Swirl port heads were designed for bottom end performance, mainly torque. They are stock truck heads and not performance heads. They have restricted air flow that becomes a problem after 4,000 RPM. Used in their original application as a high torque bottom end head in a truck for towing the do fine. These heads come on GM truck engines P/N 12568758 and P/N 12520270.

Chevy '441 Iron CHP 155/62 1.940/1.500
-
Pipe 76 55/45
81.82% 110/83
75.45% 160/118
73.75%
54.13
66.77
160.4
197.8
329 hp 194/133
68.56%
65.63
75.26
194.5
223.0
399 hp
433 hp 201/146
72.64%
68.00
82.62
201.5
244.8
413 hp
449 hp 203/148
72.91%
68.68
83.75
203.5
248.2
418 hp
453 hp
509 hp 173.6/125.6
72.35%
1.310/2.387

Chevy '461 Iron 161/63 2.020/1.600 64 - - - - 216/137
63.43%
67.40
68.14
199.7
201.9
444 hp
482 hp - N/A
N/A
1.342/2.175

Chevy '882 Iron CCM 151/59 1.940/1.500
-
No Pipe 76 70/58
82.86% 125/108
86.40% 175/135
77.14%
59.20
76.39
175.4
226.4
360 hp 204/141
69.12%
69.01
79.79
204.5
236.4
420 hp
455 hp 205/142
69.27%
69.35
80.36
205.5
238.1
422 hp
458 hp 206/142
68.93%
69.69
80.36
206.5
238.1
424 hp
460 hp
517 hp 183.0/133.6
73.01%
1.364/2.407

Chevy '882 Iron CCM 151/59 1.940/1.500
-
Pipe 76 70/59
84.29% 125/109
87.20% 175/136
77.71%
59.20
76.96
175.4
228.0
360 hp 204/143
70.10%
69.01
80.92
204.5
239.8
420 hp
455 hp 205/144
70.24%
69.35
81.49
205.5
241.4
422 hp
458 hp 206/145
70.39%
69.69
82.05
206.5
243.1
424 hp
460 hp
517 hp 183.0/135.4
73.99%
1.364/2.458

Chevy Vortec L31 Iron 170/61 1.940/1.500 64 58/43
74.14% 114/88
77.19% 173/125
72.25%
58.53
70.74
173.4
209.6
356 hp 216/143
66.20%
73.07
80.92
216.5
239.8
444 hp
482 hp 225/149
66.22%
76.12
84.32
225.5
249.8
463 hp
502 hp 222/152
68.47%
75.10
86.01
222.5
254.9
457 hp
495 hp
557 hp 190.0/131.4
69.16%
1.324/2.492

Chevy Vortec L31 / #885 Iron CCM 170/61 1.940/1.500
-
No Pipe 64 70/48
68.57% 138/101
73.19% 190/129
67.89%
64.28
73.00
190.5
216.3
391 hp 227/140
61.67%
76.79
79.22
227.5
234.7
467 hp
507 hp 239/147
61.51%
80.85
83.18
239.6
246.5
492 hp
533 hp 229/151
65.94%
77.47
85.45
229.5
253.2
471 hp
511 hp
575 hp 204.6/133.6
65.30%
1.406/2.475

Chevy Vortec L31 / #885 Iron CCM 170/61 1.940/1.500
-
Pipe 64 70/49
70.00% 139/105
75.54% 190/137
72.11%
64.28
77.53
190.5
229.7
391 hp 227/151
66.52%
76.79
85.45
227.5
253.2
467 hp
507 hp 239/160
66.95%
80.85
90.54
239.6
268.3
492 hp
533 hp 229/162
70.74%
77.47
91.67
229.5
271.6
471 hp
511 hp
575 hp 204.8/143.0
69.82%
1.406/2.656

Chevy Vortec Ported McCoy N/A - N/A - - - - 266/200
75.19%
-
547 hp
594 hp - -

Chevy Vortec / Bow Tie Small Port Iron 175/65 2.000/1.550 65 - - - - 235/161
68.51%
74.80
85.32
221.6
252.8
483 hp
525 hp 236/163
69.07%
75.12
86.38
222.6
256.0
485 hp
527 hp
592 hp 235.5/162.0
68.79%
1.349/2.508