I currently have a '90 Jeep Wrangler with a Chevy 350 (carbureted) with a TH350 auto and a Dana 300 T-case with fullsize axles (D44 front and GM 12-bolt rear) out of a blazer. I run 4.10 gears and 35-inch tires. Right now with the current setup, I run about 3,200 rpm at 65 mph. Yeah, it's high rpm! And I get like 8 to 10 miles per gallon. This is my daily driver, and I wheel it hard. I like to play at Calico, Big Bear, Dumont Dunes, and Johnson Valley to name a few. I'm stationed at Ft. Irwin, California, and I'm deployed in Iraq right now. I am trying to do all the research, so when I get back I can get right into the swap. I want to swap in a four-speed auto and fuel-inject the engine. I picked up a '98 Chevy 3/4-ton two-wheel drive truck complete for $600 that runs and shifts well. (It just has around 170,00 miles on it.) It has a Vortec 350 and 4L80E. I went online and checked out Advance Adapters, and my current adapter (PN 50-6300) will not work with the 4L80E (the new adapter is PN 50-0401). From the information I gathered, my current TH350 is 21 1/2 inches and the adapter is 3.65 inches long. Now the 4L80E is 24 1/4 inches and the new adapter is 4.65-inches long. If I swap this into my Jeep, my driveshafts will have to be lengthened and shortened. Are there any other issues I should be looking for? Is this transmission worth the swap, or should I sell it and look for a 700R4 or 4L60? What other issues will I have with the wiring and fuel injection? I couldn't find any other adapter company that makes an adapter for the 4L80E. Should I stay with the TH350 auto? I value your input and just looking for some ideas. I don't care if you publish this or not. Your expertise in this field is what matters to me. Thanks.
SSG David J. Karbo
Task Force 1/11 ACR
Camp Liberty
If you have a complete '98 Chevy truck, I'd say just go ahead and swap in the entire Vortec 350 and 4L80E tranny into your Jeep. Use the truck's wiring harness and computer. Just be careful when removing the harness so you keep all the important sensors and fittings. Even with 170K on the clock, as long as the engine has been well cared for and doesn't smoke on startup, have any knocks, or other bad signs of wear, it's going to give you a lot more oomph for your money. You'll pick up way better performance due to the fuel injection and Vortec heads, plus your mpg will probably jump up into the mid teens.
The good news is that you'll probably be able to sell off your old carbureted 350 and TH350 tranny and the adapter to recoup most of your parts costs. Try www.craigslist.org, www.recycler.com, or any of the popular off-road Web sites. You should be able to get roughly $450 for the running engine, $150 for the tranny, and $250 for the old Advance adapter.
I'd use the Advance (Advance Adapters, 800/350-2223, www.advanceadapters.com) stuff you've researched. The Vortec engine will bolt right in place of your carbureted 350 and you'll probably be able to reuse the vehicle's current exhaust. Your Jeep should already have a return line to the fuel tank that you'll need for the fuel injection. For a fuel pump, you could either run an external inline pump next to the fuel tank, or go get a junkyard in-tank pump assembly from a '91-up 4.0L-equipped YJ. The factory pump should put out enough pressure and volume to run the injected Vortec engine. You will have to shorten/lengthen your driveshafts and add a CV to the rear if it doesn't already have one. As for your transmission, the Advance Adapters 4L80E-to-Dana 300 adapter requires that you remove the two-wheel drive tailshaft and swap the main shaft out for a 32-spline GM shaft (PN 8661596, '91-'96 or PN 24204289, '97-'98) because it's adapter (PN 50-0401) changes the T-case input from 23-spline to 32-spline. You'll also need to shorten the new tranny output shaft about 1 inch for a total 334-inch stickout length or use Advance's optional 1-inch spacer (PN 51-0404). I'd shorten the shaft since your wheelbase is already pretty short and every inch counts. Finally, you'll need to install a tone ring on the tranny shaft and use Advance's 40-pulse GM Vehicle Speed Sensor (VSS) kit so the tranny will shift properly.