Anyone use a “marine” 350 for DD?

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Andrew511
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Anyone use a “marine” 350 for DD?

Post by Andrew511 » Wed Feb 06, 2019 9:31 am

I’m buying a long block this week to repower my DD boat and the salesman told me the marine engine makes about 75 more HP than the stock truck engine. It’s a little more money but I don’t know much about the marine version. I have a intake, carb and other misc parts from a non vortec 350 that I would like to use the parts from. Does anyone have experience with these marine engines? Are they any better or worse than a truck engine besides more HP? Will they use the same parts? He says it’s a 80-85 motor which is from what I understand pre Vortec

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Re: Anyone use a “marine” 350 for DD?

Post by John Fenner » Wed Feb 06, 2019 10:01 am

It will work fine, marine applications are ideal for DD the year is good to match your accessories.
The HP is irrelevant, the torque #s are what you want @ 3k
I never finish anyth,,,.

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Re: Anyone use a “marine” 350 for DD?

Post by Andrew511 » Wed Feb 06, 2019 10:12 am

John Fenner wrote:It will work fine, marine applications are ideal for DD the year is good to match your accessories.
The HP is irrelevant, the torque #s are what you want @ 3k
That’s why I wanted to hear. Are the marine engines set up for more low end torque like an RV compared to a truck engine?

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John Fenner
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Re: Anyone use a “marine” 350 for DD?

Post by John Fenner » Wed Feb 06, 2019 10:17 am

It depends on the camshaft profile
I never finish anyth,,,.

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Re: Anyone use a “marine” 350 for DD?

Post by scottyroll » Wed Feb 06, 2019 12:12 pm

I believe I've heard that some marine engines spin counter clockwise. Maybe someone else can confirm.

It would be imperative to know the rotation when selecting a prop.
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Re: Anyone use a “marine” 350 for DD?

Post by OneBFC » Wed Feb 06, 2019 1:49 pm

John Fenner wrote:It will work fine, marine applications are ideal for DD the year is good to match your accessories.
The HP is irrelevant, the torque #s are what you want @ 3k
Welllllll, not exactly. John is giving you solid advice for sure, but, I just want to clarify that it is indeed hp what you want and the torque number is not what to concentrate on when comparing engines to swing a prop.

I don't know of any AC engines that come rated in "Torque" as an example. It takes power and, yes, under 5250 rpm more torque always equals more power so this is why John said what he did.

Just find out what power the engine makes at the RPM you will operate it at and then you can compare any engine properly for which will work better for you.

In closing, Power turns a prop, not Torque.

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Slidin Gator
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Re: Anyone use a “marine” 350 for DD?

Post by Slidin Gator » Wed Feb 06, 2019 4:21 pm

Andrew511 wrote:I’m buying a long block this week to repower my DD boat and the salesman told me the marine engine makes about 75 more HP than the stock truck engine. It’s a little more money but I don’t know much about the marine version. I have a intake, carb and other misc parts from a non vortec 350 that I would like to use the parts from. Does anyone have experience with these marine engines? Are they any better or worse than a truck engine besides more HP? Will they use the same parts? He says it’s a 80-85 motor which is from what I understand pre Vortec
You are good and John is correct, ask for maximum torque. The Hp figures the salesman is quoting will be made up around 5,500 RPM, which is of no value in a DD. The peak torque figures will be in the 3,500 RPM range, providing a much better indication of what the motor makes below 3,000 RPM. If you can get a torque or Hp curve for the motor, all the better to compare below 3,000, but more than likely the performance curves will stop around 3,000 either way.

The truck engines will have a cam designed to make high vacuum at idle to work well with the old TBI system. The marine engines in that era ran carbs and generally ran without vacuum timing advance so they will run a different cam. Add some vacuum advance and you can wake them up some with timing. If you have an option of different cams you might post the options for more input.

If you are not too budget constrained you might want to give more consideration to a Vortec motor. The marine motors probably come with a cast iron vortec intake, but to stay aluminum you would need another $200 intake. Drill out the water bypass port in the to keep your present water pump and accessory drive system, otherwise it gets a bit more complicated with the reverse flow water pump. In either case you are going to need new valve covers so that is a wash. You might also want to consider replacing the plastic timing cover that comes on the vortec, but it will work as is. Finally, the motor mounts are different, so that is another adapter.

The Vortec offers three advantages worth considering. #1 is the Vortec heads that were designed to improve low end torque without sacrificing high end power, so you should get a bit more torque below 3K. #2, you are getting a roller cam motor that runs quieter and gives you room to go more aggressive in the future with the cam and heads. #3 is the aluminum oil pan that I think comes with a long block? Just some considerations, ask the salesman for vortec specs to compare.
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Re: Anyone use a “marine” 350 for DD?

Post by Grizzily2 » Wed Feb 06, 2019 5:52 pm

Scotty is correct, Marine engines come in Left or Right rotations. Also if this is a previously used Marine engine, was it closed circuit cooled with a heat exchanger or raw water cooled and possibly run in salt water. If it was run in salt water, I would be very cautious, they build a lot of rust in the water passages.

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Re: Anyone use a “marine” 350 for DD?

Post by Andrew511 » Thu Feb 07, 2019 5:59 am

Thanks for all the info. I’ll find out more info on the engine today. Are there any modifications I’ll need to make to the marine engine to make it work for an airboat? For example additional water passages or something that only applies to the marine application? I’ve also read the distributors are different so my old one won’t match up. I’m slightly concerned with my current prop not working due to increased power. I’ll have to get a measurement on it today after work

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Re: Anyone use a “marine” 350 for DD?

Post by SWAMPHUNTER45 » Thu Feb 07, 2019 7:39 am

You got some really good advice posted on here. For DD the science is usable torque and the easiest way to make it is displacement derived by stroke. One you find that displacement and stroke it becomes a mission to obtain "velocity" thru the ports. The right heads, intake, cam and headers help with that. You will be far better off selecting a 383 or 400 that was built to run between 1800 to 3000 than getting something more modern made to run in a higher rpm range.

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Re: Anyone use a “marine” 350 for DD?

Post by Slidin Gator » Thu Feb 07, 2019 11:17 am

Andrew511 wrote:For example additional water passages or something that only applies to the marine application? I’ve also read the distributors are different so my old one won’t match up. I’m slightly concerned with my current prop not working due to increased power. I’ll have to get a measurement on it today after work
The distributors used in the original applications are different, but yours should plug right in. Particularly since you already have the intake and carb set up so you know there is no interference.

I don't think you are going to have too much power with a plain Jane swap. If you follow Swamps lead you sure will though :!:
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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Re: Anyone use a “marine” 350 for DD?

Post by kideplacksh » Wed Jul 10, 2019 2:16 pm

Mostly It depends on the camshaft profile ebook gratuit

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