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LS Heads: Cathedral-Port vs. Square-Port Heads

By Richard Holdener, Photography by Richard Holdener

Given the flow numbers and chamber volume, we assumed the AFR 245s would combine the low-speed torque of the 317s with the top-end power of the LS3 heads, but we got even more than we expected. With AFR 245s, our 408 produced 604 hp at 6,500 rpm and 556 lb-ft of torque at 5,400 rpm. Note that both peak numbers occurred higher in the rev range than with either of the two stock heads, but the seemingly high-rpm power was combined with plenty of torque. Not only did the AFRs produce the highest peak torque output (556 lb-ft), but (like the 317s) they easily exceeded the torque production of the LS3 heads below 4,000 rpm. With the exception of a merge at 4,200 rpm, the AFR 245s out-performed the LS3 heads through the entire rev range, with gains of 20 to 25 hp at the top. Truth be told, both the cam timing (skewed for rec-pot heads) and the bore size (AFR 245s were designed for 4.125-bore motors) likely hindered the 245s on this application. The airflow numbers suggest the 245 heads will support more than 700 hp, and we have seen big-bore combinations that verify this fact. The question now is: Does it make more sense to perform an LS3 head upgrade or go with a set of aftermarket cathedral-port heads? The aftermarket-head approach is a lot more expensive, but this test illustrates that the LS3 head swap isn’t the only game in town.

Flow Numbers*: Stock 6.0L Truck (317) vs. LS3/L92 (0821 casting) vs. AFR

317LS3AFR 245
LIFTINEXINEXINEX
0.050322433273626
0.100665375617356
0.200140102157117156112
0.300197145223161227166
0.400236171273190280201
0.500240185307205319220
0.600243191318216349230
0.700244197307222330235

*Flow Data: CF at 28 inches test depression

408 Stroker Power Numbers: 6.0L Truck (317) vs. LS3/L92 (0821 casting) vs. AFR 245

317LS3AFR
RPMHPTQHPTQHPTQ
3,000271475263460270472
3,200285469278455283465
3,400304470295456302467
3,600325474314459325474
3,800346478334461347480
4,000367482368483373490
4,200397496412515412515
4,400429513443529447534
4,600456522467533479546
4,800481526491538504552
5,000496521516542528554
5,200507512538543550555
5,400516502554539572556
5,600520487562527587551
5,800528478569515593537
6,000540473577505597522
6,200543460581492602510
6,400541444578475604495
6,500537434575464604488

DESCRIPTIONSOURCEPNPRICE
AFR 245 headsAir Flow Research1680$1,350 (each)
6.0L truck heads (317 casting)Summit Racing12572035479.99 (each)
LS3/L92 heads (0821 casting)Summit Racing12629063359.95 (each)
LS3 intake rocker armsChevrolet1256916794.00 (set of 8)
LS3 intakeSummit Racing12610434699.95
LS3 rocker-arm standChevrolet126009368.74

➔Sources:

Air Flow Research (AFR); Valencia, CA; 877/892-8844; AirFlowResearch.com

Comp Cams; Memphis, TN; 800/999-0853; CompCams.com

L&R Automotive; 562/802-0443; LNREngine.com

Moroso; 203 453-6571; Moroso.com

Probe Racing; 310/784-2977; ProbeIndustries.com

Procomp Electronics; 909/605-1123; ProcompElectronics.com

By Richard Holdener
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