I was referring to his HC 241s which when welded and recontoured but don't look like a 243/799 chamber
Id highly doubt that he would invest the magnitude of time to weld a 317 chamber in order to use a 243/799 CNC chamber program. I guess I've never held all these in my hands to look at though

 

At one point welding up the 317 chamber to use the 243 cnc program was an option, looks like it is no longer on the website.

 

So nobody else finds it interesting all the advantages the LS3 has over the cathederal engines?

 

For some applications, there are obvious advantages offered by the rectangle port heads. You are correct, sir.

 

And a 6000rpm 6.2l is NOT it.

 

The 376" air pump is 8.67052 % larger than the 346
The 2.165" intake valve is 8.25 % larger than the 2.0"
The 305 cfm of peak airflow is 15.09434 % more than the 265 cfm of 243 heads
The 261 cc intake runner volume is 24.285714 % larger than the 210 cc 243
IIRC you said 15 % larger throttle body
and the compression ratio increases from 10.45 to 10.7 roughly 1/4 point
cam specs are similar intake side but the C5Z cam does have a few more degrees on the exhaust side
C6 Vette with dual mode exhaust option has 436 horse and the C5Z is 385 (01) and 405 (02-04) representing an increase of 7.654321 % increase
Apparently either GM gave us a cylinder head that would/could make crazy power in cam only form if a proper stall converter was to mask the soft under 3500 rpm port speed or perhaps they already knew that the direct injection was coming and that the air speed would no longer need to be responsible for maintaining an atomized fuel mixture.........
After holding an 821 head in my hands and really looking at it good; I feel it's a pretty darn good design, BUT......the larger the air pump you can afford to stuff underneath it, the better it will be. I'd love to see a set of AI exhaust only ported heads on a 454 LSX with a Cam Motion LLSR and an old school Holley 9375 Annular discharge Dominator.....But that's just me..

 

Pat G simply have told me you have to understand that these heads are not ideal for a 4" bore. The big 2.165" intake valve is slammed right next to the chamber wall and cylinder bore. He was simply speaking upon the LS3/L92 head.

Brian Tooley simply mentioned in a old thread that the LS3/L92 head is very sensitive in overlap events.

I study all motor combos probably more than any other member on here and what I tend to see out those big heads the cam specs/combos seem to be hit or miss. Guys that run the fastest with those heads won't share their cam specs either.

 

Go back up to post 12, then consider the 317 vs 243 discussion. Then even on a stoker the losses are all the way to 4000.

I think we are looking at 20hp more at peak with big losses below 4000, causing a need for more gear or stall. And it isn't the "cam" as is so often blamed. Hell there is a mast vs mast cathedral vs rectangle test and the flow of the rectangles makes no more peak and even all aftermarket the torque loss at lowend is there.
It is all about a peak number at the expense of average.

 

I seen the test in GMHTP.... Richard mentioned something about coefficient and discharge. He simply was referring to how the cathedral heads basically was the winner out the test that was done.

 

Is this another cathedral vs rectangle port argument?

 

I think so

 

No, I think it's technically a ls6 vs ls3 argument... But being as how one pretty much replaced the other, I think the answer has been given to us.

Do I personally prefer the cathedral port heads? Yes, I do. I prefer average power over peak power, any day and all day. Am I saying that the cathedral port heads make more average power than rectangle port heads...? Nope. Just saying that I prefer the cathedral port heads, and I happen to also prefer average power over peak power.

Honestly, it's all pushing dirt with a different type of shovel. Which design is better? Probably neither, depending on what monkey is choosing the parts to be assembled, and equally dependent on the abilities of the monkeys doing the actual assembly of those parts.

 

I think dude is more so asking if we all think the LS3 design justifies itself.
If the LS6 is making 405 horse from 346 inches or 1.17 per/cid then a 376 should be 439.92 horse right ????
15 % more throttle body with 15 % more head flow from 24 % more runner volume and similar compression and cam timing yet ONLY 31 more factory rated ponies.
I'm gonna crawl WAY out on a limb here and say Dwayne is not a fan of the big ports.....even though IMO his new SS does scoot pretty darn well

 

I don't think the increase in performance justifies the amount of change. Or, rather, I feel that a design change of this magnitude should have yielded a larger increase in performance.

PS. I, too, am not impressed by the large volume ports.

