There has been a resurgence of interest in 90’s Japanese cars as of late and with that a surge in new parts development with specific popular models. In our case, it is the Nissan Z32 300ZXTT that was Sport Compact Car’s famous project car back in the ’90s. The car has been sitting in indoor storage for the last 20 years and it sprung a leak in one of the freeze plugs which means we have to pull the motor. We thought that since the engine had to come out, it would be a good time to modernize the VG30DETT engine and address some of its weaknesses that have been discovered over the years, one of which is a weak, compared to modern engines, bottom end.
The VG30DETT block is a cast iron part which gives it great stiffness. When we first built this motor, anything making 550 wheel hp was considered to be really good and the VG block could easily accommodate this power level. With improved exhaust manifolds and better turbos, VG’s started to be capable of much more power and soon people were making over 800whp. About this time the structural limits of the block started to be reached. On the VG the area where signs of distress occur is in the area of the main caps.
When building customers’ VG engines, we started to notice that the main caps were starting to get fretted and the registers of the main caps were all beat up. The main bearings would show uneven wear and signs of distress as well. These are indications that the main caps and even the webbing of the block were starting to flex from the strain. The fretting and bearing damage looked like the picture above. This isn’t a VG engine but it was a good example of what we were seeing. The damage we would see was often worse than this!
Fretting also shows between the cap and the bearing shell. It is caused by the metal surfaces rubbing against each other under a high clamp load. Anytime you see these sorts of patterns when you disassemble an engine, it is a sure sign of trouble where you are approaching the design limits of the block! We never thought we would see this in an iron VG block but our last customer VG exhibited extreme fretting even though the car only produced about 650 whp. We think it’s because it was mostly run on crappy 91-octane California fuel and the fretting load was caused by transient detonation.
We decided to reinforce our block with some billet main caps from EPR/Engineered Performance. The cast iron stock main caps are replaced with 1045 billet steel parts. 1045 steel is ductile and forgiving in this application and is many times stronger than cast iron.