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| Revision as of 07:53, 9 June 2010 ddgonzal (Talk | contribs) (->H92) <- Previous diff |
Revision as of 07:56, 9 June 2010 ddgonzal (Talk | contribs) (->Regular Oval Port) Next diff -> |
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| == Regular Oval Port == | == Regular Oval Port == | ||
| - | The A14/A15 Oval-port Heads include | + | The A14/A15 Oval-port Heads include large 37 mm intake valves and 30 mm exhaust valves. |
| - | * Intake: 37mm | + | |
| - | * Exhaust: 30mm | + | |
| * There are many part numbers, which differ for year, emission control, accessory fittings, coolant passages, etc. | * There are many part numbers, which differ for year, emission control, accessory fittings, coolant passages, etc. | ||
| Line 403: | Line 401: | ||
| Oval-Port heads include: | Oval-Port heads include: | ||
| - | * H72: Dry, Large Oval, Open Chamber. The original A14 head, designed for USA market | + | * H72: Dry, Large Oval, Open Chamber. The original A14 head, designed for USA market. With Air Pump passage |
| * H77: Same as H72 but drilled for more emission controls | * H77: Same as H72 but drilled for more emission controls | ||
| - | * H75: Same as H72 but for non-USA market | + | * H75: Same as H72 but for non-USA market w/o Air Pump |
| * H89: Closed Chamber Wet manifold use in B310 | * H89: Closed Chamber Wet manifold use in B310 | ||
| * M24: For twin-carb A14T, similar to H89 but with dual-valve springs | * M24: For twin-carb A14T, similar to H89 but with dual-valve springs | ||
Revision as of 07:56, 9 June 2010
Nissan A-series Engine cylinder heads are of one type: inline valves, pushrod valve system (non-overhead cam), two-valves per cylinder. The head is non-crossflow meaning that exhaust and intake ports are on the same side (left side).
Cylinder Head Identification
Most A-engine heads do not have unique casting numbers. For a process of identification see Cylinder Head Identification. This article will discuss various features of cylinder head.
Distinguishing Features
Any A-type cylinder head will bolt onto any A-type engine. However compression and intake ports are big consideration, as are the manifold bolt patterns. For best results, match port types (e.g. round-port manifold on round-port head). The most critical difference is the rocker shaft oil passage. It is in a different place between early and late engines.
Oil passage in the head
An extra oil passage in the head is needed for some engines. For early engines, make sure your head gasket has the hole! You can punch or drill a corresponding hole in the gasket if needed.
Top: 1974, no passage. Bottom: 1973, has passage.
The old 1967-1973 head has the oil passage:
Boss on outside identifies the head
Compare to newer head: no passage:
The newer engine has the passage in the block instead. The solution for Old engine block, Newer head: drill the passage in the head.
Interchanging
Pre-1974 heads fit on all engines.
1974-up block works with any head.
But for newer head on older block, an oil passage must be drilled:
I took off the head, marked it with the old head gasket, and drilled it on a 45 angle. junior
I have seen a crude system where a 1200 head gasket was placed on the head to determine the position of the oil feed hole in the block. This was centerpunched & a very shallow hole was drilled. [about 1 to 1.5mm] then an angle grinder was used to grind a small trench across the gasket face to provide an oil passage froom this shallow hole to the nearest head bolt hole.Crude as hell, but it worked. A very steady hand would be a prerequisite.
Personally, I would suggest a milling machine if this method is used.
question about oil blockage
Combustion Chamber
- A,B: Heart-shaped high-compression chamber is good for high-octane gasoline
- a.k.a: closed chamber, peanut-shaped, butterfly-shaped or kidney-shaped
- C: 360 degree open chamber for reduced emissions
- D: Bathtub chamber (from 1982 Sunny Truck G61 head)
Any combustion chamber design can fit on any A-series engine.
Comparo - Closed Chamber vs. Open Chamber
Comparo
Chamber Size
- A12:
- A12 GX: 29.1 cc (as per FIA papers)
Intake Ports
- Round: These are best for low-RPM operation
-
- All A12, new A13s, some A14s, and (reportedly) Vanette A15s
-
- Small oval (28 mm x 30 mm). The 1974 A13 has this design.
