Help with initial start up

[19Suburban69]

I’m installing 6.0 w/4L80 in my ‘69 C20 suburban. First time playing with LS. I’ve got most mechanicals done and it’s down to wiring and exhaust. I need to know if I can do initial start up with open headers. I’ll install O2 bungs in collectors and plug in sensors. If not I’ll have to trailer it 40 miles to and from exhaust shop, then go thru start up. I’m wiring challenged so I’m at a point I need to find someone to come over to guide me. I’ve got more questions, but I’ll stick with exhaust issue first.

[mongocanfly]

I ran mine with open headers....no issues...just make sure theres nothing behind them thatll melt
If you use a quality wiring kit, it's actually fairly simple...most all of it just plugs in..

[paul mora]

Do it all the time. Just make sure you don’t have anything that will burn at the end of the exhaust. Don’t rush the starts up double check as much as you can. Every time I have a problem at start up is because I rushed and want to hear it run before the neighbors went to sleeped

[19Suburban69]

Thanks guys. Clearance at collector isn’t a problem. I’ve gone over engine connections. Powered fuel pump today to clear lines. Then found I had 5/16 instead of 3/8 AN fitting that connects fuel at rail. Another trip to parts store. Hoping to get computer flashed this week.

[LS short box]

The cool thing about a LS swap if all the connectors are connected as they should be and the fuel pump turns on it will start and run very quickly. On my LS swaps on first start I don't add water. Engine oil, trans fluid and power steering fluid on first start. Just run it for a 30 seconds or so. Look for fuel line leaks. Look for vacuum leaks.
Once I'm happy I add trans fluid as needed. Add power steering fluid and turn the wheel back and forth to make the air is out of the system. Then add coolant and make sure there isn't any air in the heads. I look for check engine lights. I do have a scanner.
The tune may be off until you get the exhaust on. O2 sensors can be confused by open exhaust.

[clay68c10]

You can leave the O2s unplugged while the headers are open. It won't drop into closed loop and try to use bad data from them.