502 crate motor recommended upgrades.

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John C
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502 crate motor recommended upgrades.

Post by John C » Wed Feb 24, 2016 2:45 pm

A good friend of mine is thinking about a new 502 crate motor. Its going on a 15x8 Hammant hull. Are they good for an airboat application right out of the crate? Or are there some necessary modifications that should be made to help one perform well and live for a long time pushing an airboat. Cam change, different Heads, etc, etc??? Any recommendations would be appreciated.

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Re: 502 crate motor recommended upgrades.

Post by Bdriller » Wed Feb 24, 2016 2:49 pm

Ive always heard the valves are a weak link

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Re: 502 crate motor recommended upgrades.

Post by John C » Wed Feb 24, 2016 3:20 pm

thanks, that's the type of info I was looking for. Keep the info coming. His mechanic said it wouldn't take much to get 11:1 compression ratio out of one. Is this OK or is it asking for detonation issues on pump gas? Anyone know what the proper upgrade for the valves would be for an airboat application. He has a 3 blade 82" Sensenich super wide (S) for a prop with a 268 rotater gearbox.

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Re: 502 crate motor recommended upgrades.

Post by Joe » Wed Feb 24, 2016 3:37 pm

John,good high quality stainless 1 peice valve will do. But stainless intake and inconel (sp) exhaust valves is what I have in my 454 with no issues in 7 years of running. Don't forget to upgrade the keepers at the same time! I also have the S blades and 2.68 but the 2.3 gear is a better gear for a BBC.
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Re: 502 crate motor recommended upgrades.

Post by John C » Wed Feb 24, 2016 4:03 pm

Thanks Joe. Whats your thoughts on 11:1 compression. any risk of detonation issues if you get some skunky pump gas??? I think 9.6:1 is stock. or at least that's what I was told. I don't know much about the 502. I have never run one. Just trying to gather some info before my friend orders one.

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Re: 502 crate motor recommended upgrades.

Post by Olf Art » Wed Feb 24, 2016 4:21 pm

John, it's been years since I built a big block so take what I'm saying with a grain of salt, OK? Big blocks live on their torque ... they ain't happy when you try to spin them, so I like what Joe posted above a lot. A little attention to the valve train (definitely roller rockers if it doesn't come with them) and a 2.3 gearbox so that your buddy won't have to turn it as high as on a 2.68.

There's an old drag racing joke that says that a big block's lifespan lives under the driver's right foot. I think there's a lot of truth in that. :lol:
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Re: 502 crate motor recommended upgrades.

Post by Joe » Wed Feb 24, 2016 7:40 pm

If it's aluminum headed you should do ok with 11:1 just dont let your tune get to far off or it will not be good,if it's iron headed then don't go above 10.1 or your inviting trouble. Depends on how far he wants to get into it. You could always bore and stroke it to a 540!!
I have turned my 454 6k for a for a day when my blades moved on me. It sure is snappy at 6k but I like to keep it at around 5200.
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Re: 502 crate motor recommended upgrades.

Post by SWAMPHUNTER45 » Wed Feb 24, 2016 7:46 pm

I have never been a fan of the 502 BBC but understand much of the reason why, is centered around people failing to rig within the actual limits of the engine. In this venture two things JUMP off the page at me.

1) New crate engine will more than likely not have a warranty for an airboat or marine application

2) If purchasing a new crate engine clearly having a local vendor disassemble or alter would have the engine builder and local shop mechanic pointing fingers and blaming each other in the case of a failure.

11:1 on 93 octane in Florida heat sounds a bit to much compression for pump gas without blending in some race fuel or Av gas. In a car the pump gas probably would work but under a severe load from a big propeller I predict an epic fail.

I think I would find a high quality builder and have them do the entire special purpose build and avoid a mail order engine.
Waterthunder Dave would be someone to talk with for sure. I recall a new bbc he had for sale a few months back.

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Re: 502 crate motor recommended upgrades.

Post by Kenny627 » Wed Feb 24, 2016 8:27 pm

At 11.1 he will have to run more than 93 octane.
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Re: 502 crate motor recommended upgrades.

Post by Olf Art » Wed Feb 24, 2016 10:19 pm

Kenny627 wrote:At 11.1 he will have to run more than 93 octane.
Yes he would. He'd be playing with fire where reliability is concerned too, and over a period of time his fuel costs would waste anything he'd gain in performance. When I used to build engines I never had pockets deep enough to play around on the edge of reliability. My thoughts were always, "OK, how can I do this as inexpensively as possible, get the job done, and have it stay together for a long time? I can't afford to do this over six months from now!" That's why I suggested minimal changes from stock in my first post.
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Re: 502 crate motor recommended upgrades.

