Volvo Cylinder Head Differences - Type 531 and 530
B23ET B23FT B230ET B230FT and B230FB - by Anthony Hyde

First listed Feb. 2004 - Updated August 2008

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How to identify - Easy, number is between 2nd & 3rd Exhaust ports

General production versions of the 4 cylinder B series alloy head engines: 531 HEAD - Volvo #1326783 - Found on the following engines: 1985 B23ET 760 turbo; B230ET 760 turbo; 1991-92-93 240 & 940 B230FB (non-turbo with VX3 cam), plus AQ151 Volvo Penta marine engines. Note 1: 1984 B23ET turbo came with 405 head (big coolant passage, although some are small coolant passage); Note 2: the B23FT for USA had a 398 head; Note 3: 531 head is small coolant passage. Due to inlet port design, the 531 head is a desirable item for higher performance engines. All standard turbo heads feature exhaust valve stems that are partly filled with sodium -> details below. 530 HEAD - Volvo #1326777 - Found on nearly all B230 Engines - Turbo and non turbo.

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531 INLET PORT Channel The 531 inlet port design is more advanced than the 530. Looking straight at the pic, notice the port bias is tilted to the left influencing flow to the left hand side, then it rolls toward the right as it swirls up into the combustion chamber (and past the spark plug). The curve of the inlet channel as it approaches the bowl is referred to as a 'swan neck' (shape is slightly up down and around) A1. 531 The lower fillets on either side of valve stem have different shapes. Also see pic below.

530 INLET PORT Channel The 530 inlet port has a rounded shape - straight in and up with no port bias or flow enhancement

A2. 531 Inlet Port from Top of Chamber clearly shows different fillet shapes

A3. 531 Combustion Chamber - Looking inside the (left) inlet port, clearly shows the port bias

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EXHAUST PORTS - 531 and 530 - There is very little visual exhaust port difference between the 531 and 530. The 531 has a good bowl and bottom radius that blends well into the port. After the bowl, the port becomes rectangular with an increasingly larger exit taper. The top shortside radius is virtually non-existent (not good ?), and work is required to shape one, however small, to get good flow transition.

Valve diameters : Both 531 and 530 use the same valve sizes. Exhaust Ø 35 (left) Inlet Ø 44 (right) Spark plug points towards the hot exhaust valve (good anti-knock design). There is quite a difference in spark plug angle between the 530 and 531. The 531 sits at a much lower angle (layed over more) aimed more toward the exhaust port than the 530. Good plugs are NGKBP7ES, or for performance driving use cooler NGKBP8ES

Combustion chamber Volume : Blue area indicates the 531 chamber is larger around the exhaust valve than the 530 (Pink area). Both combustion chambers measure 94 mm width across. Cylinder bore is 96 mm dia for 2.3L. Illustration by A.Hyde

Volvo B21 / 23 / 230 Valve springs Large 29 mm OD - Small 25.9 mm OD - Medium 32.5 OD

VALVE SPRINGS - Information on 3 different versions. Diameters listed under picture, Lengths much the same. The 531 HEAD uses a large diameter valve spring. Both the early 84-85 B23ET (turbo) and latter 91-93 B230FB (non turbo) use this spring. Part # 463739 (this size is used on a lot of early B21/23 240's with K-Jet). The 530 HEAD uses two different spring sizes, say small and medium. Small - The 85-89 B230 low-friction motors use a small diameter valve spring - and like nearly all the low-friction motors, components had to be redesigned / beefed up again a few years later ! Service kit - the small low-friction springs were revised to a medium size spring and a 'service kit' # 271793 developed being available from your dealer (x8 req'd) . The 530 head 'service kit' contains one medium diameter spring plus the larger top and bottom retainers. Inlet valve Stem seals need to be bought separately (x4 req'd). Medium - from approx 1993-94-onwards the B230 530 head engines use the medium size spring # VO-9135130

Left 531 head from B230FB non turbo 7 = day 6 = month 90 = year (1990) Note at top of pic H 1 cast Numbers located behind #4 spark plug

Right 531 head from B230FB non turbo 30 ? = day 3 = month 14 / 92 = likely week 14 of year 1992 Note at top of pic H 2 cast  H1 , H2 different foundries?

Head Gasket #1378646, Inlet manifold gasket #1378879, Exh manifold gasket (set 4) #271704, Throttle body gasket #1271488, Sealing ring (Water pump to head) #1336255, Camshaft front seal #6842273, Nipple (or tailpiece) 3/8" NPT connects to heater hose, and screws into head (under 4th inlet) #976040, Inlet valve #463395, Exhaust valve turbo #354724, Valve spring #463739

Note that Volvo did not do any porting or change valve sizes for the turbo motors. The intake to exhaust flow is already less than ideal for the turbo motor. Obviously you can still make good power with it and run reliably for years, but there is power and efficiency to be had if you are willing to spend some time and money.
The 531 head definitely should get larger exhaust valves if used on a turbo motor and the 530 head should if it is being more than very lightly modified. The exhaust flow is valve limited much more than port limited. Port all you want, but you still cannot get more than about 123 cfm of air through a 35mm valve according to Superflow.

As I understand, once the 530 combustion chamber is opened up to the 531 size (see pic above A.H.), the 531 will take no bigger valves than the modified 530. Neither can be opened further due to the piston bore size. The advantage in the 531 is that the intake flows more and perhaps that the intake and exhaust will both take more porting. The walls on a 530 definitely have limits and it is possible to hit water without too much effort. Maybe someone has details on the 531.

Don't be unhappy with your 530 or 531 head. You can still make great power with them, perhaps have better low end torque if the porting job is well done and the cam well chosen, and you can always turn up the boost a little to compensate.

The exhaust gasses are at high velocity as they are expelled from the engine through the relatively small area of the exhaust valves. High velocity means that the exhaust gas has a high kinetic energy, which is equivalent to pressure, through the relationship described by the Bernoulli equation:

Pt=Ps+1/2*rho*V^2/Gc. That is, the "total pressure" is equal to the "static pressure" plus the "dynamic pressure."

A properly-designed exhaust system will have a greater area downstream of the exhaust valves, and will decelerate those exhaust gasses smoothly to recover as much of the kinetic energy as possible in the form of increased static pressure. This allows the static pressure at the exhaust valve to be as low as possible, thereby reducing the back pressure on the piston during the exhaust stroke, and extracting as much work as possible from the engine.

When the exhaust gas is expelled from the end of the tailpipe, its static pressure is essentially equal to that of the surrounding atmosphere, and the less pressure you have at the inlet end of the exhaust system, the greater the work output and efficiency of the engine.

An improperly designed exhaust system will not recover as much kinetic energy from the exhaust gasses and will be inefficient.

If you have 531 head information to share, please contact Anthony