EVO X 4B11T Cylinder Head Development

After our guys in the head shop did some flow testing and measurements, they found that the EVO X head is pretty good for a stock head. There’s no doubt we will improve its efficiency even more since Lyon will develop the ports, Steve will develop the bad ass seat profiles, and we’ll be using oversize valves. We have a formula here at Cosworth that Lyon developed to calculate a cylinder head’s efficiency and the factory EVO X head is the highest efficiency head that we have measured out of a production engine. The factory Nissan VQ35 takes 2nd place. We’ve never measured a Honda K20, but I have a feeling it would be king. I don’t have too much K20 experience myself, but the little experience I do have has told me the K20 head rocks. Anyhow, we’re talking 4B11T EVO X heads. We are starting port development, but we’ve developed an initial chamber design. It looks like the chamber will need some work because of casting core shift and an uneven shroud area behind the valves. If you want the ports to flow the same, you have to deshroud them the same too after all.

The top cylinder has oversize stainless intake valves and oversize inconel exhaust valves. The two chambers are actually machined differently. After Steve designs the seat profiles and the chambers see a second revision, flow testing will determine which chamber design to go with. Development can be super time consuming.

Mark the machining wizard set up the head on the CNC to do some initial cutting. Before actual port shape development is started, you have to start with consistent ports. This quick initial CNC cut will make all four ports consistent.

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Of course if you’re going to offer a nice CNC ported head, then you’ll have to offer a proper head gasket to go with it. The factory Mitsu 4B11T gasket is good and is better than any factory gasket we’ve seen, but they did some strange things on the sealing ring to improve sealing. Mitsu did achieve a higher sealing force, but at a price. Cosworth has designed a better gasket with not only even more sealing force, but a more consistent seal over time. Coming soon to a Cosworth dealer near you.

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