- Small oval with swirl obstruction. These are good for emissions and fuel economy (H95 head, 1981-1982 USA all engines)
-
- Regular oval (28 mm x 34 mm). These std A14/A15 ports are best for high-RPM operation, or for the bigger engines
-
- NOTE: the top of the port comes up to the centerline of the top bolts
-
- Large oval (GX and A12T, 30 mm x 36 mm). From A12GX Engine and B210 or E10 A12T engines.
-
- NOTE: the top of the port comes up as high as the top of the top bolt holes (port comes up past the bolt hole centerline)
-
GX Oval vs. A14 Oval Comparo
Top: GX ports go much higher than A14/A15 ovals.
Port Sizes
| Ports | Size (mm) | Exhaust | Raised | Note |
| round | 28 | 27x26 | no | 1971 A12 |
| round | 28 | ? | lowered | 1977 GFU |
| Oval - small | 28x30 | ? | no | 1973 A13 |
| Oval - Medium | 28x32 | 28x26 | no | A14E |
| Oval - Regular | 28x34 | 28x26 | no | Many A14s |
| Oval - Large (GX) | 30x35 - 36 | 27x29 or 28x26 | Yes | A12Gx (1971-1973) |
- GX extra-large oval ports (36 mm tall)
Port Comparison
Wet, Dry Intake Manifolds
Coolant passages are below the intake ports (present or not). If present, they can be large holes or small holes.
- A12GX has Four Large coolant holes, one beneath each inlet
-
- Other heads have either no coolant holes, small ones, or a mix:
-
- Standard Datsun 1200 heads have no coolant holes on the intake side.
Interchange
A-series heads will interchange with either dry or wet intakes with the following caveats:
- If the intake doesn't have coolant passages, tap the head's coolant ports and install plugs
-
- If the intake does, but the head doesn't, cold-weather starting and cold-idle may suffer due to insufficient heat. However, warm-engine operation should be OK.
-
Intake/Exhaust manifold bolt pattern
The 1971-1973 A12 differs from the A13/A14/A15 and some A12s after 1973. A12 Wagons and Trucks continue to use the old pattern for some time
Top: New bolt pattern
Bottom: Original bolt pattern
The bolt pattern on the cylinder heads also differ. early A10/A12 heads are only drilled for the older pattern. Newer A12 (1980s/1990s) are drilled for newer pattern. Some newer heads are drilled for both.
Bolt pattern
Valve Springs
The following A-series heads had dual valve springs. There is a small-diameter spring inside the main spring.
- A12GX
- A12T
- A14T
- A14E
- Heads retro-fitted with dual springs
So dual springs are a good indication of a special head, but not conclusive. You will need to check the intake port sizes and other features to make a final determination.
Valve sizes
| Valves | Intake PN (13201) | In. Size | Exhaust PN (13202) | Ex. Size | Length |
| A10, early A12, late A12 Van | 13201-H1000 | 35mm | 13202-18000 | 29mm | 103.8 |
| A12GX/A12T | 13201-H2300 | 35mm | 13202-H2300 | 29mm | 103.8 |
| Late A12, A13, A12AS | 13201-H2300 | 35mm | 13202-H7400 | 29mm | 103.8 |
| A13(1974),A14 & A15 | 13201-H6200 | 37mm | 13202-H6200, H8900 | 30mm | 103.8 |
| A12A, A14, A15 1981-82 USA | 13201-H9500 | 35mm | 13202-H9500 | 30mm | 100.0 |
| A12A, A14, A15 1981-82 canada | 13201-H6200 | 37mm | 13202-H6200 | 30mm | 103.8 |
Nissan Competition
VALVES (A-SERIES)
4 of each required
- 13201-H2300 35MM/1.38" INTAKE VALVE A12, A12GX
- 13201-H6200 37MM/1.46" INTAKE VALVE A14, A15
- 99996-H1100 COMPETITION 37MM/1.46" INTAKE VALVE
- 13202-H2300 29MM/1.14" EXHAUST VALVE A12, A12GX
- 13202-H6200 30MM/1.18" EXHAUST VALVE A14, A15
- 99996-H1110 COMPETITION 30MM/ 1.18" EXHAUST VALVE
Competition Valves are "Polished and tuliped for improved flow characteristics".
Reference: 1984 Nissan Competition Catalog
Early A Engine
The 1967-1973 heads provide oil to the rocker armshafts in different locations than 1974-up, so when swapping you may need to redrill the oil passage.
