Kaltech Tuning

iTrader: (17)

There's been a lot of talk lately about GM's square port heads versus the Cathedral Port heads we've all become familiar with. Frankly the majority here seem to frown upon the Square Port stuff for a variety of reasons, many of which are based on false information. Here's a very good read I came across to shed some light on reality. The math here is the interesting part since it's hard to argue with numbers. Enjoy.

http://www.afdracing.com/square%20po...sx%20heads.doc

Isolde

iTrader: (4)

for performance above 3000 rpm, well, probably tolerable from 2500 on a 6.0L, the squares are great. But for those of us putting this cam: http://www.compcams.com/Company/CC/c...csid=1247&sb=2 in a 4.8L, and never running over 4500, the cathedrals may as well be squares.
My Fiero wants MAST squares on an LS3, but then again, it's an entirely different app. It's lightweight, very aero, and inherently overgeared, and that can't be fixed, so it'll get better MPG with large intake ports and late intake closing. But with a Z28 doing 1430 rpm at 65 mph, square ports can only hurt MPG.
Squares have their place, but so do cathedrals.

darkvader0

Thanks for posting this. I want to build a 4.125" bore 427 and so far have no idea what to top it off with.

camz28arro

iTrader: (12)

Good read, Looks like there is no downside to square ports besides it's just not as understood yet with cams.

Stage7

iTrader: (1)

Is that Dennis from Air flow development?

hirdlej

iTrader: (31)

Yes it is

98Aggie

iTrader: (19)

He needs to do the math or flows at lower lifts to see what it does not just max.

Cylinder heads are intersting. Jon Kaase has some heads that for BBF that are completey different designs but flow the same cfm. One heads makes 100hp more than the other on the same motor. Wonder what would cause that. Chamber design, port design? Makes you wonder - got to be something simple math can figure out.

Isolde

iTrader: (4)

I went and reviewed the Oct. '07 and Nov. '07 issues of HotRod. If you compare test D against test N, you find that just switching from #317 heads and LQ9 intake and cam, with Dynotech headers, to #364 L92 heads with L76 intake, costs 26.9 ft-lbs down at 1600 rpm. And the L92 heads continue to give less torque on up to 4300 rpm.
If you're running a 4,000 stall converter, then this means nothing. But if you have a pickup, in which the stock converter seems to be a 1,400 stall, then the cathedrals are the only way to torque.

Josh18Fan

iTrader: (2)

Can all of this be attributed to the cylinder heads? Did they start with a truck intake on the LQ4 and move to a car intake (L76) when they went with the L92's? Truck intakes have always been known to produce more torque down low than car intakes, and may skew your numbers a bit for that reason. If they started with a car style manifold (LS1/2/6 on LQ4) and changed to a car style manifold (LS3, L76 on L92's), then my point is null and void, however.

Kaltech Tuning

iTrader: (17)

That's one of the beauties of this article, the math is right there for anyone to use with any cylinder head data they have. Many here claim the square port stuff is sluggish and won't make power. While I haven't actually sat and ran the math for all of the flow numbers and such that I have but I have driven new stock trucks and cars with square port heads and once you ditch the torque management they don't feel sluggish to me, especially compared to stock ls1's.

So then GM has just screwed everyone by ditching the cathedral port heads in favor or square port stuff on the new vehicles?
All the new trucks have square port heads. Are you saying with emissions and fuel economy concerns the way they are GM is going to give up all of that low end torque to get those new trucks moving? The new trucks get better fuel mileage than the old ones.

Patrick G

iTrader: (14)

As you know, GM still uses cathedral port heads for the majority of their trucks (which run 5.3L and 4.8L engines). The early 6.0L and 6.2L truck engines with square port heads got less than stellar fuel economy until GM added cam phasing. VVT is one of several reasons (AFM/DOD being another) why the cathedral and square port truck engines have made recent gains in fuel economy. Just wanted to add that tidbit of info.

mike c.

iTrader: (1)

DARKVADER0-Top them with a set of t.e.a trickflow 235cc heads with a 11.8 compression. Thats my dream one day..

malibutwins

iTrader: (1)

I wonder why GM would spend $$ designing a new cylinder head. The l92 head flat out works. "Liars can figure but figures dont lie"

FastKat

iTrader: (10)

Are there any indicators pointing towards GM switching to square port heads for their 4.8L and 5.3L engines?

Patrick G

iTrader: (14)

Not with the current large valve configuration. The 2.165" intake valve is too big for the 3.78" bore of the 4.8 and 5.3" engines. It would be too much bore shrouding. Look for a scaled down version of the rectangular port or a higher flow version of the cathedral port in the future. Perhaps a "mosque" style head.

Isolde

iTrader: (4)

In the October issue, test D was nearly identical to test N, with the fewest parts changed, just intakes, rockers and heads, nothing else. Test D was the truck intake, test N was L76. Test E added catalytic converters, which seem to have stayed on for tests F, G, H, and I, but come back off by test N. Test E kept the truck intake. F was the Ls1 intake, G was LS6, H was LS2, and I was F.A.S.T. 90mm. The 90 was down by 4.3 ft-lbs at 1600, but even so, theL92 heads still cost 22.6 ft-lbs.
If you want more, check www.gmperformanceparts.com for links to the relevant articles.

Isolde

iTrader: (4)

So just imagine the almost-decent low-rpm torque that should arrive if they ever grow enough brains to put the #799 heads on a VVT 6.2! I want that in a 2WD, SWB, 2-seat Silverado 1500 sport truck, with 6L90E and true-locking 3.42:1 14-bolt 9.5". Or better yet, a TR6060!

FastKat

iTrader: (10)

If I was a little less mature/politically-correct I could really take this one and run with it!

Josh18Fan

iTrader: (2)

Good info. I'll have to check out all of their numbers.

SHovV

iTrader: (1)

cathedral and square port heads each have thier own +'s and -'s given certain engine combonations. there are combos where a cathedral head will out perform a square head and vice versa. neither head is hands down better 100% all day every day