I am trying to locate some good reading on cathedral ports and why they are better, also canted valve heads and the effect of valve angle on flow and velocity through the port. Basically just some good hard info on head ports and what effects what and why type of deal. Im looking for some online reading for right now not books. Thanks

 

Your somewhat in luck, we are in the process of putting together an article on cathedral port heads for the new LSXTV. I hope to have it out on Monday.

 

Brad,
That sounds good, keep us posted. Also, welcome to the neighborhood!

Steve

 

what are catherdol ports?

 

Think of the ports in your head looking like an old church window or a short pencil

/ \
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this is what it looks like

 

I am by all definitions a complete noobie when it comes to something like this. When i think about a cathedral port versus a standard sbc port i think about buildings spaced far apart and close together. On a somewhat windy day taller buildings spaced closer together will have alot stronger wind between them (more velocity)

 

Don't kid yourselves. By far the largest reason that the ls1 had cathedral ports is so they would not have to use an offset rocker design.

I am not saying there is anything wrong with them, I am just saying that they were not used because they were "better".

Think about it, would GM have stopped using them if they were better????

 

Appears there is considerable reading material here...
http://www.google.com/search?q=Cylin...e7&rlz=1I7ADBR

 

I agreee, the cathedral port heads certainly are not the 'better' design. I have always heard that GM had the cathedral port to control an emissions issue with the injectors. Eventually they figured out away around it.

 

Yeah i head that it was a design they used to accomodate the physical aspects of the heads.

 

What most people don't realize is that the intake manifold is just a standard rectangle port, and that the olny reason the head looks like is does is to get the injector pointed at the intake valve... The region of the head that is "cathedral" has nothing to do with the flow of the head once the intake is bolted on.

 

Thank you for the link Old Geezer. That pro stock port looked crazy. Ok so if cathedral ports arnt making the port flow better, what is? Is it the valve angle? Properly sized ports whats the deal? I understand the Ls7 does not have cathedral shaped heads and flows a lot better then a Ls1 head so what is the key factor that makes that engine so much better. I am sure cam timing, exhaust tuning, and intake tuning play a role but i would think the head port would have the largest impact. Am i wrong to assume this? Thanks

 

Ultimately the ammount of air going in and out of a head is controlled by the size of the valve...LS7 heads were designed around the 4.125 bore therefore allow a larger valve with less shrouding.

 

Along the same lines...

What about the LS1 head was it that gave it about 50+ HP over the LT1?

Was it just a much bigger valve on the LS1 compared to the LT1?

 

Not necessarily. This applies to both statements.

Think like air. Good head guys do.



Jon

 

The valves act as gates to regulate the flow of gases in and out of the cylinder. The relative size and placement of the valves (axis and location) are all important. However, the routing (shapes/contours, etc) of the gases before, through the valve seat region and after are extremely important. The challenge of good head design is making the passage of very high velocity gases in and out of the cylinder as easy as possible and there are a number of good paths to this goal and many more paths or routes that are filled with encumbrances. Do some reading on fluid dynamics to get your heads into cylinder heads. Here's a tidbit of information with some references (not necessarily all of the references or even the best ones) http://en.wikipedia.org/wiki/Fluid_dynamics.

Steve

PS
There's nothing sacred about a cathedral port, just a resemblance to an architectural style. Also, if you want to read some about why the Sperry brothers designed the narrow and tall intake ports as they did, study Will Handzel's book http://www.themotorbookstore.com/ls1...8-engines.html. This book is the best single resource on the why and how of these small block (Gen III and IV) engines that I know of.

 

Steve,

The boldface is mine. If you look just at that, does it give you ideas?

I'm not sure if you meant "paths" or "encumbrances" physically, but I think taking it that way is useful in a study of what works and more importantly WHY it works.

"Think like air."

Jon

 

Jon,
Yes, I did mean physical paths and encumbrances, but I also think that it's important to think in a metaphorical way if one ever wants to think out of the box. If someone is trying to learn about this sort of thing (fluid dynamics in general and routing a lot of gas into and out of a cylinder in specific) some study will be involved (actually, over a period of years if you want to get into the details). The goal of moving large quantities of gas molecules (which do have mass) at very high velocity around physical barriers is a daunting task.

Steve

 

A little known secret of most engineering student is if you want to have fun learning fluid dynamics, use a beer bong! Seriously, thinking like air is your best bet, think about what it's like to have to try running but need to start and stop when valves open and close, now add turning corners, through changing shapes, ect.