IMCO or Sportmaster on Straight V
 

I've been looking for a pair of -2 drives and I have a line on a pair of Sportmaster -2's. From all the searching on here, it really seems that the Sportmaster is slower on a Straight bottom V than the IMCO. So here is what I have: and '89 Formula 292 that is running around 71 GPS right now with the old school blunt nose bravo lowers. This boat has deep drives and in my opinion could really benefit from a shorter drive to get the X up. That said, the general thought is that the IMCO is faster than the Sportmaster, but seeing that I'm raising the X I would still think it would be a big improvement over my current lowers. I've been digging for at least a year on the Formula section, for info on anyone that has run shorties on an older bird. But there is just lots of talk about it, and from what I can find- nobody has really ever done it. So, has anyone with an old, deep x boat, used sportmaster shorties and seen an improvement in speed? If you've used them, would you post your gains or loss, and what kind of boat you had it on.

You are on the right track. The IMCO skag is shorter than the Merc so the Sportmaster scrubs 1-2 MPH compared to the IMCO but both will allow you to raise your X. If you drives are currently 5-7" below the bottom, you likely have a + 7-10 MPH opportunity if you are up for a total re-rig of the drive train. The re-rig cost will likely exceed the value of the boat. However, if you do this enough times, I have seen some fools exceed the value of their boat by 10X.:D

So by re-rig of the drivetrain what exactly are you referring to? I'm not going to go so far as add stand-off boxes but used lowers can be had for some fairly reasonable deals.

The cost to get your prop shafts 2-3" below the bottom of the boat will likely mean boxes, changing the engine heights which could mean custom hatches or sticking your carbs thru the hatches.....ask me how I know.��
If you just want to install -2" lowers, you can likely get +3 to 4 MPH and the Mirage props will likely still be the best for top end. I doubt you will get much more speed because your drives will still be too deep to pick up significant efficiency. The real speed improvements come from really high X dimensions....like -2" below the below the bottom.

your going to have to find the shortest drive possible,I like the imco as for the same reasons stated above.

Well I know I'm not going to start moving engines and filling and re-cutting my transom. I don't live in an area anymore where I can do that and my boat is 5 hours away from me. If it's not a bolt on solution then it won't be done. I could raise then engines a good 2" and still keep my hatches. If I can find a good deal on some -2's I may start there, otherwise it sounds like I really may need -3's. Right now I've been running Bravo props. The boat walks on plane like a ski boat. I've tried a variety of 4 blade props but never tried any 3's. It was pretty much agreed on in the Formula section that while you gave up 2 mph the Bravo's and Hydro's, they were superior. When I go up to the boat this weekend, I'm going to get some measurements. I really don't remember what my X is, I just know its deep.

thats because it was set up for ride comfort and keeping the props planted in the water.
I know first hand ,I take my 2.5" spacers out and my boat gets flighty on every wave,,way more throttling.w/ the drives deeper( a whole 2.5"s) is way smoother,but I do give up about 2-3mph.
whats nice is I can go back and forth in about an hour so,I can runhard and fast during poker runs and then go back to relaxing most weekends.:)I don't need it on kill all the time.

In my experience, ^^^^^^ this is exactly what you can expect except my guess would be 1-2 mph with 2" shorties versus Sutphen's 2-3 mph w/ 2.5" spacers. If you boat on Lake Michigan or are on and off plane frequently, you may not care for the trade offs for such small gains, especially if you are a pleasure boater. Keep in mind that you will have to change props, may have water pressure issues to deal with, boat will not walk on plane anymore and you will have low water pickups, which are more likely to pick up garbage than the side pickups I assume you have right now. I have no scientific facts to back this up, but I believe that deeper drives live longer. IMO, shorties are not magic on the older straight bottom boats, especially if your boat likes a fair amount of trim and if you like the way it handles as is. They can and do work, but are not necessarily the simple bolt on they appear to be. BTW, I was given this same advice several years ago, I'm just adding my .02 and passing it along. LOL

If buying used, it is best to assume it is all junk inside, even if the guy advertises them as having "about 60 hours". He may have inadvertently left out "in both directions" and "on kill the whole time". Lastly, they are not that easy to sell if the experiment fails, everybody wants to pay less than the cost of a new bare case for a complete lower, which is understandable after what I went through.

Good luck with your decision, I personally think the correct path is more horsepower or leave it alone, not shorty lowers.

So do you guys really think there is only 2 mph to gained by switching to a shorter drive? For the 5-6k its going to cost I would rather buy new heads for that money and gain a whole lot more than that. That is the one thing I hate with this idea, is nobody has done this on my boat, so its a pretty expensive test.

Try a set if you can find them. If they are not what you expected. Sell them. They are always for sale on the site. It's only money!

