Airboat Engine Builds - Automotive

Automotive powered airboat discussion.
SWAMPHUNTER45
Site Supporter - III
Site Supporter - III
Posts: 2252
Joined: Thu Nov 21, 2013 11:38 am
Location: Naturecoast, Florida

Airboat Engine Builds - Automotive

Postby SWAMPHUNTER45 » Tue Feb 13, 2018 11:28 am

It seems like that about once a week or two we see a posting on someone with an automotive engine problem or some type of issue that many times can be avoided. This got me thinking a little and I want to explain some general differences in building an engine for an airboat application vs other uses.

Some people reading this may have a different opinion and I encourage them to post a follow up and explain if they disagree with a certain point made.

First lets agree that an automotive airboat engine experiences a "severe duty" application. If you disagree with this wait until you sober up or the pills wear off before posting your comments. The airboat engine endures far more loading than it ever was intended to experience as it is turning a propeller under constant resistance and not propelling a rolling wheeled object. As such this requires consideration of upgrading select components too either enhance strength and reliability or tailor the engines performance. The unique needs of an airboat engine may also require the builder to adjust the engines internal bearing clearances or other finite adjustments to allow for it to survive extreme loading.

Did you know that the main bearings or rod bearings that the crankshaft journals rotate through are not in contact with the surface of the crankshaft journal? The journal rides inside the bearing in a coat of oil that shields contact. If the clearances set by the builder are tight the oil will be inadequate to shield or cushion from contact. In the case of an excessive clearance it may cause another problem as the pressure may bleed off to soon or the engine may see a short life as normal wear enhances the clearance far beyond a usable tolerance.

Frequently we read or hear fellow boaters talk about having a engine that makes extreme horsepower on a "dyno" machine. Well that's something that generally speaking is not what an airboat requires if it is being used for general purpose riding. The airboat needs it's power to be broad with the power curve being wide. Often times an engine built for high horsepower will only make that power at it's peak rpm and an airboat engine typically lives at 50 to 75% load. An engine that lacks mid-range power is a poor choice for a recreational airboat. A Master engine builder who is a member of the Southern Airboat community has told us that with an airboat engine the "proof is in the prop" and dyno data can be misleading if not totally inaccurate. The selection of an engine based on any dyno data should not target peak horse power but show a steady curve upward and have broad torque. The experienced Master builder will be able to tell you exactly what prop and setting the engine will turn when you purchase it. Try that as a test when ordering a engine. If the builder or vendor can not tell you what the engine will spin with a recommended prop and drive ratio then consider the source a less than ideal supplier.

Selection of a builder requires some investigation and takes effort on the part of the buyer. Using the example of a Cadillac build, I can tell you in the past few years I have seen firsthand several nightmare builds or rebuilds. The reason is the Cadillac engine is different in many ways from a Ford or Chevrolet. A machine shop or builder who is not a Cadillac expert will not know the strengths and weakness of the platform and will fail to build a platform that can sustain a long life on an airboat. Anyone can build an engine, it's not rocket science! It is however the Master engine builder who can build the engine to perform at a high level and have a long life in a severe duty application. If your buying a new LS series airboat engine and you seek extreme high performance longevity then go to a builder who specializes in that platform, not a local machine shop or auto crate engine vendor with no real experience in powering airboats for the best results. This is true with every specific platform, choose a builder or source with a proven product and reputation for building an airboat capable build. As a disclaimer some crate engines work, some users get good service and are happy with the purchase but generally speaking it's not for everyone. Some of the most frugal are using salvage engines and making modifications to enhance longevity and getting good service from these platforms but this requires either DIY handiness or a network of support most do not have available. We all have a budget to our builds and in the case of needing to remain very low cost the salvage take out can be a savings.

Think how much money has been spent on engines that fail on an airboat! Learn from the mistakes of others on this site and do your homework.

Generally speaking a automotive engine placed into an extreme duty application should have forged internals if available. The use of roller camshafts, upgraded rocker arms or shaft systems, heavy duty timing components, enhanced oiling, select bearing materials, high quality valves and a high performance ignition. The master builders have "tricks or custom fab parts" that a crate engine, machine shop or race car builder will not employ. Some of the most screwed up airboat engines I have seen come through the shop at my builder have come from the circle track specialist shops. The clearances are off, the cam selection is wrong and in general they appear like an engine with 300k miles or more on them after failing in a year or less. Usually this is because the circle track engines are built to run a season and run wide open most of the race. To build a good circle track engine you do things far different than the airboat engine builder especially on certain engine families. It only makes sense that the two are not made from the same blueprint as their needs are totally opposite.

