MIXED MATCHED DRIVES

[tcob]

I Noticed checkrocket and at least one other using xr drives with imco lowers . whats up with that ? i have been leaning towards replacing my bravo 1 with an xr , but i sure dont want to be breaking the xr . if / when my bravo fails , what part of it should i expect to fail ? i have a friend who ran stock bravo lower and bravo shop upper against 850 hp , no problem . i guess my question is it more logical or common that one area of the bravo will fail and could i replace that area / section . new motor is on the dyno and at 650 hp and maybe a little more (another carburator enroute ). GOT BEADS ?????

 

[tcob]

I Noticed checkrocket and at least one other using xr drives with imco lowers . whats up with that ? i have been leaning towards replacing my bravo 1 with an xr , but i sure dont want to be breaking the xr . if / when my bravo fails , what part of it should i expect to fail ? i have a friend who ran stock bravo lower and bravo shop upper against 850 hp , no problem . i guess my question is it more logical or common that one area of the bravo will fail and could i replace that area / section . new motor is on the dyno and at 650 hp and maybe a little more (another carburator enroute ). GOT BEADS ?????

 

[checkrocket]

The Imco lower has a nosecone and is quicker in the water. Its also got a bigger water pickup and everything is heavy duty. The outdrive was built on onieda lake at the drive shop in the syracuse area. No problems, very reliable. The boat originally came with a bravo I drive. The boat had problems after problems with that drive. Gearsets and shaft problems. Decieded to get the XR drive, it was supposed to correct all of the short comings of the bravo I. I decided to eliminate every Problem by taking the best of both drives. The superior upper of the XR and superior lower half which is the IMCO. I saw this setup on a lot of boats in the syracuse area, with boats with much more HP then mine. My boat is around 500.

 

[jrumon]

IMCO lower units are a trick piece and are shorter than the Merc stuff... most common is Imco's 2" shorter one...NICE STUFF!!! By using it, you get the "bullet" shape and a 2 inch higher X-dimension for better top end. Jim.

 

[checkrocket]

That is true about the X-Dimension. When I changed from the GPS from 74-77. Without any other modifications.

 

[tcob]

THIS SUBJECT CONTINUES TO BLOW MY MIND BECAUSE THERE IS STILL MORE THAT I DONT KNOW THAN I DO . i've heard kip say that most checkmates are already 2 inches above x , and about as far as you can go . i've also heard that with a boat that neads a lot of trim (mine) that i actually need some drive in the water to carry the bow . you betcha i'm confused !!!! but this is the area , that i'm most interested in (efficiency)even more than durability. and hey ,where are these guys on oneida now ? in the old boathouse facility ? and is it the same chris that worked at tri-bridge ?????? RISENSHINE !!!!!

 

[checkrocket]

If you are going to be running 650 hp ++ then efficiency should not be in your vocabulary. The IMCO will add some speed. The x dimension depends on the hull. I have a 1999 convincor 251 classic. That's why I went with the IMCO Shorty as they call it. A little bit of Tab goes a long way.

 

[checkrocket]

I used to have a Sonic 33 and that boat had a pair of SternPowr drives MX06. Older Technology with cleaver props. Those drives were bullet proof. Never needed to get a part for one, good thing, becasue they are hard to find. Had 500+ horse to each side and ran them hard. Never had a problem, of course they were coupled with Borg warner Trannies.

 

[tcob]

ok , i just called sterndrive specialists , your guys on oneida , they are in the old boathouse store . and i will go out some day next week and see what they recommend . send lawyers guns and MONEY !!!!!!

 

[vinny p.]

I have been doing some research on this very topic. Next winter , I am planning on freshening up the motor and adding a Whipple. So, I have been looking for information on drives. Be it XR, Imco, or a combination of the 2. I posted this question here a while ago hoping to get a response from Kip, but I never got it. I called the factory and spoke to Mike about it. I also called Stern drive specialists---http://sterndrivespec.com/---- to get his answers to my questions.
Now, the answers may surprise you. Both Mike and Chris ( from Stern Drive spec.) agree that my best drive would be a stock XR. They claim that the bulleted Imco bottom would actually slow me down. I was also told not to run a shorty lower, because my 259 already has an aggressive "X", making it shorter can lead to problems. While experimenting with it would be the best, I can't spend $8K on a drive to find out it wont work for me.
As it was explained to me, the theory behind the bullet slowing you down is this: If you are not running 100 mph or over, a bulleted lower will not give you any benefit. It is designed to cut through the water at high speeds. A stock lower can not break the water fast enough to allow the water to get back together and hit the prop at high speed. A bullet is better hydrodynamically for high speed because it will break the water more gently allowing it to regroup, so to speak, so it can hit the prop. Otherwise, you run the risk of cavitation. But, the main downside is this, being that my 259 requires alot of trim to get up and run, the bullet would be pointing down, thereby creating drag.

Now I have not done or no of anyone who has experimented with this. This is just what I have been told by 2 of what I would consider to be, reliable sources of information.

What do you guys think???? Because I am also confused..

 

[Enforcer 24]

Vinny P, I don't quite follow you an how the "bullet would be pointing down." If that was thw case, you would be over trimmed and airating the prop. As far as I know, you can only trim up so far before loosing "grip" on the water. The only reason you do trim is to get the bow up and out of the water for less resistance and more speed. With that said, the drive, theoretically, should be perpendicular to the water surface the faster you go. (within reason of a few degrees) The nose or bullet of the drive shouldn't be "dragging" or "digging in" to the water. If you over trim, you can "feel" the prop loose "grip" and hear the engine rev up a bit with no increase in speed. Hope this helps you a little bit, as I am by no means an expert on outdrives and their properties while in motion. This is only my best "I think I know how it goes" guess.

