What makes a purpose built Airboat motor?

[spencer321]

I'm curious what the difference is between taking a crate motor and putting a reduction drive on it, vs a purpose built airboat motor, what is being done to airboat motors that make them different then any other car engine. For example, a crate LS3 vs an airboat engine builders LS3, assuming stock cam, heads (power basically) what is being done to call it an airboat motor

[GCRedfisher]

This should be good!

[glades cat]

Simply put:
A propeller puts constant high load on engines without much of a chance for them to cool off sometimes. These high cyl temps and pressures produce heat, high component loads and cause fatigue and ultimately, component failure. Valves get burnt, pistons take a beating and ring landings break, detonation will pound pistons to death, etc.
Good components=good engines=more money
Bottom line…are you asking more of the engine than it can withstand…for how long?
The more power you squeeze out of a given engine, the greater the stresses placed upon it.

I remember the Rescue Trucks on our Fire Dept back in the 80's. Chevy van cab & chassis ambulance with SBC 350's. They would burn-out in a short time and the shop always had a couple of crate long blocks ready on pallets. Then they went to the Ford 7.3's cab & chassis with ambulance box and that was the end of that. The Diesel could take the heat, the Gasoline engine couldn't.

Also…Power does not equal absolute power.
You build an engine to perform work in a certain manner, at certain RPM's, at certain manifold pressures. Not all 400Hp engines are created equally.
Greyhounds and Bloodhounds are miles apart in the manner they perform work.

[SWAMPHUNTER45]

Every platform is different and being purpose built means the engine will "live" in the application it was designed for. It matters as the builder fixes all the weak spots for that specific engine in the designated application.

As you referenced the LS3 the first and foremost modification over a "crate" or stock take out would be getting forged pistons into the engine. The hypereutectic shatter if put in detonation.

I'm sure Waterthunder has a long list on what is needed to keep his engines going for the long haul.

That's why it costs a little more, you get what you pay for!

[digginfool]

Forged pistons, forged rods, fuel map optimized for the application. As mentioned by swamphunter45, hypereutectic pistons will shatter under detonation. The powdered metal rods used in most of the LS3s are pretty tough but in the long run, forged will serve you better. I went the crate motor route (yes, I bought it from Marine Power but it's a crate motor nonetheless) and I find myself holding my breath every time I have to beat on the motor, such as starting off on dry, getting un-stuck or trying to keep from getting stuck. Sure, I could choose to run only when and where there's enough water to float the boat but you don't always have that option and that's what I have my other boats for. To be fair, the engine management system on my engine will go a long ways towards preventing catastrophic damage but nothing is foolproof. Even a fully forged motor can fail but the margin of error is much more comfortable. I recommend you spend the money and buy purpose-built. The peace of mind is worth every penny. You have to remember that the crate motor is built for a car, where it might see a half-dozen foot to the floor events a week. The rest of the time, it's just easing down the road utilizing 50-60 of its HP. As glades cat stated, there's no rest on an airboat. The engine is heavily loaded and working hard all the time. Get the right tool for the job.

[Bruce]

the price tag is the difference in the airboat world all that forged nonsense is just that unless you're racing (high rpms or a power adder) i dont see any reason to go with all that extra crap gm spent a lot in r and d to put these packages together

[Bruce]

Forged pistons, forged rods, fuel map optimized for the application. As mentioned by swamphunter45, hypereutectic pistons will shatter under detonation. The powdered metal rods used in most of the LS3s are pretty tough but in the long run, forged will serve you better. I went the crate motor route (yes, I bought it from Marine Power but it's a crate motor nonetheless) and I find myself holding my breath every time I have to beat on the motor, such as starting off on dry, getting un-stuck or trying to keep from getting stuck. Sure, I could choose to run only when and where there's enough water to float the boat but you don't always have that option and that's what I have my other boats for. To be fair, the engine management system on my engine will go a long ways towards preventing catastrophic damage but nothing is foolproof. Even a fully forged motor can fail but the margin of error is much more comfortable. I recommend you spend the money and buy purpose-built. The peace of mind is worth every penny. You have to remember that the crate motor is built for a car, where it might see a half-dozen foot to the floor events a week. The rest of the time, it's just easing down the road utilizing 50-60 of its HP. As glades cat stated, there's no rest on an airboat. The engine is heavily loaded and working hard all the time. Get the right tool for the job.

