Raising X dimension
 

Looking for some pros and cons. I tried this on the formula section of the site, but didnt get many hits. I'd like to see better handling, cruise speed, top end out of the boat. I already am having the transom redone so it wouldn't really cost much more to raise the dimension.

I have a 93 271 with a 502 efi in it. I was wondering if anyone has raised the x dimension on their boat. Any benefits? Negatives? How much should i raise it if any at all. I called formula and talked to scott. He also wasnt sure about the effects it would have. The boat was built back when they didnt have 4 blade props available, so im wondering if i were to raise it and run a 4 blade if it would handle better/increase speed. Thanks for your help

I'm far from an expert but IMO I wouldn't modify the transom to raise the prop depth(X and prop depth are 2 different animals by the way) The easiest and cheapest way to raise or lower the prop depth is via shortie lowers and or spacers. After your transom work gets done and the boat is back together running again, I would pick up a pair of -2 lowers and try them as is and see what happens. If it's too loose then you could space back down. If it doesn't work for you at all, you can easily sell the shorties and go back. Modify the transom and your stuck with it. Every boat and hull is different and responds differently to changes, It's all trial and error so permanent changes are not the way to go IMO.

What is the original x-dim? If it's low like 6-8" I would say raise it. You can always space down. Problem with running a shorty, being it an XR or SC, the nosecone can be a negative thing, unless you run 80+ or so. If it was me, I would put the prop shaft at 5" below ie. an x-dim of 16.725"-17" and then space it down if needed.

Not 100% sure of the current x dimension, the boat is at glassdave's shop so hopefully he will chime in. I also have a call in to formula regarding the difference between my x dimension and a newer 271. Thanks for the comments, keep em coming!

Your boat may have an X for a Mirage style propeller. The Bravo 1's had higher dimensions. That's the issue I ran into with my boat.

I modified my transom, raised the drives/engines 2 inches and picked up speed all over the RPM band. My drives were 7 1/2" propshaft depth, now they're 5 1/2". I could have went even higher but I went by what the manufacturer suggested for X Dimension with a Bravo 1 prop. http://s706.photobucket.com/albums/w...view=slideshow

Dave will know what to do, I called him many times during my project for advice. If you do decide to go up, nows the time to do it because it's much cheaper than buying a lower unit IMHO>

if your transom is not notched first thing you need is an extension box then raise your drive as much as you can with shorter lowers which is -3 when you do that you will need a 6 blade hering nothing else will work as good been there done that .bow lift is what you don't want to loose with a non stepped bottom.

It is set up for a mirage prop, thats what it came with from the factory. I think you might be on to something. Did you experience any negative effects like longer planing time, or decreased handling. Thats something im really not willing to lose

I will pop the jig on it tomorrow and get the boats actual X dim. It is pretty deep though.

You should be able to set it up with the propshaft about 5" below the bottom and still get decent bow lift.
I wouldn't go any higher than that though. You need it deep enough to carry the bow.

I raised mine 4" last winter. Its now 4.5" below. The problem I ran into was the 4 blade props would blow out when turning sharply .. ie water sports. Slip also went up. The boat is faster. I swicthed over to 5 blade props to stay hooked up & that kills most of the speed advantage. I'm going to lower the drive back to 5" below & hope the slip improves.