1999 Pontiac Trans Am SLP Performance Parts Test - Trans Slam
Dyno- And Strip-Testing SLP's 400HP Performancepac
From the March, 2007 issue of High Performance Pontiac
By Dan Foley
Photography by Dan Foley, Evan J. Smith, Jim Campisano
We were back with our subject...
We were back with our subject '99 T/A (LS1, auto, 3.23) to test SLP's 400HP PerformancePac. This time, a pair of Nitto Extreme Drag Radials (245/50R-16) were mounted on the stock wheels for good hook and strip-test results.
Our plan was to test the merits of SLP's PerformancePac line on an LS1 T/A. To recap what was accomplished thus far, we successfully strip-tested SLP's 350HP PerformancePac on a bone-stock '99 T/A owned by Kelly Holloway (Dec. '06 HPP), which lowered e.t.'s over 0.3 and added 3 mph to trap speed. Next (Jan. '07 HPP), we moved up to the 375HP Pac. Though we attempted a strip test, the additional 21 rwhp and 13 lb-ft of torque revealed in dyno testing and the four-year-old, dry-rotted tires conspired to limit traction. Because of that bad track experience, we ordered a set of Nitto Extreme Drag Radials to properly test the SLP's next stage-the 400HP Pac.
Dyno-testing the 350HP Pac provided 347 flywheel horsepower as converted accounting for 20 percent driveline loss using the 289-rwhp figure of SLP's chassis dyno. After installing the 375HP Pac, the LS1 developed 310 rwhp on the chassis dyno, equal to 372 hp at the crank. SLP's PerformancePac power ratings are based on the flywheel horsepower of the '01-'02 LS1s, which come from the factory with the LS6 intake as standard equipment. To ensure we could easily surpass those ratings with a '99 LS1, we opted for the popular LS6-intake swap for this story. SLP's LS6 intake includes the hardware and will enable us to retain the legal EGR emissions equipment.
The LS6-manifold swap was performed at SLP's installation center (which has been reopened to the public). During the swap, we cut off the part of the EGR tube that disrupts airflow into the intake. SLP's catalog states: "Add up to 15 hp to your LS1 with the LS6 intake manifold." After changing intakes, the blue Bird was strapped down to SLP's in-house dyno (which also has been reopened to the public). When we spun the rollers, we realized a 17-rwhp gain! That's impressive considering we didn't touch the computer or anything else. Now we were up to 327 rwhp and happy to be beyond the Pac's 375 hp rating with 392 at the crank.
Pleased with the results, we were anxious to install, dyno, and strip-test SLP's 400HP Pac, which includes everything we already installed and tested from the 350HP and 375HP Pacs plus SLP's tuned-length, long-tube stainless steel headers. The headers include a high-flow, 3-inch Y-pipe but require the install kit and high-flow cats to keep the Bird flying legal.
LS1 F-body header installation is not a walk in the park and needs to be done on a lift by a competent technician. It can take anywhere from 8 to 12 hours. SLP's engineering fabricator, Ken Estelle, handled the task in roughly 8 hours.
Upon post-install startup, we enjoyed the deeper and louder tone when revving it up, but the engine actually seemed quieter at idle. Remarkably, at highway-cruising speed, interior-exhaust drone was reduced. This is due to the long tuned-length tubes (SLP has a patent on its headers) that work together with each exhaust pulse to produce a smoother and more solid-sounding exhaust tone. Still, full-throttle blasts will get people's attention.
When we tested SLP's 375HP...
When we tested SLP's 375HP Pac (Jan. '07, HPP) we gained 21 rwhp but were only up to 372 flywheel horsepower. SLP's Pacs are based on the '01 and '02 LS1s, which sport the LS6 intake as standard issue, so we wanted one too. Here's the original LS1 intake (before the swap), equipped with the ugly EGR tube located right behind the throttle body.
The unsightly '98-'00 LS1...
