LLLosingit

iTrader: (4)

Ok, So on the dyno under full load there is around 10ft lbs difference and cruising your at light load so your looking at 2-3 ft lbs difference if that.
Even a 10* temperature/baro swing would change power output more than that, Your butt dyno must me pretty damn sensitive lol

JoeNova

The LS3 has more compression, more displacement, and a more aggressive tune. It should have had a LOT more low end than the LS2, but it didn't.

pantera_efi

iTrader: (1)

OK, as we know the GEN-III LS-1 engine had MANY PROBLEMS.
The Truck Engine (LS-7) was designed in that era with improvements though many problems were found especially with the head/camshaft fix/valve distance from wall.
The LS-2 was designed later from those learned improvements.
The Hendrick Head engine (L-92 & LS-3) was an IMPROVEMENT of the LS-7 by the NASCAR Engineers.

My CHOICE is based on requirements though when possible I FAVOR the LS-2 head.
I LIKE the HIGH SWIRL smaller port, valve placement, rocker arm placement of the LS-2 design.
The "smaller" port has a higher gas velocity allowing for a larger intake lobe at the same torque.
The LS-2 "HIGH SWIRL" design is GREAT for a Turbo/SC engine with BIGGER Exhaust valve size possible.

Lance

G Atsma

Don't you mean the LM-7?

HioSSilver

iTrader: (8)

All ls stuff don't come until 3500rpm. Maybe it's your combo if you can't get past a soccer mom.

redbird555

iTrader: (14)

The ls3 actually has less compression, 10.9 vs 10.7. It has 12 more cubes and no it doesn't have a more aggressive tune. The ls3 knock sensors are VERy conservative and so is the timing.

So basically you have an engine with 12 more cubes that makes better power everywhere and dominates the ls2 when the both go cam only....

If you're going to make an argument for cathedral heads like you seemed to try a different metric because it does not look good at all

KCS

iTrader: (20)

Fine I'll bite. My old 6.2L combo with 241 heads and an LS1 manifold made 420ft-lbs at just 3000RPM on a Mustang dyno. Cam only LS3's would typically make 30-70ft-lbs less on the same dyno.

Tuskyz28

12 cubes difference is worth a estimate of 20 horses alone....

Take warmed over engines pump gas makes 1.5 horse per cubic inch.

99 Black Bird T/A

iTrader: (4)

I may have my LS3 and LS7 design comments criss crossed based on Pantera EFI's comments. I stand corrected.

In all seriousness, I do think the LS3 head is better for 5500 rpm up performance and racing than cathedral ports. However, the cathedral has proven itself excelling in the 5500 and lower rpm. I drive more in the under 5000 rpm range. In a race only engine sure go big LS3/LS7. The majority of dyno results that I've seen that were apples to apples or close seemed to back this impression up.

It's really Windsor head vs Cleveland head argument to me.
I have an acquaintance that for fun filled in the ports on a Cleveland head with epoxy and improved street ability, throttle response and horsepower. The stock LS3 runner could likewise probably be improved by carefully filling at least for stock 376 cube applications. I guess that's to be expected since the port was initially designed for 427 cube initially.

I'm probably joining the "LS3 club" with my 416 build - the LS3's are not the Trick Flows I want but it's what my budget can afford. I do wish I had never purchased the ERL 416 and just built a LS2 403 I'd planned and kept the cathedral heads.

Besides giving an LS3 a beat down with LS1/LS2 stuff is just as much fun as stomping an LS1/LS2 with a mid 90's LT1 or mid 80's TPI or a carb'd small block chevy

Variety is part of what keeps the car hobby fun.

BTW - LS3 intake manifold is excellent and better than its factory cathedral counter parts. It's the one bright spot in having to go to LS3 heads for my 416 build.

99 Black Bird T/A

iTrader: (4)

That's a down right ugly curve.
Would love to see that it made at 2500 rpm

NAVYBLUE210

My .02, on stock LS3 heads is that they have been mis-cammed
so often they have gotten a bad rap. On a 4.0" bore or larger
with 3.62" stroke compared to stock 243s
6-8* less intake duration for the same RPM
range seems a good place to start, with ~+8-12* Exhaust
Split NA, ie 228/234 for 243s becomes ~222/230 for LS3s
235/243 becomes ~229/239, as RPM increases split increases.
this is with long runner plastic intakes, and efficient exhaust
systems.

big hammer

But it makes more low end torque and more torque per liter

JimmyGTO

My car drives fine while cruising LS3 head/LS2. cam 230/238.

Martin Smallwood

iTrader: (2)

Guys, it's not cathedral versus rectangle/square. It's not the entrance shape to the port, although square/oval ports are better than a cathedral shape for a port.

It's the AREA of the port and throat that matters the most, period. All ports are limited by their MCSA (minimum cross sectional area).

Repeat after me, A-R-E-A...

NAVYBLUE210

JimmyGTO
Nice curve! What is your Compression,Header Size, & LSA?

Hmm +8* Exhaust Split......

KW Baraka

iTrader: (7)

I realized that a couple of weeks ago.

Exactly my sentiments!!! And it doesn't have to be "a truck engine" to do that, either

KW

JimmyGTO

compression 11.2:1, 1 7/8" Kooks headers, Cam Motion cam 230/238 duration, .626" lift 113 + 3.

Tuskyz28

I'm go say you wouldn't want to see what it made at 2500 rpm..... probably the same as stock ls1 at 2500 rpm

Navyblue..... we all know the LS3 head is the most poorly misunderstood cylinder head it is but after all NO ONE I've seen has yet to figure them out. Aftermarket.... a different story.

64post

iTrader: (5)

A lot of good arguments here for each side. Still contend that a smaller group know how to get the square port to work well vs. the cathedral in the 370 to 416 c.i. range. If your building a motor in that c.i. range and can't afford to get it wrong.......cathederal

SoFla01SSLookinstok

This may be what's in hammers mind:

Cathedral=tow truck
Square/rec port=race car

No in between...