1HDT head on a 1HZ block
Posted: Wed Aug 31, 2005 12:32 am
OK, the "Stump the Dunce" thread got me very interested in this topic, but I'd like to start a new thread so as to keep the discussion purely on the subject 
and invite the other experts to add their knowledge.
If a 1HDT head is bolted to a 1HZ block and the same turbo camshaft is used (same valve lift and duration), will the valves hit the pistons? The 1HZ has a much higher compression (22:1) than the 1HD-T (17:1) and the piston top may come closer to the head.
Is it true 1HD-T pistons are dished to lower the compression ratio?
There is a factory 1HZ-T used in 1993+ Coaster buses in Euro markets. Interestingly Toyota used these to replace the 1HDT in 90-92 Coasters. The pistons have a different part number than non-turbo 1HZ pistons. Maybe thicker? Different shape to lower its compression ratio?
Dave
and invite the other experts to add their knowledge.If a 1HDT head is bolted to a 1HZ block and the same turbo camshaft is used (same valve lift and duration), will the valves hit the pistons? The 1HZ has a much higher compression (22:1) than the 1HD-T (17:1) and the piston top may come closer to the head.
Is it true 1HD-T pistons are dished to lower the compression ratio?
There is a factory 1HZ-T used in 1993+ Coaster buses in Euro markets. Interestingly Toyota used these to replace the 1HDT in 90-92 Coasters. The pistons have a different part number than non-turbo 1HZ pistons. Maybe thicker? Different shape to lower its compression ratio?
Dave
dumbdunce wrote:yes the head and the block will bolt up, I am pretty sure a 1HZ block is more or less identical to a 1HD-T except it is drilled for the oil supply and drain for the turbo. The bopre and deck height are the same, the big end bearing cradle is the same. The crank is the same (same journal size for mains and big ends, same stroke) but early 1HZ cranks were not nitrided. now the same part number is used for replacement cranks for 1HZ, 1HD-T, 1HD-FT, 1HD-FTE. The pistons are very different (combustion chamber in the direct injector piston), and the heads are obviously different. conrods probably the same. camshafts are different between turbo and non turbo. timing belt and all timing gears, timing cases, vac pump and power steer pump, sump are the same.Mytqik wrote: Will a 1HZ block bolt up to 1H-DT head??
so - no you can't make a 1HD-T just by bolting on a top end, but yes you could build a 1HD-T (effectively - the engine number would still be 1HZ) on a 1HZ block.