Longer rods

[Testament]

I've read quite a bit of discussion on the subject of longer rod conversions for the 2 litre twincam. Have you built many race engines with longer rods, and has there been a worthwhile gain in engine performance and/or reliability at high rpm? There is certainly room with the compression height on TC pistons being generous, or is there a very good reason for the compression height on factory TC pistons?

[Guy Croft]

Hi

Long rods - I've done very detailed maths on that, I don't believe there is a worthwhile benefit. Though the acceleration tends to reduce with a longer rod the much increased stress from extra rod weight will inevitably balance out or undermine this gain and as for power benefit from longer dwell, well, I do have access to quantifiable test data and would tend not to bother with it because of the weight issue. Moreover as for any gain on the intake stroke you have to make the rod massively longer to have any real (effective) effect on the piston velocity-intake flow relationship.

GC