15x7 engine choice

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Pilkington34
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15x7 engine choice

Post by Pilkington34 » Wed Oct 16, 2019 10:43 pm

I currently have a 15x7 with a 454/425hp, 2-1 ratio, and a 78inch water walker 3 blade.
I do a lot of duck hunting and have to run dry sometimes. The boat will do it but it really dosnt like sticky stuff and when running 4 people in deep water my cruise is 4K but just me i can cruise around 3100 rpm.
My question is after season I’m looking at maybe replacing my engine for more power and less weight. I’m trying to figure out what would be the most effective route to go without totally breaking the bank. I know I’ll probably need a new prop and my reduction bumped up to atleast a 2.3-1 . I’m just wondering if i should do a 450hp ls engine or go small block and then also need a new engine stand

crazycoonass
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Re: 15x7 engine choice

Post by crazycoonass » Thu Oct 17, 2019 12:07 am

I replaced my engine this summer. Not knowing exactly what my old engine was making I do know for sure I gained over 100hp and 100lbs/t. I guesstimated the old engine was about 400hp. New engine dynoed at 560/560. I'm somewhat disappointed in the money I spent to get the results I got. So in my opinion if you only gain 25hp you will be disappointed too. I realize you'll have some weight savings but I don't think that will over ride the cost of a new engine. My engine weights were the same. So if I were you I'd get the biggest bang for my buck that my budget would allow.

Pilkington34
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Re: 15x7 engine choice

Post by Pilkington34 » Thu Oct 17, 2019 12:27 am

I’ve also looked at stroking my motor to a 496 but I’ve been told by others i won’t be happy with the performance and if i want to make over 500hp in my small boat i should look at a ls3 or a 427

One Eyed Gator
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Re: 15x7 engine choice

Post by One Eyed Gator » Thu Oct 17, 2019 8:57 am

With a 7' wide hull you don't have a lot of flat planning bottom and add to that the weight of BBC. Gaining 25-50 is great but losing weight would be better. BBC with iron heads is around 700lbs or more, aluminum ls 425lbs. Dropping 250lbs off the back of an airboat is huge specially with a narrow running bottom. LS2 or ls3 easy to make 500hp. Can use iron block 6.0 as well but it weighs about 90lbs more than the aluminum blocks.

I run a 7-6 wide x 14' alumitec with a iron 6.0 maybe 425hp. It is a junkyard bottom end with an upgraded topend. When I am loaded to go fishing 3 guys, gear and 2 coolers I cruise around 3400-3600. I run a 2.68 ratio with a 79.5" 3 bld R. Last year I built a 15x7-6 diamondback with a stock junkyard 6.0 carbed with 2.55 and 80" 3 bld maximus all ss rigging. Fairly heavy boat, cruise is around 3600, pushes like a tractor very impressive on the coastal dry stuff but not very fast.

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Slidin Gator
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Re: 15x7 engine choice

Post by Slidin Gator » Thu Oct 17, 2019 9:14 pm

General rule of thumb is 8 lb per Hp for running ground. In DeepWater, weight savings is pretty much everything, especially on a narrow hull.

250 lbs equals +30 Hp. Adding Hp means adding torque roll. Loosing weight means less torque roll, more stability.

Focus on loosing weight. If you gain power all the better. The load condition described originally is 4 guys. Taking 250 lbs off the stern and adjusting the prop angle is like deleting 2x 180 lb front seat riders.

Don’t throw money at the cast iron anchor. Spend money on less weight #1, more power is #2.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

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digginfool
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Re: 15x7 engine choice

Post by digginfool » Fri Oct 18, 2019 8:08 am

I have a 15' DB that originally had the 8.1 Vortec on it, rated at 465 H.P. I managed to blow that engine and replaced it with an aluminum block LS engine. Made a huge difference in the way the boat rides. The 8.1 weighs 765 lbs, the engine I installed weighs approximately 500 lbs. Running dry is not even an issue. To be honest, I did pick up around 150 H.P., which certainly doesn't hurt but the main point is that getting rid of that pig of an engine hanging on the back of the boat was well worth it. I agree with Slidin Gator; don't throw money at the BBC. At 15 feet, your boat will do everything you want it to with a healthy LS engine and probably more.
“When plunder becomes a way of life for a group of men living together in society, they create for themselves in the course of time a legal system that authorizes it and a moral code that glorifies it” - Bastiat

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