The unsightly '98-'00 LS1 EGR tube protrudes into the intake and disturbs airflow due to its location right behind the exit of the throttle body. For '01-'02 engines, the LS6 intake was used on LS1 F-bodies and the EGR system was eliminated.
On the topside, it's hard...
On the topside, it's hard to see a difference between the LS6 and LS1 intakes. The only notable one is the SLP LS6 intake has a brass EGR tube fitting to keep the '98-'00 LS1s 50-state emissions-legal.
The LS6 intake provides an...
The LS6 intake provides an increase in plenum volume (5.06 liters to 5.19) that can only be seen by looking at the underside of the castings. On the left, the LS6 is flat versus the curved underside on the LS1.
SLP's LS6 intake includes...
SLP's LS6 intake includes the hardware, gaskets (already installed), and instructions to get the job done. Most important are the supplied LS6 coolant line (shorter) and block-off blocks (PN 30041K). The LS6 intake will not fit if you try to install it with the longer LS1 coolant lines in place.
We will remove these longer...
We will remove these longer LS1 coolant lines, which run under the LS1 intake from the front to the rear of the heads, so the LS6 intake will fit with it's larger flat bottom.
The short coolant line (PN...
The short coolant line (PN 30041K) and rear block-off blocks (not seen, bolted to the rear side of the heads) will be installed just as the factory did to fit the LS6 intake to the LS engine. Even without the line flowing coolant to the rear of the heads, GM engineers didn't see any adverse effects in keeping the hot LS6 cool.
On The Dyno
With the T/A safely strapped to the SuperFlow dyno, SLP's director of engineering, Hank Daniecki, put the hammer down. Peak power was now up to 349 rwhp and peak torque was 352 lb-ft. The headers dramatically broaden the power curve. Now there's over 300 rwhp from 4,500 to 6,500 rpm. Before the headers, 300-plus rwhp was only between 4,800 to 6,000 rpm. Peak at the flywheel was up to 418 hp. This had us surpassing the 400HP Pacs' rating, which was our goal.
Ironically, without the LS6-intake swap, we would have just made it to the 400hp mark. Now the T/A can proudly wear its 400HP PerformancePac badges!
When the Poncho was on the lift receiving its headers, we decided it would be wise to install SLP's bolt-in subframe connectors. With the added power and sticky tires, we wanted to stiffen the chassis to prevent possible creases in the quarter-panels. On the 30-minute ride home, the Bird felt much more solid (like a full-frame car), without any T-top or dash rattles.
Next, the Nitto Extreme Drag Radials were mounted (Shore Wheels, Tuckerton, New Jersey) on the stock 16-inch wheels. Afterwards, tire spin was virtually nonexistent on the streets. Pre-Nittos, out of the hole, and on a WOT one-two up-shift, the car wanted to go sideways and off the road. Now prepared with the SLP frame connectors and new Nittos, it felt safer and more surefooted for our return to Raceway Park.
It was a hot and humid, early-October, Indian Summer-type day upon arrival at E-town, New Jersey. The temperature rose to 82 degrees, which is not conducive to low e.t.'s as compared to cool 50-degree air. We popped the hood and flipped the fan switch to let the LS1 engine cool down from the 90-minute ride. Tire pressure was adjusted to 40 psi for the fronts and 22 psi for the rears. In past testing, we have found drag radials work best with anywhere from 18-24 psi, depending on vehicle weight.
Due to the added weight of the frame connectors (30 pounds), we were surprised when the scales showed us a test weight of 3,690 pounds (test weight for the 350 and 375 Pacs was 3,680 pounds). At a test weight of only 10 extra pounds, we figured the weight savings must have been from the lighter headers versus the heavier cast-iron manifolds because even the fuel level was the same.
We swapped all the parts (injectors,...
We swapped all the parts (injectors, fuel rails, brackets, hoses, and throttle body) from the LS1 manifold to the LS6 without any modifications. (It's important to attach the power-brake hose, shown connected to the vacuum port, at the back of the manifold.) The back of the manifold also has a connection for manifold vacuum and the MAP sensor. We will connect them before the intake is bolted in place, because once its bolted on, we can't get our hands back there.
