B21 Motor Guide
1981-1985: The B21FT Motor
Basically, the difference between these two motors is that one has an intercooler and the other does not. The intercooler cools the air between the turbocharger and the intake manifold, allowing more air molecules to be forced into the combustion chamber, since cooler air is more molecularly dense. Because of this cooling effect, the turbocharger can safely be turned up to a higher boost setting (~10psi vs only ~5psi for a non-intercooled turbo).
Thus, intercooled cars are faster, but because of the longer distance that air must travel to get from the turbo to the combustion chamber, there is more lag time between when you put your foot on the gas and when the extra horsepower kicks in.
The intercooler kit was available from the dealerships to retrofit non-intercooled 240′s, so many of them are already intercooled. The 1984.5 and 1985 240 turbo’s came intercooled from the factory (and the engine was officially called the B21FTL) which is nice, as the cars came with a bigger clutch, an extra electric cooling fan, and a 5-bar oil pressure guage and sender (instead of a 3-bar guage).
1981-1982: The B21F-9 (B21F-MPG) Motor
The B21F-9 (aka B21F-MPG) is very similar to the B21F-5. It can be found in 1981 & 1982 240′s before the change was made to LH-Jet in 1982. The main differences that can be used to identify this motor relate to the ignition system. The B21F-9 has a white distributor cap that is held down by two phillips-head screws instead of the B21F-5′s orange cap that is held down by two metal clips.
Another difference is that the B21F-9 has three wires at the throttle microswitch (orange, yellow, and black) instead of two wires (yellow and black) that the B21F-5 has. The B21F-9 also has a different Ignition Computer (which resides in the engine compartment next to the windshield-washer fluid tank.) This ignition computer has a metal diaphragm with a vacuum hose attached to it. The B21F-5′s ignition computer lacks this diaphragm and vacuum line.
The B21F-9 reportedly gets slightly better gas mileage than the B21F-5, perhaps due to it’s lower idle speed (750 rpm instead of 900 rpm). From my personal experience, there is little difference in the driveability or cost of maintenance between these two cars, however parts for the B21F-5 are going to be more common than for the B21F-9.
The B21F-9 was an option only on 2-door, DL models (242′s) in 1981. Most 1981 242′s in the USA probably have the B21F-5, but there are undoubtedly some 1981 242′s with the B21F-9. For 1982 models, all cars came with either the B21F-9 or the B21F with LH-Jetronic EFI.
In 1981 at least, these B21F-9 242 DL’s had a lower rear axle ratio (3.54:1 instead of 3.73:1), no power steering (unless equipped with an automatic transmission) and no sunroof. The idea, apparently, behind these B21F-9 242 DL’s was to create a very inexpensive and fuel efficient car.
The 1981 B21F-9 also had an A-cam instead of a B-cam found in the 1982 B21F-9 and other B21F’s. Although there is not a lot of little difference in these two cams, it is interesting to know.
Whether or not the 1982 cars B21F-9 cars continued with the same specs as the 1981 version, they at least look the same and share the same essential components and ignition system. The cam type and rear axle ratios may be different from 1981 to 1982 however. 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.
Note: Distributors, ignition computers, and spark coils (located on driver’s side strut tower in engine compartment) are not interchangeable between the B21F-9 and B21F-5. The B21F-9 and B21F-5 engine wiring harnesses are interchangeable, as long as the cars both have the same type of idle control – an idle air motor or an auxiliary air valve. Thanks to Dave Barton for pointing this out.
1981: The B21F-5 Motor
There are several differences between the “California” and “Federal” B21F-5 motors. If you check your metal emblem on the passengers-side strut tower, it has your VIN number and a two-digit number next to it. The two digit number can be deciphered as follows:
30 = United States / Federal (49-States)
31 = United States / California Model
39 = Canada / Mfg. in Sweden
83 = Canada / Mfg. in Canada
Please see the “New Car Features 1981 USA/Canada” Greenbook for more information on decoding all the metal plates and stickers on your 240.
The differences between the California and Federal motors largely deal with the emission systems, but can have fairly significant effects on other things. Here are some of the differences that are easiest to see: (please refer to my K-Jet in Detail page for further info on each component described here.)
1. California cars have an idle air control valve (black cylinder above the intake manifold), while Federal cars have an auxiliary air valve (silver cone above the intake manifold.)
2. The two cars have different throttle bodies. You can’t see the differences as well in the above pictures, but the main one is that the Federal cars have a large, black plastic idle adjustment screw (about the size of a quarter) coming off the front side of the throttle body.
3. California cars have a throttle microswitch (best seen in the lowest pictures) that sits underneath the intake manifold on the driver’s side. Federal cars do not have this switch.
4. The california cars have an extra engine control unit (ECU) that controls the Constant Idle System (CIS). It is located below the Lambda-sond ECU behind the front passenger’s right kickpanel. It recieves signals from the throttle microswitch, coolant temperature sensor, and coil to tell the air valve what to do to maintain constant idle speed. The Federal cars do not have this extra ECU, since they do not have the CIS system.
This brings us to a huge difference between driving the California cars and Federal cars. The CIS system in California cars is a very nice feature. On a properly tuned CIS car, you can just let the clutch out in 1st gear without giving it any gas, and the car will roll forward and go. If you try this in a Federal car, you’re going to stall the motor. Overall, this makes the California cars easier to drive and less tempermental when warming up.
5. The california cars have different engine wiring harnesses than the Federal cars. The replacement wiring harnesses are different as well. Here are the part numbers so you make sure you get the right one.
|Car||Old Harness Part #||New Harness Part #|
|1980 B21F||1259454||3515395 or 9139228|
|1981-1982 B21F California||1307597 or 1308890||3515381|
|1981-1982 B21F 49-States||1307597 or 1308890||9139228|
|1982 B21F with LH-Jet 1.0
(instead of the beloved K-Jet)
|1981-1985 B21FT (Turbos)||1348155||3515393|
You can get replacement wiring harnesses from your Volvo dealer, aftermarket dealers such as IPD and Swedish Engineering, or from Dave Barton, who pulls them out of cars at junkyards and sells them for about half the cost. He’s reliable and I have bought two harnesses from him so far.
Dave Barton’s Wiring Harness Page (lists what he has in stock)
Well, that should help clear up the differences between the different types of B21F motors. I still need a picture of the dreaded 1982 LH-Jet, since it is a B21F, and some pre-1981 B21F’s.