Now that the buzz surrounding the simple pushrod design, the big-lift cam, the truly high-performance ignition and the race-ready heads has died down, the 1998-present LS1-powered F-bodies are adding to their solid reputations as affordable used hot rods '98-up F-cars can be had with high miles for as little as 10 grand at the popular auto trader web sites, finally allowing the budget-minded to own a world-class powerplant. Of course, the fun really starts once that alloy screamer is in the driveway. The LT1's successor had no trouble putting tons of power to the ground in factory form, but the Gen. III engine has such a hunger for airflow that it soon became known for making big power with even the cheapest mods. The people buying these suckers used aren't exactly Rockefellers, so it stands to reason that they will be as creative as possible in squeezing the most power out of them with the least amount of money. But how cheap can you be while still picking up usable power? Can the thermoplastic fantastic LS1 respond favorably to a no-bucks mod-fest?
Ex-staffer and reigning wordmeister Jay Heath, who recently purchased a 40,000-mile '99 Trans Am, was brainwashed into wondering the same thing, and we've talked him into a before-and-after dyno thrash/track bash starring his box-stock baby. Only five simple modifications would be performed: cutting the airbox, porting the throttle body, cutting the EGR tube, bypassing the throttle body coolant line, and de-screening the MAF. All of these changes could be done at home with basic tools and a grinder--the question was, would they add power without adversely affecting driveability?
Accurate Dyno Testing--How SLP Does It
By Brian Reese
SLP Performance Parts spared no effort in creating a first-rate engine and chassis dyno test facility at its home base in Toms River, NJ. The four-room testing complex offers a SuperFlow SF-901 engine dyno and a SuperFlow SF-840 dual eddy-current chassis dyno. The two dynos are each set in an independent test cell split between both a customer observation lobby and a dual-purpose control room. While in the observation lobby, an enthusiast will not bore easily when offered a view of each dyno cell through four-foot windows, a snack and soda machine, a thorough selection of car mags like GMHTP, and of course a full line of SLP's latest catalogs. Looks aren't everything though, especially when it comes to dyno testing. There really is no point to testing if the results are inaccurate or inconsistent. SLP understands this well.
SLP goes to great lengths to ensure as accurate of testing as possible, starting with setup. An experienced and knowledgeable dyno operator will recognize that every setup procedure will impact testing and should be completed in a ritualistic, prescribed, consistent manner. At SLP, it all starts with something as simple as driving the vehicle onto the dyno. When positioning drive wheels on the dyno rolls, the car is set perpendicular to the rolls and tires are properly centered on the rolls (not biased to the front or rear of the roll). The drive wheel tire pressure is always set and equalized. The vehicle is strapped down both from the front and from the rear. Strap tensions are equalized and always consistent. Strap down points are also consistently the same and at the same angles. All this effort is made because the tire-to-roll contact is critical. Most importantly, the tire-to-roll contact is the transmission point for generated torque. However, a certain percentage of power will be lost to tire friction so it is best to minimize the loss by carefully following the aforementioned steps. Consistency in vehicle setup on the dyno is absolutely critical for repetitive testing consistency. A significant difference in vehicle strap down can incorrectly erase or amplify any power gain from a modification that is being tested. Poor contact can cause tire slippage, erroneous dyno loading, and inaccurate dyno results. Additionally, several other undesirable side effects are possible, including safety hazards, tire wear, differential wear, and vehicle or dyno damage.
Precision vehicle setup is just the beginning of good dyno testing at SLP. Setting up and calibrating the dyno itself is just as important. Testing accuracy can only be as good as the calibration accuracy. The two most critical calibrations are the dyno load cell and barometer. Other calibrations and specifications are also important and must be correctly set as well.
The dyno load cell is calibrated by checking the measured load when a precision weight is applied. The calibration of the load cell is checked on a weekly basis at least--more often if needed. In the case of the SuperFlow chassis dyno at SLP, the calibration is never off by more than 0.5 percent. The barometer and vapor pressure arei the most critical atmospheric conditions requiring measurement. Barometer readings (along with the rest of the atmospheric conditions) are used to 'correct' the torque and power measurements at WOT (Wide Open Throttle).
All testing results should be corrected to SAE standards. This allows a fair apples-to-apples comparison between tests completed at different times (and therefore under different atmospheric conditions). For absolute numbers, stick to SAE (Society of Automotive Engineers) corrections as opposed to STP (Standard Temperature and Pressure) corrections. SLP only uses SAE corrections, unless specifically requested to use STP by a customer. STP corrections will yield higher numbers than SAE corrections--be cognizant of this when comparing results.
In addition to the calibrations, vehicle specifications impact the dyno's torque calculation. For this reason, SLP considers them critical to the testing. Specifications include total weight, axle weight (aka weight directly on the rolls), rotating mass (a sum of trans internals, driveshaft, diff, gears, axles, brakes, wheels, tires, etc.), tire size, gear ratio, vehicle frontal area, and drag coefficient.