With an airboat engine it is fairly safe to say that in most cases you get what you pay for and if you disregard your builders advice to upgrade internals or other components "cheaping out" will cost you more in the long run.

CarMotorBarge
Site Supporter - I
Site Supporter - I
Posts: 772
Joined: Thu Jul 14, 2011 8:32 pm
Location: Lake Harney Woods

Re: Airboat Engine Builds - Automotive

Postby CarMotorBarge » Tue Feb 13, 2018 6:05 pm

I am trying to sober up. So what is done differently between an airboat motor and a circle track motor? Isn't the circle track motor under a high load while racing?
14x7.5 Al David hull with 14 inch transom
419 CI Horsepower Barn LS3 with 2.68 Rotator soft drive swinging 4 blade 83.5" R
GTO Rigging and B&S Tilt Trailer
Member of Seminole Airboat Club

SWAMPHUNTER45
Site Supporter - III
Site Supporter - III
Posts: 2252
Joined: Thu Nov 21, 2013 11:38 am
Location: Naturecoast, Florida

Re: Airboat Engine Builds - Automotive

Postby SWAMPHUNTER45 » Tue Feb 13, 2018 7:25 pm

A race car engine is typically rebuilt at the end of every season. They don't generally see years of reliable use at the tracks I have been around. Since they are restricted in modification by rules of the classes it becomes a game of loose clearances and concealment of modification to gain an advantage. The race engine is about getting max performance out of a specific displacement and specific components.

The airboat builder will strive to build a high performance high endurance engine giving years of service while attempting to bullet proof it.

Builders like MAS, WaterThunder and Branch have tricks they have learned by studying design and doing autopsy tear downs.

As as example WaterThunder discussed on his FB page has re-engineered a component from an earlier LS platform, welded and modified for use on the new LS3. If I recall correctly it was to gain additional clearance and lubrication.

To give another example Branch modifies the crank and timing sets actually drilling into them and mating the set with pressed pins to bullet proff it. He also spends hours with block prep to speed the return of oil from the top of the engine and direct additional flow to the cam and timing chain.

I have tried to get him to explore doing a rear oiler but the R&D cost would be a risk I can't afford to fund.

The serious airboat engine builders focus on building big power that stays together for years.
The serious racers change engines frequently for a reason.





Glad to hear your giving the liver a rest.
Last edited by SWAMPHUNTER45 on Tue Feb 13, 2018 7:49 pm, edited 2 times in total.

User avatar
OneBFC
Southern Airboat Member
Posts: 451
Joined: Tue Sep 11, 2012 1:04 am

Re: Airboat Engine Builds - Automotive

Postby OneBFC » Tue Feb 13, 2018 7:45 pm

I think carmotorbarge is responding to your line, " If you disagree with this wait until you sober up "

I must be a bit drunk too because I don't think an engine on an Airboat sees severe service all the time. My little 4 banger is making 75 or so hp at 3000 rpm cruising along in deep water at 28 to 32 mph. Skinny water, much less...

That is no more severe than a truck pulling a loaded trailer 75mph?

Now, running across 10 miles of dry is much more load, but it's still only 150hp most of the time.

I submit that how long an engine lasts has a significant amount attributed to the owner and how they operate it.

If everyones engines were loaded 75% of max, they would be consuming 15 to 25 gallons per hour of fuel. You would need a might big tank to go anywhere....

Your intentions are good, not intending to counter any of your advice. However, the loads on these engines are not exactly outside of design limits most of the time.

Driving into a field and holding the throttle open for 30 minutes is just not what most people do?

Built engines are a good path. Just not the only path imo.
-Russ
-----------------------------------
The only thing stopping you is FEAR
400+hp Ecotec, 12x7.6 DBDO, 80" 3B Maximus, 2.3 OX,85+mph, water = purely optional
Life begins at 2 BAR, Just a good ole boy

SWAMPHUNTER45
Site Supporter - III
Site Supporter - III
Posts: 2252
Joined: Thu Nov 21, 2013 11:38 am
Location: Naturecoast, Florida

Re: Airboat Engine Builds - Automotive

Postby SWAMPHUNTER45 » Tue Feb 13, 2018 7:54 pm

That truck has wheels it rolls the boat is in the majority of the time under load.

A towing application is a great example and the factories limit weight rating, use computer transmissions and enhanced cooling and capacity to reduce the stress.

