HarryB's Strato blue NB2

[HarryB]

Have been planning the engine rebuild for a while now. Decided to ask Mazda for a complete rebuild gasket kit, and asked them to also price all individual items on the kit, as I already have some brand new OEM parts from the 1.6 that can be reused (water pump gaskets, front and rear crank seals, exhaust cam seal). Buying all required parts separately was cheaper, so I ended up doing that, adding a few more bits here and there, such as new freeze plugs, sump long bolts and flywheel bolts for instance.

Another quest was to find valve springs suitable for my needs. Seeing boost only on the intake, using stock cams and rev limiter set to max. 300RPM above stock meant that I only needed to upgrade the intake valve springs with stiffer ones. The thinking here was to be able to counteract boost trying to blow intake valves open. Using a Rotrex instead of a turbo means that there's no additional exhaust backpressure, so no need to upgrade exhaust valve springs (heavier springs would only add to parasitic losses). Ideally I would like to be able to bump them by 10-20% to account for aged springs and barely higher rev limiter if needed; more on that later.

On the intake side, and with a stock valve (33mm with 6mm stem), 1bar or 14.5psi of boost means I needed an additional 18.6lbf of seat pressure, compared to stock (45lbf). Thanks to a folk in MT.net, I found out that Impreza STi 2.5 valve spring dimensions are identical to a 1.8 VVT. Aftermarket Brian Crower springs (part no. BC1600-1) seem to fit on stock retainers and shims, and when installed give a seat perssure of 65.5lbf, which is perfect. They are also $5ish each, which is dirt cheap, especially for high quality components.

Coming back to the exhaust side, I think of repurposing the OEM intake valve springs. Overall dimensions are identical, but intake valve springs on VVT engines were upgraded (3.78mm vs 3.6mm wire diameter). This means that if I swap them (and considering they are the same material and both have 7 coils), they will give me a nice 20% bump over what was already there. Grand total of this is less than $50. Will be putting an order soon, will update this thread again in a couple of months with my findings.