I'm wondering if it's possible to make a cathedral port head a rectangular port? Without running into issues! I would like to try this rather than go buy a expensive set of heads. Oh this is for a GM 6.0 lq4 thanks any answers are greatly appreciated !!!

 

No its not possible. Just have to pick which one you like better. What are your goals for your build ?

 

all the heads for LS motors are rather cheap in cost.

 

Rectangular L92 heads can be had used for a few hundred bux. Not exactly "expensive". Plus selling your old cathedrals will help offset that cost.

 

To be honest, I find that at less than 400 CI, the cathedral ports feel snappier - though I can't quantify it scientifically. They also seem to be less sensitive to cam changes. It might be worth considering a port and polish on your 317's and then mill them down to 64cc combustion chambers. Or a set of 243's.

 

Someone on here right now is selling both a pair of 799 heads and a pair of L92 heads

 

If you think port size is THE determining factor and bigger is blindly better drop the project.

 

I've yet to see a small cube n/a rectangular port engine run as well as it "should" locally.

Several people tried to convince me to switch to cnc ls3 heads when going from ls1 to ls2. I'm keeping my 799s and just getting more porting done. I'll take the extra velocity over the hogged out ls3 heads for a small cube street car 100% of the time. Surely wouldn't ever put rectangular port heads on a truck.

 

Look at the lq4 vs the ls2. Both are 6.0 L. There is a lot to be gained with high port velocity and improved compression without going to rectangular ports. Add a good cam, and you can be over 450 horsepower with very good reliability to boot

 

To my understanding, like the others have said, a rectangular port is more sluggish down low.

 

Il settle this debate when the small bore ls3's go on my LS6.

Remember, the square ports are MUCH more sensitive to how they're cammed. You can't cam it the way you would a cathedral port.

Do I expect 400lbft under 3krpm? Hell no. I don't really care how it feels under 3k anyway. When I want to really get on it, it'll be above that anyway, right?

I personally don't care how "snappy" it is taking off from a stoplight. I don't care to drive like that in town to begin with. Now around 4k I expect a rocket ship.

Just a thought, well, my personal feelings anyway.

 

If I had the money and time I'd dyno a factory ls3, then swap the heads and dyno again with everything else held as constant as possible. Probably find the torque curve is flatter on the cathedrals and peak power is higher on the rectangles. Make for a fun little science project.

In the end it comes down to how you plan to drive it, as always

 

Agree 100%

 

I would think the smaller valves would make for more throttle response.

 

One thing I believe gets lost in the rectangle/square debates is the rectangle ports came along I believe after everything went DBW which can be used to mask some lack of lowend response, but most folks in this section aren't modding DBW vehicles.

 

Agreed. Same with VVT.

 

If only the mods were done with their combos and could overlay the dyno graphs.....KCS seems to go cathedral/big valves on 6.1/6.2 liter combos and the DR has ultra kickass MAST rectangle ports (smaller C.S.A 240cc runner) for a 5.7 liter. Now if that super nice KIP fella would back door a couple of low lash rollers to minimize the variables here, I believe they are both stick cars with plastic intakes..........GAME ON tech junkies....

 

I'm still slowly but surely piecing my build together. Patience is getting thin though, lol.

 

I'm game. I've got 799's, L92's, and my Trickflows.

 

240cc is pretty small for a rectangle, heck there are companies opening up 243s over 230cc.