So your opinion is an airboat is not a severe duty use. To that I say we disagree. Your taking a engine designed for one use and placing it in a other job description. Think that Eco Tech isn't seeing severe duty? In a car they go 150k no issues on a boat seems they don't last as long.
Last edited by SWAMPHUNTER45 on Tue Feb 13, 2018 8:03 pm, edited 1 time in total.

User avatar
OneBFC
Southern Airboat Member
Posts: 451
Joined: Tue Sep 11, 2012 1:04 am

Re: Airboat Engine Builds - Automotive

Postby OneBFC » Tue Feb 13, 2018 8:02 pm

You know what my boat is, but that isn't the point at all. Drag is drag, doesn't matter if it's wheels, hulls or wings.

Steady state driving 75 mph with the boat behind my truck the 3.5 liter engine in it is using around 7 gallons per hour. That is what the engine is consuming, non stop with no breaks for hours at a time.

How is that any different than cruising along in an Airboat at 5 to 7 gph?
-Russ
-----------------------------------
The only thing stopping you is FEAR
400+hp Ecotec, 12x7.6 DBDO, 80" 3B Maximus, 2.3 OX,85+mph, water = purely optional
Life begins at 2 BAR, Just a good ole boy

loudmouse
Southern Airboat Member
Posts: 404
Joined: Tue Jan 22, 2013 3:20 pm
Location: Ocala Fl

Re: Airboat Engine Builds - Automotive

Postby loudmouse » Tue Feb 13, 2018 8:38 pm

I'm going to throw my 2 cents in here and go against the norm. The prop puts a constant load on the engine. This load is not a problem as long as the engine is tuned for the load. Making an engine live in a higher rpm, higher load application is the tune and good valvetrain. Stock gm engines will accommodate the load without an issue. This load magnifies the engine operating parameters(tune). If everything isn't right, there's no margin for error in a high load/rpm application as an airboat, the engine will damage itself. Too lean and/or too much timing and detonation or pre ignition will cause headgasket to burn out, valves to tulip or break and drop into the cylinder, hammered bearings and cause overheating, low power output ect. Too rich causes wear on cylinder walls, rings and pistons with higher than necessary fuel consumption. Too low timing causes high exhaust and cylinder temp which causes exhaust valve to become overheated and fail. Low timing also causes the engine to labor (low output) which creates high operating temps.
If the valvetrain is up to the task from the rpm, the tune is on, the engine temp is safe, if the oil pressure remains constant, the engine will take just about any abuse an airboat can give it. With that said, gm took an LS engine, put it on a dyno, loaded it and put the throttle wide open for almost 300 hrs without failure. This was an everyday LS that is installed in the 1500 trucks.
The engine will display symptoms of not being happy. As an owner it's up to you to fix the problem causing the symptom and quit operating the boat until it's fixed. Because if you don't I will promise you that engine failure is coming.
15' Alumitech deckover LSX TT Oxbox 84" JX 4-blade
Gas required Water optional :dontknow:
Built and Tuned by Me
14'X8' JW, Chevrolet 122CID LNF Turbo Engine, Ox box, 80" NGR 3 blade

Life is short, eat your dessert first! :downtown:

CarMotorBarge
Site Supporter - I
Site Supporter - I
Posts: 772
Joined: Thu Jul 14, 2011 8:32 pm
Location: Lake Harney Woods

Re: Airboat Engine Builds - Automotive

Postby CarMotorBarge » Tue Feb 13, 2018 9:55 pm

Just started my second 12 pack, but I think OneBFC and loudmouse did a really good job of explaining everything. The primary differences between an airboat and a car is that an airboat has a higher average load, spins higher RPMs on average, and has more vibration. A good tune and valve train can handle these differences.
14x7.5 Al David hull with 14 inch transom
419 CI Horsepower Barn LS3 with 2.68 Rotator soft drive swinging 4 blade 83.5" R
GTO Rigging and B&S Tilt Trailer
Member of Seminole Airboat Club

User avatar
Slidin Gator
Southern Airboat Member
Posts: 6
Joined: Sat Feb 03, 2018 11:33 pm
Location: Jupiter Farms, Florida

Re: Airboat Engine Builds - Automotive

Postby Slidin Gator » Tue Feb 13, 2018 10:38 pm

I’m new here, but I’ll throw my hat in this ring. I will go with Loudmouse, Swamp and CMB on the extreme application. Who reading this normally throw’s mamas minivan into second gear and runs 3-4K RPM with WOT excursions to 5+ for minutes/hours?

