well, hence an easier handling of higher pressures in the standard settings.
The lines between DB/DC and ASB/ASC are really very blurred until you examine cruising condition, where the larger supercharger fitment is clear.

I'm back!

I think you're letting the similar expected performance of the DB605ASB/C and DB605DB/C confuse the issue of base engine type. Both the AS And D engines had the same volume, the same supercharger and used the same rpm and boost settings on the same fuels, so it is to be expected that they would have very similar performance. As for why they would produce a previous version in parallel with a newer variant, the Germans did just that throughout 1944-45. They were using old stock and refurbishing existing stock right up to the end. They built the K- and G-10 in parallel and the DB505A and the DB605AS, as well as the 190A and more potent D. In fact the K-4 entered service a bit before the G-10 did. If the DB605ASB/ASC engines are in fact DB605D variants, then you've discovered something that has escaped notice by some very knowledgeable 109 researchers! :wink:

As for my reservations regarding 1.98 ata and the 605DC, it's known that at the end of January 1945 that 1.98 ata was still not cleared (according to Olivier Lefebvre 1.8 ata had just been cleared for the DB on 14 Jan) and testing still showed reliability, as well as cooling problems. It appears that as of 14 March 45, the DC was still awaiting clearance for 1.98 ata, but I don't belive I've seen a definitive translation of that document. After that, there is no documentation of official service clearance or use. However, there is an OKL document that outlines some proposed changes to gruppen equipment in late March that shows four gruppen of K-4's that are to use C3 fuel and 1.98 ata. Few of the changes listed (conversion to 190D-12s, Ta 152C/H, etc.) were made which isn't surprising considering the state of affairs at that stage. It's quite possible that 1.98 ata was implemented in the last six weeks of the war, but it's also quite possible that it wasn't cleared or used, especially considering the state of the Luftwaffe in late March. Hence my reservations.

Brent