After a one-hour cool-down, we went to the line with the needle just coming off the 160-degree mark. This was after a 6-second burnout to heat up the new Nitto drag radials. Off the line, I looked at the board and noticed a decent 1.96 60-foot without any hint of tire spin. The T/A boogied down the track. On the return road, I looked up and saw the score, a 12.83 at 107.77 mph. We pulled right back up to the line for our usual minute-later hotlap and slowed to a 12.95 at 106.83 mph.
Though we were expecting mid-12s, we shouldn't with the lousy air (for the time of year). The weather conditions were possibly costing us a few tenths and mph. We made two more pairs of passes with cool-downs and couldn't manage to go quicker. We'll just have to persuade the T/A's owner to get to the track when the air is cool and crisp (35-55 degrees).
Installing and testing each stage of SLP's PerformancePacs proved to be well worth the effort. With better, cooler air, mid-12s may have been possible, as stated in SLP's catalog for its 400HP Pac. The LS6 intake and SLP headers proved themselves as very effective power producers. Now with over 400 flywheel horsepower, the owner can remain fearless if a new GTO pulls up alongside her SLP-equipped T/A.
Once the intake was installed,...
Once the intake was installed, we covered the motor and cut the EGR tube with a handy hacksaw right below the hat-mount ridge. Then we deburred the shortened tube before installing it into the brass fitting. (This photo is a mockup. Always cut away from your fingers and use protective gloves, or hold the item with a clamp instead of your hands if a vice can't be used.)
The LS6 intake looks virtually...
The LS6 intake looks virtually stock on the LS1 engine except for the brass fitting and nut that enables the use of the EGR system. We also bypassed the throttle-body coolant line to keep the hot coolant from flowing through it. The 5/16-inch rubber hose that goes from the radiator can be extended and connected to the coolant line we installed earlier.
Now that our LS1 is blessed...
Now that our LS1 is blessed with the stellar LS6 manifold, it's good to see the obstructive EGR tube out of the picture. With the EGR tube removed and the LS6 intake installed, airflow volume will increase and be smoother.
Another spin on SLP's dyno...
Another spin on SLP's dyno showed us a whopping 17-rwhp increase (310 to 327) from the LS6 intake. This brought us from a 372 at the flywheel to 392. Now we were beyond the 375HP Pac's rating. The additional lift and duration from the '98-'00 LS1 cam is claimed to add 5-10 hp.
SLP's 400HP Pac includes everything...
SLP's 400HP Pac includes everything we previously installed and tested (350 and 375HP Pacs) plus the company's tuned-length, long-tube, stainless steel headers and cool 400HP PerformancePac fender badges. The headers are ceramic-coated inside and out for extra-long life and will look good for years. Included is a power-matched, 3-inch Y-pipe. Also shown and required to connect the headers to the Y-pipe are the high-flow catalytic converters.
The header-install kit is...
The header-install kit is also required to hang the headers. Multi-layered steel header gaskets, EGR gaskets, 3-inch Torca exhaust clamps, 02-sensor extension harnesses, and heat-shield tubing for the passenger-side wiring harness.
It's easy to see how the factory...
It's easy to see how the factory Y-pipe was compromised with restrictive cats and a 2 1/2-inch pipe. The flat (for ground clearance), left-side section of the Y-pipe shrinks to less than 2 inches, causing another reduction in exhaust flow.
There's a drastic size difference...
There's a drastic size difference between the header and exhaust manifold. The manifold outlet is less than 2 1/2 inches, while the headers 1 3/4-inch tubes merge into a 3-inch collector outlet.
Hank Deniecki is fishing the...
