A game plan of efficiency and performance can go hand in hand as long as all-out power isn't the goal. For my wife's daily driven '00 Grand Prix GT, efficiency is a priority. So far (if you read Part I in the last issue) we picked up 2-3 mpg and 13 front-wheel horsepower from the SLP Performance Parts bolt-ons (1.8:1 rockers, airbox, and catalyst-back exhaust). Like most who want more of a good thing, we were confident SLP's 151/48-inch equal-length stainless steel headers with 3-inch collectors and a 3-inch flexjoint could add even more punch and thrift to our 3800.
These headers cost $749.95, can be used with supercharged or normally aspirated GPs, and are found under PN 30070. Mandrel-bent 409 stain-less steel tubing and OEM flanges are employed, and an aluminum-ceramic coating is applied inside and out for lasting luster and durability. Provisions are made for the factory EGR and oxygen sensors-the latter have their fittings located to eliminate sensor-to-body contact when the engine torques in its mounts. Neither welding nor cutting are required for a proper fit (air pump-equipped GPs will require welding of the air tube and flange, however). SLP's performance guarantee and lifetime limited warranty are also included.
A high-flow catalytic converter (SLP PN 30073, $179.95) or an off-road race pipe is required with these headers. Of course, we took the converter to keep the GP street legal. Also needed is an installation kit (PN 30071, $89.95). In the SLP catalog it claims its W-body headers, "Produce up to 25 additional horsepower, depending on application." That's a big power gain for a V6-even if it's supercharged. We wondered if our nonsupercharged six would come close to that power increase on the chassis dyno.
Ignition Upgrade
Before we made our date with SLP, we knew it couldn't hurt to replace the aging factory-installed ignition wires (date coded 8/99) and coils. Performance Distributors had just released its LiveWires (PN C9043, $89) and Screamin' Demon coils (PN 31735, $99) for the '95-up 3800 front drivers.
LiveWires feature heat-treated glass-braid sleeves that are resistant to chemical corrosion, moisture, and temperature damage, from -76 degrees F to 1,400 degrees F. A silicone jacket and insulation also keep moisture away, and swivel boots are employed to ease installation. A spiral-wound core thwarts electronic interference, and the 300-350 ohms-per-foot low resistance allows for excellent spark travel. The set is custom fit and assembled (no add-on sleeves) and each wire is numbered for foolproof installation.
Screamin' Demon coils employ a brass terminal to attach the coil wire. According to the company, the brass terminal is more conductive than a typical aluminum terminal and will resist corrosion better. Increased coil energy allows for a wider spark plug gap, which could increase power and mileage.
Though Performance Distributors ignition products have shown improved performance in previous strip and dyno testing on other makes of motors, back at SLP we ran identical numbers to our last pull on the rollers. This is possibly because, though Performance Distributors recommends increasing spark plug gap to 0.060 (due to the increase in coil power) to improve mileage and horsepower, the stock plug gap for the GP is already 0.060. Another factor is the power increase is generally found at 5,000+ rpm and our GP makes peak horsepower at just 4,790 rpm. Regardless, our intent was more to increase durability and reduce maintenance with these high-quality ignition parts.
Header Happenings
After baselining our GT once again, we moved to the installation room to install the SLP headers. It took roughly 611/42 hours for SLP's Tony Kalpach and myself to hang them. Unfortunately, our GP came equipped with the California air pump package, requiring the air tube and flange to be welded to the rear header (thanks, Ken Estelle). Our 3800 happened to be only the second application in many installations that SLP has seen with the smog pump. As most 3800s don't have the smog pump, hard-core gearheads with decent hand tools, a floor jack, and jackstands should be able to bolt-up SLP's headers in about a day's time.
Once strapped down to the dyno with the new headers, front pipe, and high-flow cat in place, the SLP guys informed us this was the first nonsupercharged V-6 to test their tubes. Director of Engineering Brian Reese mentioned they have seen as much as a 29hp increase on blown applications. After spinning the rollers, we were pleased to learn we picked up 20 hp on our natural six. SLP's headers clearly kicked butt! No doubt, the previous intake and exhaust mods from Part I contributed to the header's performance.
Cooling Caper
In search of a few more horses, we attended to the cooling system. The 3800 retards the timing a few degrees when the coolant rises over 195 degrees. On all our previous dyno pulls, the coolant temp was between 201 and 212 degrees. We backed off the dyno and headed back to the installation room to drain the coolant to install the SLP 180-degree thermostat (PN 100180, $17.95). The radiator was filled with straight distilled water and a bottle of Redline WaterWetter (it was August and over 90 degrees outside). Next, SLP's fan-control switch (PN 63013, $69.95) was installed. The switch features three positions-manual low, high speed, and stock.
We positioned the fan switch on manual low for the GP's return to the rollers. On back-to-back dyno pulls, the coolant temp ranged from 180 to 190 degrees. As you can see, the coolant change, the 180-degree thermostat, and the fan switch lowered the temperature an average of 21 degrees. SLP's SuperFlow dyno computer showed us the knock retard sensor didn't retard the timing, and we were rewarded with 2 extra horsepower for our efforts.
More MPG
With the newfound power, we were anticipating gas mileage gains. Happily, after many mileage checks, we noted another mile to the gallon. The added mileage was recorded on the same 180-mile round trip (70 mph, A/C on with three passengers). Here's the breakdown of the recorded highway mileage statistics-stock, 25.4; Part I, 28.2; and Part II, 29.1 mpg. Around town also showed increased mileage, stock was 17-19 mpg; now we're seeing 20-22 mpg.
Conclusion
- After all that dyno testing, we wanted to see how quickly the thrifty six could go down the quarter-mile. But getting the car from my busy wife is tough-the GP is our only car.
We have witnessed many bone-stock 3800 GP GT's running mid to low 16s-we're expecting to go a second faster. Tune in next time as we take the Pontiac from my wife and go strip test it!
Test Notes: Air inlet temp at the airbox in the dyno room averaged 108 degrees F for all tests Baseline conditions: 86 degrees, 52 percent humidity, 29.91 barometer Part I after-mods conditions: 90 degrees, 49 percent humidity, 29.85 barometer Coolant temp was 201-212 degrees F during baseline and Part I after mods testing Part II after-mods conditions: 91 degrees, 58 percent humidity, 29.81 barometer Coolant temp was 180-190 degrees F during Part II after-mods testing
