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iTrader: (1)

going from 375hp to about 600hp (Twins) ...in my 311 ..V hull about 9K wet ... I am running 24 Hydromotives now ..........where should I start ? I am thinking 28's ?

throttleup

First we need to know what rpm the old motors ran at WOT and at what speed. What is the target WOT rpm for the new motors? Are the new motors supercharged or naturally aspirated? Do you have dyno runs on the new motors?

Matt

bbladesprops

If you are keeping the rev limiters at the same level because the hp curves run the same lines between old and new engines.......

yes, 4 inches of pitch growth will be a good test point.

We really should know more about the engines and their desired WOT range.

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iTrader: (1)

old motors would push 68mph at about 4900 ....from about 75-80% Throttle to WOT was pretty much a dead spot ..meaning at 80% I would be at about 46-4700 rpm @ about 64mph ...you would not notice any acceleration from 80% to WOT ...but milking the drives would get you to about 68 or so ...

New motors are naturally aspirated and likely will not be Dyno'd. I am not sure where we will end up on RPM range but the building did say we would bump the limiters up some .... I guess thats where data from the Dyno would help. thanks ..m

iamfaster

Do you have TRS or Bravo's. It would be tough keeping bravo's together with 600hp ,especially if they are the originals. Check your bottom. Many (if not all) of the 311's had a hook intentially put into the bottom to help plane and keep bow down. I assume you still have the original power steering? You will have to go hydrolic. Your hull gets difficult at speeds over 70mph. Call Formula, they are very helpfull.

My bro had a 89' 311sr1, and I had a 89' 357sr1, both with 420's and TRS drives. Really classic looking boats!

Good luck

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iTrader: (1)

yep Bravos ... But I am not hard on em so I think they will last.... a while ...Matter of fact we were looking at the Hull the other day and seems pretty straight ... would like external Steering but not yet ...$$$ ... smart thing would be to swap out the Assembly's drives and add steering .....but why be Smart now ?

throttleup

With a horsepower increase of 225 raising the rev limiter is all but unavoidable. I would consider running the motors in the 5600-5800 range. I would guess that is about where peak horsepower is produced. Peak horsepower is where you will see max speed.

A pair of 26 pitch props (actual pitch) at 5800 should get about 84 mph at WOT. This is assuming you are making 600 horsepower.

I would try the props you have now and see what kind of speed and rpm you actually get and then go from there. If you turn those 24's at 5800 you should expect to see about 78. Then see what kind of rpm you are actually turning, how hard you are into the rev limiters and then go from there.

Matt

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iTrader: (1)

Matt .. great Idea .. I had just assumed to go ahead and sell the Hydro's now and get some new props but it makes a lot more sense to just get a base point from these props. The motors will prob not be Dyno'd so it definitely be a trial and error process .....m

throttleup

You can use different pitch props and use the boat as a dyno. By changing the pitch of the props thus changing the WOT rpm you will find at what rpm the boat is fastest. With that information you can then make a decision what pitch prop will work best overall.

We have lots of prop in our prop test program. This would be the most cost effective way to find out what pitch prop works best for your new motors. Of course you can always borrow props from other boaters, just make sure you know if the props have been modifies or not. It's nice to have all stock props for the testing so you are comparing apples to apples.

Matt