i disagree i got more hours on a crate ls engine then most ever get in a lifetime got another crate engine 8.1 pcm motor with more hours than 4 normal people wll ever put on a boat in a lifetime neither one have ever had so much as a valve cover off

[HuntingBigun]

the price tag is the difference in the airboat world all that forged nonsense is just that unless you're racing (high rpms or a power adder) i dont see any reason to go with all that extra crap gm spent a lot in r and d to put these packages together

I always tell people crank up your LS truck and run it at 4000 rpm for hour than run it at 6000 rpm for 5 mins, then 2500 rpm for hour do that for 100hours see if that motor will not puck it guts, had 3 airboat custom carmotors in the past 9 years never had valve cover off on any of them so I disagree, heck my current motor with car tune is 900+ hsp Mast detuned it to live 808, these are not aircraft engines that designed to run high rpm crate motors are just that.............

[GTSIO-520]

Any marine mechanic will tell you the same. Marine motors live under constant load unlike in a car or truck. Go ask a marine mechanic to install a standard GM crate motor in a inboard/outboard and see what he says, if he doesn't just start laughing.

[chuckitt@earthlink.net]

What ever you buy, make it a torque motor. Not a horse power motor. If you buy a 600 HP @ 6500 rpm engine you will be lucky to get 530 at 5400.
The LS376/480 is a perfect crate engine for an airboat.

Chuck

[Bruce]

What ever you buy, make it a torque motor. Not a horse power motor. If you buy a 600 HP @ 6500 rpm engine you will be lucky to get 530 at 5400.
The LS376/480 is a perfect crate engine for an airboat.

Chuck

Its a nice engine for sure i run the 376/430 which is just a different tune and less cam got over 1700 hours and still goin strong and gets ran 3600-4k constant a pleasure boater will never put that kinda time on one

[akblackdawg]

What ever you buy, make it a torque motor. Not a horse power motor. If you buy a 600 HP @ 6500 rpm engine you will be lucky to get 530 at 5400.
The LS376/480 is a perfect crate engine for an airboat.

Chuck

Its a nice engine for sure i run the 376/430 which is just a different tune and less cam got over 1700 hours and still goin strong and gets ran 3600-4k constant a pleasure boater will never put that kinda time on one

so you guys with your 376/430 or 376/480 what did you do to the motors to make them work well in your airboats. do they have the standard automotive fuel injection, and ignition and cam that came with those crate motors, i know you need headers, pully's, etc, what else...and did you have to flash the emc in your tuning or just the way it came out of the crate? Bud

[digginfool]

i disagree i got more hours on a crate ls engine then most ever get in a lifetime got another crate engine 8.1 pcm motor with more hours than 4 normal people wll ever put on a boat in a lifetime neither one have ever had so much as a valve cover off

You jump on this all the time but be honest; those motors are on tour boats that never see the hard use a typical airboat does. Yes, you run all day, every day, have thousands of hours, blah, blah, blah. How often are these motors running a mile of dry, or worse, a mile of muck? Ever have a little side-by-side action with a buddy? How about climbing the Ridge? No, the job your boats do could be performed by a 150 Mercury but that's not good for the Mickey Mouse crowds your tour boats serve. They pay for the big fan out back. You get long life because your motors don't do the work that a true airboat motor sees. My 8.1 died with (supposedly - I'm pretty sure it had a lot more hours than the previous owner claimed - only takes a new tach) 230 hours on it. Piston shattered and destroyed the engine. Happened getting un-stuck from some willows. VERY common problem with the 8.1. Look it up. Dozens of stories. Motor can't hack hard applications. LS might not be an issue but hard to say; most of the LS motors out there these days came from Waterthunder and he built them forged. Wonder why he went to all that expense when he could have just thrown some fancy coil covers on a crate motor and called it a day?

