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I have now covered a further twelve thousand miles since my 3.2 JTS engine was rebuilt. Whilst happy with the performance, an issue I failed to address when the engine was being rebuilt - due to time pressures - was that of disparity between front bank and rear bank cylinder head flow rate capacity.

This is fundamentally; I believe, due to the misalignment of the oil feed from the block to the rear cylinder head, in conjunction with the rear head gasket also obstructing the oil flow. On occasions, particularly as the weather is now colder and oil is taking longer to come up to temperature, the engine experiences what can only be described as a small power - surge. This occurs at low - ish revs. When the engine has had an extended time to warm up on a moderately long drive, this feature is completely absent.

Several potential solutions were thought of during my initial investigations, wrt the modifications I intended to do.

1.) Feed the front camshaft bearing caps with oil from a separate electric pump. This would provide only the inlet camshaft VVT and the front bearing cap of the camshaft. with oil feed. A more complex mod. would have done the same for the exhaust camshafts but would have required extensive work with the heads off.

Difficulty however was being experienced in sourcing a suitable electric pump for either option, so a second option was considered.

2.) Link the two front bearing caps but this I felt would be "Robbing Peter to Pay Paul", insofar as it would reduce the speed of the front bank VVT's. So that too was abandoned in favour of:-

3.) Feed oil to both the front and rear bank, front bearing cap from the output of the Cooler/Filter Unit. It was this method that would have been adopted, had the project not been delayed by Engineering/Garage resources. So when they became available, I opted not to further delay matters and abandoned the idea.

However, having driven the car for 12,000 miles; I realise, it is doubtful the front bank VVT's can be speeded up to any degree which would make a tangible difference. I say this because their oilways are completely unrestricted, insofar as there is no restrictions from the main front bank gallery to the front cylinder head and the capacity of the oil gallery is large and closest to the output of the engine oil pump.

However, this is not the case with the rear bank, which is severely restricted between the block and the cylinder head. I discount all other restrictions
which I feel I have addressed with my oil way modifications.

So now I plan to take an oil feed from the horseshoe link of the C.L.L.S., which feeds the front bank main oil gallery directly, to the rear bank front bearing cap of the camshafts. The pressure in this line will keep the non - return valve in the cylinder head feed closed and this line will replace totally the oil feed this non return valve hitherto performed, for the rear bank inlet camshaft!

In doing so, the oil that used to flow will now be wholly devoted to the rear bank Exhaust Camshaft VVT Solenoid + hydraulic lifters and remaining bearing cap lubrication. Removing the oil supply load of the inlet camshaft of the rear bank, should improve the response time of the exhaust camshaft - increase its setting - speed!

Although important to improve the exhaust camshaft response time, the greatest benefit should come from speeding up the rear bank inlet camshaft as the pressure balance between front/rear should now be much more equal!

What increased performance it achieves, I won't know until it is done. But if it can be seen to eliminate the "Power - Surge", that in itself I will regard as a major plus!
 

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