Oval Manifolds.

[Caito]

Hi guys!


Though I doubt that pic is F1, it serves the purpose. Ive seen several times exhaust manifolds which have the engine side of it with an oval shape. Whats the reason for the oval shape? Is the engine block oval too??


Thank you!

Bye

[Formula None]

Whats the reason for the oval shape? Is the engine block oval too??

Yes. See left side of this image, 2nd to last cylinder bank:



There's not much space between the exterior of the engine & the combustion chamber so they opt to not force the separate exhaust ports into one singular circular shape within that space, but rather in the manifold itself.

[Caito]

Interesting, thx for such a fast answer. Which leads to the following question, why do they join them in the manifold rather than in the block?

[Formula None]

Just thinking about the path of travel for the exhaust gases, the farther away your junction is between the two ports, the more gradual of a curvature you can achieve from exhaust port to joint. A larger radius sweep would be less restrictive than a smaller one.

[Formula None]

Does anyone know if structural integrity plays a role in this decision? Two small diameter holes with a wall between them would be stiffer than one large void in the cylinder head.







Although worth noting that they're not always obround at the entrance, so it might also be an issue of vertical clearance (oval shorter than circle of equal area):

[riff_raff]

Formula None,

With regards to twin exhaust ports specifically, the ports are kept separated in the head casting to allow coolant flow around the exhaust valve seats in the deck. This is an area with very high thermal loads.

riff_raff

[Formula None]

In the Cosworth V10 pic above there doesn't appear to be much of a gap between the ports for a coolant line, & the Renault's (also above) appears to be circular.

[Formula None]

For comparison, split & joined ports, both are F1 engines (1st is Cossie V10, 2nd I'm not sure of man'f):





It seems like the split is not for a coolant channel at port exit (although there is one there in proximity to the valve seats, regardless, as riff raff mentioned), but for optimizing the exhaust flow path and/or maximizing port area when height port height is limited (to my eye).

[Sayshina]

F-none, I would assume riff was talking about closer to the valve, yuou wouldn't want a coolant passage out by the manifold anyway.

There have been lots of engines that have tried both, and the usual comment from the designer goes something like "We tried (the other one) and it didn't give us any advantage so we went back. Seems to be yet another one of those designer preferences.