Last issue we track tested then covered an installation of Holley's StealthRam EFI intake on a modified 1986 IROC (see Part 1, May 2003). Also included was a detailed listing with pricing of the ancillary items needed to install the StealthRam on '85-'92 TPI F-bodies. Please note that the part number for the StealthRam intake is and should have been indicated in the last issue as 7540, not 7450.
A recap of the test vehicle's combination of parts shows the IROC to have a 9.8:1 compression 355ci small-block with box-stock TFS G1 heads. The cam is a custom grind flat-tappet hydraulic from Competition Cams (218*/228* duration at .050-inch lift). Fuel is added by flow-balanced 24-pound SVO injectors. A homemade ram-air system utilizing K&N filters feeds the engine through a modified mass airflow sensor and 52mm BBK throttle body. The exhaust is comprised of 1 5/8-inch Hedman shorty headers a single 3-inch Race Series Dynomax muffler with dual outlets. The TH350 transmission, TCI 10-inch stall converter, stock 3.23 rear, and Auburn limited slip unit rounds out the drivetrain. Traction is supplied by 26x11.5 ET Streets with the only weight reduction coming from skinnies up front.
The induction system replaced by the StealthRam was a fully ported GM base and plenum with ported and optimized length SLP runners. Baseline testing of the modified TPI/SLP intake system showed elapsed times to be in the 12.9-to 13.0-second range in 88* weather. There was an abundance of traction-limiting torque from this induction system, and the trap speed for the quarter varied significantly depending on the amount of wheelspin. The midrange response was very good but power dropped off quickly past 5,600 rpm.
The installation of the StealthRam was easier than a TPI system. Just comparing the 32 bolts and eight gaskets needed to install the TPI to the 16 bolts and four gaskets needed for the StealthRam should give some indication. There were only a few minor modifications needed for the StealthRam to work on our application, mostly for the older style "V" belt-driven accessories. Our test vehicle had the large coil-in-cap HEI and required a swap to the newer small-cap remote coil distributor to clear the StealthRam. Even though the StealthRam was not designed specifically for the third-generation F-body the installation went surprisingly well. The IROC fired off with the second twist of the key. The initial timing was set to 10 degrees and the fuel pressure was set to 42 psi. No adjustments to the idle set screw or TPS were needed.
Any question whether the intake was going to work or not was put to rest during the initial three-minute test drive. The tachometer zinged to 6,000 rpm and unlike the TPI combination, the StealthRam allowed the car to pull from any speed you dropped the accelerator. Although there seemed to be a slight reduction in initial throttle response, it was unlikely the StealthRam would like the same initial timing and fuel pressure as the TPI/SLP intake system it had replaced. Normally, a few changes would have been made to the initial timing and fuel pressure to help determine best guess settings before going to the track. Nevertheless, there was just enough time to tune it at the track if we hurried. So no time was wasted getting to Tuscola Motor Sports.
Less than two hours after completing the installation of the StealthRam, we did our first burnout. As soon as the car launched you could tell the tune was off. It felt sluggish throughout its first pass and it showed with a somewhat disappointing ET of 13.120 at 105.43 mph. Knowing a much better ET was there, the initial timing was increased to 12* and the car was allowed to cool before the next run.
On the second pass, an uncapped Mustang with the top of the carburetor visible over its fender line pulled out and staged beside the IROC. Three seconds after the green light the Mustang was four car lengths behind and that lead was stretched throughout the quarter. The IROC responded favorably to the change with an ET of 12.990/105.90 and literally set the Mustang on fire! Thankfully the driver, believed to be the victim of a transmission leak, was able to douse the Mustang's flames without injury to himself or the car.
Initial timing was set at 14* for the next pass and the IROC reacted with a promising 12.891/106.92. The engine no longer felt sluggish. A couple of things became obvious after only three runs: The StealthRam's plenum cooled much faster to the touch and the car could be launched much harder than on previous outings.
For the fourth run the initial timing was set to 16*, the fuel pressure was bumped to 46 psi, and the air pressure in the tires was dropped to 20 psi. A heavy burnout was completed and the car left hard with little to no wheelspin under a full-throttle launch. The engine pulled effortlessly to the 6,200 rpm 1-2 shift point. However, when the shifter was moved for the 2-3 shift, the transmission did not shift. Since the car launched so well and there was no sign of the engine dropping off its powerband, the run was not aborted. Astonishingly, the IROC stopped the clocks with a 12.673/107.84 while approaching 7,000 rpm in second gear!
By the time the shifter linkage was fixed there was time for one more pass. Only the foot-brake stall speed was changed for the final run (increased from 1,800 to 2,000 rpm). The car left hard and there was no problem shifting into third. This was a very good run and the time slip confirmed it. It was the best eighth-mile run of the night with the second best 60-foot time. Unfortunately the track crew did not switch back to the quarter-mile timers after the eighth-mile "big tire" final. Best guess based on the night's previous time slips was the IROC should have run a high 12.5 or low 12.6 second ET around 108.5 mph.
Before one can compare times, variances or changes have to be considered. In this comparison absolutely no changes were made other than the intake system. Best-tune adjustments to initial timing and the fuel pressure was done for both intake systems using the same 1988 GM 350 EPROM. The track and weather conditions were near identical for both outings. Even the amount of 93-octane gas in the tank was kept constant. Therefore, it appears the StealthRam improved elapsed times approximately .3 second and added close to 3 mph over the modified TPI/SLP intake system's best run. The StealthRam also improved 60-foot and eighth-mile times and speeds.
