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Hydraulic Roller Cam Swap

Bolt On 50 HP!

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Once we had the roller cam in place, it was time for the power test. To evaluate just the change in the cam, we retained the 1.5:1 roller rockers used with the flat-tappet cam. The first test immediately raised the engine's peak horsepower point to 6,200 rpm from the flat-tappet cam's best horsepower peak of 6,000 rpm. Frankly, we expected the roller's additional 10 degrees of duration to push the rpm peak closer to 6,500 rpm, so 6,200 rpm was mildly disappointing. But the power that we gained was anything but a disappointment with a nice increase to 478 hp. With this simple cam swap, we had just jacked the power by nearly 50 hp. We attributed a majority of the power increase to the roller cam's additional valve lift that bumped the intake lift from the flat tappet's 0.504 to the roller's 0.560 inch, an increase of more than 0.050 inch. Since this added lift really helped the power, we assumed that if some is good, then more is better, so we added a set of 1.6:1 roller rockers to both the intake and exhaust in search of more power.

The problem with adding rocker ratio is that this also increases valve acceleration rate, which makes the valvespring's job more difficult. Most of the time, the spring can handle this increase in valve acceleration. In our case, adding 1.6:1 rocker ratio to both the intake and exhaust resulted in a dramatic loss in power above 5,400 rpm, and the engine suffered serious valve float at about 6,200 rpm when it began popping out of the exhaust. We then experimented by returning to a 1.5:1 rocker on the exhaust side and retaining the 1.6:1 rocker on the intake. This gave us the best power of the session with an excellent 483 hp at 6,200 rpm. While the heavier intake valve usually pushes the intake side into valve float before the exhaust, in this case, our valve control issues might be attributed to a more aggressive lobe design on the exhaust side.

We then tried a Holley Strip Dominator single-plane intake on our hydraulic roller combination, thinking that it might help the peak power, but again, our 357 rejected the single-plane, losing more than 30 lb-ft of torque below peak torque while gaining barely 5 hp at horsepower peak. Clearly, the inconsequential horsepower gain wasn't worth the massive torque loss, so our best power combination remains with the Edelbrock Performer RPM (not the Air-Gap) dual-plane intake. We also tested a 1-inch open plenum spacer on the dual-plane in search of more horsepower, but this attempt also resulted in no additional power.

Overall, we jacked up our 357 small-block with 80 more horsepower while only losing a small amount of torque below 3,500 rpm. In the first story, we plugged the 403hp curve into our Quarter-Pro simulation program which estimated elapsed times for our Chevelle at 12.50s at 104 mph. With the hydraulic flat-tappet cam package, that estimate improved to 12.20s at 111 mph, and when we plugged in the roller cam package, the times improved to an estimated 11.95 at 114 mph. That's a solid 0.50-second and 10-mph gain over our original combination, which is downright excellent for a simple cam swap. The reality is that the heads and intake complement the larger hydraulic roller cam package very nicely, and we now have a very strong small-block that offers 480 normally aspirated horsepower at the flywheel at the touch of the throttle pedal. Not bad for a small-caliber, small-block Chevy.

Flat-Tappet Cam Test

Test 1: This is the best power test from Part 1.

Test 2: All we added was better conical Lunati valvesprings. This test also used Westech's dyno headers as opposed to the Hedman headers used in Test 1.

The red HP1 curve is with the original valvesprings, while the green line (HP2) is with the stronger, conical springs. Note how the weaker springs gave up at around 5,300 rpm, while the conical springs offer improved valve control, making more power starting down as low as 3,700 rpm. That's a 53hp difference at 6,000 rpm! Do you think you'd feel 50 hp in the seat of your pants? Damn straight.

Valvesprings Specs

Description Seat Load Open Load at 0.500 Open Load at 0.600
Stock 1.250 springs 100 lbs at 1.775 290 lbs NA
Lunati conical PN 74818 (flat hyd.) 140 lbs at 1.780 280 lbs 320
Lunati dual spring PN 73925K2 (roller) 160 lbs at 1.850 360 lbs 420

Parts List

Description PN Source Price
Jeg's 195cc w/ 1.440 spring 514030 Jeg's $1,199.98
Lunati flat hyd. cam/lifter kit 10120704LK Summit Racing 204.97
Lunati 1.5:1 roller rockers 15300-16 Summit Racing 264.97
Lunati conical valvespring kit 74818K2 Summit Racing 256.97
Lunati hyd. roller camshaft 20120713 Summit Racing 299.97
Lunati hyd. roller lifters 72530-16 Summit Racing 729.97
Lunati dual valvespring kit 73925K2 Summit Racing 228.97
Lunati spring seats 86731-16 Summit Racing 39.97
Lunati roller pushrods, 7.200 7020-16 Summit Racing 146.97
Lunati plastic thrust button 90006 Summit Racing 9.97
Edelbrock Performer RPM 7101 Summit Racing 177.97
Holley 750-cfm HP carburetor 0-82751 Summit Racing 509.97
Lucas Assembly lube 10153-1 Summit Racing 5.97

Cam Specs

Cam: PN 10120704 Lunati Hyd. Flat Duration at 0.050 Lift: Inches (1.6:1 Rocker Lift) Lobe Separation
Intake 233 0.504 (0.537) 110
Exhaust 241 0.525
Cam: PN 20120713 Lunati Hyd. Roller Duration at 0.050 Lift: Inches (1.6:1 Rocker Lift) Lobe Separation
Intake 243 0.560 (0.597) 110
Exhaust 251 0.565

The Hydraulic Roller Cam Test

Test 1: This was with the Lunati hydraulic roller cam and 1.5:1 rocker ratios on both the intake and exhaust.

Test 2: Here we added 1.6:1 rockers to both the intake and exhaust. Note how the power dropped off radically.

Test 3: We discovered it was the exhaust that caused the power loss, so this test used 1.6:1 roller rockers on the intake side only. This resulted in the best power.

If you look closely at the Test 2 HP curve (purple), it began experiencing valve float as early as 5,200 rpm and fell off the power curve above 5,900 with the higher ratio rockers on both the intake and exhaust. With more spring pressure, or perhaps a lighter valvespring retainer, we might have been able to use the 1.6:1 rocker ratio on the exhaust. We assumed that the exhaust lobe is quite a bit more aggressive than the intake lobe, causing this problem.

SOURCES
Holley Performance Products
1801 Russellville Rd.
Bowling Green
KY  42101
270-782-2900
http://www.holley.com
Edelbrock
2700 California St
Torrance
CA  90503
310-781-2222
http://www.edelbrock.com
Lunati
662-892-1500
http://www.lunatipower.com/
JEGS
101 JEGS Place
Delaware
OH  43015
800-345-4545
http://www.jegs.com
Lucas Oil
302 North Sheridan Street
Corona
CA  92880
951-270-0154
http://www.lucasoil.com
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