I wasn't at all familiar with the B21F-MPG variant, but your little challenge on the meaning of the MPG designation has changed that a bit. I'm sure most of us thought of MPG as Miles Per Gallon, but immediately dismissed that simplistic and likely irrelevant thought. Curiosity got the better of me, so I fired up Google and off I went.

I hit paydirt on K-Jet.org. All you K-Jet people should bookmark that site. It's full of goodies, from model descriptions to a fairly complete set of 1981-era green manuals, the 1985 240 wiring diagram manual plus assorted Volvo brochures and magazines.

I found out that the B21F-MPG is also called the "B21F-9" (presumably from its engine code of 49) and was sold as a "new" option on 1981-1982 242DL's (2-door) in the USA only, both Federal (49-state) and California. Quoting from the K-Jet.org site, "My guess is that Volvo didn't sell a lot of 1981 B21F-9 motors and so they just stuck the leftovers in the 1982's". It was one of a number of variants of the B21 4-cyl red block engine in those days. Other USA engines were the regular B21F ("B21F-5") and the B21F-turbo ("B21F-7"). Canada got the B21A (with SU carbs) and the infamous B23E (fuel injected -unabridged power without a turbo). I'm sure there were additional carbureted versions in Europe and elsewhere. That connector hanging on the MPG valve cover is described in the green manual as the "Magnetic Timing unit connector" as described by others -primitive perhaps, but quite useful.

From the following notes you will see that the MPG was a low powered beast with a low idle speed and low rear axle ratio. It was designed as a gas miser, B21F-lite if you prefer. So MPG as "Miles Per Gallon" is a legitimate designation for marketing purposes driven by the high gas prices at the beginning of the Iran/Iraq war which when adjusted for inflation were higher than today's prices. The only technical names I can guess at would have something to do with Magnetically Programmed Timing or Mopar Programmable Timing or some such in Swedish (where "gang" means "time"). I also saw mention of an MPG M-grind cam, but not in the official Volvo literature. Am I close?

Here's some (interesting) comparisons of 1981-era B21F and related engines: This is all info I tripped on in the offical green manuals and probably more than anyone needed to see in this thread.

All B21F variants had Bosch electronic ignition, except the MPG which used Chrysler Mopar. All fuel injected models had Bosch CI "Continuous Injection". All USA models had Lamda-sond O2 sensor, catalytic converter and ran on regular unleaded fuel (unleaded or leaded in Canada). All automatics got the AW55, except USA wagons and all Canadian 240's, which got the BW55. For manuals, the M46 was found on all GL/GLT's & some DL's, the M45 was found only on DL's. Rear axle ratios in the USA were all 3.73:1, except 3.54:1 for the MPG. In Canada, rear axle ratios were 3.91:1 on all DL manual's, 3.73:1 on all DL automatics & GL/GLT manuals, and 3.54:1 on GL automatics.

** B21F (B21F-5)** 240DL & 240GL (USA), CIS "Constant Idle System" (California only), 9.3:1 compression ratio, 107hp@5500, 114ftlbs@2500

** B21F-MPG (B21F-9) ** optional engine in 1981 242DL (USA), standard in all 1982 DL's (USA) before 1982 LH-Jet, CIS w/low 750rpm idle (vs. 900rpm all others), 9.3:1 compr, A-cam in 1981 (B-cam in 1982 like the B21F-5), Mopar ignition system, 99hp@5000, 114ftlbs@3000, 3.54:1 rear axle (vs. 3.73:1 all other USA), no sunroof, manuals had no power steering (unlike most others)

** B21F-turbo** 242GLT (USA), CIS, 7.5:1 compr, T-cam, 126hp@5400, 150ftlbs@3750

** B21A ** 240DL (Canada) w/Pulsair EGR, w/o Lamda-sond, w/o cat, reg leaded (or unleaded), 8.5:1 compr, 96hp@5250, 125ftlbs@2500

** B23E ** 240GL & 242GLT (Canada) w/Pulsair EGR, w/o Lamda-sond, w/o cat, premium leaded (or unleaded), large displacement, 10:1 compr, K-cam, 129hp@5500, 135ftlbs@3500, 3.54:1 on GL automatics (vs. 3.73:1 on manuals)

USA market 240's were almost exclusively built in Sweden, but a few USA configurations may have come from the Halifax plant in Nove Scotia, presumably when the much touted production teams were about to run into a dry spell (lest they get into the Alexander Keith's). Most of the early Canadian market 240's were built (assembled) in Halifax, but some also came from Sweden, presumably to keep up with excess demand (early 245's come to mind).

e&oe.
--
Dave -940's, prev 740/240/140/120 Never overestimate what little I know.