Hank Deniecki is fishing the passenger-side wiring harness through the heat-shield tubing, which is made from heat-resistant fiberglass surrounded by high-temp silicone that is resistant to 1,400 degrees. We added 14 inches of wire to the harnesses' crankshaft sensor, oil-level sensor, and starter-solenoid wires by cutting, splicing, and soldering. However, Hank says that's usually not necessary since there is normally enough slack in the wiring harness.
|STRIP-TEST RESULTS |
|Run/Temp, Mods, and Notes ||60-FT ||1/8 Mile/MPH ||1/4 Mile/MPH |
|March 23, 2006 |
|1./48: Baseline, bone-stock LS1 ||1.96 ||8.57/82.86 ||13.33/103.36 |
|2./50: SLP cold-air induction ||1.93 ||8.45/84.36 ||13.11/105.21 |
|Temperature, 50 degrees; Humidity, 35%; Barometer, 30.15 hg; Race weight, 3,680 lbs |
|May 9, 2006 |
|1./62: Baseline w/cold-air induction ||1.97 ||8.54/84.07 ||13.24/104.71 |
|2./64: SLP Loudmouth II exhaust ||1.98 ||8.49/84.90 ||13.14/105.99 |
|3./65: Performance Dist LiveWires ||1.97 ||8.45/85.10 ||13.10/106.21 |
|Temperature, 65 degrees; Humidity, 61%; Barometer, 29.93 hg; Race weight, 3,680 lbs |
|August 8, 2006 |
|1./85: SLP 375HP Pac, spun tires ||2.20 ||8.60/85.50 ||13.30/106.07 |
|2./85: Hotlap, more tire spin ||2.23 ||8.66/85.41 ||13.37/105.91 |
|3./86: 1-hour cool down, spun tires ||2.22 ||8.61/85.60 ||13.31/106.10 |
|4./87: Four runs, couldn't hook up, 2.20s || ||8.60s ||13.30s |
|Temperature, 87 degrees: Humidity 54%; Barometer, 29.97 hg; Race weight, 3,680 lbs |
|October 2, 2006 |
|Temperature, 82 degrees; Humidity 60%; Barometer, 30.04 hg; |
|Race weight, 3,690 lbs |
|1./79: LS6 intake, 400HP Pac ||1.96 ||8.25/87.26 ||12.83/107.77 |
|2./79: Hotlap ||1.97 ||8.35/86.27 ||12.95/106.83 |
|3./81: 1-hour cooldown ||1.97 ||8.35/85.95 ||12.92/106.51 |
|4./81: Hotlap ||1.98 ||8.40/85.51 ||12.99/106.03 |
|5./82: 1 1/2-hour cooldown ||1.97 ||8.31/86.02 ||12.89/107.08 |
|PARTS AND PRICES |
|Item || ||Part No. ||Price |
|1. 350HP Performance Pac ||28020 ||$704.75 |
| ||SLP Loudmouth II exhaust |
| ||SLP Flow Pac cold-air system |
| ||350HP PerformancePac fender badges |
|2. Performance Dist LiveWires ||C9LS1 ||85.95 |
|3. 375HP PerformancePac |
| ||SLP 85mm high-flow MAF 98-00 ||23060 ||189.95 |
|SLP 1.85 rockers w/springs, retainers ||51185 ||984.95 |
|SLP Diablo Sport II Programmer ||27007T ||474.95 |
|SLP 375HP PerformancePac fender badges |
|4. SLP fan-control switch ||63011 ||72.05 |
|5. SLP 160-degree thermostat ||100223 ||54.99 |
|6. SLP LS6 intake manifold, '98-'00 LS1 ||30041 ||499.99 |
|7. SLP 400HP PerformancePac |
| ||SLP tuned-length headers '98-'99 ||30051 ||899.95 |
|SLP header-installation kit ||30054 ||129.95 |
|SLP high-flow catalytic converters ||31037 ||349.95 |
|400HP PerformancePac fender badges |
|8. SLP subframe connectors, bolt-in ||70801 ||349.95 |
|9. Nitto Extreme Drag Radial ||Jeg's #726- ||273.98 |
| ||245/50R16 ||40133 ||(pair) |
Ken Estelle lifts the left-side...