Since I could not justify my own hot rod, a tow truck and all the other toys, I hot rodded the wife’s car. She likes it because it makes her ti*ies bounce (good enough reason) and smokes the random BMW. I like it because it pulls like a SOB to 4,500 RPM, and it’s a rocket from there to the 6,500 shift point. That 1st gear is great, then it slams second, then I have to let off because of the speed limit signs and I’m at the gas station and I promised to fill her car up blah blah blah, it’s the only way it gets premium you know. It’s mostly been a real let down I guess...

On the other hand with the boat, the only speed limit signs I have seen are in deep water. Stay out of deep water and you can run 2nd to the limit and grab 3rd, have fun you know. My point is that the hot rodded 5.7 Hemi is now turning 200,000 miles and has been reliable. It gets slammed hard for a few seconds every so often, but for the most part It lives an easy life, probably too easy. I would be looking for an explosion if I ever made that motor work like my boat motor.

I have a mud boat with a winch that is great for covering a lot of water and will cross some ground if I have to, hell it’s only a 35 Hp engine. I got an airboat to cover a Lot of Ground and get across water when needed.

So one man’s definition of extreme is very likely much different from another man’s, but I mostly seem to hear heavy accelerators in the woods.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540. A Bob Stossel original, still running strong.

SWAMPHUNTER45
Site Supporter - III
Site Supporter - III
Posts: 2252
Joined: Thu Nov 21, 2013 11:38 am
Location: Naturecoast, Florida

Re: Airboat Engine Builds - Automotive

Postby SWAMPHUNTER45 » Tue Feb 13, 2018 11:33 pm

Maybe I just run harder than some folks who knows? I didn't think so :stirpot:

If an engine is WOT 5200 and it cruises at 2600 that is 50%

If that same engine was running up at 3900 and I did the math correct that's 75%

Seems fairly realistic for most hp gear drive builds to be in that general area.

Now keep in mind my starting of this thread was not geared to a specific platform. It was vague and general but all auto engines can benefit from upgrades in an airboat application.

To take hard earned money and purchase a engine that will not be able to sustain one of the listed likely scenarios as simple as a bad tank of fuel is a risky investment.

No where did I say a purpose built engine was the only way! In fact I noted salvage engines offer an option. What I can tell you is if you run a engine on an airboat it experiences forces and demands unlike it was designed and that puts it in a severe duty class.

If your going to the piggy bank or taking on a payment you would be well advised to select a purpose built engine.

CarMotorBarge
Site Supporter - I
Site Supporter - I
Posts: 772
Joined: Thu Jul 14, 2011 8:32 pm
Location: Lake Harney Woods

Re: Airboat Engine Builds - Automotive

Postby CarMotorBarge » Wed Feb 14, 2018 6:26 am

With a WOT of 5200, the engine is not running at half throttle at 2600. You have to look at the load (fuel usage) and not RPMs to determine how much throttle is being used. I had my motor thrust tested by Water Thunder years ago. The WOT was 5300. Half of the max thrust was made at 4100 (not 2650). The engine made less than 20% of max thrust at 2650.
14x7.5 Al David hull with 14 inch transom
419 CI Horsepower Barn LS3 with 2.68 Rotator soft drive swinging 4 blade 83.5" R
GTO Rigging and B&S Tilt Trailer
Member of Seminole Airboat Club

SWAMPHUNTER45
Site Supporter - III
Site Supporter - III
Posts: 2252
Joined: Thu Nov 21, 2013 11:38 am
Location: Naturecoast, Florida

Re: Airboat Engine Builds - Automotive

Postby SWAMPHUNTER45 » Wed Feb 14, 2018 7:42 am

I understand what your saying CMB and the higher the percentage of throttle applied the higher the stress is relevant in any application. The engine operating at a percentage of power is a proper way to communicate it's load output. The thrust data really sort of validates my point as the blade pitch never changes the engine spins against the resistance. In addition the increase of rpm in certain platforms is some of the reason for the need for modification as the stock base engine was not intended to run sustained at the 50-75% rpm range.

What blades were those you tested?

The goal was to promote a discussion on why some engines stay together and run on a boat for years in a severe duty application.

I have probably seen no less than 6-7 failed engines in the past 18 months run thru the shop built by shops who knew nothing about the platform. We have heard about folks who paid big money for super charged LS engines to later learn no forged internals, heard of quite a few crate engines that wipe flat tappet cams where a $300 roller upgrade would have prevented the fail. Just feel there needs to be a discussion on the need to realize the airboat engine is not the same as the one in the street rod or race car. The load the engine is carrying between a automobile and a airboat application is vastly different.