The specifications are individually programmed into the dyno computer for each vehicle before any testing. For inertia testing, these are especially important since the test uses the acceleration of a known mass (dyno rolls) in an algorithm to calculate torque. The vehicle's rotating mass, while small in comparison to the rolls, must be included with the dyno roll mass for an accurate test. As you can imagine, significant differences in rotating mass exist between vehicles and vehicle configurations. The more accurately these parameters are defined, the better the absolute torque and power numbers will be.
The facilities--you can't overlook this! Fresh air supply, heat removal and exhaust removal are mandatory for accurate (and safe) testing. Each is related, or at least should be, if handled properly.
Most facilities handle exhaust removal because it is relatively easy, but neglect to adequately address fresh air supply and heat removal. The most common way to remove exhaust is to vacuum the exhaust out of the tailpipe and blow it out of the building with some blower configuration. This works, provided the exhaust fan is capable of moving enough cfm of exhaust for your car, but can cause an artificial supercharging effect by creating a negative pressure on the exhaust.
Heat removal is possible by using spot fans on hot areas, but if the hot air is not then blown out of the vicinity, it won't do much good. Remember, vehicles were not designed to be run at WOT temperatures while STANDING STILL. The heat will more than likely burn or ruin something.
Fresh air supply is especially important--as important as supplying gasoline, quite literally. Without enough fresh air, the vehicle will suffer from artificial EGR (exhaust gas re-circulation) because it will be forced to consume exhaust already spent from the vehicle. This will cause abnormally low power production--and wicked headaches for dyno operators!
Simply opening shop windows or doors and hoping enough air blows in does not provide adequate ventilation or fresh air. To provide adequate air, it must be forced in and out of a test cell.
To create the best system for fresh air supply, heat removal and exhaust removal, SLP designed a test cell based fresh air supply/exhaust removal system. SLP's all-inclusive system provides adequate fresh air, heat removal and exhaust removal, altogether. The system is also bi-directional, allowing for either rear-wheel drive or front-wheel drive.
Fresh air is forced into the room in front of the vehicle and traverses across the vehicle, simulating at-speed road conditions, before being vacuumed out the back of the room after the vehicle. While the fresh air travels through the room and across the vehicle, it supplies fresh air to the engine, removes heat from the engine and drivetrain, and scavenges exhaust. The air movement is handled by twin computer controlled, 54-inch tube-axial fans. The control system ensures that a slight negative pressure is held on the test cell during testing to eliminate exhaust seepage to the rest of the facility. SLP promises no exhaust supercharging or excessive overheating during testing.
The vehicle is not the only source of heat during testing. The dyno generates heat as well. In fact, the dual-eddy-current brake converts the power generated by the vehicle into HEAT. To manage the heat generation, a second airflow system is employed in the dyno pit (yes, the dyno is flush mounted in the floor--no lift necessary). A fresh air supply is plumbed to the dyno brake and a special-purpose fan is used to draw the air across the dyno and out of the building along with the generated heat.
The more data measured and reported the better! To complement accurate dyno testing, an assortment of vehicle and engine operating parameters are additionally tested and recorded. Torque and power generation are important, but nearly worthless if you don't accompany them with the rest of the vehicle and engine operating parameters. While a near limitless number of measurable parameters exist, a couple are common to all testing--the others are added on an as-needed basis, depending on the goals of the subject testing.
Air fuel ratio is perhaps the most important. Just as a safety precaution alone, the AFR should be monitored during all tests to make sure you don't run lean and damage the engine. AFR measurement should only be completed with a high speed, research-grade meter. O2 sensors and cheap meters are NOT accurate. SLP uses a Bosch Etas meter--in fact SLP has two, in case one in each engine bank is desired.
Basic engine parameters such as manifold pressure, coolant temperature, fuel pressure and spark advance are and should be measured with all tests. They should also be held consistent during each test as well, provided they are not the subject of a test. If engine coolant temperature varies more than 5 degrees between tests, the results could be influenced by the gradient.
Temperature tells a good story. A lot of information can be inferred from temperature measurements. SLP recommends a temperature measurement wherever possible--namely exhaust ports and intake ports. Transmission fluid and oil temperatures also add valuable information to a test. A cold transmission or rear axle will eat power!
With the advent of OBDI and OBDII came the capability to measure and record everything the PCM sees and does. This can be invaluable in tuning or diagnostic evaluation. SLP has a couple methods for communicating with the PCM. Advanced measurements are possible and quite handy at times--most notably, in-cylinder pressure measurement. Thermodynamically, you can calculate torque and power generation (or pumping losses) just from a crank angle resolved in-cylinder pressure trace. From this, you can calculate how efficient (or inefficient) your engine and driveline is. Knock detection is nearly foolproof with in-cylinder pressure measurement.
The final step in accurate dyno testing is the testing procedure itself. Again, elimination or control of variables is the method used. SLP makes sure everything during the tests is held consistent and repeated exactly the same during subsequent tests. Test start speeds, loads and load rates, throttle position, gear selection, and intake air temperature are all critical. Any differences in these will certainly affect test results and negate the possibility of comparing different tests.