Imco Sc lower which one?
 

looking for some set up advice , currently running a 489 pro charged big block in a 20.5 Cougar V Hull , the hull is a Round Chine Hull currently running lows 92-93 mph , looking of upgrading my xr lower to an imho sc lower , I'm just not sure on which one is best for boat , currently from bottom of hull to center of prop shaft I'm measuring at 7.5 inches with everything level. Does anyone have any input here? I've hurd from a few guys they have tried the Imco sc lower with the -2 and it had some negative effects. I obviously would like to get rid of the XR lower and go to the nose cone at the speeds im currently running.

Thanks

hey
 

anyone have any reviews on running the -2 in a smaller boat? some people say great and others say blow out issues , any input

As low as your prop is I would go to the -3 and modify the upper for clearance. You can always shim it lower if needed.
4 3/4 below the hull is about right I would think for a 21 ft boat.
Do you have tabs?

hey
 

sent you a pm

7 3/4 inches below the hull is very low for a performance boat.
At 4 3/4 inches down you might need to run a 4 blade prop but not a 5 blade.
Like I said I would go to a -3 IMCO shorty. It is very easy to shim it down but expensive to buy a new shorter lower.
I am looking for a good used -3 to have as a spare.
I have a -2 now but it is 1.5 ratio and I can get on plane just fine with the -3.
I bet you have to trim way up to get top speed.
Trimming the drive way up makes the boat heavier when the goal is to make the boat lighter.
It also can make the boat hard to control at speed

hey
 

sounds good so with a 1.36 ratio you would do the same?

I have the same challenge, prop shaft is 7.5" below boat on a 24' Daytona and everything I have researched says go with the -3. Like stated you can always shim it needed.

bigblockbill - Are you measuring from the bottom of the outer hull forward of the step or from the center pod.
That sounds a lot deeper than normal for a Daytona.
Stock mine was 2 inches lower than the lowest point on the hull.
I installed an IMCO neutral box with a -3 shorty and recut the transom up 1 inch for a total height of 2 inch above the lowest point of the hull.

daniel475 - I don't understand what you are asking.
I am running a 1:36 ratio because I don't want to run out of prop when I add the blower to my engine.
Right now I am running a labbed Bravo 28 at 6400 RPM. I would have to run a 32 if I was running 1:5 ratio. Add the blower and I can't buy a prop big enough.

hey
 

No i get what your saying about prop ratio etc, I will be doing the same with a 1.34 ratio , just hurd sometimes with single leg applications the shorty's don't seem to work , for my boat so far when I had the standard length bravo one with xr lower it was very smooth and didn't need a lot of trim to get it moving , I guess you really don't know how a shorty would work until you try one , just would suck to bolt one up and it was un safe ! thanks a lot for all the information !

With the prop down 7.5 inches I can't see how a shorty wouldn't help.
The fact that you don't have to trim much just means that your hull doesn't need much bow lift.
You are basically trimming to get the prop to suck in some air to loosen it up.
A shorty should cause a noticeable gain.
I still say to go with a -3 and shim it down IF you have to.

hey
 

and you think i would have no worries of prop blow out or handling issues? thanks for the input btw

How bad do you want to break 100 MPH.
7.5 inches down is real deep.
I had handling issues when my drives were that deep.
I raised the drives on my 34 Scarab with -2 IMCO shorties and it helped handling.
I used to have a 18 ft Glastron Carlson and I installed an Alpha SS drive that is 2.5 inches shorter than stock and gained 10 mph.
the next year I replaced the transom and raised the drive height another 2 inches and again gained 10 mph.
The drive on that boat was installed too low and the cavitation plate above the prop was actually 1/2 inch below the bottom of the boat.
Trimming the drive up for speed actually caused the cavitation plate to dig into the water and pull the transom down.
I am running a 4 blade Bravo prop on my Daytona but they are totally different boats.
I have the drive modified to allow more negative trim otherwise the boat would NEVER get on plane.
But as I said IMCO lowers are expensive so buy the shorter one and shim it down if needed.
The higher that you run the drive the more chance of blow out during turning.
Adding more cup to the prop can cure that problem and help with low speed planing.

Lower
 

I just raised the drive and motor 5 inches ,went from a trs. To bravo now drive is 2 inches below on a 23 dsytona ,any thoughts ????

hey
 

thanks a lot , changing the lower from standard to -2 you would just need a case correct and swap parts over? how fast did you get your Glastron to go? very impressive mph gain for sure

I think that was from the center pod, but back where the lower step was. Also based on the research I did says it was very common on them early 90s daytona's to have a really really deep prop. Maybe this weekend I will go get a good true measurement on it so that I can know.