A12GX Engine

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The Datsun A12GX 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. The GX engine featured a matched pair Hitachi HJE38W carburetors, larger cam, giant intake ports, and streamlined exhaust.

Also see: Hitachi Twin Carb engine

A12 GX Engine

GX Cylinder Head

GX cylinder head and intake

 Main article: A-series_Cylinder_Heads

Compare to the A12 and A14 intakes

• heart shaped combustion chambers<li>oval ports (like the standard A15 cylinder head, but taller/larger). 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>1200 & A12 GX heads have four coolant outlet holes under the ports of approx 5mm or 6mm diameter, for heating the inlet manifold runners<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 shafts 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 in some engines. Standard dished pistons have been identified in some other engines<li>Slightly longer duration cam than stock 1200.<li>Water pump inlet pipe at front of block has additional hose fitting to recieve manifold coolant outlet hose.
  Otherwise the block crank and rods are the same as the standard A12.

  Induction

  See: Hitachi Twin Carb

  
  

  <li>This featured a matched pair of left- and right- hand Hitachi HJE38W carbs. Twin semi-sidedraft Hitachi carbs (Variable Venturi/SU-type) -- 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.

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

  Exhaust

  main article: Exhaust Piping

  • Dual outlet exhaust manifold that bolts to dual pipes that blend into into one pipe 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. The factory 1200/B110 Competition Tune-up manual recomends the GX manifold for Rally competition use instead of 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

  Rocker Cover

  The Rocker cover is unique to the A12GX engine:
  

  • accelerator clip is on front pad, not rear
  • fuel line clip boss is on rear left side, not front left side
  • Datsun logo (not Nissan)

  
  
  Arrows: Accelerator cable clip

  • GX: center feed
  • A12: rear feed accelerator cable

  
  Circles: Left side threaded boss for fuel line

  • GX: rear
  • A12: front and rear

  Specifications

  • Nominal Rev Limit: 6800 RPM
  • Actual Rev limit: reported fine at 8,000, float at 8,150 rpm

  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

  
  

  B210 A12 GX Engine

  The B210 GX engine was basically the same as the B110 twin carb (1200 GX Engine), but based on the newer cylinder block. The head was no longer drilled for the oil gallery that was unique to the A10 & 1200, & a revised induction was used. This involved the flat top [or square top if you prefer] carbs & the inlet mnifold had proovision for a few more fittings to allow compliance with newer smog laws. There was also provision for a vacuum takeoff for the brake booster.

  The B210 GX induction seems to be the most commonly encountered twin-carb A engine setup in Australia.

  The exhaust manifold was the same as the 1200 one, but the fuel pump was of course the newer type for the new cylinder block. GX pumps had a slightly stronger spring under the diaphram to boost fuel delivery pressure a smidgen.

  The air filter housing base plate was revised a little to accomodate more fittings too, but the main cover piece was unchanged, other than for the change in colour from red to blue. It seems that L series SSS air filters went from red to orange.

  In the USA, a B210 "GX" car model was offered, but this referred to the car only and did not include a twin-carb engine as did GX models sold in Japan.

  Photo Index