Mercury's Racing Sterndrives

[yipster]

Mercury's new Racing Sterndrives and video's at boattest
The 500 EFI is the introduction to the big-block racing machines for MerCruiser. It's used in APBA offshore racing as well as consumer boats. The 525 EFI features custom Edelbrock aluminum cylinder heads, designed exclusively for Mercury Racing, closed cooling, new stainless steel CMI tubular "sweeper" headers and the exclusive Mercury Propulsion Control Module (PCM) 555. The results? Higher horsepower and a higher torque band throughout the engine operating rpm range.

[yipster]

Or hide a supercharger... 150 extra horses! This super charger fits under the engine hatch. Stage one kit from around 5K incl. raw water intercooler. Needs a through transom exhaust and a new prop, maybe a lower unit gear change. It works with Mercruisers ECU electronic control but when installed you can lose the engines warranty. The stage two kit gives higher compression, need other injectors and electronic control changes. Well, if you got the bread, was nuts to start with, like technics or just dream... Accessible Technologies Inc.

[catmando]

The Procharger from Accessible Tech is a centrifugal design which acts more like a turbocharger than a supercharger, which means it comes online higher in the powerband than a roots or a screw type blower does.

As for the Merc racing engines, all that is old news to most of us here in the States. There are two new motors just released last year; the 525, which comes with closed cooling and the 575SC, which is the old 8.2L block with a blower. The 525 is also 8.2L.

GMC is using the new 8.1L block, which is 496CI.

[yipster]

catmando thanks for the info, maybe very old news to you but i just got the video on that closed cooled 575SC block. new long prop skeg, only good for 90+. 2fast4 me but interesting.

[yipster]

i've been reading merc has now a racing option on their BIII sterndrive that also lifts the drive verticaly up and down.
who has been racing such systems (like in F2 OB's) does it work like a speedbrake or who can explain?

[tom kane]

I do not think merc stern drives lift up and down verticaly,maybe this stern jack is as close as you will get. www.land-and-sea.com/marine/sternjack

[yipster]

http://www.activemag.co.uk/BookReade...wop/2005/03/24
http://www.boatdesign.net/gallery/sh...00/ppuser/1988
now is or isnt this ITS vertical ajustable?
hmm, think i'm way short in change...

[marshmat]

By "flexibillity of drive height" they refer to the ease with which the standoff box can be mounted at different heights. The driveshaft inside the box includes universal joints so that the drive's input shaft and the motor's output shaft don't have to be perfectly level with each other. The drive is trimmable, but not height-adjustible, while running. The general idea is that mounting the prop lower gives better acceleration, while mounting it higher puts less gearcase in the water to cut drag and boost speed. To adjust the mounting height on the B3XR or any other ITS drive you must unbolt the entire drive leg and housing.

[tom kane]

Originally Posted by marshmat

By "flexibillity of drive height" they refer to the ease with which the standoff box can be mounted at different heights. The driveshaft inside the box includes universal joints so that the drive's input shaft and the motor's output shaft don't have to be perfectly level with each other. The drive is trimmable, but not height-adjustible, while running. The general idea is that mounting the prop lower gives better acceleration, while mounting it higher puts less gearcase in the water to cut drag and boost speed. To adjust the mounting height on the B3XR or any other ITS drive you must unbolt the entire drive leg and housing.

That`s the way I understand it.It is nice to have height adjustment,infact it makes the I/O much more a pleasure to use.It realy is essential.

[yipster]

so thats how it works but is not what i thought.
thank for mentioning Tom and your enlightment marshmat before getting the wrong idea.

can i pop in one more dumb question on a surface prop?
do they run in a complete haze or does the lower side of sigle prop tend to walk sideways more tahn a submerged prop???

[tom kane]

The article at http://www.powerandmotoryacht.about....4surfacedrives has good info and also keep an eye out for articles by Paul Kamen NA in links.

[yipster]

Good read Tom, here Surface-Piercing Propellers by Paul Kamen, N.A.
http://www.well.com/user/pk/SPAprofboat.html

[tom kane]

Thanks yipster,I downloaded that article several years ago.American boaties seem to favour big slow turning surface drive props,which means that everything else must be big and heavy too,and deeper draft.Kiwi boaties seem to like small fast turning props,light shallow draft.there is realy more than one principle to running surface piercing props.Angle shaft propulsion powers most of the fastest boats in the world and will be hard to replace for simple efficiency.

[yipster]

using this surface drive calculator i find about 1/3 speed increase over other drive systems using the same power, seems Paul Kamen is right in that it is a better system

[tom kane]

It would appear that Paul Kamen article was published in 1995,there has been much work done prior to that.