Dyno Numbers and Price List

Ccrp 1208 Ls Cathedral Port Vs Square Port Heads 01

Ccrp 1208 Ls Cathedral Port Vs Square Port Heads 10

The 317 and AFR 245 heads were run with the FAST LSXR intake designed for cathedral-port heads, while the LS3 heads received a FAST manifold designed for the rec-port configuration.

The 317 and AFR 245 heads were run with the FAST LSXR intake designed for cathedral-port h

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.

Ccrp 1208 Ls Cathedral Port Vs Square Port Heads 11

To ensure uninterrupted airflow, both manifolds received the same 102-mm Big Mouth throttle-body from FAST.

To ensure uninterrupted airflow, both manifolds received the same 102-mm Big Mouth throttl

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

	317		LS3		AFR 245
LIFT	IN	EX	IN	EX	IN	EX
0.050	32	24	33	27	36	26
0.100	66	53	75	61	73	56
0.200	140	102	157	117	156	112
0.300	197	145	223	161	227	166
0.400	236	171	273	190	280	201
0.500	240	185	307	205	319	220
0.600	243	191	318	216	349	230
0.700	244	197	307	222	330	235

*Flow Data: CF at 28 inches test depression

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FAST also supplied the 75-pound injectors and aluminum fuel rails used with the LSXR intake.

FAST also supplied the 75-pound injectors and aluminum fuel rails used with the LSXR intak

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

	317		LS3		AFR
RPM	HP	TQ	HP	TQ	HP	TQ
3,000	271	475	263	460	270	472
3,200	285	469	278	455	283	465
3,400	304	470	295	456	302	467
3,600	325	474	314	459	325	474
3,800	346	478	334	461	347	480
4,000	367	482	368	483	373	490
4,200	397	496	412	515	412	515
4,400	429	513	443	529	447	534
4,600	456	522	467	533	479	546
4,800	481	526	491	538	504	552
5,000	496	521	516	542	528	554
5,200	507	512	538	543	550	555
5,400	516	502	554	539	572	556
5,600	520	487	562	527	587	551
5,800	528	478	569	515	593	537
6,000	540	473	577	505	597	522
6,200	543	460	581	492	602	510
6,400	541	444	578	475	604	495
6,500	537	434	575	464	604	488

DESCRIPTION	SOURCE	PN	PRICE
AFR 245 heads	Air Flow Research	1680	$1,350 (each)
6.0L truck heads (317 casting)	Summit Racing	12572035	479.99 (each)
LS3/L92 heads (0821 casting)	Summit Racing	12629063	359.95 (each)
LS3 intake rocker arms	Chevrolet	12569167	94.00 (set of 8)
LS3 intake	Summit Racing	12610434	699.95
LS3 rocker-arm stand	Chevrolet	12600936	8.74

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All the heads were run with the same 13⁄4-inch, long-tube headers from QTP. The headers were run with MagnaFlow performance mufflers.

All the heads were run with the same 13⁄4-inch, long-tube headers from QTP. The headers we

➔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

With the 317 heads installed, our 408 stroker produced 543 hp at 6,300 rpm and 526 lb-ft of torque at 4,800 rpm.
With the 317 heads installed, our 408 stroker produced 543 hp at 6,300 rpm and 526 lb-ft o
Up next were the stock, rectangular-port LS3 heads. The additional port volume hurt low-speed power, but there is no denying the flow potential of these heads.
Up next were the stock, rectangular-port LS3 heads. The additional port volume hurt low-sp
The LS3 heads required offset rocker arms on the intake valves, but all heads were run with factory 1.7:1 ratio rockers. You can use stock LS1/LS6 rocker arms for the exhaust valves.
The LS3 heads required offset rocker arms on the intake valves, but all heads were run wit

With LS3 heads, power jumped to 581 hp and 543 lb-ft of torque. Though the LS3 heads improved both peak power and torque, torque production was down below 4,000 rpm compared with that from the 317 heads.
With LS3 heads, power jumped to 581 hp and 543 lb-ft of torque. Though the LS3 heads impro
Impressed as we were with the flow numbers and power gains offered by LS3 heads, we couldn’t help but wonder how they would compare with a set of dedicated, aftermarket cathedral-port castings. AFR’s 245 heads offered not only exceptional peak flow numbers (349 cfm) but also smaller combustion chambers, which increased the static compression ratio.
Impressed as we were with the flow numbers and power gains offered by LS3 heads, we couldn
This final head swap of the day netted the best power numbers. The AFR heads demonstrated that you don’t need to have rectangular ports to make big power by producing 604 hp and 556 lb-ft of torque. The 245s out-powered and out-torqued the LS3 heads through the entire rev range, indicating that not only is an aftermarket cathedral-port head an alternative to an LS3 upgrade, but one that will ultimately offer even more power. Add a matching cam, and the 245s will make even more.
This final head swap of the day netted the best power numbers. The AFR heads demonstrated