Post by John C » Thu Feb 25, 2016 12:01 am

So from the info I'm getting, It looks like a stock crate engine out of the box will do the job if you do not increase the compression ratio. and you replace the valves with good one piece stainless steel valves and keepers. Anybody have any recommendations on changing the cam? Just want to upgrade the motor to make decent power and live for a long time on an airboat without breaking the bank.
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Re: 502 crate motor recommended upgrades.

Post by Olf Art » Thu Feb 25, 2016 12:48 am

John C wrote:So from the info I'm getting, It looks like a stock crate engine out of the box will do the job if you do not increase the compression ratio. and you replace the valves with good one piece stainless steel valves and keepers. Anybody have any recommendations on changing the cam? Just want to upgrade the motor to make decent power and live for a long time on an airboat without breaking the bank.
That would be my recommendation ...... an air-gap intake, good carb, long tube headers w/good mufflers, and run it with respect. As I mentioned before a set of roller rockers would probably give him at least 30 (maybe more) horsepower and save both oil shear (cam life) and increase reliability long term. Zink additive in the oil when it's first run, and then give it some break-in time and an oil and filter change before he hammers on it too hard. It should run him for years. I'm just an 'old school' talkin though :)
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Re: 502 crate motor recommended upgrades.

Post by Spoonbill » Thu Feb 25, 2016 6:14 am

I've been running a ZZ502 for 11-12 yrs now...and I love mine. I did have trouble the first year I had it. Blew the top radiator hose off( my fault) while running hard and ended up blowing head gasket and messed up a couple of valves...Heads are aluminum oval port and valves are stainless with roller rockers. Replaced valves, had to shave heads to make them flat and went back with ARP studs for head.( It came with bolts) It always ran a little hot, in my opinion (200-210 degrees), so I drilled /tapped back ports on intake cooling water jacket then piped them to a Moroso thermostat housing. I've have been running for 10+ years now and have not had an issue since. My boat is a 15 x 7 1/2 Diamondback that's heavy, 2:1 belt drive and a 4 blade Water Walker. Blades are pitched so the motor only turns 5000 rpms. I added a very beefed up 4 ft back deck and a grass rake built like a bulldozer blade. I built it to haul a load. It doesn't matter if I have 500 lbs or 2000 lbs...It'll haul it. It does burn a lot of fuel, especially if you get your foot in it.
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Re: 502 crate motor recommended upgrades.

Post by John C » Thu Feb 25, 2016 6:54 am

Thanks spoonbill, Glad to hear your happy with your zz502. The reason the motor needs to be replaced on this boat is exactly what happened to yours. Blew the radiator hose off and didn't realize it until it was to late and the damage was done. Looks like double radiator hose clamps are in order. much like exhaust hoses on an inboard offshore boat. they are always double clamped. Good insurance. Does anyone know if you can order a 502 crate motor with one piece stainless steel valves???

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Re: 502 crate motor recommended upgrades.

Post by digginfool » Thu Feb 25, 2016 8:09 am

Go to the GTO website and look at the MAS motors they sell. The guy that builds them gives a great warranty and stands behind it. You will have a purpose built BBC and probably wouldn't be any more than buying the crate 502 and upgrading it. A friend of mine runs a tour boat with a MAS motor on it and except for one problem, the motor has been bullet-proof. BTW, he runs the holy hell out of that motor; every time he drives it, he drives it like he stole it. JS
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Re: 502 crate motor recommended upgrades.

Post by akblackdawg » Thu Feb 25, 2016 11:05 am

take a look at the build info Crowhater posted several years ago on a 496 he built, i'm sure lots of that same info will apply to a 502. i would suggest aluminum heads if sticking with higher compression, and i have a 15x8 alumitech with high sides and believe a bbc is too heavy for my boat, don't like the way it handles and difficult to push around on mud when it gets stuck, and yes, it does get stuck in sticky tidal mud.
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Re: 502 crate motor recommended upgrades.

Post by Debo75 » Thu Feb 25, 2016 1:01 pm

digginfool wrote:Go to the GTO website and look at the MAS motors they sell. The guy that builds them gives a great warranty and stands behind it. You will have a purpose built BBC and probably wouldn't be any more than buying the crate 502 and upgrading it. A friend of mine runs a tour boat with a MAS motor on it and except for one problem, the motor has been bullet-proof. BTW, he runs the holy hell out of that motor; every time he drives it, he drives it like he stole it. JS

I have a MAS 509 on my boat. Dyno'd at 589 horsepower. Mine is an ex-tour boat. It won't run dry with more than one person on board. If I were doing it again, I would probably spend a few more K and get a fuel injected LS motor. My engine runs like a champ, but it's heavy, carburated, and burns about 8-9 gph.