Probably why no one has made a pedal airboat!

loudmouse
Southern Airboat Member
Posts: 404
Joined: Tue Jan 22, 2013 3:20 pm
Location: Ocala Fl

Re: Airboat Engine Builds - Automotive

Postby loudmouse » Wed Feb 14, 2018 8:33 am

Flat tappet cams need Zinc in the oil to survive. Modern off the shelf oils, the zinc has been removed due to modern engines having roller cams not requiring it. So the epa mandated it's removal for emissions. If you have a engine with a flat tappet cam search out an oil that still has high zinc content. USE that oil. Rpm and spring pressure is what wears a flat tappet cam not engine load. The cam never sees the load only the rpm. Also forged internals isn't required for 99.9% of the power levels most airboat engines produce. Factory Gm Ls bottom ends (cast crank, powdered metal rods, cast piston) have been pushed to almost 1500hp before breakage. In an airboat at 500, 600, 700hp is in its capable zone easily. Folks the tune required in an airboat is totally different than that of an automobile that must meet epa requirements and fuel milage standards. The airboat engine needs fuel to keep the cylinders cool to withstand the constant load. An afr of low 13 to high 12s for a airboat at WOT where in the automobile it's tuned for high 13 to low 14 at WOT because the load is light on the engine and it will live at that level. Most people have to rely on the shop that replaces the engine to make sure it's running properly. Unfortunately MOST of these haven't a clue about an engine or the tune.

Swamp, what shop do you work at where a conversion to roller cam is only a $300 upgrade? Typical conversion I do is 900 to 1000 minimum by the time you buy the cam $125 to 350, the roller lifters $200 to 500, pushrods $60 to 120, springs for the valves $140 and up, new retainers and locks if required $50 to 200, and labor to install with degreeing the cam. Try to tell that price to an airboater and you will figure out quickly that's not gonna happen. But that will be the people who continually have engine troubles because they NEGLECTED to FIX the engine for the intended purpose.
Last edited by loudmouse on Wed Feb 14, 2018 9:44 am, edited 1 time in total.
15' Alumitech deckover LSX TT Oxbox 84" JX 4-blade
Gas required Water optional :dontknow:
Built and Tuned by Me
14'X8' JW, Chevrolet 122CID LNF Turbo Engine, Ox box, 80" NGR 3 blade

Life is short, eat your dessert first! :downtown:

SWAMPHUNTER45
Site Supporter - III
Site Supporter - III
Posts: 2252
Joined: Thu Nov 21, 2013 11:38 am
Location: Naturecoast, Florida

Re: Airboat Engine Builds - Automotive

Postby SWAMPHUNTER45 » Wed Feb 14, 2018 9:24 am

Sounds as if there could be an opportunity for a person to establish a airboat ECM tune service.

I feel the LS3 platform should have forged pistons to bullet proof it. I think knock sensor failures that caused pistons to crack was why.

Mouse do you run a factory bottom end on your twin engine?

loudmouse
Southern Airboat Member
Posts: 404
Joined: Tue Jan 22, 2013 3:20 pm
Location: Ocala Fl

Re: Airboat Engine Builds - Automotive

Postby loudmouse » Wed Feb 14, 2018 10:03 am

SWAMPHUNTER45 wrote:Sounds as if there could be an opportunity for a person to establish a airboat ECM tune service.

I feel the LS3 platform should have forged pistons to bullet proof it. I think knock sensor failures that caused pistons to crack was why.

Mouse do you run a factory bottom end on your twin engine?


Yes and no knock sensors with a speed density tune at about 800/850 true hp. Knock sensors on an airboat is almost useless due to false knock from the prop and vibrations. My lil LS 364CID is turning the JX 4 blade with more pitch for gearbox ratio than many BBC's that's advertised as 800/900 hp. Cast crank powdered rods cast pistons. Cracked pistons is a rpm or tune related failure and is a very rare problem.
15' Alumitech deckover LSX TT Oxbox 84" JX 4-blade
Gas required Water optional :dontknow:
Built and Tuned by Me
14'X8' JW, Chevrolet 122CID LNF Turbo Engine, Ox box, 80" NGR 3 blade

Life is short, eat your dessert first! :downtown:

ladyblackwater
Southern Airboat Member
Posts: 225
Joined: Tue Jan 15, 2013 9:01 pm
Location: Davie, FL
Contact:

Re: Airboat Engine Builds - Automotive

Postby ladyblackwater » Wed Feb 14, 2018 11:16 am

This is a good thread and will be great information for people now and in the future. Bottom line if you ask a motor builder that knows how to build an Airboat motor they will tell you nothing is harder on a motor than an airboat.
Greater love hath no man, than to lay his life down for a friend.