[SWAMPHUNTER45]

Great point FOOL !

I just dont want to see some hard working guy with a family throw their coins in the shizter.
If your going to run an LS3 if you do nothing else put in forged pistons.

[Bruce]

i disagree i got more hours on a crate ls engine then most ever get in a lifetime got another crate engine 8.1 pcm motor with more hours than 4 normal people wll ever put on a boat in a lifetime neither one have ever had so much as a valve cover off

You jump on this all the time but be honest; those motors are on tour boats that never see the hard use a typical airboat does. Yes, you run all day, every day, have thousands of hours, blah, blah, blah. How often are these motors running a mile of dry, or worse, a mile of muck? Ever have a little side-by-side action with a buddy? How about climbing the Ridge? No, the job your boats do could be performed by a 150 Mercury but that's not good for the Mickey Mouse crowds your tour boats serve. They pay for the big fan out back. You get long life because your motors don't do the work that a true airboat motor sees. My 8.1 died with (supposedly - I'm pretty sure it had a lot more hours than the previous owner claimed - only takes a new tach) 230 hours on it. Piston shattered and destroyed the engine. Happened getting un-stuck from some willows. VERY common problem with the 8.1. Look it up. Dozens of stories. Motor can't hack hard applications. LS might not be an issue but hard to say; most of the LS motors out there these days came from Waterthunder and he built them forged. Wonder why he went to all that expense when he could have just thrown some fancy coil covers on a crate motor and called it a day?

fool im as honest as they come and you have no clue what i do and a mercury will never run where i do with a boat load of people i dont do barge tours like you see in the glades i can will and do run the hill fully loaded everyday and run between 3600 to 4000 rpm cruising now i dont get sloshed like some FOOLS and hold one to the wood for minutes on end when its not moving until it melts down instead of gettin out and getting it goin again i guess thats where experience comes into play but if that doesnt make my tours authentic then hell i dunno what to say and if u think that a constant high rpm then stopping and going repeatedly isnt hard on an engine then i dont know what to tell you however on these tourboats in the area i have seen some of those big money all forged builds bite it after they try and take them away from stock while my ls3 just keeps right on bumpin

[Bruce]

Great point FOOL !

I just dont want to see some hard working guy with a family throw their coins in the shizter.
If your going to run an LS3 if you do nothing else put in forged pistons.

pistons never been an issue in the ls3 we tried an ls2 when the boat was new and it broke a piston after 4 or 500 hours put another piston in it and put it on a play boat and had no issues

[Bruce]

What ever you buy, make it a torque motor. Not a horse power motor. If you buy a 600 HP @ 6500 rpm engine you will be lucky to get 530 at 5400.
The LS376/480 is a perfect crate engine for an airboat.

Chuck

Its a nice engine for sure i run the 376/430 which is just a different tune and less cam got over 1700 hours and still goin strong and gets ran 3600-4k constant a pleasure boater will never put that kinda time on one

so you guys with your 376/430 or 376/480 what did you do to the motors to make them work well in your airboats. do they have the standard automotive fuel injection, and ignition and cam that came with those crate motors, i know you need headers, pully's, etc, what else...and did you have to flash the emc in your tuning or just the way it came out of the crate? Bud

its all factory all the way down to the fly by wire throttle pedal the only thing different is its got whatever tune panther puts on them other than that and the aeromotive fuel pump its all how it came from gm

[CactusJack]

You have to remember also, mass production of engines like crate engines are all about happiness for the manufacturers bank accounts, not customer happiness. Of course, the manufacturer wants the customer to be happy enough with their product, so the customer will be happy to buy another when needed and of course recommend this product to others. In Australia, with the Ford and Holden (our GMC called GMH for General Motors Holdens) would often have cars that were 'lemons' and were just dogs, yet the motors in the ones produced before and after the lemon were perfect...

