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500 Caddy

M

mickey5978

Active member
I am getting a Cadillac motot for my airboat. Fairly new to airboats, no to motors. The motor I am building is set up for DD, will have approx 600 lbs torque at 2800-3200 rpm and around 400 HP at the same time. I was told this configuration would be best for a 76X36 wood paddle prop. Can anyone concur with this? I was also told that the wood props are not as hard on the engine. I am pretty sure I should run 2 blades. Any suggestions on size/pitch/brand. Hull is a mid 80's Panther aluminum, 16X7. Any help from the experienced would be wonderful!!!! THanks in advance.
 
I to run a DD caddy 500. I don't know what HP I'm at but I do know that I have .030 over flat top pistons and 120cc heads with a Comp Cam. Elderbrock Intake and a 750cfm carb.

I have a Power Shift 72" set at 38 deg I max out at 3200 rpm. I love my Power Shift Prop wouldn't trade it for anything.
If you don't have the greenback for the composite prop the wood will do fine. If you can fine a 76" x36 that you can try out , do that first.

Are you looking to run on dry ground? If so go get a 2-1 box.

If you can try to get a box for you Caddy, then you could go with a 3 blade paddle prop to push that 16' Panther around. That's my next step
 
won't do too much dry ground if at all possible, but supposedly that boat should have no problems running dry loaded from what I read and what others write. I have seen several on the tx coast similar unload their boats in the lot, throw all the decoys and 4-5 guys in the boat and take off from the pavement in the water. seen it many times with my own 2 eyes and they have same/similar setups with 500's. I will just be able to turn a bigger prop with the improved motor. What cam do you have? Any insight to running dry with your boat? what to look for?

they also have no reductions
 
Don't know what size cam. The guy that build my motor lives next town over and builds them to race. I purchase the airboat with the motor in it.

I have a 14' GTO and I can run dry sometimes. I've had to give it all she's got sometimes with this black mud around here. I can park on a sand bar and take off with just myself but not with anyone else in the airboat.
The airboat is HEAVY

I just would like to go anywhere and not worry about getting stuck that is why I'm going to a gear box ASAP.
 
is a 2 to 1 redcution too much for a caddy. most props spin at 2500- 2900 right? 2 to 1 would put your motor at at least 5000? Not too many caddies can handle that without shorter lower end setups? would seem like 1.7 would work better for a 500? not sure, trying to find out all of this stuff. i do know the motor side and the caddy isn't built to run that high. your torque curve on a suped up motor stops around 4200 rpms. But with the reduction does this info change? or do the 3 blades spin slower?
 
You running slower with a box due to the torque. You would run about 3500 rpm with 3 or 4 blade you prop would be turning 1750 rpm.

Your pitch would be like 60 deg or something like that.

Slower prop means lower noise also.

Only time you would crank it up is to get going on dry land

My buddy has a 502 Chevy with a 2-1 box and a 4 blade Whirl Wind prop. The snap is great gets up on a plan in a second and cruises about 3000 rpm.
BUT get on the chat tomorrow night @ 8pm. You would get some great in put from it.
Here is what she looks like.

http://www.southernairboat.com/photopos ... 500/page/1
 
so the more blades, the higher the pitch, lowers the sweet spot for the props? sorry if this sounds stupid, just needing to find out all this stuff... is the forum eastern or central time?
 
On a stock 500 0r 472 caddy your hp will be more like 300 and tq around 500 at 3000 rpms. these motors are very strong but to make all the hp and tq they are rated at 4200 after 4200 you stand a good chance of valve float without putting stronger valve springs in it ... if you want one of these monsters to perform stock then put a 1.74 0r 1.55 to one gear or belt reduction on it and dial it in to turn the motor 4000- 4200 a wood prop something like a 78x 54 paddle prop on a 1.55 and a 84x 50 on the 1.74 and you will have a bull dozer... just my 2 cents
wayne
ps. and it wont be so loud you cant stand it because you dont turn up 5000= rpm most of the time you will run th motor at 25-3000 rpms
 
Plenty of impressive 500 Cadis around here WCentralFL. Greg Abbott, Dale Fields, Mark Thomas and a host of others get by pretty well on 14/15' glass Cadiboats.

They do not, however, run dry ground with 4 or 5 passengers, dogs and decoys. Would love to see that one.

The hidden magic in 472 / 500 Cadis is reportedly in the cam & heads & rocker arm asemblys - also, they seem to produce better with stock exhaust manifolds and cast iron intakes. Go figure.
 
