This information has been gathered from various engines that I have used in this car, Some engines where used simply to aquire spare components whist others were rebuilt and utilised in this car.
S15 Turbo Engine
Engine A failed:
Valve shim split, one half of the shim caused the timing chain to jump one tooth on the crank sprocket, Advanced timing caused detonation failure of pistons, cylinder bores and head - Pistons and Block were scrapped before I started to colate this information.
Cylinder Head never used
Engine B was built using cylinder head A but eventually failed:
A blown head gasket + Oil pump damage caused by Turbo bearings failure, Strip down revealed some detonation damage to pistons and bores.
There are various valves used in different heads - The tabel below tries to make sense of the variations i have found to date.
Inlet Valve ID
Exhaust Valve ID
Turbo Head with VCT
E72 - Single Cut 6mm
J3 - Single Cut 7mm
Non Turbo Head with VCT
53J - Back Cut 6 mm
64Y - Back Cut 6 mm
VCT Turbo head v VCT Non Turbo head
On the outside these 2 cylinder heads appear to be identical. The ports are the same size and the valves are the same size. Using a non turbo cylinder head may seem like a good idea as they are usually in better condition having not suffered any damage caused by excessive boost and or poor tuning.
Deep inside out of view is one very small but important difference.
The valve stems on the Non Turbo engine are 6mm in diameter. (right image)
The Valve stems on the Turbo engine are 7mm in diameter. (Left Image)
The extra 1mm in diameter can make a huge difference as the 7mm valve is 36% larger in cross section and 16% larger in circumference. The larger cross section of the valve stem allows for better heat transfer up the valve stem and the larger circumference or contact area with the valve guide also allows for better heat transfer from the valve into the cylinder head.
Whist there is probably no decernable performance difference between these two cylinder heads the bigger valve stems will help to keep the exhaust valves cooler and prevent heat damage and detonation should the exhaust valves get too hot.
Oil feed to tensioner
S14 and S15 engines fitted with Variable Cam Timing (VCT) have one very small external difference in the front timing case. When viewed from the front of the motor the top left mounting screw on the front timing cover is moved about 15mm to the left on engines fitted with VCT. Whilst this may seem like a very insignificant diference the reason is very important.
On VCT engines an extra oil way has been added to the engine block and the front timing cover bolt had to be moved to accomodate this change. The extra oil way feeds the timing chain tensioner
This extra oil way runs behind the water pump and down to the main oil gallery. Its so close to the front of the engine that the water pump recess in the block has been made smaller on VCT engines resulting in a different water pump as well.
Non VCT Engine "D"
Engine fitted with VCT "B"
Front Timing Case
Note the relocated mounting hole
(looking at front right corner)
Non VCT engine is missing the extra oil feed
Extra oil hole that feeds the chain tensioner
Water Pump Recess
On the VCT engine the water pump recess is not as deep to allow for the extra oil feed to pass behind the water pump
Obvoisly there is also a very subtle difference in the head gaskets to accomodate the extra oil feed as can be seen by this document produced by Permaseal.