Because of all of the money driven production, factories that supply pistons for example, might have a hiccup on the line and 'a couple of suspect pistons' get thru the production.... the people making the pistons are contracted to supply 1000 pistons on a specific date and if they have to go searching and checking for a couple of duds, it might make them miss the deadline, so they just 'forget to mention' to the motor manufacturer 'there might be one or 2 duds' in the batch.... after all, there is always the possibility the motor that a dud piston in might get wrecked falling off the delivery truck or for some other reason not make it thru to crunching the motor.... Same goes for cams, valves or heads,

When someone like thunder buys quality forged pistons, part of the quality is that if there is a problem, he will spot it.... so his piston supplier better have their act together... because the pistons aren't going in a factory stuck together motor, who no one had time to inspect and it's likely no one will see again unless something breaks... an expert will be putting it together and looking at absolutely everything. Massed produced engines that are built to a cost and bunged together by a machine or a person who has to explain every second of their working day simply cant afford the time to look at something and check it. That is why with Holden car engines and your crate engines, some are spot on and give no trouble and some are a pain in the butt and always give trouble... and they might have been one behind the other on the assembly line.

So, 2 mates might order a crate motor each, they both arrive, made on the same assembly line in the same batch.... one is perfect and reliable and the other a better boat anchor than motor

To me, a car motor that isn't a lemon from the factory, with a hidden dodgy component waiting to break, should be fine on a boat and I would think that a car motors life in an airboat would be easier than in a stick shift truck, where there is a constant coupling and uncoupling of power, from idle to big revs, a few missed gears with big free revs, accelerating hard on rough roads and pot holes.... whereas a boat has a big prop, but no free reving and not being started cold and run hard many times a day, every day, day in day out.

So, my point is, unless a higher percentage of a particular motor keep breaking making the whole motor seem 'not up to it' but if most are good, there has to be a couple of duds occasionally unfortunately, I always seem to end up with duds We call them 'Friday afternoon engines' when the worker was in a hurry to go home for the weekend and missed something

[SWAMPHUNTER45]

We disagree Bruce, hypereutectic pistons will shatter in a detonation scenario. FACT

If you run a mild factory tune you are probably gonna get away with it running a quality fuel.

Just know that the pistons are your weak spot and when the ECM gets a flawed message from the sensor your good luck may be over.

[Bruce]

We disagree Bruce, hypereutectic pistons will shatter in a detonation scenario. FACT

If you run a mild factory tune you are probably gonna get away with it running a quality fuel.

Just know that the pistons are your weak spot and when the ECM gets a flawed message from the sensor your good luck may be over.

yall are all right im wrong go forged stock will never make it away from the trailer

[Deano]

We disagree Bruce, hypereutectic pistons will shatter in a detonation scenario. FACT

I believe it would far more accurate to say that hypereutectic pistons can shatter when exposed to excessive detonation.

It could likely be stated that a specific given hypereutectic piston will succumb to excessive detonation quicker than the same specific given forged piston will. However, that does not mean that every hypereutectic piston will always puke as soon as everything is not perfect, which is kind of how the above quote reads.

Realistically, it is additionally the specific piston, it's design, application and other factors that contribute to the likelihood that it will ultimately puke. It is not simply a matter of material itself being substandard as was implied.

I claim to know nothing about the LS-anything pistons y'all are talking about, but as a casual observer
it would appear to me like GM has used a few million of them without having such shattering issues.

For example, take a look at the 472/500 Cadillac with which you are familiar.

The KB382 pistons made for the early, closed chamber heads are for practical purposes, junk. If you rattle them just a little bit, the top ring land is prone to break off between the perimeter and the dish. In fact, they should be removed from the catalog entirely. They are not good for anything other than melting and using to plug exhaust crossovers and air pump passages. Chevy sb pistons are cheaper and just as well suited for that purpose anyway.

