shakenfake

@Summitracing Why would we run cathedral ports instead of rectangle? I've talked to a head guy and he said nowadays he would just run everything rectangle. Any idea why? Benefit between the two that would push us truck guys to one side or the other perhaps?

arthursc2

iTrader: (5)

welllllllllllllllll

Rectangular heads don't fit anything smaller than a 6.0, for one thing hahaha

Secondly, its pretty well documented that cathedrals offer better off idle torque than rectangulars

So, a number of reasons that hold a lot of merit

shakenfake

Good thing I don't have anything smaller than a 6.0

Didn't know that second one though. I wonder why.

arthursc2

iTrader: (5)

Port velocity

and good thing the LS world doesn't revolve around what you own :lol;

shakenfake

That would be quite boring wouldn't it.

Summitracing

@shakenfake You pose a great question/debate. Like a lot of comparisons, "it depends" on the combo/scenario

Arthur made two very valid points. The rectangle port heads are only suitable for 6.0+. The reason is the valves will come in contact with the sides of the piston walls on anything less than a 4.000" bore. He's also spot-on with the argument that cathedrals are better for off-idle torque than the rectangle port heads.

Basically, it comes down to what the vehicle is being used for. Let's take trucks for example. If more often than not it's below peak torque we would stick with Cathedrals. This is where we typically find most of our truck customers spend their time. On the other hand, if you have a 6.0+ LS and you're building an all-out drag truck or just like to rev to the moon rectangle port heads are the way to go. As with anything, there are variables. It all comes down to the combo and goals.

Check out this article on our OnALLCylinders Blog on this very subject. There are plenty of other articles and videos out on this topic. Just hit up the ol' Google and type in "LS cathedral vs. rectangle port heads". Happy reading!

68Formula

In addition to Summit's very helpful article from their OnAllCylinders series, here's general article on the relationship between port velocity, runner volume, and cross-sectional area. https://www.musclecardiy.com/cylinde...tions-part-10/
Note the impact of torque vs port volume in fig. 10-13. Keep in mind, this is also engine displacement dependent.

Engine Masters video series also did a engine test with 3 different port sizes in a 408 Ford with a moderate (for it's engine size) camshaft. They also showed too small sacrificed peak power; while too large lost torque with no increase in peak power.