I'd take more (reliable) horsepower or higher Bravo drives any day, even if they both got me to the same top speed. My frame of reference is what I would call performance pleasure boating, not racing. If I had a step bottom boat, I may have a different opinion as I think those tend to respond better to high X-dimensions.

There is a reason they are always for sale on these sites. The same ones are probably being passed around like a Fountain skank.

BenPerfected, I have heard through the grapevine about all the work you have done in rigging your Scarab. I have a lot of respect for that kind of perseverance. I too, am one of those fools to far exceed the value of my boat (same hull as yours). I'm very attached to my Scarab; have had it for 20 years and foresee many more to come. I would be very curious too hear what you have found to be the fastest set up for our 30 foot Scarab hull. Particularly: what was the prop shaft relation to the bottom of the boat and did extension boxes help in "high" x-dimension set ups on this hull? Also, can this old straight v-bottom hull plane without drama with a high "X". Planing quickly is important to me because I like to water ski behind my Scarab. My 540s dyno at 640HP, I'm running the TRS drives still in the stock location (prop shaft 8 inches below the bottom!) turning labbed (trimmed down) 28 pitch Bravo 4-blades. At 5600 RPM I see 83 MPH on GPS. Changing the drive height will be the next phase of work for me. It would be great to hear what set ups you found to work well.

Thanks for all the input guys! I'm buying the shorty Sportmasters, soon I will see what raising the X does on a straight bottom Formula. Benperfected, it sounds like you have been through many stages in your project. When you first added the short drives, what was the effect on the props? I'm currently running Bravos, and I'm at least 400 rpms from where I really want to be at WOT rpm's. Did both rpms and slip increase with the addition of the shorty drives? When I work on the boat this weekend, I'm going to get some measurements and I'll report back.

Find a set of Imco's not Sportmasters

What what I've read, the only reason the IMCO is faster is because the skeg is longer on the Sportmaster. That is a pretty easy fix, I'll just trim the skeg to the same length as the IMCO. One of the members on here tested the Sportmaster and Imco's back to back and there was no speed advantage at all to either until over 100 mph. At which point the advantage went to the Sportmaster I believe.

I have used both Imco & Sportmaster shorties with great results. The Imco has a longer case, and a bit more nose cone. I will add that the Imco IMO does need modification to the water inlet for a couple of reasons. First, water pressure, second cavitation.[ATTACH=CONFIG]551131[/ATTACH][ATTACH=CONFIG]551132[/ATTACH][ATTACH=CONFIG]551133[/ATTACH]
The pics are of the Imco, you can see the water pickup is long and sloppy, it also causes cavitation as you can see from the pic. It actually burned into the case, and what do you think that does to the props performance... not good. But The nice thing is it can be modified to fit your exact needs for water pressure as you can see what I do in the pic. Both drives have long skags that too can be cut down to fit your needs. Both Merc & Imco make the skags long to accommodate a very high X for cats. They cast the cases not knowing what application they will be used on. I cut different lengths off of both brands to fit there application. Usually 2 to 4 inches.
I don't think you can go wrong with either case, I will say, I think there is more used Imco's out there for sale, and if you decide to sell for whatever reason, the Merc's will bring more resale.
Will you see big speed increase? You don't know till you try. I will also add that every boat that I put shorties on, drove and handled better, that is if it worked out.

One more thing if you have to adjust the Merc water pressure, you simply drill, tap and plug water inlets until you get you desired water pressure. So the Merc might be a better buy for you if you can find them reasonable. Also as stated by someone above, if you get used drives, have them inspected for wear.

Congrats to you for taking the plunge, I am following this with great interest as a fellow straight bottom Formula owner. I run the same speeds as you, only difference is my hull has a notch at the transom. No one has really tested shorties thoroughly (several different props, etc) and documented it well.
I do need a lot of trim to hit top speed, usually about 6 on the indicators

What kind of engines are you running rex? The 336 is very similar to the 311, which even though bigger, typically runs the same speed with the same power as the 292. I've got to run a lot of trim on my boat as well. The best prop I ran on mine was a Hydromotive QIV. The only reason I kept the bravos is Blades said he could make them out preform the hydros. I was going to ship them off to him to work on, but now with the shorties I don't want to do anything with the props until I know how this new set up is going to run.

Do more searches, there has been extensive testing with the -2 Imco/Merc lowers and lots of info posted on OSO over the last 10+ years.

I think he is talking about straight bottom Formula's. Nobody on here has done it, or at least posted about it. That is why I was hesitant to bite the bullet.

