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 GTR 25BB Modifications for speed 
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Joined: Wed Aug 22, 2018 10:25 pm
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Post GTR 25BB Modifications for speed
I have a brand new GTR 25hp Big Block, on a Gatortail 1748. Currently I can run between 21-24 with just 2 people and no gear. I was wondering where I should start to try and get a little more out of my engine. I’d like to be able to go around 25mph loaded down and be able to get through some tough mud in the event I need to. Any thoughts or ideas would be Appreciated.


Wed Aug 22, 2018 10:35 pm
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Post Re: GTR 25BB Modifications for speed
Sell it and buy my Delta level 3.


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Thu Aug 23, 2018 4:49 pm
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Post Re: GTR 25BB Modifications for speed

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Fri Aug 24, 2018 9:42 am
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Post Re: GTR 25BB Modifications for speed
Willey Fast LLC has some 25BBs ROLLING!


Sun Aug 26, 2018 11:42 pm
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Post Re: GTR 25BB Modifications for speed
25 BB Delta heads, valves, pistons, cam, push rods, stock carb, and voodoo on Uncle J 16x44. I was running 32 unloaded with stock prop. 3 man load and 9” prop I was running 25mph. I added a mikuni and it got me up to 35 with stock prop


Wed Sep 05, 2018 10:32 am
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Post Re: GTR 25BB Modifications for speed
Short story - I'm a rookie and seeing 20 mph with a 25BB hybrid Delta mods on an open layout Uncle J 18x48 with stock 2 blade prop. Light load but full 13 gallon tank in bow. Tach doesn't like to go above 3,400 rpm at cruising speed.

I read on here people are typically cruising at 3800 rpm, which I've seen briefly and could feel it. Do y'all think I'm trying to push too big of a boat/load or is there some tuning, prop work, and stick experience with the thing to unlock the extra 400-500 rpms?

I'm coming from a CC bayboat with 150hp on the back so I'm giving myself more stick time to adjust. Just learning as I go.



Details -
25 BB w Delta mods on an 18x48 Uncle J mod v bateau. I think Delta mods would be level 3 but went with 35 hp stock carb instead of a mikuni. Its a wide open layout to the front deck with 6" catwalks and 22" sides. Been out twice and haven't put any electronics yet.

Iphone speedometer app has me holding 20mph on the stock prop with 250lb load. The kicker is that I can only consistently get 3,200 to 3,400 rpm max. I trim all the way up and then down about 2-3 button pushes to get best speed.

Once I hit cruising speed, I can back it down to 3,000 rpm and then squeeze down WOT and it will go up to 3,700 rpm for a few seconds and back down. There have been times when not changing throttle it would randomly shoot up to 3,800 rpm for a few seconds and it felt magical, but I'm unable to replicate. No depthfinder yet so I don't know if I just ran up on a flat or something.

Out of the water in neutral I can rev up about 4,400 rpm. I didn't get mine dyno'd, but per a modded 25 BB dyno video on their facebook it looks like 3200-3400 rpm is putting out about 35-37 hp. In the 3700-3800 rpm range it put out 40 hp.


Tue Sep 11, 2018 11:11 am
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