O.S. Engines 21VZ-B V-Spec
 

Hi! I have this engine.For 25% nitro 12% oil do I need the included extra head shim ? or I need it only for 30% nitro?

don't need it for either. But some like it for 30% but not neccesary

You don't need the extra head shim for 25% or 30%.

+1 on no extra head shim needed for 30%. I run coldfusion magic. Lend it's 30% & 11% oil in my os speed, same head shims and no problems at all. Add the extra shim to increase top rpm and decrease compression to make the engine have a little less bottom, otherwise run it stock.

Just got a used V-spec in parts, and I wonder about whats the correct shimming for 20-25% nitro.

The stock shims on the V-Spec, Speed and Mugen Ninja JX-21 are one 0.2mm (0.008") aluminum shim and one 0.1mm (0.004") copper shim. This is for 25% or 30% nitro. If you are running 20% nitro remove the thinner copper shim.

Thanks. I'm innstaling a new cylinder/piston, con rod and bearings so it vill be god as new:D