Round Port
All early (pre-1974) A-series round-port engines uses the following * 35 mm Intake valves 13201-H1000 * 29 mm Exhaust valves 13202-18000 * Dry type manifold * 14035-18000 GASKET-manifold to head * Original manifold bolt pattern
A10 head
The 1970 B10 is 9.0:1, same as the B110 ratio. Yet they use the exact same head. This indicates the B10 piston dish is 20% larger.
* (optional) Rally Springs (dual valve springs) * Early heads have non-A12 fittings * Late A10 heads are same as A12
B10 Coupe Head
B10 Coupe with A10 engine had different part number. It is unknown how it differs from the regular Datsun 1000 cylinder head.
It is fitted with flattops pistons (same as the Hi-Gas A12GX pistons), and a dual-outlet exhaust manifold.
A10 M01 Head
11041-M0100 HEAD ASSY-cylinder E10 JDM 11041-M0101 HEAD ASSY-cylinder E10 JDM (from '72-1) 11041-M0102 HEAD ASSY-CYLINDER E10 JDM
A12 H10 Head
H10 head has no casting numbers * JDM B110 * USA B110 Early 1971 model (until April 1971) * Closed Chamber
Known in SCCA racing circles as the "H Production" head, legal alternative for H39 head.
See discussion: Are these A series GX or comp heads? Experts needed!
Some say a ported and polished standard A12 head with larger valves fitted flows about the same as a standard GX head. See head trivia.
A12 H15 Head
From Nissan Cherry E10
A12 H39 Head
* USA B110, from April 1971 head has no casting numbers * Same as H10 head, but with open chambers * Compression ratio 9.0:1 with dished pistons
Open Chamber heads are most common in USA. They were fitted mid-1971 to remove the temperature-spiking "quench" area therefore reducing NOx (nitrogen oxides) emissions.
Large Oval Port
All Large Oval-port engines use the following: * 35 mm Intake valves 13201-H2300 * 29 mm Exhaust valves 13202-H2300 * Wet type manifold * 14035-H2300 GASKET-manifold to head * Original manifold bolt pattern
A12GX Head
Cast "JAPAN" and "NISSAN" * Large Oval Ports (30 x 36 mm)
The A12GX Engine uses a cylinder head with dual-valve springs for 6800 rpm operation
(compare to stock A12 6400 rpm operation). It used an intake manifold with dual Hitachi HJE38W side-draft carburetors. Compression ratio of 10.0 and combustion chamber of 29.1 cm3 with flat-top pistons.
Dual valve springs, GX cylinder head and intake
- 11041-H2302 A12 GX cylinder head (to 6/73)
- 11041-H5703 GX cylinder head (from 7/73) same specs, but for newer engine style
- Nissan Competition called the newer head a "GX" head. But this appears to be the A12T head (11041-H5702).
NOTE: Dual valve springs alone is not an indication of the GX head. N10 A14E engines also used dual-springs, but were not large-port heads. Also over the years many heads have had dual springs added. For ID, check the intake port sizes.
For more details, see Main Article: A12GX Engine
Early A12T Head
Cherry E10 model has a head same or very similar to the A12GX head (11041-H2300):
11041-M0800
Late A Engine
1974-up A Engine Redesign heads provide oil to the rocker armshafts in different locations than earlier heads. The new heads do not have the oil passage on their face, so when swapping into earlier blocks you need to drill the oil passage.
Round Port
Round ports heads were used by all A12s & some A14s and one A15.
- Some A12s use the original bolt pattern while other A12s have the new-type bolt pattern.
- Valve sizes vary
A12 M30 Head
The new-style A12 head (without oil passage on face of head), Low-po Van/Truck engine.
