Inlet valves 1.6” dia, exhaust 1.375”

[cadwell]

I am just stripping down my newly acquired S4 and have found that it has the above size valves. Ie larger than the Big Valve head. It has the S/E single groove camshafts.
All looks to be in good condition but I wonder what the low down torque will be like. Bearing in mind that the Big Valve engine had its torque curve shoved up the rpm range, this engine would presumably need revving higher than the BV.
Has anyone any experience of engines with these valve sizes? At present my thoughts are to have smaller dia seats in to reduce the valve sizes to standard.
Any views would be welcome
Peter

[nmauduit]

I would think that torque curve will have a lot more to do with cam timing (esp. overlap) than with valve dimensions, so if you're not installing a totally wild profile timed with a lot of overlap, a larger input will not hurt more than it helps as the revs increase (all else on the button, esp. care in carbs tuning).

[rgh0]

The valve sizes alone will have little impact on the torque curve. Alone they will move the peak to be a little higher and that will be up a little in the rev range but will not reduce it much if any at the original peak . Its what else that has been done that may make the impact more significant.

i.e.
porting of the inlet tracts,
carb chokes
compression ratio
exhaust headers
cams reground ?

Going back to standard big valve seat diameters will probably also be difficult assuming that the area behind the seats has been ported to match the bigger valves.

The starting point is to understand intended future use and current state of all the components including current valve lengths and valve springs used and then the best way forward can be better defined.

cheers
Rohan

[2cams70]

Usually cowboys drop 1.6 inlets in just for bragging rights without doing the necessary blending or porting and the flow ends up worse than it was with the original size valves.

[elangtv2000]

Usually cowboys drop 1.6 inlets in just for bragging rights without doing the necessary blending or porting ...

That was the case with the motor in my S4 when I bought it. No other work has been done on the head to improve flow and performance. When I rebuilt the motor I had all new seats installed and blended properly for standard big valves, installed new higher lift cams with all new valvetrain components.

[cadwell]

That’s a possibility, could you tell me who did the work on your seats. Reliable machine shops seem to be rare these days
Peter
Ps Sorry I see you are over the pond, but would appreciate recommendations from UK members