700lb-ft and 43PSI at 4,000RPM | 4G63 Head Cylinder Sealing Julian Godfrey [TECH TALK]

You can make as much power as you want with a high boost turbocharged application, but if you can’t seal the head to the block correctly it’s all for nothing.

Julian Godfrey runs us through building a 4g63 rallycross engine that uses a 45mm restrictor plate and the challenges that presents when it comes to hitting 3 Bar of boost as low as 4,000RPM. Explained is how the 700 lb-ft of torque that can be produced at those low revs is in the cylinder for longer due to the slower piston speeds in comparison to high boost and high revving applications. This means the pressure in the cylinder remains for longer, causing flex and putting everything under more stress particularly the head gaskets.

Touched on is some of the testing Julian has done in regards to bigger head studs and how for this 4g63 application they made things worse until the fitment of a 12mm steel plate for added strength, which comes with its own complications relating to cambelt length and manifold positioning. If you're still trying to put the name and face together, note Julian is well known for is work with YB Cosworth engines in the likes of Ken Blocks Ford Escort Cosworth, RS200 builds and more.

Also discussed by Julian and Andre are cylinder liners, aka sleeves and the NIKA-steel and Titanium nitride coatings required for steel to steel contact, the benefit of a longer rod relating to component stress along with a little knowledge bomb on how 2 head gaskets together proved a great solution for this specific setup rather than going to the time and expense of o-ring style sealing.

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