B120 Sunny Truck 7510-7907 B210 JDM Late A12 (Van) B310 JDM A12S Van -7909 F10 JDM A12S Van N10 JDM A12S Van * Intake valves: 35mm 13201-H1000 * Exhaust valves: 29mm 13202-18000 * Dry manifold * Closed Chamber * Original bolt pattern 14035-18000 Manifold gasket
H74
H74 Head was fitted to late JDM B210 Van * Intake valves: 35mm 13201-H2300 * Exhaust valves: 29mm 13202-H7400 * Round Port * Dry Intake * New intake bolt pattern * 14035-H7400 Gasket-head to manifold 11041-H7401 HEAD ASSY-CYLINDER A12S S,K -7612 11041-H7403 HEAD ASSY-CYLINDER A12S S,K 7701-
A12 G25 Head
* G25 cast number * Dry manifold * Closed Chamber * New bolt pattern 11041-G2560 HEAD ASSY-CYLINDER 7908-8109 11041-G2561 HEAD ASSY-CYLINDER 8110-8910
G32
* Round Port A14 * Intake valve: 37mm 13201-H6200 * Exhaust valve: 30mm 13202-H6200 replaced by 13202-H8900 7907- * 14035-H7201 GASKET-MANIFOLD to CYLINDER HEAD * 14035-H7400 GASKET-MANIFOLD TO CYLINDER HEAD A14S.V 7906- 11041-G3202 HEAD ASSY-CYLINDER A14S.V JDM A10 7907-
A12 G61 Head
11041-G6100 HEAD ASSY-CYLINDER B120 8910- Wet manifold Closed Chamber, deep shroud New bolt pattern 58 hp
A14 FU Round Port head
For the FU Engine 1976-1977
Intake: 37mm
Exhaust: 30mm
Has round intake ports (like the A12 head). Casting numbers are under the valve cover area: "990" towards the rear and "454" towards the front. These cannot be ported out to match the oval port heads (you'll hit a water jacket). It has two small coolant holes below the intake ports, to provide heat for the intake manifold. These came on the "GFU" and "MPG" cars (USA-market B210 and B310 fuel economy champion models).
Has "990" cast near #4 cylinder and "415" at the #1 end
A14 FU High-Swirl head
1977 & 1978 lowered-port high-swirl design for the FU Engine.
These have quench chambers (not open chambers) but instead of being used in high-compression engines, they are designed for high swirl (for better fuel economy and improved emissions). They are used with dished pistons. Unlike the swirl-port heads, these have unobstructed ports. The ports are lowered so that the charge is forced to swirl as it enters the chamber.
H85
* Intake valves: 35mm 13201-H2300 * Exhaust valves: 13202-H7400 * Round Port * Intake Water Ports * New intake bolt pattern
* 11035-H8501 GASKET-MANIFOLD TO CYLINDER HEAD A12S.S,K 11041-H8500 HEAD ASSY-CYLINDER A12S.S,K B310 JDM N-7909 11041-H8501 11041-H8501 HEAD ASSY-CYLINDER S,K.A12S B310 JDM 7910-8010
* 11044-H8660 GASKET-MANIFOLD TO CYLINDER HEAD A13S, A15 JDM 8011- 11041-H8503 HEAD ASSY-CYLINDER A13S 8011-
A14 H78 Round Port Head
A14: (H78) Round Port, dry manifold, large valve A14S Van * 11044-H7400 GASKET-MANIFOLD TO CYLINDER HEAD 11041-H7863 HEAD ASSY-CYLINDER A14S V A10 7807-7906
Small Oval Port
A13 H62 Head
The 1974 A13 engine for north america featured small oval ports.
H95 Small-Oval Shrouded-port Head
- Used on all USA engines 1981-1982 (A12A, A14 and A15)
- Intake: 37mm
- Exhaust: 30mm
- peanut-shaped combustion chambers
- Small-oval ports, guide is shrouded
- wet intake
- 14035-H8901 manifold gasket (same as Larg Size ports)
Has an H95 cast into it, under the valve cover area, has what some call a "swirl" port has an obstruction cast into the port to cause the flow to swirl but it reduces total flow. If you look into the port, from the manifold side, you'll see a heavily shrouded port, almost half of the size it would normally be on an A14 head.
If you try to grind out this obstruction, you will hit a water jacket and render the head useless. It too, has the coolant holes in it.
They also have a small but deep combustion chamber, hence a different dish in the piston.
Regular Oval Port
The A14/A15 Oval-port Heads include large 37 mm intake valves and 30 mm exhaust valves.
- There are many part numbers, which differ for year, emission control, accessory fittings, coolant passages, etc.
- These heads first appeared with the 1975 A14 engine.
- Open Chamber versions can can be milled .080" or more to raise compression.
Oval-Port heads include:
- H72: Dry, Large Oval, Open Chamber. The original A14 head, designed for USA market. With Air Pump passage
- H77: Same as H72 but drilled for more emission controls
- H75: Same as H72 but for non-USA market w/o Air Pump
- H89: Closed Chamber Wet manifold use in B310
- M24: For twin-carb A14T, similar to H89 but with dual-valve springs
H72
The original A14 head. Designed for north america, it has open combustion chambers and is drilled for air pump passages.