The motor is no where near stock and will be pushing the numbers I said earlier. Have built several motors for race cars with similar setup. Also built many of these motors for wreckers. The real honest true dyno sheets give those numbers. I have no doubts about what the motor can do, I am wondering what will happen on the boat and with what prop. Any of you guys hae more suggestions about sizes/styles of props for a DD caddy 500 with close to 600 lbs tourque (580-600) at 2800-3000 rpms HP will be at 400-415 around 3000 rpms. HP will continue to come up to around 450 at top side of curve.
 
The best way to start is with a composite adjustable prop. The hear of your boat is your engine and prop. You spent the time, money, and effort on your engine which is excelent but you shouldn't lack on your prop. With a wood prop it is a set pitch and if it is not matched to your engine you wasted the $700+ on a chunk of wood. With an adjustable pitch prop you can tune it to match your engine. I run a DD 500 Caddy stock with a 74" Sensenich Q blade adjustable pitch 2-blade prop. I would suggest you use a 76" min lenght if you use the Sensenich. I have the prop set on 2-1/2 out of 3 and I am turning it at 2700 at wot. I can run a cow pasture with myself and 3 other guys in the boat no problem at 3/4 throttle. If you get to the sticky wet mud or sand you can stick any boat regarless of reduction and hp. My boat is a 1978 panther aluminum 15 x 7 boat so it is close to the same setup you have. I would just suggest that if you are buying a new prop that you spend the extra and get a good one. If you must go with the wood I'd call the prop comanies and ask them. On my stock engine I started with a 72 x 38 prop and turned it at 3000 rpm.
 
I run a 500 Caddy, 750 Edelbrock, Edelbrock intake, headers and an RV low end cam grind, with a Power Shift Maximus and a 1:173 Stinger box. The hull is a Hammat aluminum 16x8 with side boxes. I guess hull & rigging weigh in around 2200-2500 lbs. It's a very heavy boat.

My prop produces it's max thrust at 2000-2300 rpm, the engine maxes about 4000 rpm, with a planeing cruise of 2800-2900 rpm. The boat will run grass fine with 3-4 folks but by no means is a ground burner. It's also fairly quiet with the twin stainless mufflers as it turned 85 dBs in the Florida G&F sound testing while on an operational plane.

My advice is a gear box is optional as you want to maximize your torque curve. You're better off investing in a good composite prop (Power Shift) and don't forget to put a metal spacer plate between the prop & flywheel as the composites props need dampning from the crank.

You may drop Big Boom a line as he knows this rig very well. Also Patty at 863-528-4266-c Power Shift will be happy to give advice.
 
Gator

You mentioned something about a metal plate between the flywheel and the composite prop. Can you and anybody else explain this? I have read here that some people have problems with harmonics and the hub cracking where the blades attach. I thought this was on isolated cases on specific props manufactures. Should I put this piece of metal on? If so how big? How Thick? What type of material?
 
Gator or Anyone,

Could you please comment on KJ's question?

Lotsa ears here with need to know :)

Thnx, Gben
 
as far as running high rpm on the caddy.the one comment of valve
float is correct. at 4200 rpm they tend to float the weakest part of
the caddy motor is the rocker system and weak valve springs.
without running aftermarket springs and a custom rocker setup
you will have a catostrophic failure if you shoot for 5000 rpm.even as simple as putting an aftermarket high lift cam can bust valve springs nothing larger than
520 lift on stock and that is still pushing it.as far as the horsepower
projections and the torque projection i have not, myself seen
a cadillac motor giving 400hp at 3000 rpm most i have seen on a dyno
was 325 at 3000 but i have not travelled everywhere.torque wise that is pretty close somewhere in 560-575 range.a caddy can be succesfully
built to for d.d operation and be impresive.i personally built my 472 to get as much grunt as i can, and i run a 74inch prop pitched to 44deg. and
it holds me to 2800 on the trailer and 3000 on the water.my motor is
on a 15 foot rivermaster set up for five i run the ground with five can stop
and start again.but if you can pull the power out of your 500 get a 76inch
carbon fiber prop that is adjustable.cause if you have a smaller prop you wont be able to pitch it up enough to slow your motor down.there is
only so far you can pitch a prop before it becomes inefficient.
 
Valve springs are cheap I would install new springs, retainers, locks and a roller BBC rocker arm. Then turn it what you want. End result DD Caddy runs good. Caddy with 2to1 gearbox turning 4,500 runs better a DD Caddy with 2to1 gearbox turning 5,000 to 5,000 run’s the best. If your on a budget go DD if you can afford it go all they way and spend your money on reliability as in good valve train parts. Oh step up the rocker ratio and watch your torque curve come in lower because you will increase your intake charge and valve velocity!
 
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