There is plenty of info on OSO related to straight bottom hulls with high X. In about in 2000-2002 the -2 Imco lowers became available that turned out to be a relativity inexpensive way to raise the X on an existing hull. The Bravo 1 props then allowed the new factory boats to have a much higher X which provided more speed. If you search back about 10 years and you should be able to find numerous threads about -2 lower info on older straight hulls from Wellcraft (Scarab), Formula, Cigarette, Checkmate, etc. The stepped vee hull manufactures led big time by the master marketer Reggie Fountain took most of the credit for the speed. In reality a large part of the speed came from the Mercury Bravo 1 props, coupled with high X dimensions (just rigging) and lighter lay-ups and some with cored hulls that increased speeds.The ventilated hulls did add speed (2-4 MPH?) on some boats but not significantly compared to the other changes. There are lots of old guys that know more than me, maybe some with add to this post of correct whatever BS I have posted.

I was reading some of your old posts about the marketing factor of the stepped hull and that most of the speed gains were really from higher x and props. It's funny how much power marketing has. There is certainly more than one way to increase speed, and I would rather make my boat more efficient, than just keep throwing more power at it. At which point drive durability starts to become an issue.

Exactly. Why throw power at a problem when you may be able to increase efficiency. Why sacrifice engine reliability and drive reliability when things like less drag and less weight can do the same?

I have more research to do on the subject, but what worked on a straight hull Fountain with a different X than I have is not always directly comparable. In addition, there are many more props available today than in 2000, more than just the Bravo 1. Who knows how these props available today would have changes the results 15 years ago?

Yes, I have noticed the speeds on the 336 are similar to the 311, even though the 336 is a tad heavier and longer. I have 450hp 454s from Mercruiser, basically an HP500 carb but in a 454 instead of a 502. Cam and everything else is the same. Normally I run about 67 with a full load of people and a good amount of fuel, 71 is with a very light load. Plans I have for sure are to get a set of aluminum heads next year and shave some weight in the ass end along with bump the hp up to close to 500. I never plan on running more than 500hp.

Right now I am running 23" Rev 4 props which handle great, and give me the same top speed as Mirage Plusses. Really I would like to have a solid 74-75mph boat regardless of load, and I will be happy.

How far is your driveshaft below the bottom of the boat right now?

Several years ago I raised the X dimension on my Apache. I gained 4 mph on top and over 6 mph mid-range. It was still at a conservative setting (5") below the bottom. I took the cheaper route (form me) and filled the transom and raised the X. Whole job cost me around $2K but MANY hours of labor. As a pleasure boat, I'm not sure I would go any higher than 4" below the bottom so you don't have planing problems.

http://s706.photobucket.com/user/Fun...sion%20Project

When you measure do you just run a straight edge forward and measure straight up to the hull? What if you have a notch do you measure to it or to the main hull? My notch is a few inches IIRC

I measured my prop depth today- I'm currently at 7" below the hull. So with the Sportmasters I'm going to be at -5".

Your engines are very similar to mine as is your current speed. My engines are HP 450 clones, except I used the 741 cam instead of the 731 cam. Last summer I was spinning a Bravo 1 Merc labbed 25 pitch @ a 5200 rpms. Top speed was 70/71. If your drive depth is the same as mine, you could most likely expect the same results as me if you installed shorter lowers.

Are you sure they are 25" pitch? Bravos only come in even pitches. I am out of prop at 5300 at 70, which is fine right now. Rev4's tend to run like a prop with more pitch, Bravos like a prop with slightly less pitch than their rating.
Once I get back to the US I will measure to see my drive depth

Yes they are 25 pitch- Bravo's that come from the Racing division at Mercury come in 1" pitch differences. Standard Bravo's are 2".

The new lowers came yesterday, so I am now lightly profiling the cases and the skegs. I'm going to cut some the skeg off because it is so long. I'm thinking about starting at removing 2". Any opinions on this? Also for those that have raised there drive height what did you see in regards to RPM increase or decrease with the same props. When spring comes I want to be able to start testing, so if I need to, I want to have a few sets of props on hand.

Here are the -2 Sportmasters.

I measured my shafts today and they are 7" deep if you measure to the main hull, about 5.5" below the small "step" at the transom, so about the same depth as your 292

Ill be watching, cant wait for results!

The new sweptback bravo uppers arrived Friday, so everything is here to get this project rolling. I also picked up a pair of highly worked over Bravo 1 props to test. I have been running a set of labbed B1 25's from merc racing. I now also have a pair of B1 Labbed 30's de-pitched to 27 with the defuser rings cut off. There is a night and day difference between the Merc labbed props and the other set when it comes to blade thickness. Soon I will see how they work.

After testing the Bravos, if you feel you need more bow lift consider a 25" Rev 4. They create more lift than the Bravos, and have great grip. A pair of 25s should go 75mph easy. A set of 26" Bravos would be interesting also. Ken the Prop God offers trades if you purchase the props from him. Just have to pay shipping

Getrdunn has a set of 26" Bravos that I'm sure he would let me test. As far as Bravo's go- I'm pretty set to find out what works.