B210 USA '75-0777 * Cast "H72" and "108" * Cast "H72" and "104" is H77 * Open chamber * Dry Type * Oval Ports * Air-exhaust passage 14035-H7200 Gasket-manifold to head
Sometimes erroneously called the "low compression GX head", it has a casting number "H72". Has a larger 360-degree "open" combustion chamber for reduced emissions. It does not have the coolant holes below the intake ports, so uses a 'dry' type inlet manifold. It has the nice straight big oval intake ports. It is better than the A14 oval "swirl port" (H95) head, and certainly better for high RPM use than the round intake port A14 heads. Air pump galley drilled from front face all the way back through, intersecting all the exhaust ports.
Open Chamber design
So is Oval-port "H72" a good head or not? [Naukkis] says the "high-compression" (closed chamber) head is a better design, and not just because of the compression (see New A series oval port head). The quench design of the combustion chamber is more efficient. The best combo for low compression would undoubtedly be a high-compression head used with half-dished pistons (half-flat-top, half dish), but are these available for the A-type engines?
Note air pump passage
Note the "extra water port" at the rear, plugged in 1975, but fitted with a sensor/switch in others:
The original A14 head (H72) has the oil boss casting like early A12 heads, only it is not drilled & plugged:
H75
A14: (H75) JDM Late B210 A14S Van A10 JDM A14S.S,K -7803 * 14035-H7200 GASKET-MANIFOLD TO CYLINDER HEAD * Intake valves: 37mm 13201-H6200 * Exhaust valves: 30mm 13202-H6200 * Oval Ports * Dry Intake * Open Chamber design, 31cc
H77
Same as H72 but with different emission provision * Cast "H72" and "104" * rear port face boss (for water sensor) is undrilled * B210 USA A14S 0877- non-5speed models * N10 USA A14S Federal 0878-0779 * Open chamber * Dry Type * Oval Ports * Air-exhaust passage 14035-H7200 Gasket-manifold to head
A14 H78 Oval Port Head
A14: (H78) Oval Port, dry manifold, large valve A14S Van * 11044-H7860 GASKET-MANIFOLD TO CYLINDER HEAD 11041-H7860 HEAD ASSY-CYLINDER A14S V B210 11041-H7861 HEAD ASSY-CYLINDER A14S V A10 -7806
H89
A14 Oval-port "High Compression" was fitted to B310 Coupe and Sedan in the JDM market (but not to Van (wagon).
- Closed Chamber
- Oval Port
- Intake Water Ports
- New intake bolt pattern
H99
* USA N10 A14S 0879-0780 * Similar to FU Engine and late model G61 A12 * Round Port for A14 * Closed chamber * Wet type
M24
M24 Head from A14T engine * Intake valves: 37mm 13201-H6200 * Exhaust valves: 30mm 13202-H6200 * Dual valve springs * Oval Ports (smaller than GX, same size as standard A14) ** Intake-to-Head gasket 11044-H7200 11041-M2460 HEAD ASSY-CYLINDER A14T B210 JDM
M66
A15S new type combustion * USA N10 (Pulsar) "Datsun 210" 0880-0781 * Wet type * Oval Port * INTAKE 35mm: 13201-H9500 * EXHAUST 30mm: 13202-H9500 * 14035-H8901 Gasket-manifold to head ** interchangeable with 14035-05H01 11041-M6600 HEAD ASSY-CYLINDER
M49
Medium Oval Port
28x32 intake ports were used by A14E and A15E EFI heads.
H92
The EFI heads. Fitted to A14E and A15E in Asia-market B310s and N10s.
N10 JDM A14E B310 JDM A14E, A15E * Intake valves: 37mm 13201-H6200 * Exhaust valves: 30mm 13202-H6200 replaced by 13202-H8900 7910- * Dual valve springs 14035-H9201 Manifold gasket * Wet manifold * Medium Oval Ports with notch for injector * 28x32 mm with injection cutout of extending up to 40mm * compare to standard A14: 28x34
Large Oval Port
H57
Late A12T from B210 Sunny and E10 Cherry. Appears to be the same as the earlier A12T engine, except the head has no oil passage on the face of the head.
Competition Head
- Intake: 35mm (optional 37mm)
- Exhaust: 29mm (optional 30mm)
The Competition Head has the large oval ports and a small heart-shaped chamber and was available from Datsun Competition, later called Nissan Competition and then Nismo. The part is unforunately now NLA (No Longer Available). This race cylinder head reported has the same 29 cc chamber volume as the A12GX head.