If your buddy insists on a 502 or similar, he would do well to get an MAS motor. They warranty airboat applications, and it'll come set up with the correct powerband.

If he's putting in a homebuilt, two things I would say are critical are an internally balanced crank, and an anti-dieseling solenoid on the carb. My boat came with a crate 454 on it and it ran great until it threw a rod through the oil pan. My local engine builder tore it down for me and suspects it was dieseling that led to the failure.
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Re: 502 crate motor recommended upgrades.

Post by skip olsen » Thu Feb 25, 2016 7:46 pm

Hi there john hope everthing is going good, If I was your friend he needs to look at an ls motor for his small airboat, been mounting a few of them up here on airboat. Have put in Mast, levitator, and water thunder they perform great and with a small airboat he will be happy with it and he wont have to buy as much fuel to feed it as the big block.

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Re: 502 crate motor recommended upgrades.

Post by Joe » Thu Feb 25, 2016 8:11 pm

11:1 is doable on 93. With a custom cam,and a proper tune. It's on a smaller boat,15x8 not a tour boat, and a 2.68 box so not like its gunna strain real hard. Why is everyone affraid of compression?
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Re: 502 crate motor recommended upgrades.

Post by SWAMPHUNTER45 » Thu Feb 25, 2016 9:52 pm

A true 11:1 is a dangerous compression ratio for today's ethanol infused pump gas. Without an EMM and anti-knock sensors an engine running that ratio won't last long on an airboat in Florida.

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Re: 502 crate motor recommended upgrades.

Post by SWAMPHUNTER45 » Thu Feb 25, 2016 9:59 pm

John if your friend wants a BBC MAS is the best option and built to run on pump gas.


http://www.gtoairboats.com/engine-packa ... hp-bb.html

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Re: 502 crate motor recommended upgrades.

Post by Olf Art » Fri Feb 26, 2016 12:03 am

SWAMPHUNTER45 wrote:A true 11:1 is a dangerous compression ratio for today's ethanol infused pump gas. Without an EMM and anti-knock sensors an engine running that ratio won't last long on an airboat in Florida.
My point exactly ..... thank you. Why would anybody want to pay up to 20 cents more per gallon for 93 + octane when he shouldn't have to? I'm not the sharpest tool in the shed but I can figure that one out. I really don't trust that just because you're supposed to be pumping 93 octane gas, that in all cases you're actually getting 93 octane gas .... especially at some moogebon gas station out in the middle of BFE. I can live with less compression and not have to to gamble my engine on the fact that I'm always getting good fuel. JMO
Last edited by Olf Art on Fri Feb 26, 2016 12:11 am, edited 1 time in total.
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Re: 502 crate motor recommended upgrades.

Post by aggiejim » Fri Feb 26, 2016 12:10 am

been running a 502 for 3 years but its a marine motor roller cam and rockers stay below 10.2 to 1 watch running it lean they dont like it I have played with timing 35degrees was the sweet spot but I am running a lot of lift so smaller cam with more duration will take 36 no mid grade gas my 2 cents
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Re: 502 crate motor recommended upgrades.

Post by Rich Andrews » Fri Feb 26, 2016 7:02 am

Don't forget a well tuned carburetor. Might help w those problems as well
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Re: 502 crate motor recommended upgrades.

Post by Joe » Fri Feb 26, 2016 7:53 am

Olf,since you last build a motor there has been leaps and bounds in technology! If your worried about 20 cents a gallon more for 93 don't build a performance motor. IMO it's just plain stupid to put that kinda money in a motor and not run 93. And if your dumb enough to buy gas at a run down gas station In BFE you deserve what you get!!! A custom cam will work with 11:1 in florida. Many of them running strong. Tune it right and keep up on maintenance and it'll last. It's funny how many people on here still think about motors like it's the 70s or 80s.
And rich is right,a properly tuned carb will solve many many issues. Very few people know how to tune a carb correctly. I know I can get close but ed mack and few others are truly experts.

John,11:1 is doable. But like I said the tune and cam have to be put with it. 10:1 is safe and an idiot can make it live even with a bad tune,guess that's why olf likes 10:1 so much.
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