6 hours ultramarathon without specific training?

My take on your situation is a little different from what others are saying. (My experience is over 100 ultras including 50 miles (i.e., 80K) in 5:35.)

In a six hour ultra you do not need to eat real food. Gels should be sufficient. However, some people really like salt after a few hours so I would have chips available.

As far as starting pace: run what is easy. Do not do an artificially slow pace. I would run at least two hours before there is any walking. The walking breaks should be short (a minute or two) and frequent rather than long and infrequent. If you walk too long your legs will stiffen up making it difficult to get back to running.

Not knowing where you are running, this may not be applicable. Have sunglasses available.

Good luck! This is not as difficult as people are making it seem.

Based on your info, you should try to go for 5:00/k. That should feel easy enough (really easy at the beginning) but still be comfortable. If you can do that for the whole 6 hours, you would run over 72k. With short breaks to drink, (every couple laps) and maybe eat a snack or two, you should be able to get over 70k. If your legs or stomach do go, just keep walking at as fast a pace as you can. I'm an old guy and I hiked the last 6 hours of a 12 hour race at a little under 9:00/k pace.

Go do a couple hours at 5:00/k and you should have an idea if that is an easy enough pace you can do for 6 hours. If you feel like it is too slow during the race, you can always speed up the last couple hours.

I agree with all of it except the last sentence.

This will be a lot more difficult for a beginner than for an ultrarunning veteran. Picking the right starting pace for an ultra is not something you can learn without trying.

70K?!, no way. I'd just shoot for something like 36 miles (6 miles/hour-58K), 60K would be the 'A' goal. caffeine for sure but go easy on it, First 3 hours will be a cakewalk and then it's just a matter of time before the hurt starts. If you can avoid cramping, you should still be mostly running at the end. I love slipping into some dry shoes a bit past 1/2 way (have the laces way loosened so you can quickly slip into them). Those short loops will even afford you to change out a bandana with ice rolled up in it every 2nd or 3rd loop if it's hot. You'll lose more time during these 'transitions' than those more experienced, just accept that. It might help to hook up with someone before the start who is planning on running your approx. pace or ideally a little slower. They will most likely talk your ear off that first hour and you can learn a lot from their experience. I like to have my own small table with my stuff spread out on it rather than have it in a pile on the ground. Maybe a chair for changing shoes, addressing blisters... With so few racing opportunities right now, I say go for it, you're not going to come out crippled. So what if it takes you a week to recover? Sunscreen!!

Pace is not relevant if you haven't completed an ultra before. Anything above marathon, it's about time on your feet, nutrition, hydration, GI issues, and how to deal with being in the hurt locker for hours. You can run a 50K on gels and some water, but 6 hours is a different animal. Nobody talks about GI issues. Listen to some ultra podcasts (e.g., Jason Koop's Koopcast), he interviews experts and apparently close to one-half of ultra DNF's are due to GI and nutrition / hydration issues. Also ensure you have proper gear (again, look at aid stations and what you need to carry, do you need a hydration vest or will a belt work?). Wishing you much success!

It's a 2K paved loop. What gear? /. A perfect first time 'ultra' other than total lack of specific training!

Oops. Sorry missed that part. My other points still valid.

Thanks very much to all for the great advice, much appreciated. I've decided it's too big of a leap for me at this point in time, but I'll be keeping this thread in mind for the future!