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O-ring receiving groove? and Cosworth headgasket question.

Engine Building Fundamentals

Discussion and questions related to the course Engine Building Fundamentals


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This question applies to my evo 8 4g63 engine. I do not have much experience with O-ringed engine blocks, so my question is, does the cylinder head require a receiving groove to make a good seal?

Also, I was looking to purchase the Cosworth head gasket. As I read the product description, it read "Cosworth gaskets feature a "stopper" sealing layer for additional torque around each cylinder. The width of sealing area is specific for each application thereby providing ultimate sealing properties."

I assume this "stopper", acts like an oring that has been "built in" to the design of the headgasket, So I wonder if this "stopper" sealing layer would cause any issues with a engine that has been already o-ringed?

Just saw something on that a day or two ago - IIRC, the Cossie H/G effectively incorporates an "O" ring in the centre part, as you surmise. There was also mention that this type gasket should NOT be used with a conventional "O" ring as fitted to a receiver groove, as it would prevent the oil and waterways from sealing properly.

There's a variety of techniques employed with o-ringed blocks so there isn't a 'must do' technique I can offer, but rather I can tell you what I did. First of all the o-ring with receiver groove technique is mostly employed with copper gaskets in pro mod, top alcohol and top fuel drag applications. The idea is that the o-ring deforms the soft copper gasket into the receiver groove. I've tried this on a 4G63 and it was completely ineffective.

If you're using a MLS style gasket then I wouldn't recommend the receiver groove. You won't deform a steel gasket so the receiver groove won't help you. What I personally did with our drag engines was machine a groove into the block for a 0.051" stainless wire ring. This needs to be a light interference fit of about 0.001". The groove was machined to provide around 0.006" protrusion into the gasket. I used this in conjunction with an HKS stopper-type gasket and it was good for 55 psi boost and 1166 whp. It wasn't however infallible.

The technique that most high boost engines are using now is a copper gasket to seal oil and water (although it's not actually great at doing that to be honest, coupled with an aluminium-bronze sealing ring that is located into an groove around the top of the cylinder. This takes advantage of the thermal expansion rate of the aluminium bronze to help seal the head and has been used in Colin Wilshire's Jett Racing Eclipse which runs in excess of 100 psi and makes in excess of 1900 hp.

The solution all depends on how much power and boost you need to support.

I've utilised wills rings (more commonly in our industry just referred to as gas filled o-rings) with success in the past but they are expensive and the lead time on manufacture is killer. It seems that the big boost guys have moved towards the aluminium bronze sealing ring which is a fraction of the cost and seemingly superior. One issue with the wills ring is that they are designed for sealing under a static pressure such as they would experience in the nuclear power generation industry. They aren't ideally suited to cyclic pressure like we see in a combustion chamber, even though on paper they are capable of sealing much higher pressures than we will ever experience.

Thank you both for answering my questions. I really do appreciate it.