Cathedral vs Rectangular Port in FI
 

What is everyones opinions/knowledge on Cathedral (LS1/2/6) style heads versus Rectangular Port (LS3/7/9) when used in Forced Induction Setups.

Are they going to add a noticeable HP increase? Is there any reason to try and use Rectangular heads now that they are more readily available? I am asking because the engine I want to start my build up on is limited by the intake manifold design, which is only available for the standard cathedral port right now, and it could be up to 8 months before a LS3 or LS7 style manifold is on the market.

If this has already been discussed, could someone provide a link. The search didn't find anything.
Thanks

depends on what size engine your building,what you hp goals are etc,

427 LSX with about 13-15psi on pump gas (hoping for 900+ RWHP). The pump gas is the factor that limits me, so I want to maximize the rest of the setup to make the most power. If the rectangular port heads would only net me a couple percent gain in HP, then they really aren't worth waiting 8-9 months for.

This is just Andrew's theory. Forced induction = the biggest port you can get! Velocity goes out the window really when you are cramming 15 psi or more boost in the intake track
? Am I wrong to assume that the biggest port (rectangular) possible would be the best? Someone technically explain to me otherwise.

Greendragon - If you are going PD blower then good luck finding a manifold for a rectangular port.

Yeah that's the entire point of this thread, to know if it would be worth the wait for that manifold. I've talked with Mike at Kenne Bell a couple times and he has assured me that the rectangular port manifold is in the works. They didn't have a completion date, and it is already 3 months past the original release date it could be up to 1 year before it is out. I still have some time to get this engine together, but I don't know if I want to wait 1 MORE YEAR.

There are cathedral ports flowing 380+cfm at 265cc. I would just get those and enjoy the car why wait a year for a few more hp?

I wouldn't wait you can run five bolt cathedral heads and make 1000 rwhp why wait.

13-15 psi from what? Turbo or SC? Obviously 15 psi on a more efficient flowing head and intake will make more power than 15psi on a less efficient one. However, if it is supercharged, I don't think you will see any improvement with a rectangular over cathedral. Simply because you are forcing a certain CFM into the engine regardless of the head port design. So for example if you make 15 psi on a cathedral and 13 on a rectangular, the power would be the same.

Isn't the only intake available for use with rectangular port heads for a 427 LSX the GM carb style intake? I was told the GM intake isn't that great.

Go with ETP cathedral port LS1's with 6 bolts per cylinder. Thats what I'm using on the 427ci LSX + S91 that Weber is gonna build for me.

I'm pretty sure W2W went 6's with Cathedral heads :)

Thats what I was thinking. I am going to try my hogged out TPIS heads and see how it goes.

A good flowing set of cathedral ports heads will work fine for that power,i would recommend something in the 225-235cc range

Good thread i have been wandering the same. Have been thinking about building an LS2 just to run the l92 heads.

Thats what I have in the works, with FI its not AS important but I always thought that a nice set of cathedral heads will make allot of power. Screw the wait, not worth it IMO.

I'm in such a state of Limbo right now it is ridiculous! I have the money for this engine build, but I WANTED LS7 style heads and Kenne Bell has been slow to develop the manifold, and I WANTED an aluminum block and all the options available got VERY expensive to make the block "reliable" to the HP I want. My car also has a lot of prep work to be done before I even need an engine, like finishing the interior, the custom headlights, and other body work so I may just wait a couple more months to see if the stars will align and miraculously Kenne Bell will release the LS7 manifold and GMPP will release the Aluminum LSX and 6-bolt LS7 heads!!!

Hey I can dream can't I?

I hate waiting, but what's another 6-8 months when the project has already gone 2+years.

exactly!! Nothing wrong with dreaming and you never know what will happen.

Ive been considering getting new heads, I did a search and got this old thread. Just wanted to get some opinions since so much new development in the past year or so.

My understanding is that cathedral design flow a little more on the exhaust side, but with all these new rectangular heads coming out not sure but if it still the best choice for F/I.

how do they act versus one another on and off boost on street engine not an all out race motor?

A lot has changed just wanted to get new info with current developments

no input? still the same things apply? Nothing changed?

Well I like the cathedral design with FI for a Street car better. Because they flow alot more Exhaust and they Keep off boost driving manners very nice . Im using The PRC 237 heads. nice heads for a great price. You might make a little more power with the TF235 but i dont think its worth the price increase.


The rectangular heads flow a lot intake but doesnt matter as much when FI People have pushed stock ls2 heads with no porting in the 950 Rwhp Range So a PRC 237 with like 70 more Cfm of intake flow will get you plenty of HP
Both can make good power but i see some great numbers from the Cathedrals over a greater RPM range. Now for all out Power and racing a set of All pro ls7 heads would be great but they cost big. With a 270CC intake runner im pretty sure DD will be alot better with a PRC 237 head

i thought rectangular style flowed less on the exhaust?