A12GX Engine

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Revision as of 20:10, 23 December 2006

Datsun A12GX Engine

A12 GX Engine

The A12 GX Engine is legendary. While it may not be a powerful as a racing A14, this was a stock package offered in Japanese Domestic Model 1200 GX Sedans and Coupes and has more horsepower than the Standard A12 engine.

GX Cylinder Head

GX cylinder head and intake

Compare to the A12 and A14 intakes

• heart shaped combustion chambers<li>oval ports (like the standard A15 cylinder head). Standard A12s have smaller round ports. The best heads have the ports up higher than the round-port version. There are Oval port heads with the ports lower down.<li>double valve springs<li>valves. Compare to A14/A15 with 37 mm inlets & 30 mm exhaust valves<li>Later GX heads have two little water jackets under the ports, for warming the inlet manifold<li>intake ports shaped differently for flow and swirl</ul>A ported and polished standard A12 head with larger valves fitted flows about the same as a standard GX head. Also see head trivia. The head bolts on an A14/A15, but is very similar to the oval port A15 head (might even use the same casting). The A12 heads and later head provided oil to the rocker armshafts in different locations so you may need to redrill the oil passage. There is apparently an A14 Oval Port GX head which flows more than the A12GX head.
  reference: GX Head or A15 The 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.

  Engine Block

  <li>Balanced crank<li>Flat top pistons for 10:1 compression ratio<li>Slightly longer duration cam than stock 1200.
  Otherwise the block crank and rods are the same as the standard A12.

  Induction

  <li>Dual twin-sidedraft Hitachi carbs (SU-style) -- 38mm bore (~1.5 inches)<li>oval port inlet manifold with or without water jackets to match the cylinder heads<li>Intake manifold has 2 studs at the top of each pair of inlet ports (cylinder head matches this). Standard A12 has only one stud per pair of intake ports.

  Reportedly, British vehicle SU carburetors (H4 or HS4 1.5 inch carbs) will fit the manifold, with some linkage creativity.

  Exhaust

  • two piece exhaust manifold that has two pipes which bolt up to another two and go into one further down. See Photo: Twin exhaust downpipe

  Word has it this works as good as common extractors (headers), though not as good as the best tuned-length extractors.

  Extractors may not clear the GX inlet manifold.

  Identification

  For the cylinder head, the best way to tell a GX head is to check the casting number in the valve train area.

  <li>1200 GX frequently have no casting numbers at all <li>A12 should have "180" or "H10" <li>A12 GX should have "H23" [very early A12 GX engines used 1200 GX head castings without the extra drillings for rocker oiling] <li>A13 should have "H62" <li>A14 could have several different ones, such as "H72", "H74", "H98" depending upon year and emission control equipment.

  The casting number will be the first 3 digits of the last half of the part number, as all cylinder head part numbers begin with the same 5 digits reference: Various cylinder heads

  Specifications

  references:

  • FIA Amendment March 1970

  Datsun 1200 group 1 FIA recognition

  Comparison

  part	A12GX Engine	A12 Engine
  Carb	Hitachi HJE38W side-draft (two carbs)	Carb Hitachi DCG306-1 down-draft
  Carb Venturi	?	Primary: 26 mm, Secondary: 30mm
  compression ration	10.0	?
  combustion chamber	29.1 cm3	36.6 cm3
  valve opens	BTDC 20 degrees +- 7 degrees	?
  valve closes	ABDC 56 degrees +- 7 degrees	?
  valve opens	BBDC 58 degrees +- 7 degrees	?
  valve closes	ATDC 18 degrees +- 7 degrees	?
  In. Valve dia.	29 mm 1.14 in	?
  valve lift	9 mm 0.35 in	?
  exhaust ports	27w x 29h +- 1.5 mm	?
  intake ports	30 mm circle with 4.5 mm elongated section (30 x 34.5 oval?)	?
  exhaust ports	26w x 28h with 3 mm radius +- 1.5 mm	?
  center ex port	69w x 28h	?
  intake ports	28/27 mm circle	?
  Flywheel weight	?	9.5 kg
  Flywheel with all turning parts	?	13.1 kg
  hp	83ps @ 6,400 rpm	hp 68ps JIS @ 6,000 rpm
  max rpm	6,800 rpm (80 ps)	hp 68ps JIS @ 6,000 rpm
  max torque	10.0 kg-m at 4,400 rpm	9.7 kg-m at 3,600 rpm
  max speed car	160 km/hour	150 km/hour