I just got a set of quicksilver 4" thru hull tips and before I drill massive holes in my transom I figured it would be in my best interest to ask a question lol the tips are 4" but there is lip for the exhaust house that's a little less than a 1/4" so when I drill the hole should I drill a 4 1/4" hole or should I keep it as small as possible and if I drill a 4" hole will I be able to squeeze it in? I'm guessing the best idea is to drill the 4 1/4 hole so I don't crack or break the fiberglass but I figured I would ask for some better advice

Go 4", then finish the hole (or any slight adjustments) with a simple sanding flapper wheel.

I'd drill a large enough hole.
Sounds like 4.25 is that size.

I'd drill the holes, then resin them after, so the transom doesn't have the option of water seepage and ultimately rot.

Also, make sure your holes are inline good with the risers, so that you dont have an angle on the rubber hose. The rubber can burn thru if theres a decent angle.

Everything he said, plus put a bead of marine silicone under the outer flange of the exhaust tips and coat your screws in LifeCaulk before you screw them in.

I would say NOT this. Go with the 4" for a several of reasons: Your flange bolt holes are already tight to your 4" hole, for this reason its always good to use at least a simple drill fixture for your main pilot hole and your mounting flange holes. Nothing wrong with having the tips snug in a 2-1/2" transom; the gel is not going to crack there...a simple chamfer to the gel with sand paper is adequate. The main thing here is carefully determining where your main pilot holes are placed. I used some simple white thin pvc drain pipe that fit perfectly on the riser. I then extended it to the transom and traced around it - determined the center of the traced circle and drilled the pilot hole using the fixture to keep things perpendicular. I drilled the pilot hole for the other tip from the outside the boat to ensure good cosmetic placement - you'll be very close on the inside as well.
Unless you can find a deep hole saw, you'll be cutting the hole in 2 steps; from inside and outside the boat, so again, the pilot holes are important. Here is a simple drill fixture that would be adequate for the job: http://www.acehardware.com/product/i...a=pla_18465513

If you are not in a hurry, a great way to make sure you never get rot from your screw holes is to drill them out oversize, say 1/4 inch, and then pack marine epoxy into the hole. After it has cured, drill your holes in those spots to the appropriate size for your screws. You will get excellent bite, and you will never need to worry about how well your caulk is sealing. This might be overkill for something like exhaust flanges, but it is a very good idea for something like trim tabs or K-planes.

Budman II I like the way you do things.

Why you would want to drill a hole that's not large enough for the pipe to pass through and then use an abrasive wheel to enlarge as opposed to just drilling to proper size hole escapes me. Having 1/8" of "play" around the tips is not detrimental.

To be clear Keith p........are you saying that the greatest outside diameter that needed to pass through the transom is 4.25"?
If so, you will never "squeeze" a stainless tip through a lesser opening than the tips largest outside diameter.