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Thread: Gt Pro -- New Class For Region 8

  1. #1
    Team Member Chairman's Avatar
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    Default Gt Pro -- New Class For Region 8

    This year (2007) the Twin City Powerboat Association (Minnesota, Region 8) introduced a new OPC Sportsman class called GT Pro. This class was designed as a graduation from our very successful Mini GT class.

    While Mini GT uses 25 hp fishing motors with aluminum propellers, GT Pro steps up to 35 hp and allows any propeller as well as trim.

    For 2007 there were only two full-fledged GT Pro boats on the water, and the addition of some Mini GT boats was required to make up the numbers. But we pulled off GT Pro races at most of our events, and managed to generate some close racing and spectator enthusiasm.

    For 2008, we are on course to have six to eight drivers in the class, with the possibility of more. GT Pro is shaping up to
    be a boatbuilder's class, with three boats already built, another under construction, and three more to be built this winter including one by yours truly. (FULL DISCLOSURE: Plans for all these boats were purchased from me at dillon-racing.com).

    However, you do not have to build your own boat to race GT Pro. Composite boats from such makers as Gran Prix, Critchfield, Camo, Racemaster, Rinker, Mirage, Furnel and others should make excellent GT Pro raceboats.

    Here are the basic rules:
    Minimum age 14-years-old
    Boats of any style, any material, at least ten feet long and four feet wide, 650 lbs. total weight
    A seat, and a foot throttle are required
    35 hp Johnson, Evinrude or Mercury fishing motors, 32 cubic inches max.
    Hydraulic trim is allowed
    Any propeller is allowed

    So far, speeds in the upper forties have been achieved using slightly modified off-the-shelf propellers. We anticipate breaking the 50 mph mark with proper racing props. Ron Hill is working on some for us right now.

    If you live in or near Minnesota and are looking for a simple, inexpensive class to race, GT Pro might be for you. Or start even simpler in Mini GT (production molded boats only, minimum age 12-years-old). Both classes are great places to get started in racing, or back into racing, or maybe as an alternative to driving on your knees.

    More information at http://www.dillon-racing.com and http://www.twincitypowerboatracing.com.

    Last edited by Ron Hill; 10-21-2013 at 08:45 PM.

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    Administrator Ron Hill's Avatar
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    Default Up Date Needed

    I saw some pictures of GT PRO in the APBA Propeller Magazine...

    How about an up date here???

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    Team Member mercmack's Avatar
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    Talking Merc Eng

    There Is A Merc Ob Thats 32 Cu's Serial No's 1960827 Thru 2874703..
    Its A Merc 350 The 350's Before That Were Only 30 Cu's..
    I Raced One Of The Older Once In "c" Production, Did Pretty Well Till Apba A Said It Was To "old" At Least I Got 4 Heates In....
    Anyway Would This Eng (32 Cu's ) Be Leagal??

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    My information is that the Merc 350 and 402 are 33 cubic inches. If there are some 32s in there somewhere, that only confuses the issue. We have been trying to figure out what to do: increase the cube limit to 33, or simply eliminate the Mercury altogether.

    Now we are finally in the process of refining the rules and making a few changes. One of those changes will likely be to eliminate the Mercury and go with the two cylinder OMCs only. The market is awash in these 31.8 cube motors, so no one will have any trouble finding them. Plus, we already have the tech specs for these motors.

    I hope to have the updated rules ready for our next club meeting this Thursday, 1/10/08. I'll post again when all is ready.

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    Sam Cullis Mark75H's Avatar
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    Default

    Quote Originally Posted by mercmack View Post
    There Is A Merc Ob Thats 32 Cu's Serial No's 1960827 Thru 2874703..
    Its A Merc 350 The 350's Before That Were Only 30 Cu's..
    I Raced One Of The Older Once In "c" Production, Did Pretty Well Till Apba A Said It Was To "old" At Least I Got 4 Heates In....
    Anyway Would This Eng (32 Cu's ) Be Leagal??
    1963, 64 and 65 they were 30 ci; 66 to 69 they were 32.5ci ... 32.5 is more than 32 so the 66 to 69's would still be illegal

    I guess you'd have to also make the old 30ci 4 cylinder Merc illegal too, even though they probably wouldn't be competitive without being modified (people would try any way) Probably the same for the 30 ci Merc twin ... probably not a real threat to the more modern looper twins
    Since 1925, about 150 different racing outboards have been made.


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    Administrator Ron Hill's Avatar
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    Default More Inside Info....

    Chairman...

    Thanks for the Up date... I agree with OMC ONLY, not that I'm a lover of the OMC Power...Just like the concept of K.I.S.S. (Keep It Simple Stupid)...

    What I would like you to do, is give ME some insight to how you are making steering bars, throttle and maybe trims for these motors. Also, what MODS are allowed for GT PRO.

    Over all weights that you guys are weighing....

    I will have props for 2008...no BS here.....

    MORE PICTURES!!!!

  7. #7
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    Default

    Throttles are standard Hot Foot and cable. We start at the beach, so electric start is desirable, though you can also start idling in neutral. Our minimum weight is 650 lbs. The rules will spell out allowable mods, and I'll post those soon.

    I've made my steering bars from 1/4" x 2" aluminum bar. These OMC motors already have two mounting points on the back of the pan. I brace them using two of the powerhead mounting bolts, and add a tie piece across the the back to tie it all together. The main pieces are bent down so that the cable attachment points are aligned with the tilt tube, so that cable tension is maintained as engine tilt changes.



    My tilt systems use a Mercury/Mercuiser pump and a Mercury cylinder. I made the bracket for the motor from 3/16" x 1" mild steel from the hardware store (stainless would be better, no doubt). First, remove all of the tilt lock mechanism. Wrap a length of steel around the base of swivel bracket. A bolt holds that in place. A second bolt attaches the cylinder. Bracing pieces are added, using holes abandoned when the tilt mechanism was removed. The other end of the cylinder attaches to the transom using aluminum angle or channel.

    I've set up two boats this way, and they held up well last summer.

    Some more information at http://www.dillon-racing.com/mini-ve...ee-page-14.htm




  8. #8
    Administrator Ron Hill's Avatar
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    Default Thanks for the Pictures

    What size props did you say you were a needing??? These are 9 1/4 X 13 to 15...
    Attached Images Attached Images    

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    What we had talked about earlier was 10x17. I ran 10x17, 3-blade OMC props last summer, but also a 10x15 that had a pretty severe cup. I was getting 6800+ rpm. With a small hub prop, with more blade area, that may be more pitch than I want, but it still seems a good place to start.

  10. #10
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    Default

    see next post

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