 

The SS ran 13.1 at 107 the one pass I made with 1200 miles on it TC off let it shift normal. 1.9 60ft, it hooked. Gearing is similar to a 4L60E car with 4.10s.
Power is very soft, I know that can be modified some with tuning.

Gets a decent ET with the peak HP number. My Caprice ran 13.2 at I think 103mph with a lot less peak HP, more weight, less gear 3.06first/3.42rear compared to 4.03first/3.27rear and a 2800stall.
Caprice was b-body LT1 10:1 compression iron heads with a ZZ4 crate motor cam 208/221 .474/.510, Dyno'd 290rwhp.

The SS chassis is great, the LS3 is great unless you have driven something with good torque at low rpm, then you know what it is missing.

 

Yeah, the rectangle port heads seem lazy until you have a 4" crank and 400+" under them.

Even the BIG aftermarket cathedral port heads have smaller volume intake ports than the stock ls3 heads. And if the motor is under 400ci, then I imagine you will be hard pressed to beat a good cathedral port head in average power.

I think the gigantic intake port volume of the rectangle port heads works well with positive displacement blowers. The blower moves volumes of air, and the large volume ports facilitate moving that volume of air into the cylinders. You need massive amounts of volume, because the additional volume HOPEFULLY equates to more mass (obviously dependent on density).

For naturally aspirated engines and turbo applications, I feel the smaller cross sectional area ports have the advantage do to port velocity. Turbos are mass moving devices, they don't need large volume ports. When dealing with a set mass, more volume equates to less density.

 

David, since you just said in another thread how displacement would help make more power how much power do you think LS6 cam, 243s on a LS3 shortblock would make?

 

Probably about the same as the ls6 h/c/i make on the 383 stroker motors out there using that combination.

Ls3 is 6.2L, 383ci is 6.3L, both max out what the oem ls6 heads and cam are capable of producing (with the 243's in stock form). It's usually in the high-mid 400's @ the wheels. Different cam and the same stock 243's on this displacement nets 500+rwhp. Port the heads with a good cam and you can obviously get more.

If I had to guess what a stock ls3 shortblock would make with ls6 heads, cam, and intake, I would say 450rwhp in a typical combo. I think that's about all you can expect from the ls6 cam when using 1.7 rockers. Some slp 1.85 rockers MAY actually help take advantage of the extra displacement, and you may be able to get a little more out of an otherwise typical setup.

And it would be an absolute missile up until ~6200rpms, the throttle response would be borderline epic. That's the thing about having enough displacement to max out your heads, everything down low is just crisp, that's the best way to describe it.

 

Here is the story you mentioned, one of my favorites.

http://www.superchevy.com/how-to/ght...-head-to-head/

 

I posted the graph from that in Gen IV yesterday. Two issues with that test: 1) the 4.030" bore doesn't help the LS3 head and it's huge valve. 2) the FAST intake manifold is garbage.

It homogenizes the performance so bad that it essentially creates the same result.

The real test would be to put a Super Victor on both with a single plane cam. I bet there's a 30+HP difference and no visible change in torque between the heads. Torque would be down vs the FAST, but power would be up significantly for both heads. Add a solid roller to the mix and you have even more of a runaway for the rectangle ports as the RPMs keep climbing.

Now, does that equate to best "street" head? Not really. But it does show a clear advantage on that type of motor. And that's where the rectangle port head is worth it.

I will say this - 1.55 to 1.60HP per CID is a rule of thumb that Tooley threw at me the other day for plastic stock style intakes and hydraulic cams. I went back and looked at just about magazine article and engine dyno I could find. It holds up well regardless of the combination. It's just physics.

But move to a single plane and solid roller and it moves up pretty significantly. To something more like 1.75HP per CID.

I think what we need are better intakes that don't choke out the heads. No aftermarket intake that isn't a Beck, Victor, or MAST intake even comes close to matching these insane flow rates of these new heads. It's where the next revolution needs to come. Then, you'd see more out of any of the heads you're looking at. Otherwise, stick with 243s and port them. TEA 243s hit 625HP with the same cam and 408 setup for Hot Rod as the MAST heads did when they hit 630. So did TFS 235s, PRC 237s, AFR 247s... etc etc. The FAST just kills the heads. Everything was within 10HP of everything else.