The changeover to the Indy SRs was as simple as bolting on a pair of stock heads, with the exception of the Indy valley plate. It must be bolted on before the heads are installed. Remember that upgrading from 906s to Indys does require longer pushrods and the installation of an external oil line kit for the rocker assembly. We were impressed by how well the Indy intake ports aligned with the ports on the heads.
Initially, we set up the hydraulic lifters at zero preload then turned the rocker adjusters in another quarter turn. The quarter-turn setting made for a noisy valvetrain, even after a 20-minute warm-up. Ken Lazarri at ICH suggested we try a three-quarters to a full turn from zero lash. At three-quarters of a turn the valvetrain was quiet and the 440 was more responsive than ever.
The revamped RB was warmed up and checked for any possible fluid leaks. A half-hour ride was taken to bring everything up to operating temp. Then the oil and filter were changed. The oil we used was Mobil1 synthetic 15-50 weight. The carb was adjusted and the idle was set at 1,100 rpm. The timing was set the same as it had been with the 906s (42 degrees total, and all in by 2,000 rpm). The shakedown drive on the back roads near the shop told us the Indy heads greatly increased the all-around powerband, especially at 5,000 to 6,000 rpm according to our seat-of-the-pants dynamometer.
Baseline testing with the 906 heads on the chassis dyno at SLP Performance Parts showed us 366 hp at 5,600 rpm at the rear wheels.
The Indy 433
We were anticipating substantial gains from the Indy heads, therefore it was back to the SLP dyno to see how much we really gained. On our baseline pull we were impressed to find we gained 60 peak horsepower at the same 5,600 rpm. Peak torque was up 20 lb-ft at the same 4,200 rpm. The powerband was broadened so much, the 440 made 90 more horsepower at 6,000 rpm. With the stock heads, power dropped off after peaking at 5,600 rpm.
We wanted our dyno time to be useful, so we brought along a timing light, a box of carb jets, a Wilson four-hole tapered carb spacer, and a K&N X-Stream air-cleaner lid. Our first effort toward tuning for more power was in the timing department. Baseline timing was 42 degrees, then 38, then 35, and finally we found seven more horses at 40 degees total timing. Peak power was now up 67 hp (433 hp at 5,600 rpm) over the ported 906 heads.
Next, the chrome air-cleaner lid was swapped for a K&N X Stream airflow top. The K&N lid increased the throttle response, torque, and horsepower. Power was up 6 hp and 6 lb-ft of torque at 4,700 rpm. Strangely enough, peak horsepower at 5,600 rpm remained the same. Average horsepower and torque numbers were up between 4,000 and 6,000 rpm (See charts). The K&N X Stream is a tested winner in lowering e.t.'s, and now it added horsepower on the dyno.
The 906 and Indy heads' baselines were done with the same 1-inch open spacer under the Demon 850 carb. We swapped the open spacer for a Wilson Manifolds tapered four-hole spacer. In previous strip and engine dyno testing, the Wilson spacer has demonstrated respectable e.t. reductions and increased power. This time, the proven spacer gained us 10 hp and 12 lb-ft of torque at 4,300 rpm over the open-hole spacer. Horsepower and torque were up across the board, but ironically remained the same from 5,500 to 6,000 rpm.
The K&N X Stream air-cleaner lid and the Wilson spacer helped us out enough to move on to the carburetion. We expected the 850 Demon's 84 primary and 88 secondary jetting to be on the rich side (a puff of black smoke exited the pipes when nailing the throttle). Leaning out the secondaries to 85s lost us 8 hp. A pair of 90s was then tried, but power was still down. With that, we returned the jetting to the initial 84 and 88, which restored maximum power to the rear wheels.
A 28-degree back-cut was given...
A 28-degree back-cut was given to each intake valve at Ray Barton Racing Engines' facility. Back-cutting the intake valve always improves the low- and mid-lift flow. This modification also improves throttle response and drivability.
The Max Wedge gaskets demonstrate...
The Max Wedge gaskets demonstrate the smaller 906 intake-port size. Gasket matching raises the roof of the ports 1/2 inch higher. Flowbench numbers went through the roof after we opened the heads to Max Wedge size. The Indy intake also received port matching, but at .050 inch smaller than the gasket all around. This can prevent air turbulence, a possibility when the motor is bolted together.
One major difference before...
One major difference before bolting on the Indy heads is to install the Indy valley plate first. The valley cover is sealed with RTV at the end rails and where the head's deck surface meets the edge of the valley plate. We regret we didn't opt for the two-piece removable valley plate for future cam swaps so it can be done without removing the heads.
The Indy SRs bolted right...
The Indy SRs bolted right up to seal and capture the valley plate. Notice the large Max Wedge-size intake port openings. Box stock, these castings flowed 288 cfm at .700 inch lift. With extensive porting and polishing, they flowed 357 cfm at .700 lift. Even in stock form, these heads are proven performers.]
Adjustable rockers are a must...
Adjustable rockers are a must to achieve proper lifter preload (hydraulic) or valve lash (solid). We moved up to 1.6-ratio rockers from Indy. This meant the .501-lift Comp Cams stick would have .531 lift at the valve with the 1.6 rockers. The 1.6-ratio rockers will also aid the air velocity going through the larger-than-stock ports. Out of focus are the external oil lines at the rear of the heads.
Once the timing was set, we...
Once the timing was set, we decided to do some air cleaner testing. The same 850 Demon Carburetor and 4-inch K&N filter with chrome lid were employed for baseline pulls with the iron and aluminum heads. Changing to the K&N X Stream air-cleaner lid netted us 6 hp and 6 lb-ft of torque at 4,700 rpm.