Words And Photos: Jeff Smith
In acting, timing is everything. The same could be said for performance engines. But instead of ignition timing, let’s talk about valve timing. While opening and closing points are critical, the secret to a strong performance valve lift curve is the aggressive combination of lift and duration. Duration is time in degrees of the valve event curve between valve opening and closing but lift is limited by the duration. Flat tappet cams are more limited in lift than their roller cousins. So, among other advantages, a roller cam offers much more lift potential for the same amount of duration. Combine the simplicity of hydraulic roller lifters with a roller lobe’s ability to crank up the lift and we now have better ingredients to make more power.
Recently the moon and stars aligned in such a way that we had the opportunity to underscore this hydraulic roller idea with a strong 0.030-over 454 street engine. This engine started life with a good solid foundation of SRP forged 10.25:1 pistons topped with a pair of factory iron oval port heads and a dated solid lifter flat tappet cam. The long block was sound so all it needed was a decent cam to awaken this engine’s potential power. The engine was going into a ’67 El Camino with tall street gears and an overdrive automatic. We consulted the COMP Cams Book of Armaments and decided on the retro-fit Xtreme Energy XR276HR with 224/236 degrees of duration and 0.510-inch lift.
COMP calls this a retro-fit cam as all the early small- and big-block Chevys were originally designed for flat tappet style camshafts. This means there are some important modifications that must be made in order to make a hydraulic roller cam work in these earlier engines. The first step COMP has already done for you. Roller lifters must always remain aligned to the lobe. It’s pretty obvious what would happen if the lifter was allowed to turn 90-degrees to the lobe so COMP attaches each pair of lifters with tie bars that prevent that from happening. The second step will require some minor installer effort. All helical cut distributor drive gears on a camshaft create a minor forward thrust. On flat tappet cams, this is counter-acted by a slight angle machined into the cam lobes. This angle accomplishes two tasks.
The first is to ensure that the lifters rotate in the bore for a more even wear pattern. This angle also counter-acts the cam’s natural forward movement. For obvious reasons, this angle cannot be employed on a roller lifter camshaft, so the thrust must be limited by some other means. On factory hydraulic roller lifter engines, this forward movement is limited by a cam thrust plate. Pre-roller engines do not have this feature, so a cam button is used to minimize cam movement to between 0.001 and 0.005-inch. COMP offers two different styles of cam buttons that we will look at as well as a very nice two- or three-piece billet aluminum timing chain cover for our big-block that offers several advantages. These covers also offer an ideal place to check the actual endplay.
Just for fun, we also put this engine up on the dyno, not really expecting to make great power with it. But this beast surprised us. The rest of the engine was configured with an Edelbrock Performer RPM dual plane intake and a Holley 850 cfm Ultra XP carburetor. We took the engine to Westech Performance Group and Steve Brule’ and crew quickly bolted the engine to the dyno. Since the engine had been previously run, we put a few minutes on the engine to warm it up, but didn’t have to worry about breaking in the cam and lifters. With water and oil temperatures stabilized, our first pull pushed the torque scale way up past 550 lb-ft and after finalizing the timing at 37 degrees and setting a lean-power air-fuel ratio, this big Rat bent the beam to 570 lb-ft of torque at 3,800 rpm with peak power a respectable 508 at a ridiculously low 5,200 rpm.
The peak horsepower rpm point was low because of the conservative nature of the cam as is the peak torque rpm point of 3,800 rpm. We plugged these numbers into a drag strip simulation program and with a 3,800-pound car with a 3.08:1 rear gear with good traction, this engine could run 11.50’s at 115 mph all day long. How much fun would that be? Stick this Rat in a lighter 1980 Malibu and it would be a rocket although traction might be a bit of an issue!
So if you are considering a retro-fit hydraulic roller camshaft conversion, take a few moments to walk through this installation with us. We’ll show you a couple of tricks that might save you some aggravation and reveal just how easy it is to update that flat tappet to a more modern hydraulic roller version. Then check out the power we made with a very conservative cam and you can begin to really see the advantages to a hydraulic roller cam.
|Cam – XR276HR-10||Adv. Duration (Degrees)||Duration at 0.050 (Degrees)||Valve Lift (inches)||Lobe Sep. Angle (Degrees)|
Hydraulic roller cam valve spring load recommendations
|Camshaft||Seat load||Open load|
Averages were calculated from the full dyno curve with data every 100 rpm.
|COMP BBC Hyd. roller cam-lifter kit||K-11-423-8||Summit Racing||$911.97|
|COMP BBC hyd. roller cam||11-423-8*||Summit Racing||290.97|
|COMP retro-fit hyd. roller lifters||854-16*||Summit Racing||435.97|
|COMP valve springs, hyd. roller||911-16*||Summit Racing||88.97|
|COMP timing set||2110*||Summit Racing||37.97|
|COMP steel valve spring retainers||748-16*||Summit Racing||54.97|
|COMP retainer locks||612-16*||Summit Racing||22.97|
|COMP High Energy pushrods||7815-16*||Summit Racing||44.97|
|COMP umbrella valve seals||504-16*||Summit Racing||12.97|
|COMP nylon thrust button||205*||Summit Racing||4.97|
|COMP Ultra-Pro rockers, 1.8:1||1828-16||Summit Racing||407.97|
|COMP aluminum 2 pc. timing cover||212||Summit Racing||257.97|
|COMP Hi-Tech pushrods||7663-16||Summit Racing||117.97|
|COMP Hot Rod 10w30 oil, each||1594||Summit Racing||8.97 ea.|
|COMP BBC valve covers||281||Summit Racing||205.97|
|COMP 8 oz. assembly lube||153||Summit Racing||8.97|
|COMP 7/16 rocker studs||4512-16||Summit Racing||56.97|
|COMP valvespring seat inserts||4697-16||Summit Racing||34.97|
|Milodon oil pan,6 ¼” depth, 6 qt.||30970||Summit Racing||252.14|
|Milodon oil pump pickup||18202||Summit Racing||56.95|
|Fel-Pro 1 pc oil pan gasket||1884R||Summit Racing||28.97|
|ARP head bolts||135-3601||Summit Racing||84.70|
* Parts included in the K-kit
We used the following tools in the process of this installation. Not all of these tools are essential and some you can make yourself.
|Powerhouse crank socket||POW103055||Powerhouse Products||$38.36|
|Powerhouse Pro degree wheel||POW101600||Powerhouse Products||200.29|
|Powerhouse dial indicator||POW151102||Powerhouse Products||61.57|
|Powerhouse dial indicator 2” ext.||POW151112||Powerhouse Products||6.48|
|Powerhouse magnetic base||POW151125||Powerhouse Products||30.33|
|Powerhouse cam handle||POW101035||Powerhouse Products||32.46|
|Powerhouse height mic||POW101200||Powerhouse Products||69.94|
|Powerhouse pushrod length kit||POW101240||Powerhouse Products||66.04|
|Powerhouse crank gear installer||POW101525||Powerhouse Products||21.26|
|Powerhouse balancer puller/installer||POW300000||Powerhouse Products||138.56|
|Powerhouse degree kit||POW101545||Powerhouse Products||146.13|
Automotive Racing Products (ARP)
Westech Performance Group