Ken Estelle lifts the left-side header into place. It may be necessary to remove four of the six K-member bolts (leave the two center bolts threaded in about five turns) and all the bolts to the trans X-member. Prying the rear of the trans towards the passenger side can also aid in squeezing in the headers. Sometimes the steering-column shaft U-joint needs to be disconnected from the steering box for header- installation clearance.
Here's a look at the passenger-side...
Here's a look at the passenger-side header to the wiring-harness, heat-shield-tubing clearance. It looks tight in this shot, but there's about 1/4 inch of clearance. It's important to install the heat-shield tubing to protect the wiring from frying.
As you can see, the headers...
As you can see, the headers are a tight fit, but we didn't experience any interference around them. We didn't forget to reinstall and re-torque the K-member and trans X-member bolts. We popped in SLP's O2-sensor extension harnesses prior to installing the high-flow cats and Y-pipe.
Note the dramatic size and...
Note the dramatic size and obvious flow advantage over the stock Y-pipe and cats shown earlier. We reinstalled all four 02 sensors into the SLP headers and Y-pipe. A trade-off of losing some ground clearance (1-2 inches) was worth the significant gain of 22 rwhp. So far, we have yet to bottom out with the headers.
As Ken finishes tightening...
As Ken finishes tightening the nuts and bolts (provided with the connectors) to complete the installation, you can see the crossbracing and where the connectors bolt up to the framerails and transmission crossbrace. Made from tough 14-gauge steel, these powdercoated beauties provide a tighter and more solid-riding F-body.
The 400HP Pac adds over 75...
The 400HP Pac adds over 75 hp to a bone-stock LS1. With the additional power, we didn't want to chance creases in the quarter-panels while strip-testing. We needed a stiff chassis for consistent strip-test results without any unibody flex. SLP's bolt-in subframe connectors tie the front and rear of the car together with additional crossbracing to minimize T-top and dash rattles.
Spark-plug access actually...
Spark-plug access actually improves after bolting on the SLP headers. Before installing the EGR and smog pluming, we tightened all the header bolts from the inner to the outers. We made five passes on the bolts until they were all torqued to 18 ft-lb. We will retorque the header bolts (cold motor) after the engine goes through a dozen or so hot and cold cycles.
While the T/A was receiving...
While the T/A was receiving the headers and connectors, we decided to treat the 84,000-mile car to a gear-oil change to Red Line 75W90 All-Synthetic gear oil. It contains an additive for limited-slip differentials and is claimed to provide increased gear protection, reduce differential temperatures, and improve drivetrain efficiency.
We knew the only way there...
We knew the only way there would be enough bite to test the 400HP Pac was to get a pair of sticky meats. The Nitto NT555R Extreme Drag Radials (we ordered stock size 245/50R16) provide outstanding traction and handling on both the strip and street. The Nitto's are manufactured with a deeper tread (than other drag radials) and a hybrid compound for a 15,000-mile rating of normal use.
Considering the bad air (82...
Considering the bad air (82 degrees, 60-percent humidity) but great hook (thanks to the Nittos and E-town's crew), we were happy to run 12s with SLP's 400HP Pac. It was a load of fun testing each Pac and feeling the difference each step of the way.
375HP Pac Dyno Results The...
375HP Pac Dyno Results
The LS6 intake brought a peak 17 rwhp at 5,368 rpm. Before the LS6 intake, the 375HP Pac was worth 310 rwhp; after, it was 327 rwhp or 392 hp at the flywheel. It's no wonder that the LS6-intake swap is so popular.
400HP Pac Dyno Results The...
400HP Pac Dyno Results
The 400HP Pac was worth 22 rwhp at 5,353 rpm (peak). From 5,500 to 5,700 rpm (not peak), SLP's headers proved to be worth roughly 30 rwhp. The LS6 manifold and SLP headers put out nearly 40 more rwhp, making those bolt-ons well worth the effort and expense. We tried the SLP DiabloSport power tuner (from the 375Pac) but didn't see a change in power above 3,500 rpms. (We did observe a couple horsepower below 3,500 rpm).