2 3/4 " to 4" exhaust holes

I need to transform my 2 3/4" thru transom exhaust to 4".
Since I will not have pilot hole for the hole saw,how do I do this properly?
Thanks in advance.

I would screw a cleat to the inside with the screws placed within the 4" radius so they will be gone when you're done. Then just cut as normal. Run the pilot in the but before the saw touches the gel, switch to reverse to grind throught the gel so you don't chip any out before switching to forward to finish the hole.

I would screw a cleat to the inside with the screws placed within the 4" radius so they will be gone when you're done. Then just cut as normal. Run the pilot in the but before the saw touches the gel, switch to reverse to grind throught the gel so you don't chip any out before switching to forward to finish the hole.
Thanks phebus. That makes sense.
Screws at 3 1/2" in the back through wood cleat,extra long pilot bit.
Thanks again for the knowledge.

I went from 3.5 to 4 inch TT holes and i used a 3.5 holesaw inside of the 4 inch hole saw as a pilot, there was just enough thread inside the arbor to screw on the smaller holesaw inside the 4 inch and worked great.

I went from 3.5 to 4 inch TT holes and i used a 3.5 holesaw inside of the 4 inch hole saw as a pilot, there was just enough thread inside the arbor to screw on the smaller holesaw inside the 4 inch and worked great.
Thanks Vee-Driven.