"symmetrical" head description?

[Circlotron]

Why are heads with the valve layout IEIEIEIE called symmetrical? That word is for something that is mirror image about a centre line. The only heads I can think of that would qualify for that description are early Holden 253 / 308 CID that are IEIEEIEI.

[Stan Weiss]

Why are heads with the valve layout IEIEIEIE called symmetrical? That word is for something that is mirror image about a centre line. The only heads I can think of that would qualify for that description are early Holden 253 / 308 CID that are IEIEEIEI.

For me examples of Mirror would be EIIEEIIE or IEEIIEEI.

Stan

[SchmidtMotorWorks]

Why are heads with the valve layout IEIEIEIE called symmetrical? That word is for something that is mirror image about a centre line. The only heads I can think of that would qualify for that description are early Holden 253 / 308 CID that are IEIEEIEI.

It is a misused word.

[Circlotron]

Why are heads with the valve layout IEIEIEIE called symmetrical? That word is for something that is mirror image about a centre line. The only heads I can think of that would qualify for that description are early Holden 253 / 308 CID that are IEIEEIEI.

For me examples of Mirror would be EIIEEIIE or IEEIIEEI.

Stan

Oh yeah, my bad. Lots of different ones.
Looking further, it seems that symmetrical refers to the port size and shape, not it's position as I thought.

[midnightbluS10]

I always thought it referred to the fact that every port has the same shape, there are no "bad" ports and because they're spaced evenly on the head and not the standard 2-2 intake ports and 1-2-1 exhaust ports that you find on any oem gen 1 head.

[Walter R. Malik]

Why are heads with the valve layout IEIEIEIE called symmetrical? That word is for something that is mirror image about a centre line. The only heads I can think of that would qualify for that description are early Holden 253 / 308 CID that are IEIEEIEI.

I think it is based upon "symmetry" as all the cylinders seem to be exactly the same;
but, usually there are some small differences between them which are not obvious.

[CamKing]

I always thought it referred to the fact that every port has the same shape, there are no "bad" ports and because they're spaced evenly on the head and not the standard 2-2 intake ports and 1-2-1 exhaust ports that you find on any oem gen 1 head.

Yes, it refers to the ports. The ports are symmetrical. You don't have 2 ports curving to the right, and 2 ports curving to the left.

[Walter R. Malik]

I always thought it referred to the fact that every port has the same shape, there are no "bad" ports and because they're spaced evenly on the head and not the standard 2-2 intake ports and 1-2-1 exhaust ports that you find on any oem gen 1 head.

Just think about the big block Chevy Mark IV head for a few minutes;
All the valves are spaced equally for a I E I E I E I E to be symmetrical ... yet, 2 intake ports swing to the left and 2 intake ports swing to the right, therefore it is not readily referred to as a symmetrical head.

Now, a big block Ford head is usually referred to as being symmetrical.
Although it is not really. However, all the intake ports do swing the same direction ... simply 2 of those ports have slightly more swing than the other 2 for slightly different port spacing at the flange but. without actually measuring them, they look to be the same.

[englertracing]

Whats really funny is the only one that is by defenition symetrical is the sbc head, fold it in the middle, its the same on both sides.

[engineguyBill]

Good example of a "non-symmetrical" head is the OEM big block head which has two distinctly different design/shape of exhaust ports in each head. Current aftermarket BBC heads have symmetrical intake ports and symmetrical exhaust ports, therefore all of the intake ports are similar shape and size and likewise for all of the exhaust ports.

[CamKing]

Whats really funny is the only one that is by defenition symetrical is the sbc head, fold it in the middle, its the same on both sides.

That's only one definition of symmetrical (bisecting)

Here's two others, that would fit the Ford head.

: having corresponding points whose connecting lines are bisected by a given point or perpendicularly bisected by a given line or plane

correspondence in size, shape, and relative position of parts on opposite sides of a dividing line or median plane or about a center or axis