Maintenance Mystery
First off, I'd like to say I love the magazine; keep up the good work. My reason for writing concerns regular vehicle maintenance. I have an '00 Chevy Silverado that I've owned since it was new. I always religiously changed the oil and filter at 2,500-mile intervals using synthetic 5W30.The truck now has 72,000 miles on the clock and I've been told that I should switch to one of those high-mileage oils. Why? I believe with the type of maintenance schedule I adhere to, the inside of the motor must look brand new. What's your opinion?
John Nelson, Evergreen Park, Illinois

Oil change intervals and oil types are at the root of many discussions in the industry. If you look at the new Ford F-150, the company suggests oil changes at 7,500 miles instead of the usual 3,000- to 5,000-mile intervals we lived with for years. As a rule of thumb, with conventional oil, recommended oil change intervals are every 3,000 miles. With synthetics, you can stretch it out to 5,000 miles, according to several of the chain lube stores. As for how the engine looks inside, your best bet is to pull a valve cover and see if there is any buildup under it. Chances are, with synthetic oil changes at 2,500 miles, your motor is as clean on the inside as the day it was produced. As for the "high-miler" oils, we first thought they were some marketing gimmick to sell more oil for older cars; there's even truck and SUV oil on the market now. While we're still convinced these specific-market oils are really the brain child of the marketing department, we've been told by the manufacturers that these oils contain specific additive packages that help renew old seals and such. Since we're kind of old school, we stick with the synthetics and the 3,000- to 5,000-mile oil change interval.

Streetable Stroker
Your article "Streetable Stroker" in the July '03 edition says that the Vortec 5700 L31 V-8 engine was used in '96 to '99 Suburbans. Is that also the same 5.7L engine used in 1500 and some 2500 trucks for those same years, or is that a different engine? If it is different, are they interchangeable as far as the transmission bolt pattern? And if it is different, do you have any suggestions for a 383 for the late-'90s 1500 or 2500 trucks? At the end of the article, you mention exploring some power-enhancing strategies in future articles. I hope you'll include headers in those articles. Are shorty, regular, or tri-Y headers the best way to go for the 383 engine in a towing situation? I'm in the market for a late-'90s Chevy truck and will be doing some towing. I like the idea of a 2500 with a 454 engine, but am afraid of the gas mileage; the 383 seems like the best way to go.
Steve Colorado, via e-mail

The Vortec 5700 L31 V-8 engine was standard on all Suburban models from '96 to '99 (including 2500s) and was the option engine on other light-duty pickups and Tahoes until it was replaced with the Vortec 5300 SFI V-8 LM7 engine in model-year '99. The L31 engine also powers '96 to '98 Sierra and Silverado pickups and Yukon and Tahoe SUVs. In addition, GM kept the L31 in a limited production of Chevy C/K pickups in 1999 when the current generation of Silverado and Sierra pickups were introduced.

As far as the power mods and header recommendation, we had Powertrain Electronics LLC [6600 Toro Creek Rd., Atascadero, CA 93422, (805) 466-5252, www.powertrain.net, st383@powertrain.net] recalibrate the computer for a test in the Sept. '03 issue and it made this combo a sweetheart to drive. The truck tested cleaner than stock and made 52 lb-ft of torque and 42 hp more than the stock tester we used as a control. That's almost half of the increase you'd net from a blower (emissions-legal), so that's not a bad return on the money invested. We have to stress that recalibrating the computer is key to the power output and factory-like driveablity of the combo. We never did get to install headers or a cam on our test truck; however, Powertrain Electronics recommends installing a good set of high-quality towing headers from Gale Banks or Hedmann. You might also check with Comp Cams for camshaft recommendations. If you install a set of headers and a cam, you'll definitely need to have Powertrain Electronics recalibrate your engine's computer to compensate for the new cam and headers, especially if you're into some heavy-duty towing.

Option Number Two
Smeding's Chevy Stroker 383 TBI is a direct replacement for the TBI motor that came in thousands of Chevrolet and GMC trucks. This stroker motor is smog-legal and works with the truck's stock computer. It features an 8.8:1 compression and produces 310 hp at 4,200 rpm and 420 lb-ft of torque at 3,300 rpm when installed with an upgraded exhaust system - that's a gain of 100 to 120 hp over the factory 350. These engines are not rebuilds: All Smeding crate engines feature brand-new engine blocks and brand-new premium components; it even comes with a one-year warranty. For more information, contact: Smeding Performance, Dept. ST, 3340 Sunrise Blvd., Ste. E, Rancho Cordova, CA 95742, (916) 638-0899, www.smedingperformance.com.

Power and Mileage?
I have a '95 Chevy Tahoe that doesn't miss many gas stations. I've already installed a K&N FIPK Gen II air intake kit, a Hypertech Stage 1 chip, a Magnaflow muffler with 2-1/2-inch dual exhaust pipes, 8mm Accel plug wires, an Accel cap and rotor kit, and a 160-degree thermostat. I've only been able to achieve around 11 miles to the gallon in town and about 13 to 14 on the road. Before, I was getting 13 in town and 16 to 17 on the road. After the initial installation of the chip and intake, I could get 240 miles to half of my 30-gallon tank; now I'm only getting 180 to 190 for half a tank. Is my thermostat too cold? I'm still running my factory plugs (AC Delco CR43TS) because my chip ran my Delco Rapidfire plugs too hot and caused them to fail. What is wrong? I saw the article you guys did on a '95 Tahoe that added a lot of power with the same upgrades, minus the headers and rockers. Why does mine suck gas?
Thirsty in Paducah, Kentucky

Seems that everyone wants the best of both worlds: 400 hp and 20 mpg. Unfortunately, it doesn't work that way. In broad terms, it takes fuel to make horsepower. Your chip upgrade essentially fattened up the fuel curves and moved the timing around a bit to make some extra ponies for you. And as is usually the case with a truck that runs better and sounds better, you often drive it a little more aggressively since it's more fun to drive.

How do you measure mileage from a half-tank of fuel? GM fuel gauges are notorious for being inaccurate, so how do you know the mileage has actually suffered by 50-plus miles without an accurate measurement? The most accurate measure of fuel economy, assuming the speedometer is correct, is to zero out the trip meter when you fill the truck, then divide the numbers of miles by the number of gallons you add when it's time to fill up again - not rocket science. This will give you the actual fuel used versus the distance traveled.

Your guess regarding the 160-degree thermostat affecting your mileage might have some merit. Today's electronically controlled engines have sensors that are calibrated to "see" certain operating temperatures during normal operation. If the engine temperature falls below this threshold, the computer thinks the truck is warming up and enriches the fuel table to compensate for the lean condition. Running a 160-degree thermostat in an engine that is designed for a 195-degree unit will cause it to run rich, and use more fuel. If you're looking for cooler temperatures to reduce engine knock from an aggressive timing curve, try a 180-degree unit. It will bring the engine up to proper temperature while still providing a 15-degree cooling condition over stock.