On the other hand, take the KB353 pistons for the later, open chamber heads which work very well and will take quite a bit of long term abuse without having any problems. Granted, because of their design they lack the dish, but they are made from the same material, which just goes to show that is not the lone issue, in, of and by itself.

Granted, a forged piston will ultimately take more abuse. But I agree with Bruce in that, even while that is the case, it does not make forged pistons necessary in every case; nor does it make every hypereutectic piston prone to failure.

[Bruce]

We disagree Bruce, hypereutectic pistons will shatter in a detonation scenario. FACT

I believe it would far more accurate to say that hypereutectic pistons can shatter when exposed to excessive detonation.

It could likely be stated that a specific given hypereutectic piston will succumb to excessive detonation quicker than the same specific given forged piston will. However, that does not mean that every hypereutectic piston will always puke as soon as everything is not perfect, which is kind of how the above quote reads.

Realistically, it is additionally the specific piston, it's design, application and other factors that contribute to the likelihood that it will ultimately puke. It is not simply a matter of material itself being substandard as was implied.

I claim to know nothing about the LS-anything pistons y'all are talking about, but as a casual observer
it would appear to me like GM has used a few million of them without having such shattering issues.

For example, take a look at the 472/500 Cadillac with which you are familiar.

The KB382 pistons made for the early, closed chamber heads are for practical purposes, junk. If you rattle them just a little bit, the top ring land is prone to break off between the perimeter and the dish. In fact, they should be removed from the catalog entirely. They are not good for anything other than melting and using to plug exhaust crossovers and air pump passages. Chevy sb pistons are cheaper and just as well suited for that purpose anyway.

On the other hand, take the KB353 pistons for the later, open chamber heads which work very well and will take quite a bit of long term abuse without having any problems. Granted, because of their design they lack the dish, but they are made from the same material, which just goes to show that is not the lone issue, in, of and by itself.

Granted, a forged piston will ultimately take more abuse. But I agree with Bruce in that, even while that is the case, it does not make forged pistons necessary in every case; nor does it make every hypereutectic piston prone to failure.

thank you deano for being able to think on your own not just read and absorb what others tryin to push a product want you to believe i guess i can come off a little arrogant but i know what this ls3 and 8.1 have been through and i believe in them where all the high end products im sure are better i just havent seen a use for them yet in my application and these get beat harder than your average joe will ever beat one

[scottyroll]

As usual - Deano put it quite well.

Also, other people browsing this forum should know that there are plenty of "junkyard" LS style engines with gearboxes clocking over 100k miles on them ticking away with no major issues to speak of.

If you don't spin the hell out of them and perform the maintenance checks at proper intervals you can expect to get a good amount of time spent with one of these newer GM engines. Replacement cost is quite reasonable once you have the conversion aspects taken care of.

Aftermarket "specific built" engines are a plus for obvious reasons but you can do just well with a used engine & good setup.

With that said...I probably need to dig in and replace that old oil pump on my 6.0...

EDIT: This is in regards to 5.3 6.0 engines. Not 6.2's.

[crowhater]

Bottom line you get what you pay for. My purpose built Felber 496BBC performed better than most aftermarket 540 big blocks. The devil is in the details, cam, cylinder heads, pistons, intake, combinations. Then throw in different reduction ratios, different prop combinations, different hull, different cage / engine stand configuration. If you are not going to go with a proven engine builder or follow someone else's blue print you run the risk of learning new lessons.

[Waterthunder]

Very entertaining thread I had 2 people call this weekend with blown up motors one was a 6.2 out of a wrecked car he got a whopping 13hrs out of it. The other bought one was one of those circle track LS3 GM crate motors I warn people about till Im blue in the face. Both of them blew up with a combined 30 hours max. Both had cast pistons and both broke a piston. Hell I don't care what they thiunk about cast pistons both people are bringing me whats left of their motors for me to build a bullet proof motor. I will start logging their phone numbers (IF THEY DONT MIND) and post them since so few believe and so many people keep doing the same thing over and over!