Bitterly clinging to my guns and my religion!

I am that conservative republican your momma warned you about!

User avatar
OneBFC
Southern Airboat Member
Posts: 451
Joined: Tue Sep 11, 2012 1:04 am

Re: Airboat Engine Builds - Automotive

Postby OneBFC » Wed Feb 14, 2018 12:02 pm

ladyblackwater wrote:... Bottom line if you ask a motor builder that knows how to build an Airboat motor they will tell you nothing is harder on a motor than an airboat.


I know that is a common belief among airboater, but it's simply not true.

Ask yourself, whats harder, 1000 miles in a Baja truck or 1000 miles in an Airboat?

How about a 24hr endurance race?

How about a marine engine for offshore boats?

I could go on...

The average load of all of those engines is much higher than an Airboat application. By far.....

So, to not derail the original intent of this thread too much, built engines are a good option and a smart move if you have the budget and the right builder at your disposal along with a proper "tune". A bad tune will kill a $20k engine just as fast as a $500 one.....

My point is, when you can run certain factory engines sourced from secondary markets at often times sub $1k costs, you can go through 5 to 20 of those for the same cost as some built engines. Some engines are much more than that even...

Does the built engine last 5 to 20 times longer?

I get that you want to prioritize reliability, but, no-one really builds their engine with bullet proof parts and then runs them at near stock or modest power levels.

Most people build the engine to supply much higher power levels and so the reliability is better than a pure stock engine at the same power level. It's just, how much better are they? Do you have any data that can be referenced on that? I would love to see something like total hours on a build like loudmouse is running vs a similar output built engine and compare a cost per hour analysis. That would be super interesting to me!

In short, not really disagreeing here with the overall topic. I just don't see the evidence to support the notion that Airboat engines live in extreme duty all the time and I think for most people it makes financial sense to seriously consider using the right factory base engine over a 5x to 10x more costly custom or high perf build. Not all people, just MOST.

A heavy equipment seismic style boat needs a lot of reliable power for extended periods of time as one outlier example of a good use case for built engines.

Look at some tour boats that run bone yard sourced engines for thousands of hours. Big boats, big loads, run every day.

That is pretty strong evidence on top of all the other points made here.

Hope we can continue this debate in the friendly nature we have managed so far. These threads quote often devolve quickly and are much better in person conversations over a few cold ones.

:thumbleft: :salute:
-Russ
-----------------------------------
The only thing stopping you is FEAR
400+hp Ecotec, 12x7.6 DBDO, 80" 3B Maximus, 2.3 OX,85+mph, water = purely optional
Life begins at 2 BAR, Just a good ole boy

User avatar
digginfool
Site Supporter - III
Site Supporter - III
Posts: 2634
Joined: Wed Jun 05, 2013 3:00 pm
Location: South Florida

Re: Airboat Engine Builds - Automotive

Postby digginfool » Wed Feb 14, 2018 12:19 pm

loudmouse wrote:Cracked pistons is a rpm or tune related failure and is a very rare problem.


I don't think it is as rare as you think. After I had a hypereutectic piston shatter in my BBC, I did some research and found that it was an extremely common occurrence in the marine application of that particular motor (8.1). So much so that they ceased to use them and there are a lot of similarities between a marine application and an airboat application. Having seen first hand what happens to a block when a cast piston lets go led me to installing forged units in my LS. The powdered metal rods were not as much of a concern to me but since the engine was open it seemed a prudent investment. My engine, as do most high output LS engines, came with a forged crank. I am a firm believer that if you are building a boat that will see tough duty, better build a tough engine. Yes, a lot of people get by for years on crate engines and there is plenty of anecdotal evidence that purpose-built engines fail as well but if I have the choice between a $12,000 crate engine and a $15,000 purpose-built engine, I'm going the high road. At least I'll sleep better at night. For what it's worth, after the initial investment plus the upgrades I've done to date, I could have had a similarly powered engine from MAST. Buying a crate engine, or even a salvage engine, with the idea that you will upgrade down the road doesn't necessarily mean you're getting the same end result. JS
“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

User avatar
digginfool
Site Supporter - III
Site Supporter - III
Posts: 2634
Joined: Wed Jun 05, 2013 3:00 pm
Location: South Florida

Re: Airboat Engine Builds - Automotive

Postby digginfool » Wed Feb 14, 2018 12:31 pm

OneBFC wrote:
ladyblackwater wrote:... Bottom line if you ask a motor builder that knows how to build an Airboat motor they will tell you nothing is harder on a motor than an airboat.