GIT-R-DONE

 

[tcob]

vinny, i think you are on the money ,i think checkmate knows their boats . they have experimented, and if they could make them faster and still pretty much all around usable , they would have done it . i trust what they are telling me about the x . bobs nosecones or land and sea , or somebody used to run an add showing their competitors bullet shaped nosecone with positive trim pointing to the bottom and actually robbing speed , just as you described . this is part of the efficiency that i have been questioning for the last 2 weeks. imco or whoever vs mercury ? whose got more money for r and d ? i am very familier with mercury's testing facilities in s. w. florida where i spend a lot of time , incredible facilities. they test and experiment non stop . i trust them too .they might have been a little slow with the xr , but they wern't asleep at the wheel .i'm going out to talk to sterndrive specialists next week .i think we are asking the right questions and ultimately making the decission easier. imco may be better for some applications, and overkill for others .i don't want to buy a drive that takes away one of the benefits of the boat that i currently enjoy, only to be told after the fact , "you didn't ask me that".if this was easy everyone would be running a lot faster than they are .RISENSHINE!!!!!!!

 

[vinny p.]

Enforcer24,
I agree with your theory. BUT, this is what I was told from the guys I mentioned above. I am hoping that their expertise in the field will steer me or should say us in the right direction for speed and efficiency.
Let's see what Bob finds out after he talks to SternDrive Spec.

Bob ,
As I am sure you will, post your response from SternDive, we all would like to hear the answer.

 

[Enforcer 24]

I know of the guys at Sterndrive and they do know their stuff. My room mate does a lot of buisness with them. I am sure they will not steer you wrong. Also, the "Boathouse" bar behind them is an awesome spot to go early Friday nights with a boat. Party galore!

Good luck with your set up.

GIT-R-DONE

 

[tcob]

CHECKROCKET. you said you broke the bravo 1 more than once . were you hammering it ? i had the 88 version of your hull , hammered the hell out of it for 7 years . broke motors , but never a drive .did you break the xr lower before you added the imco ? having owned one like yours, and now the 283 which has a wider beam and an entirely different feel ,the 283 is much more boyant in the stern than yours , and i'm wondering if (a)the 251(stern) actually rides lower in the water ,and might benefit from a shorty ? (b) what is the boat like now in rough water ? does it want to launch in rougher water or loose its bite? i am thinking this may be more of an issue with mine if i pick up much moe speed . again because of the extra boyancy. RISENSHINE!!!

 

[checkrocket]

The Bravo I lasted for the first 33 hours that I had the boat. I had it rebuilt. Then at 75 hours I had a problem. I had the drive removed and had the XR with the IMCO put on. I bought it set up that way. The boat handles great in rough water. Some people in this forum are saying slower with the bullet nose cone on the IMCO. I can only go by the experience with my ride. By adding the new drive I picked up 3 miles an hour. That is a significant amount. Think about how much additional HP you woul need to increase 3 MPH. I am comparing GPS readings to, not Speedo. I can't say that the Bravo didn't blow up from being used and going fast, but I didn't floor the boat out of the hole. Did launch off some waves and maybe didn't throttle down as fast as I should have. Only live once, Live and learn!

 

[tcob]

checkrocket , unfortunately ,we are basing lots of our opinions / theories /hopes on what we read .problem there is most businesses want your business , so obviously the facts tend to get slanted their way .the best way would be to experiment ,try everything, but most of us can't keep throwing $$$ at it .i wish it was easier to seperate fact from opinion . not disputing your results .you're absolutely right about what it would cost to find 3 mph via more hp. my first question would be the variables between the different hulls. would what worked for you work for me ? or would the fact that my hull was originally designed for two motors or another 1200 lbs under the hatch require something different ? stay tuned my friend!!!!

 

[vinny p.]

As I said in my post. I am only relaying the information that was given to me. I didn't try any type of drive yet. Please don't take what I said as the definitive answer. I am tyring to learn something here myself. If I know something to be fact, I will state it that way in my post. I don't want to mislead anyone..

 

[tcob]

vinny . i just read everything i could that was posted on speedwake by sterndrive specialists. the one thing i have to say is chris asks what the boat is naturally and in some cases suggests shorties ,in some not . the x and the particular hull seems to play a major part in his recomendation . one size may not fit all . everyone seems to feel these guys know their stuff , and i know that area is obsessed with go fast . still planning to get out there asap. looks like they also have props in stock ! by the way , your avitar , great south bay ??? i haven't been much more than a 1/2 hour past coney island .RISENSHINE !!!!!!!!!

 

[Dave's ZT260]

I've had several drives on my checkmates. So here goes the best I've found. Always go 1.5 gears, they run faster unless you’re running over 110mph. Either the XR upper or Imco upper works fine. (Add a drive shower to the XR)

The lower is the big issue. Raising the X dim above 17 1/2" will be a big problem. So don't if you are already at a high X or you will never get out of the hole. If your X dim is at 16 1/2" or less you can buy a shorty drive, but you may need a 1" spacer after all that.

If you run over 85mph a nose cone is the way to go, but not a Sportmaster or Imco lower. They both "dig" in too much and need far too much trim to work for us. So a standard XR up to 85mph or so is good, after that go to a nose cone on an XR lower. The reason is the torpedo tube length is shorter this way and it runs faster with less trim. The Imco and Sportmaster have their place, but only on a surface piercing drive, such as a cat, where they can perform. (Not checkmates)

Rule of thumb, if you can run an XR without blow out issues great. If not add a short nose cone like Hydromotives later. This way you still have options. There is no way to take off the cone on an Imco or Sportmaster.

You will hear a lot of BS from dealers and manufacturers. I learned the hard way so you don't have to.........