There is absolutely nothing wrong with doing this for brief period of time, it won't hurt a thing. I've done it probably hundreds of times. Just don't let the engine get too hot.

I'm a ex-Lexus tech too BTW. Don't miss it.

no dogs in this fight but i agree with a few others ... whats the point besides literally hearing it run ? . will a quick run hurt anything nope probably not but, back to my question ...why whats the point ? button it up the way its supposed to be and away you go

There is no issue with just getting it started without water. It will not hurt anything. Would I run it for minutes, NO, But 30 seconds, sure.

As far as why?

I wanted to make sure it would start as I chopped all the wiring and re-pinned most of the harness to clean it up. I also did it without my freshly painted fenders, nose and hood installed so I’m not leaning across all of it to fix anything that goes wrong. I also checked the alternator for charging and made sure all the gauges worked. All before adding water or the front end sheet metal. Once all of this checked out, I installed the radiator support, radiator, condenser, intercooler and fans. At this time I vacuumed the Ac to check for leaks and cycled the fans. THEN I put antifreeze in and checked for leaks. And last but not least hung the front end sheet metal.

This is my standard practice, it works for me.

Stan

You have enough opinions to choke a horse here. If you want to I say do it! BUT, I'd pull off the belt to limit your risk of compromising the water pump seal.

I filled mine with straight water and pressure tested it.... fixed a few small leaks....
Cycled the fuel pump with the front line in a can, got the air out any trash in my lines post filter.... then hooked up to the rails and cycled pump again and looked for leaks...
You wont hurt anything by doing it the other way, but other than hearing it run for 20 seconds I don't see the point....I'd rather have it be able to run for a longer time so I can go over the entire thing....let the cooling system build pressure etc.... there are plenty of things that you may not know about until its been running for at least a few minutes and even more once its at full temp...

I get not having EVERYTHING installed...... but by doing it this way all you really know is that you can get it to run....which is good.... but lots of other info will still be unknown until it runs for a longer time

To each his own.... nothing wrong with either way.....

We did not start my LS3 just to hear it run, we were just at a point where we wanted to make sure everything was good before continuing on. Front drive wasn't installed, it probably was only 12 seconds of runtime. No issues. Finished build, drove he car about 400 miles was run on a dyno. Then changed oil, cut the filter in half to make sure no surprises were in it. HP and torque were great for a stock 525 LS3

some additional context
 

Just to provide some additional context.

The plan was for the bodyshop to prep the firewall and dash and paint. Then return the car back to me to drop the engine back in. I was going to plumb wire and fire to work out kinks , leaks ect.. so that I was not crawling all over a freshly painted car.... then return the car to bodyshop to complete the paint work.

When I received the car back the first time.. the work that was done was not acceptable... I was asked to just drop the motor in and send it back so the "we can make this right" this turned into a 3+ year Body shop prison situation worthy of its own thread of lessons learned...

Resulting in, the car being fully painted without ever being fired.. so now I am in the exact position I DID NOT want to be in... I freshly painted car yet to be be fired where leaks and ghost issues could be a reality..

we live... we learn..

I first fire freshly painted cars all the time. LS start ups are generally trouble free. Prime the fuel and oil pressure, turn the key and they start. Make sure your hose clamps and AN fittings are tight and you should be fine imho.

Don