Sometimes the Competition Head is erroneously called the A14 "GX" head because it has the A14 size valves, but is more accurately described as a ported and polished version of the standard A14 high-compression head.
- 99996-H1167 Competition Cylinder Head (to 6/73)
- 99996-H1165 Competition Cylinder Head (from 6/74)
The Competition heads are "recommended for racing purposes only ... ported, polished ... competition intake (37 mm)... competition exhaust (30 mm)" -- in other words, the same valve sizes as regular A14 heads. However, the valves are tulip-machined for better flow.
Presumably the difference in the two Competition Head part numbers only differ in the oil passage and fittings/bolt holes.
Reference: 1984 Nissan Competition Catalog
Other heads
Anyone have more information on these?
- There is apparently an A14 Oval Port "GX" head which flows more than the A12GX head. reference: GX Head or A15
- An A15 "GX" head was used by Nissan for racing. There are several different chamber shapes and sizes but just the improved flow though the oval ports is better than the stock round ones. The valve sizes should be larger and some were fitted with dual valve springs.
High Roof Heads
- High-port heads. Are these the Competition Heads? Or some other kind of racing-only head?
-
Also see: Cylinder Head Modifications Raised-Ports.
Measuring Combustion Chamber Volume
Here's what you need:
- A large syringe marked in CCs (without the needle, or remove the needle).
- a piece of plexiglas, big enough to cover one cylinder. Drill a small hole about 6mm from edge of the plexiglas
- some grease
Syringes are available from animal feed stores or your local chemist. Get a couple of syringes one thats about 20mls and one that has 0.1 increments which is normally about 3mls. That will cost $1-$2.
Here's how to measure:
- place the head upside down as level as possible
- put a small ring of grease around one of the combusion chambers
- place the plexiglas over it and press it flat
- Fill the syringe with water, and measure how many CCs it takes to fill the chamber
This is also a good way to tell if the valves are sealing well. It should hold water for several hours with no visible leak. If the water leaks out, it's time to lap the valves!
Dished pistons (factory A15)
Note that pistons came with different dishes according to year, country, etc.
Which Cylinder Head is "Best"?
The two main factors for peak horsepower:
- combustion chamber design: closed chamber "heart-shaped" is more efficient than open chamber
- port flow: oval is better than round for high-rpm use, and larger valves can be useful
NOTE: Don't confuse "open chamber" for a hemi-style chamber. Yes, both are 360-degree 'open', but the term "hemi" refers to valves at 45-degrees to each other (all A-type engines use valves parallel to each other). The "open" chamber is not inherently better flowing, but is used to reduce compression for lower NOx emissions.
Some say to start with the A12GX Engine head due to its high-compression chamber. Adding bigger valves is good for high-rpm power. Others say a ported standard A12 head will flow as much as the A12GX, but this doesn't increase the compression.
GX heads are not always easy to find, though they pop up for sale every year.
"The best head of the easily available variety, IMO is the H89 head from the A15." - A14Force.
Or you could use the H72 head, and shave/mill it to increase compression.
The A14GX (high-compression) head is probably the best all-around head: big valves, big ports and an efficient chamber design. But you probably cannot find this Competition head ... unless you already have one.
Aftermarket piston styles vary (flat-top or dished, and aftermarket popup/domed pistons). With dished pistons, the pistons can be shaved and the block milled (up to 0.090 inch) to make high compression "flat-top pistons".
On the other hand, for a supercharged motor low compression is best, because you can use more boost and gain more power than is lost due to the low compression.
- closed chamber head with a half-dished piston is probably best due to the efficient "quench" combustion
For a low-rpm 'grunt' engine, or for maximum fuel economy, you'll want:
- Small ports<
- large valves with an A14 or A15, small stock-size valves with an A10 or A12 (anyone have another opinion?)
- closed chamber or swirl-port head
So which is better for a street engine?
- High compression engine: pay 15% premium for high-test fuel but get better mpg
- Low compresion engine: buy the inexpensive petrol, but get worse mpg
Modifying a Head
See main article: Cylinder Head Modifications
See: Head Porting (Port and Polish)
Part Numbers
See Cylinder Head Part Numbers
DOHC Heads for A-series
See DOHC Heads
AY12 Racing Head
There was one exception: The race-only AY12 cylinder head:
