Hello all, new guy here happy to read so many helpful posts on this site. I have a 1991 Camaro RS with a 305 TBI. I bought a 2002 truck with a 5.7 vortec motor, spider injected, and a 4L80E transmission. First off, my car runs OK considering it's a 5.0 and 700R4 tranny, and I get about 23 MPG. I want more power so I'm thinking about swapping out the motor & tranny. What kind of fuel mileage do you think I should expect from the 5.7 liter with the 4L80E trans? I plan on keeping the 5.7 complete since I have the wiring harness and ECM with my truck. Will this allow my dash gauges to still work? Do I need to change the entire harness or just the ECM and the harness from my firewall to my motor & ECM? I am ASE certified and I've worked on cars for over 25 years but I haven't done much in the means of swapping out this type of aspiration. I appreciate any helpful info.

 

Welcome aboard thirdgen.org.

Are you sure about the truck model year? 2002 should have been a 5.3 or 6.0 Vortec, which are LS-type engines.

The "spider injected" part sure sounds like a '96-'99 Gen I SBC type "Vortec" engine.

I've never heard glowing reviews of that injection system. It doesn't seem to be performance-modification friendly.

However, in the TBI forum, there is a sticky in the top section of that forum about a "budget 350", which starts with that engine. You might want to look that over and see if that would be a better approach for you.

The issue with the 4L80E is you need a PCM or TCM to control it. You could swap in the entire EFI system with harness & PCM along with the 4L80E, but the 4L80E swap will produce issues of its own. The TH700R-4 is capable of handling the 350, so I'd recommend the 350 longblock swap and keeping the TBI and TH700.

 

My bad, I forgot to mention that my engine is in a 2002 P-30 18 foot box truck and it is a 5.7 Vortec. So even with the complete wiring harness, you're saying that it would be in my best interest to keep the TH700 transmission? Thanks for the warm welcome as well.