Flat Tappet To Roller Swap - Rolling Thunder

In the magazine industry, when we look back at past tech articles, we usually find something new we need to do, either to fix a mistake we made or just improve an existing great combination. Usually, we hope the latter applies, but it doesn't always work out that way. In our January 2004 issue, we changed from a mildly ported set of 906 heads with 2.14/1.81-inch valves to the Indy SR 295s on a 10.0:1 compression 440. We definitely experienced an increase in peak power at 5,600 rpm, 67 to be exact. During our baseline dyno pulls with the 906 heads, we observed power gradually dropping off after 5,600 rpm, and rapidly dropping when valve float occurred at 6,150 rpm. At 6,000 rpm, the Indy's were worth 90 rwhp over the 906s. We soon realized the particular flat-tappet hydraulic cam we used for the head-swap shootout wasn't a good match for the high-flow/high-rpm capabilities of the Indy heads. It was time to revisit the engine and step up to the next level of performance-a solid street roller cam.

Rolling It
Though it is more expensive to upgrade the valvetrain with a new cam, lifters, springs, different length/stronger pushrods, timing set, bronze distributor gear, cam button, and possibly rockers for a roller cam, a roller cam will add air velocity through larger-than-stock-size ports like those in our Indy's. The roller cam's lobes have more area under the curve and are beneficial to broaden the power band on a street-driven car. Looking through the Comp Cams catalog, we decided on an Extreme Energy solid street roller cam kit. For the sake of comparison, the hydraulic flat tappet was a decent stick (.533 lift w/1.6 rockers, 244 duration at .050-inch, and 110-degree lobe separation) next to the roller cam. Speaking of the roller, the cam we chose has some extra lift and duration, .576/582 lift w/1.5 rockers, and 248/254-degrees of duration at .050-inch on a 110-degree lobe separation to be exact. We feel this will add the high-rpm power the Indy heads are known to make. by going to a roller cam, an added bonus is duration at .050-inch lift can be increased by as much as 8 degrees, yet you can still expect similar idle and drivability characteristics-as long as the lobe separation is the same.

In an effort to keep all things as basic as the typical do-it-yourself cam swap, we didn't degree-in the roller cam to the cam card (though we should have). once the rocker arm geometry was confirmed, we ordered the proper length pushrods from Comp Cams. After the new valvetrain was installed, we set the cold lash .002-inch tighter than specifications. After 100 miles of break-in time with two oil changes and dyno testing, the hot lash was checked, and we were good to go. This same type of Comp Cams solid street roller valvetrain has been in our '67 R/T test mule for over 10,000 miles and eight years. the lash is checked every 1,500 to 2,000 miles, but the settings don't change. We live in good times today with the availability of high-quality valvetrain components compared to the stuff from over 25 years ago.

The Roller To The Rollers
Thanks to SLP Performance Parts owner and founder Ed Hamburger (Hamburger's oil pans), a date was set at their state-of-the-art Superflow SF840 chassis dynamometer. Our hydraulic cam baseline was previously recorded on their dyno (this means the numbers are in their computer system). For a fair cam test, no changes were done to the 440 or the drivetrain, except for the cam and components. We reused all the same parts- heads, intake, carb, ignition, tuning, converter, gearing, and so on. We only wanted to see the bump in power the new bumpstick would demonstrate.

On the 40-minute ride to SLP, we noticed the idle and drivability was similar, but once it hit over 5,000 rpm, it pulled much stronger, right to the 6,600-rpm chip in the MSD rev limiter. Once the car was strapped to SLP's rollers, would the new roller cam prove its worth, or would it fail miserably? After the first blast, we noticed peak power was coming in at a higher 6,250 rpm. Now the 440 was revving and making power way beyond the hydraulic cam, which previously encountered valve float at 6,150 rpm. We were pleased to gain 22 hp at peak, but noticed the efficient roller was running too rich with black smoke belching out. This only meant the 440 would need a leaner mixture.

With limited dyno time, we reached into the jet box and changed the secondary jets on the 850 Demon from 88s to 84s. The jet swap netted us 4 hp, and then we checked the timing and found it to be at 35 degrees total. We bumped that up to 40 degrees, and picked up another 4 hp. That gave us a 30hp gain. We still had some unsightly black smoke, so we once again changed the secondary jets to a leaner set of 82s and picked up 2 more horsepower. We were now out of dyno time, but very pleased to gain a total of 32 hp with a cam swap.

When testing this Indy-headed 440 with the hydraulic cam, we benefited from more dyno-tuning time. We knew there was more power available from the more efficient roller cam, and we'll give the new combo a strip-tune at a later date. With power up significantly at 700 higher rpm, to get the most from this cam, a higher-stall converter will become part of the program. The 11-inch converter (2,800 rated stall) will be removed in favor of a Dynamic 10-inch converter (3,500 rated stall). The higher stall converter will enable the wedge to use its new higher and broader power range more effectively.

Conclusion
We needed a more stable and efficient cam combination that matched the high-flow/rpm capabilities the Indy heads have to offer. The Comp Cams Xtreme Energy Street Roller delivered the extra power we wanted. The roller/Indy combination outperformed the flat-tappet/906 combination by a total of 134 rwhp at 6,100 rpm-a big-time gain. There's no need to custom-order a cam when there's a good selection in the catalog. When looking through the catalog or Comp Cams web site, there are recommendations about which cam will work for the engine combination, converter, and gearing you have. If you are still undecided about what you need, Comp Cams has a CamHelp Hotline [(800) 999-0853] to help you make the right cam choice. Flat-tappet cams are definitely the cheaper way to go, but if your willing to pay for that extra power, a roller cam is the way to get there.

Chassis Dyno Results
SuperFlow SF840 SAE-corrected rear-wheel horsepower and torque at SLP Performance Parts and Engineering Center.

*Average horsepower readings were from 5,000-6,000 rpm due to valve float at 6,150 with the hydraulic cam-an unfair average to the solid roller. Peak roller horsepower was at 6,250, and it pulled well beyond 6,500 rpm (we ended each pull at 6,500).

*Accurate average torque readings were attained after 4,000 rpm, allowing for converter lock-up (less slippage).

Note: a gain of 134 rwhp at 6,100 rpm (not peak) was realized from the previous ported-head swap, and now the roller cam.

Indy Sr Heads Flow Chart
As tested at Ray Barton Racing Engines, SuperFlow SF-600 flowbench.

Note: To obtain similar flow and power numbers, Indy sells the SR295 CNC heads. The CNC heads will save you from many hours of porting.