Inlet port

General engine tech -- Drag Racing to Circle Track

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Inlet port

Post by Ratu » Wed Oct 11, 2017 2:04 am

I was asked to help a friend fix his car by his wife. She figured he was in a bit of trouble with it and I figured he has a good beer fridge in his garage- so why not. Anyway, I get over there and he seems to be doing AOK. This car is a Ford Crown Victoria which he had managed to import from the USA. I understand it had been in American Samoa at one point and then went back up to sunny California. Neat. The car has an old 4.6 litre V8 engine with sohc per bank. We got the heads off it and found our problem. Head gasket failure, which I reckon was from the car being overheated big time at some point. Impressive it still ran. He said it ate water but that was about it. Well.....OK. So, I got to do the bench work and took the heads apart while he got under the car to attend to another task.

As is well know the 4.6 sohc heads are an unusual cylinder head design with the wedge the wrong way around. The valves tilt outboard, which is the opposite sense to conventional US wedge chamber V8 practice wherein the valves tilt inboard. They are closer to the sohc Porsche 928 layout than anything else I recall seeing. In the past I had wondered why the Ford designers chose this layout, as it does make the engine somewhat wider than it would otherwise have been. There have been claims from Ford that it flowed better that way, reduced spark plug temperatures and imparted better motion to the fuel/air mix in the combustion chamber. Fair enough I guess.

I took the heads over to a local machinist and they are off to the races now. All good and I know they'll do the job right.

After coming back here and cleaning up I got to thinking about these cylinder heads and in particular the inlet ports. Now these ones are not as direct as the Porsche 928 ones. Those on the 928 come in from high up and you can see most all of the back of the inlet valve through them. The Ford port comes in a little lower and the valve is not visible in the same way as with the 928. It is a smallish port, but then again, it was not intended to be swallowing enough air to make a big amount of horsepower (I think it has around 200 bhp or so). Prabhat reckons he was told there is 300 bhp to be had, which, if he is right, is not bad for a 4.6 of this nature.

OK, I've digressed a little. Here is what I was wondering. Putting aside that Ford 4.6 for a moment and just considering the idea of the inlet port for an opposite leaning wedge. How well does this layout lend itself to good flow and mixture motion? It looks weird to me in that it is the opposite way around, but the fact that Porsche used it (prior to emissions laws propelling them into four-valves design) suggest there is something to this. Also I notice that various outfit in the USA have configured modified engines in this manner. I think Mickey Thompson did it and also there was a conversion to a big block Chevrolet done by GM which had the inlet coming in from the "wrong" side of the wedge. So what are its characteristics?


Ron E
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Re: Inlet port

Post by Ron E » Wed Oct 11, 2017 8:27 am

I agree with you. Very strange layout. I do know that Trick Flow has reversed it by having the valves toward the center of the engine instead of outboard the cam. And, pretty major flow gains were seen. So, I still don't know what, if anything the layout in stock form had to offer.

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