99 vs 900

B-ENGINES
When the 900 was introduced, it was equipped with a B-engine, almost identical to the 99, but a few bolt-on-details differ between them. (All of which are interchangeable)
- The choke cable on 99's goes directly from the carburettor through the bulkhead to the dash-mounted handle. On the 900, it was routed over the valve-cover, bent down to the gearbox and in through the grommet for the gear-rod and handbrake cables. The handle was positioned in the gear-console, next to the key.
- Engine mounts. The side-mounts are easily unbolted and swapped. But the front engine-mount is a bit more awkward. It's cast in the front cover of the gearbox, so the whole cover must be swapped. Both the 99 and the 900 were available with four and five speed manuals, it's only a matter of finding the right front cover in a scrapyard. For the automatics, it's more complicated. Sometime in 1979 the Borg Warner 35 was superceeded by the beefed up BW 37. The front cover of these gearboxes are not interchangeable! It's a matter of cutting and welding the engine mount.
BW 35: All 99's, and early 900's.
BW 37: Later 900's.
- Heater water hoses are routed differently on 900's vs 99's. The 900 has a heatervalve that returns water, when closed. The 99 has a shut-off valve.
To add to the confusion, heater hoses are routed differently for single carb, twin carb or injection engines.
- The fuel pump on all carburettor engines was mechanical and bolted to the side of the block. Injection engines had a blanking plate bolted in its place.
- The exhaust manifold is not different, but downpipes are routed differently on the two cars.

Cooling hoses 99 vs 900, H vs B

Hoses, 99 B carb	Thermostat house, H inj.	Thermostat house, H carb.	Thermostat house, H carb.	Engine mount, 99 front 5sp
Camshaft, H inj.	Camshaft, H carb.	Camshaft, H carb.	Gearbox dipstick, mayhem	Gearbox dipstick, 99 m82 5sp

H-ENGINES
The H-engines are also identical for 99 and 900 Saabs, but several bolt-on-details differ between them. (All still interchangeable)
- The choke cable: Same as the B-engines.
- Engine mounts: Same as the B-engines.
- No fun. As of m82 models, it was decided that the 99 should be an economy entry model. Those who wanted any bells and whistles should buy a 900. This coincided with the introduction of the H-engine. Consequently all H-engines destined for 99's were equipped with a single carburettor. Periode. For the 900, however, it was business as usual. Twin carburettors, injection, turbos, -you name it.
- The thermostat housing. Fuel injected, and carburetted engines have a different thermostat housing. On the 900, the outlet waterhose is routed in front of the distributor. On the 99, it is routed under the distributor. (It wouldn't fit between the radiator and distributor) Since no 99's with H-engines had injection, a 900 -housing must be used, when putting injection in a 99. The water outlet hose will have to be custom made.
- Heater water hoses: Same story as the B-engines.
- V-belt-pulleys. All early H-engines have a single V-belt for the alterator and waterpump. Later 900's has twin V-belts for this. (Plus a third one for power steering) In the cramped engine bay of the 99 there is no room for another V-belt.
- Alternator bracket and pulley: At first glance they look similar. The single belt 99-H pulley is actually so far out that it lines up with the outer of the two shaves on the 900-H twin pulley, when these two alternators are held side by side. But the 900 bracket locates the alternator a half inch closer to the bulkhead. The impellers on the alternator cooling fan will then foul the 99's brake servo. A 99-H alternator bracket must be used.
- The fuel pump on all 99's was mechanical, and bolted to the side of the alloy head. Ditto, the 900's with carburettors. 900 injection engines had a blanking plate bolted in it's place.
The mechanical pump is activated by a lobe on the camshaft, via a pushrod. On injection engines this lobe is not present... as a friend of mine found out after he'd hoisted a replacement engine from a 900i donor car into his 99, bolted over the carburettor manifold, and tried to mate the fuelpump to it. No way! You either swap the camshaft or fit an electric pump.
- The exhaust manifold on later H-engines were different.