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straight six info
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what interchanges
  • Iron Dukes: the old (153 ci) Iron Duke four cylinder engines, last produced in 1970, were essentially 230s with two cylinders lopped off. They had a 3.875 bore and 3.25 stroke, 8.5:1 compression ratio, 1bbl carbs and made 90 hp, 152 ft-lbs. Therefore, rods, pistons, valvetrain and engine accessories interchange between those two engines. GM produced a similar sized (151 ci) four-cylinder in the 80s and 90s, but very few parts interchange from those engines. See this page for more later Iron Duke info.
  • valves: same dimensions as small block. Note: the largest oversize valves that can fit are 2.02I/1.60E. 1.94I valves are recommended, though
  • valve springs: same as small block, except installed height should be 1/16" less than a small block
  • valve stem seals: same as small block
  • lifters: same as small block
  • pistons and rings: 230/250/292s have the same bore as 283/307 small blocks. the 283 piston length is 3.796, the pin diameter is .927 and top ring distance is 1.795. the 307 piston length is 3.515, pin diameter .928 and top ring distance 1.655. the 250 piston length is 3.505, pin diameter .927 and top ring distance 1.654. 194s are just SOL when it comes to pistons
  • main bearings: the main journal diameters are the same as the 283 and the 1967 327
  • rods: similar dimensions to certain small journal small blocks, except the small block rod is thinner at the bearing. the rod journals for the 230/250 are the same diameter as the 283 and 1967 327 (1.999" to 2.000") and the 292 rod journals are the same diameter as the 307 and 1968 327 (2.099" to 2.100")
  • HEI from any year six cylinder in this family. also, the HEI coil and modulator are the same as small and big blocks. also, the spring weights are interchangeable with small and bigblock distributor spring weights. (Note: when swapping HEI for points, make sure to get the correct wires and plugs. otherwise, you're not operating in the right heat range or at full potential)
  • the whole assembly will bolt up to any trans a small or big block bolts up to
  • thermostat, thermostat gasket and upper thermostat housing: same as small block
  • the 194/230/250 accepts the 292 fuel pump, which flows more fuel, though the fuel lines are slightly bigger (3/8" over 5/16") and need routed slightly different
  • the heads from any of these engines swap around. the 194 heads have smaller combustion chambers (58cc) compared to the others (72cc). theoretically, this creates an increase in compression, however, there's not enough roon in the 194 head for unshrouding and adding larger valves. Note: 75 and later heads are integrally cast with the intake manifold. they'll still swap, but are generally regarded as junk despite the fact that some came with 2bbl manifolds.
  • crankshafts from any of these engines also swap around. there's three basic crank types - the 194/230 (3.25" stroke), 250 (3.53" stroke) and 292 (4.125" stroke). keep in mind the 292's different rod journal diameters when swapping it into the other engines.
  • flywheels: interchange with small blocks
  • what doesn't interchange
  • starters: not the same as small blocks despite what i posted earlier
  • harmonic balancers: not the same, on the sixes the pulleys are integrated with the balancers.
  • pushrods from small or big blocks
  • rod bearings
  • rocker arms: not the same as big blocks despite similar ratios
  • camshafts and timing gears from 292s to any other engine. the fuel pump and right side motor mount are switched on 292s, thus the fuel pump lobe on the camshaft is in the wrong place compared to the smaller sixes.
  • fuel pumps from small or big blocks
  • distributors from V6 engines
  • other advice
  • crank bore alignment is important in these engines
  • the 407/407N casting crank is 10 lbs lighter than the 802 casting crank
  • heads can be safely milled .060 to .080
  • the head bolt bosses that run through the intake ports can provide more airflow if reduced and reshaped to resemble an airfoil
  • these engines have problems with developing cracks from the head bolt on the front drivers side to the water pump. check this when looking at boneyard or other used engines. the best prevention for this is to install head studs, which relieve the stress on that area.
  • pre-75 engines should be given hardened valve seats for use with unleaded fuel
  • 62-67 Chevy II/Nova sixes have their dipstick at the front of the engine, behind the distributor. Others have the dipstick further back. I'm not sure if this is just Nova engines or if this also applies to other engines from those years.
  • when upgrading the cam/valvetrain, it's a good idea to swap the stocker's ancient plastic/fiberglass cam and crank gears with some new steel/aluminum ones. Replace both gears -they are a matched set!




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