I know that is a common belief among airboater, but it's simply not true.

Ask yourself, whats harder, 1000 miles in a Baja truck or 1000 miles in an Airboat?

How about a 24hr endurance race?

How about a marine engine for offshore boats?

I could go on...

The average load of all of those engines is much higher than an Airboat application. By far.....

So, to not derail the original intent of this thread too much, built engines are a good option and a smart move if you have the budget and the right builder at your disposal along with a proper "tune". A bad tune will kill a $20k engine just as fast as a $500 one.....

My point is, when you can run certain factory engines sourced from secondary markets at often times sub $1k costs, you can go through 5 to 20 of those for the same cost as some built engines. Some engines are much more than that even...

Does the built engine last 5 to 20 times longer?

I get that you want to prioritize reliability, but, no-one really builds their engine with bullet proof parts and then runs them at near stock or modest power levels.

Most people build the engine to supply much higher power levels and so the reliability is better than a pure stock engine at the same power level. It's just, how much better are they? Do you have any data that can be referenced on that? I would love to see something like total hours on a build like loudmouse is running vs a similar output built engine and compare a cost per hour analysis. That would be super interesting to me!

In short, not really disagreeing here with the overall topic. I just don't see the evidence to support the notion that Airboat engines live in extreme duty all the time and I think for most people it makes financial sense to seriously consider using the right factory base engine over a 5x to 10x more costly custom or high perf build. Not all people, just MOST.

A heavy equipment seismic style boat needs a lot of reliable power for extended periods of time as one outlier example of a good use case for built engines.

Look at some tour boats that run bone yard sourced engines for thousands of hours. Big boats, big loads, run every day.

That is pretty strong evidence on top of all the other points made here.

Hope we can continue this debate in the friendly nature we have managed so far. These threads quote often devolve quickly and are much better in person conversations over a few cold ones.

:thumbleft: :salute:


I agree with most of what you said but I think you're being a bit disingenuous with your comparisons. A 1,000 miles across the Baja is not equivalent as a 1,000 miles of running the Glades. The Baja engine is garbage at the end, the Glades boat is just breaking in. Now, let's make that comparison of running 1,000 miles of Gardner's Marsh when it's dry and maybe then we're talking similar applications. Same with the offshore comparison. It all has to do with planned use. As far as the tour boat application, again, not exactly fair. The vast majority of tour boats are using big blocks, which were originally designed for extreme duty in trucks. Of course they're going to last. There's a path for everyone and not everyone needs a $15,000 motor but if you're use includes running a 15 foot welded metal barge fully loaded with friends, fuel and beverages for 3 miles of dry running out to Square Pond, you better have the engine that can withstand it.
“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

loudmouse
Southern Airboat Member
Posts: 404
Joined: Tue Jan 22, 2013 3:20 pm
Location: Ocala Fl

Re: Airboat Engine Builds - Automotive

Postby loudmouse » Wed Feb 14, 2018 12:39 pm

OneBFC, there is no reason why a factory take-out won't live in an airboat and perform as good or better than most built engines. My TT LSX is very happy at this power level with great fuel economy. I see all the time a performance built engine, $8000-$10,000 cost, put in an airboat and was sold as a 600hp engine to the new owner. Yes it made 600hp on the dyno at 6800 rpm BUT in the airboat it's only spinning 5400. So maybe 500 to 550hp now. That power level can be made with most big CID LS engines and the fuel injection creates a very good torque curve which is what's turns a prop anyways. What I do know is that some of builders of engines in the offshore racing scene use cast that's right cast cranks so it can flex without breaking. Those engines see the extreme level of use from the boat leaving and re-entering the water under full throttle.
My lil ecotec engine is one tuff lil engine. I have held it on the hammer for 5 to 7 miles @ 29psi of boost on pump gas and 5400 rpm before and not one single miss nor does it use any oil. The longevity of the TT LSx should replicate that of the 2.0 ecotec. Time will tell. The LS world record stock bottom end 1/4 mile time is 7.16 at 190mph. Factory just like GM put it together, torque to yield bolts and all. Pretty impressive and was enough data for me to replicate what has already been proven to perform. :violent1: :banghead: :scratch:

Diggn, my boat runs ground with 4 adults, full cooler 40 gallons of fuel at 3000 rpms or less at 15' welded deckover. I've not seen many boats that even come close.