The StealthRam achieved and surpassed the desired results. It was amazing how it rolled off just enough torque around the stall speed to allow the car to be launched at about 95 percent of its capability. Equally amazing was how the engine with a relatively small hydraulic cam and stamped steel rocker arms continued to pull toward 7,000 rpm without a significant drop in power. While the 7,000 rpm blast was not intended, nor will it be duplicated, it did show the StealthRam should feel right at home on larger engines or with a cam and valvetrain designed to run that high.
Giving credit when due, it is possible that with costly suspension upgrades and creative chip burning, the elapsed times for the modified TPI/SLP combination could have come close to those delivered by the StealthRam. However, the same chip was used for both intake systems and the StealthRam could benefit equally from a customized fuel and ignition curve. Also, the TPI/SLP intake system was fully ported and the StealthRam still showed a performance advantage. If the StealthRam had been compared to a stock TPI intake system, the power advantage would have been staggering.
Not content to end the story here, we wondered if more power could be had in fine tuning adjustments and where peak power occurred with the StealthRam. A quick trip to Professional Engine Services in Mobile, Ala., for a session on their DynoJet chassis dyno gave those answers.
Once strapped down, the IROC delivered a track-tuned 319 horses on the first pull. The wide-band oxygen sensor reading showed the engine was a good bit rich, so the fuel pressure was reduced to 38 psi. This generated 326 rwhp and a better, but still slightly rich, air/fuel ratio. Not wanting to drop the fuel pressure any lower, the initial timing was reduced from 16 degrees to 14 degrees and netted 329 horses. Dropping the timing to 12 degrees showed a significant loss of torque. On the fifth pull the timing was set back to 14 degrees and after a 10 minute cool down the car generated a tad over 330 rear-wheel horsepower at 5,850 rpm and 396 lb.-ft. of torque at 2,850 rpm. Since this was done with the stock ECM, 1988 350 GM EPROM, and limited adjustments to initial timing and fuel pressure, we felt this was a pretty good showing.
Feeling a slight improvement in initial and part-throttle response after the dyno session, we could not wait to see what the newly found dyno horses and cooler weather would do for the IROC. We headed back to Tuscola Motor Sports for the last "test and tune" of the year and were rewarded with a 12.590/109.86 first pass. There was more to be had by varying launch techniques and shift points and it was found by the end of the night. The IROC ran three consecutive 12.3 passes--each one over 109.9 mph. A couple of guys dropped by the pits to see what size nitrous kit the IROC was running. They were surprised to find the fuel-injected StealthRam and that the car did not have nitrous (yet).
To say we were pleased with the StealthRam would be an understatement. One could not have asked for more from an intake swap. The StealthRam gave the car a third gear pull that can keep modified LS1 cars at bay while providing a neck snapping launch with the stock suspension and 3.23 gears. The engine has a wider, more effective power band that makes the IROC a more balanced performer. For combinations similar to and stronger than the test vehicle, the StealthRam intake system has to be like having your cake and eating it too!
DO ENGINE SIMULATORS REALLY WORK?
Performance Trends Engine Analyzer (EA) software has shown to be a very useful tool in determining the potential of a particular engine combination. It was used to help determine what effect the StealthRam intake should have on the IROC before the intake swap was made. Not surprisingly, EA showed the tunnel-ram style runners of the StealthRam should add more power starting around 4,700 rpm when compared to the previous intake system. Since the program assumes proper fuel and timing, it was somewhat questionable if the potential gain could be seen with the stock ECM and GM EPROM. However, the desire to have a solid 12-second performer (regardless of the outside temperature) was strong enough to make the swap.
EA estimated 416 peak horsepower at 5,800 rpm for the StealthRam combination. That converts to approximately 333 horses to the rear wheels after drivetrain loss. The IROC actually pulled 330.47 horses at 5,850 rpm, a difference of less than 1 percent and 50 rpm. If you look at where the estimated torque output from the modified TPI combination is concentrated, then consider the converter's torque multiplication factor (as seen in the graph): it becomes clear why the IROC had traction problems with that induction system.
To Chip or not to Chip--Part Two
A 1988 350 GM EPROM was used exclusively during this project. It appears the engine combination used in the IROC is on the edge of the stock chip's working parameters. However, the programming for the 1986-1988 mass airflow models added fuel when cranking in cold conditions via a cold start or ninth injector. Even though the StealthRam does not have a provision for a cold start injector, the car was able to crank with little to no difficulty in warm weather. Not until the weather turned cool did it become apparent the IROC was going to have to have a chip burned. It would need programming similar to the 1989 mass airflow models that added fuel for cold start cranking via the standard injectors. Buying a 1989 EPROM from your local GM dealer won't work since the vehicle anti-theft system (VATS) was added that year for the Camaros (optional for the Firebirds in 1988) and would prevent earlier year models without VATS (like our 1986 IROC) from cranking.
Thankfully Mike Davis of Maryland came to the rescue and burned a few chips based on the 1989 programming. He turned off the VATS as well as tweaked the fuel and ignition curve based on his own rewarding experience with the StealthRam. While the car has yet to make it back to the dyno or track with the new chips the car cranks perfectly in 30*F weather and feels a little quicker.