Fast355

Just wanted to speak of some mild mods that I did to my 5.7 Vortec recently. Keep in mind I knew it would never be a tire smoker, but at only 255 HP, it needed a little help, without sacrificing torque. It is in a 1997 Express 2500 Conversion van with 68,000 miles . The 350/4L80E/3.42 drivetrain has always been a doggy combination pulling that much weight. The 3.42 gears and the 2.48:1 first gear of the 80E just make it pokey off the line compared to a 4L60E with 3.73s. Anyway after the modifications it runs pretty darn well for what it is and gets 2-3 mpg better on my daily commute than before, simply because I can use less throttle and the engine runs at a lower RPM to accelerate the load.

1.) First and foremost I did a full tuneup on the engine using the stock AC Delco Platinum plugs, GM Wireset, GM Cap/Rotor, New fuel filter, new PCV, cleaned the MAF, etc.

2.) The intake manifold and valve cover gaskets were leaking. I replaced both with Felpro equivalents. While I was in there the engine was given GMPP 1.6:1 roller rockers (head to pushrod clearance was checked) and the new GM MFI spider in place of the crappy GM poppets.

3.) The stock GM exhaust manifolds and pre-cat pipes were ditched for a used set of Thorley headers and pre-cat pipes from a wrecked 1998 C3500 truck bought on Craigslist. Very nice shape and the fit is perfect. Bolted right in place of the cast iron manifolds and original pre-cat pipes. Both pre-cat O2 sensors were replaced at this time with new GM sensors (turned out to be Bosch anyway, YUK!)

4.) The PCM kept storing a knock sensor code. I ohmed out all the wiring and found no trouble. Ohm'd the knock sensor and found it to be open. I replaced it with a knock sensor for a 1996 LT4 corvette in anticipation of the 1.6:1 roller rockers

5.) I installed a new K&N air filter along with modifying the stock air box to improve the flow (removed the silencer).

6.) I replaced the throttle blade in the throttle body with one of the aftermarket units, removing the EGR diverter piece.

7.) I repinned the PCM harness to use a 411 PCM (LS1/Vortec truck) running a 2002 2500 Express tune as a starting point. I have been tuning the 411 PCM with the EFI Live software. It seems to be a very good software package, rivaling TunerProRT (I use with OBDI). I have programmed out all of the Torque Management, eliminated the PE fuel delay, calibrated the VE tables, recalibrated the MAF tables, put a more performance oriented advance curve in it, and altered the shift points to suit the new found power.

8.) This is the end result. 10-60 in about 9 seconds flat. 10-70 in 13 seconds. From a 6,000 lbs Conversion van with NO gearing. The little 350 moves the big van effortlessy at 75-80 MPH uphill with the A/C on, running 87 octane.

http://youtube.com/watch?v=WydwLghk_yw