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Username Post: Vortec 350 Modifications        (Topic#161696)
Super Senior Member
Posts: 3687

Loc: Bedford, Texas, USA
Reg: 11-13-02
06-08-07 09:55 PM - Post#1182193    

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.

1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals

Edited by 1983G20Van on 06-08-07 09:56 PM. Reason for edit: No reason given.

"2nd Year" Gold Supporting Member
Posts: 1054
Age: 60
Loc: Fort Worth, TX
Reg: 11-27-06
06-09-07 03:53 AM - Post#1182231    
    In response to 1983G20Van

Sounds like you did some good tuning. Nice wrap up. Thanks for posting.
I ditched my K&N, just sold it on line. I read too many things about it and the air flow sensor. I get just as much power with the factory filter it seems.
Your experience with the headers and pre cat pipes, is what I have been thinking of doing. Mine is just a little old 1500 extended cab short bed light duty. It moves pretty good compared to my 89 with the throttle body. What do you think had the largest impact on the performance?

98 C1500 Silverado extended cab 5.7 auto 2wd Fort Worth, TX.

Posts: 138

Reg: 06-05-07
06-09-07 07:11 PM - Post#1182549    
    In response to jbknight311

1983G20Van Mind educating me on how you determine which knock sensor is which as far as voltage goes? What determines how you should select a knock sensor when you make a mod?

Old Guy
93 Z71 Basket Case Rebuild, the Never Ending Story

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