In past doing 70.3 triathlon . I did 2 large bottles skratch super carb ( 7 scoops per bottle ) on bike and was good on run drinking Gatorade first 6.5 miles then coke or Red Bull for last portion of run. I used no gels ! Strategy always worked . Now attempting full Ironman soon . Was gonna continue with the skratch super carb drink 4 bottles in lieu of 2 bottles on bike . Question now ? Thinking I am gonna get hungry. I weigh in 190 pounds male . Going for 15 hours or less to complete race . I am thinking about also doing a 40 gram beta sis gel and a Amrita protein bar also every hour on bike . I was then gonna continue with 40 gram beta sis gel every hour for marathon and then the drink available at every station? I been trying this during training but only doing half the distance close to race time during training so not sure if I am over doing the fuel intake . Yeah I get it no one person is the same but any advice would be grateful !! Thanks
seems alot to me for a 15 hr racer
the slower u go the less carbs you should need per hr so u r pushing for GI stress
also im not sure what 190 pounds is as we are in kilos , but try and work on .8 to 1 grm per of carbs kilo per hr on bike and less so on the run and just fuel by how your feeling as u run and use aid station fuel (coke gels water gatoraide ).
The scratch is 560kcal/bottle, so 2,240kcal for the four bottles over let’s assume a 6.5hr bike. That’s 346kcal per hour (1g of carb per kg would be 340kcal…so about right). If you are doing the bar and gel, you should probably cut back on the Scratch and keep the fueling level where it’s at.
My bias is to do gels on the run, since it’s hard to accurately measure intake of fluids at aid stations. What you can take in on the run will be lower, so adjust accordingly.
I would do the math. 60-90g carbs/hr. Start there & see what that would look like over the course of ~15hr race. Then think about sodium/sugar needs.
Practice in training. Get the gut ready to handle as much as you plan on giving it.
No you won’t get hungry unless you’re under-fueling. If hungry, drink more fuel.
Hunger is a response to being WAY behind on kcal need during an event, not an intrinsic need for solid fuel. If you’re hungry, then you’ve overwhelmed the hunger-suppressing effects of epinephrine (and other things) during exercise. I usually say something like this to myself when it happens: “Congrats! You’re way behind and about to be in the hurt locker!” 
That being said, as many folks have found over the years, consuming solid fuel later in a race can help blunt the hunger response when you’re totally behind on fueling rates for many hours. But it usually comes with the risk of GI issues. Tread lightly. Better to try to play a little catch up with liquid fuel. If you get to this place though, you just need to be cautious all around and start paying very close attention to gut feel and your nutritional consistency the rest of the event.
so, if going for 15 hours, you will not be able to do without supplying addtional energy.
first, i would check how many carbs you used during the 70.3…i would than try to work on hitting the 90-100 gram per hour carbs goal. do tests before on which carbs you are able to digest.
Also check for salt, also calculate the correct amount of water you need to take in for soluting the ch and do not overshoot here, many athletes drink to much.
A sweat test is also a cool tool for knowing how bad you sweat and what minerals should be supplemented during the race.
Fueling is the most important thing imo, and many athletes should put alot more time into this, as it is the major limiter when racing…
so, try to mix these yourself…many outthere use fructose, personally i am limiting fructose to almost zero, as i get stress with it…i use maltrodextrin with a mix of honey, normal sugar or dextrose…i end up with 100 gramm an hour…i do use this in my racepace sessions, as your you need to know, how your body reacts when watts and racepace are there…