A wet suit alone can lop off 5 minutes or more on your time as can having to do with out turns. Having to struggle through a course full of other swimmers can can slow you a bit. Race day adreniline canmake you go faster but you might go out too fast leaving you to slow the second portion of the swim. I am sure someone out there can probably pull out some formula that will give you an exact time...but
I think you have to go to an IM swim with a ballpark range...say 1:10 to 1:20. That will help with positives and negatives that may pop up.

Here's the reverse question of this post. I am training for IMWI and am in base for the next few months, but one of the events I'm doing for the fun of it this year involves 4 separate events over a several month period. It starts with a 100yd swim next month, a 14 mile Time Trial in June, a 5 mile run in the fall and a x-country ski race next winter. Total time wins. The swim is converted so that every second in the water is 30 seconds of actual time. So a 60 second 100yd would be a 30 minute time. For the fun of it today at the end of an easy set of 7-100's (I'm in a recovery week) I tried a full out sprint. Started in the water and was swimming in a 20yd pool. I came in a 1:03 for the 100 (This would have been a 31:30 in the race). The actual race is in a regular 25yd pool and you can use starting blocks. My goal is 55 seconds, so for any experienced swimmers out there I was wondering if a 55 is within reach given it will be off blocks, in a longer pool and won't be in the middle of a workout. I'm not altering my IMWI plan at all for this race in any way, so I'm not really doing any sprint training at all.
Also, to get back on the track of this post for IM pacing, is one's times in a longer pool going to be better for times in a shorter pool for pacing? I'm pretty quick on my flip turns, but feel that if I was swimming in alonger pool my times would be quicker.

I was wondering if there was a conversion. I would hope a start from a block would also gain me a couple of seconds. When I swam years ago we had a 25 meter pool and my PB for 100m was around a 56-57, but that was 17 years ago! Overall, it is a very slow pool in that there are amost never any lane lines in it, it is only 4 lane and usually the afternoon crowd consists of me doing laps and 5-6 people doing aquarobics. Believe me, those people can get the little pool stirred up pretty choppy.

It's so hard to predict IM swim, bike or run times. It's the same as saying, "I train at 22mph for 94 miles in the hills, what will my IM bike time be at AZ......?" There are so many outliers and extrenuous situations (not talking flats or bike mechanicals) that can't be accounted for in training.

For instance: in my area I can't get an open road for longer than about 10 miles before stop light after stop light. Therefore, it's almost impossible to gauge time predictions.

Back on the IM swim. I just started reading about this Front Quadrant stuff. Granted I thought I was a strong swimmer al abit 15 years ago from 5 or 6 thru highschool mainly a sprinter. But for the most part i am no were near getting my "catch up" close to what Im seeing in some videos and others talking about Front Quadrant. Is this technique really that great??? I can try this with out a problem but is it worth changing my stroke???

I'm really curious to see how I come in. It was also about 17 lbs ago too!

On the IM swim, I think your pool time should give you a definite idea of where you should come in at, but there are so many variables it's hard to tell. My longest race has been a half. About a week before I swam 1.2 in the pool in 29:30. In the race I had a wetsuit, so I was hoping for faster time, but it was very choppy so that slowed us down. I found a good person to draft off of, but we kept catching up to slow traffic in the water from the waves in front of us, so that didn't help. Final time out of the water, a comfortable 30:08. So for every plus, it seemed there was a negative so it all equalled out in the end.

Same here, woring on being able to do a comfortable 120+/- at IMWI. I want to ingrain that pace/effort level between now and september and I know it will put me in a good place for the swim. Could maybe go a little faster, but if I can come without having exerted too hard then I figure I'll be in a good place after the swim and not too fatigued. One of my favorite workouts is to do a set of 15-20 100's on 1:30 working on my pace. I don't want to come in much more than 3 seconds from the slowest one to the fastest one. It really gives me a good feel for the effort level I'm putting out and where my time/pace should be.