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Chevy Small Block Part 12 - PT. 12: Rockin' Ratio

Testing Different Exhaust Rocker Arm Ratios

By Mike Petralia

COMP Cams offers its Pro Magnum roller rocker arms for small-block Chevys in both 1.5 and 1.6 ratios. Previously, we had found the most average power using 1.6 rockers on all valves. This month we tried 1.5's on the exhaust only and got little in return.




Our main goal for this whole test was never realized. We wanted to run COMP's 1.3:1 (PN 1012-16) special break-in rockers on the exhaust to see if the reduction in lift would make more power as some claimed. But, in order to decrease the ratio, the rocker arm's pushrod cup must be moved away from the trunion centerline. This in effect caused the pushrod to hit the cylinder head (note top of pushrod in photo). Had we not checked for this interference and ran the motor, power would have been down tremendously and damage could have resulted. Always check for proper pushrod clearance when installing new rocker arms or changing ratios.

Test: 25 Swapped COMP Cams 1.5:1 Pro Magnum roller rockers on exhaust only

  Test 24 Test 25
RPM TQ HP TQ HP
2600 347 172 352 174
2800 346 184 348 186
3000 351 200 351 200
3200 367 224 369 224
3400 370 240 370 240
3600 367 252 366 251
3800 363 262 361 261
4000 366 278 366 279
4200 372 298 374 299
4400 383 321 387 324
4600 400 350 398 349
4800 404 369 402 368
5000 400 380 399 380
5200 406 402 402 398
5400 406 417 410 422
5600 406 432 407 433
5800 405 447 402 444
6000 394 450 395 452
Max 407 451 410 453
Avg 381 315 381 316

We're always looking for new ideas. Do you have a better one for Danger Mouse? Send your test suggestions to:

Super Chevy MagazineAttn: Danger Mouse720 Hundley WayPlacentia, CA 92870Or Email: mike.petralia@primedia.com

SOURCES
Accufab
1516 E. Francis St.
Ontario
CA  91761
909-930-1751
www.accufabracing.com
Russell Performance Products
225 Fentress Blvd.
Daytona Beach
FL  32114
904-253-8980
www.russellperformance.com
COMP Cams SX Performance
7700 Gravois
St. Louis
MO   63123
Edelbrock
Dept. 5.0
2700 California St.
Torrance
CA  90503
310-781-2222
www.edelbrock.com
Summit Racing Equipment
P.O. Box 909
Akron
OH  44309
FUEL, AIR, SPARK, TECHNOLOGY (F.A.S.T.)
151 Industrial Dr., Dept. SC
Ashland, MS 38603
Westech Performance Group
11098 Venture Dr., Unit C
Mira Loma
CA  91752
9-09/-685-4767
www.westechperformance.com
MSD Ignition
El Paso
TX
9-15/-857-5200
msdignition.com
By Mike Petralia
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