Chevy Small Block Part 12 - Comp Cams

Testing Different Exhaust Rocker Arm Ratios

By Mike Petralia

Chevy Small Block Part 12 Roller Rocker Arms

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
MSD Ignition El Paso TX 9-15/-857-5200 msdignition.com	Accufab 1516 E. Francis St. Ontario CA 91761 909-930-1751 www.accufabracing.com
SX Performance 7700 Gravois St. Louis MO 63123	COMP Cams
Summit Racing Equipment P.O. Box 909 Akron OH 44309	Edelbrock Dept. 5.0 2700 California St. Torrance CA 90503 310-781-2222 www.edelbrock.com
Russell Performance Products 225 Fentress Blvd. Daytona Beach FL 32114 904-253-8980 www.russellperformance.com	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