There are a few engine builders that I could/would trust among the many that claim they can build an engine. For my dollar, if I didn't build it myself, I would take my chances with GM for dollars spent.
Last edited by loudmouse on Wed Feb 14, 2018 12:59 pm, edited 5 times in total.
15' Alumitech deckover LSX TT Oxbox 84" JX 4-blade
Gas required Water optional :dontknow:
Built and Tuned by Me
14'X8' JW, Chevrolet 122CID LNF Turbo Engine, Ox box, 80" NGR 3 blade

Life is short, eat your dessert first! :downtown:

CarMotorBarge
Site Supporter - I
Site Supporter - I
Posts: 772
Joined: Thu Jul 14, 2011 8:32 pm
Location: Lake Harney Woods

Re: Airboat Engine Builds - Automotive

Postby CarMotorBarge » Wed Feb 14, 2018 12:42 pm

5 years ago on Memorial Day weekend I ran across Gardner's marsh from Big Hole in the wall all the way to North Cove. There wasn't any water in the marsh. Didn't see any boats at all. Motor had stock block, stock heads, stock intake, stock lifters, stock rockers, stock oil pan, etc. Motor ran 160 to 180 degrees and turned 4000 RPMs all the way. Give me another 12 pack and I would do it again. LOL
14x7.5 Al David hull with 14 inch transom
419 CI Horsepower Barn LS3 with 2.68 Rotator soft drive swinging 4 blade 83.5" R
GTO Rigging and B&S Tilt Trailer
Member of Seminole Airboat Club

User avatar
digginfool
Site Supporter - III
Site Supporter - III
Posts: 2634
Joined: Wed Jun 05, 2013 3:00 pm
Location: South Florida

Re: Airboat Engine Builds - Automotive

Postby digginfool » Wed Feb 14, 2018 1:11 pm

loudmouse wrote:Diggn, my boat runs ground with 4 adults, full cooler 40 gallons of fuel at 3000 rpms or less at 15' welded deckover. I've not seen many boats that even come close.

Be honest. The LSX is a purpose-built platform designed for high HP applications. Yes, you can get it with an iron crank but I'm betting you went with the B15 for your setup. Either way, both have forged rods and pistons so my point proven.
“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

loudmouse
Southern Airboat Member
Posts: 404
Joined: Tue Jan 22, 2013 3:20 pm
Location: Ocala Fl

Re: Airboat Engine Builds - Automotive

Postby loudmouse » Wed Feb 14, 2018 1:54 pm

20160711_153812_resized.jpg
Diggn, my engine is a LY6 just like GM put it together with a few changes I made. Never opened the bottom end. The newer gen 4 ls engines gm gave them the LSx badge.
Attachments
20170829_221712_resized.jpg
Last edited by loudmouse on Wed Feb 14, 2018 5:15 pm, edited 5 times in total.
15' Alumitech deckover LSX TT Oxbox 84" JX 4-blade
Gas required Water optional :dontknow:
Built and Tuned by Me
14'X8' JW, Chevrolet 122CID LNF Turbo Engine, Ox box, 80" NGR 3 blade

Life is short, eat your dessert first! :downtown:

One Eyed Gator
Southern Airboat Member
Posts: 1152
Joined: Wed May 30, 2007 11:33 am
Location: Ocala,Fl

Re: Airboat Engine Builds - Automotive

Postby One Eyed Gator » Wed Feb 14, 2018 1:56 pm

Well I run a 5.3 out of a truck with 113K put it on my buddy heavy 14' Alumitech deck-over 2.55 with 3 blade maximus, loaded with 3 people for fishing in the gulf take 3,600 to be on plane we run some nasty stock pushing hard. Took the motor of after putting about 300hrs on it. Then we put it on my 14' 7-6 open alumitec with a 2.68. Doesn't take as much to be on plane but getting run hard while fishing, it now has another 300 plus hours on my boat.

It is stock except for the carb swap motor is 275-300hp on a good day lol.
I will say that we spent the time to tune the different carbs tried with a wideband.

SWAMPHUNTER45
Site Supporter - III
Site Supporter - III
Posts: 2252
Joined: Thu Nov 21, 2013 11:38 am
Location: Naturecoast, Florida

Re: Airboat Engine Builds - Automotive

Postby SWAMPHUNTER45 » Wed Feb 14, 2018 2:28 pm

Mouse my reference to the roller cam upgrade was for the sbc at time of build. It used to be a few hundred more if ordering a BP crate.

But well worth the money !


Return to “Automotive Power Only”

Who is online

Users browsing this forum: No registered users and 10 guests