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I am thinking about building an airboat about 14' long.I am a licensed
A&P mechanic but am considering using a direct drive 500 caddy for power.Of course I would build the motor with a mild cam and about 10to1 compression and am curious about how well the boat would run dry.I would also like to run around 65mph.Any insight on how this combo would perform will be greatly appreciated.
 
Weight= Horsepower lost... Just keep that in mind. Built right with the /right prop, say 72/34 or somewhere in that area, your boat will run dry ground; assuming that you are the only one in the boat. I can tell you from experience that a well built BB Caddy on a 13.5 snake hull will run dry ground very well. However, I weight bout 300 lbs, now if I took on one passenger, the boat would not slide worth a hoot. So, my breaking point for extra weight is bout 300 - 350. Now just like other setups, nothing is a guarantee, there are places boats will get stuck. Now as for a 65 MPH sled???? Hummmm......In my opinion, won't happen. I do however reccomend the BB Caddy for a powerplant, it is by far, the most reliable, smoothest, quietest, most peaceful motor you can use.
 
Thanks for the info flatzhonkey,Its sounding more and more like I am
going to have to go with an aircraft engine to get the perf. and reliability
that I am looking for.Nothing against chevys Iam a diehard fan of them
but if you put a reduction gear on one and spin it 4500-5000rpm all day
like I would it wouldnt last very long.
 
I had a 500 on 12'6" fiberglass hull. It had a single front driver & double rear passenger. It swung a 72-38 paddle prop about 2800. This thing ran the hill real good & was real fast. I didn't have a GPS back in 80's, so I don't know about 65 mph, but it would make your eyes water. I agree w/Flatz Honky, you need to keep it light if you want to have fun on the hill.
It's definately my favorite motor to run "off the crank".
 
If you meant to say carb, I used the one that came stock with my 500 for a long time. I think it was a Rochester Quadrajet. It had a little hesitation at low rpm's, so I changed to a Holley. It's been a long time ago, but I think it was a 650 and it definitely made my motor more responsive when you had to punch it.
 
I did mean to say carb :oops: The reason I ask is because I just got a 472 or 500 and the only thing it doesn't have is the alternator and carb. I have a 350 Chevy with a 600 CFM Edlebrock on it that I was planning on using if it was big enough. I don't really know if it is a 500 or a 472 and don't want to tear it apart to find out. Either is big enough for my boat. I run a 350 Chevy direct right now and it gets along ok (a lot of work to keep running and from leaking). I know it won't run a hill but here in Nebraska there really isn't much of a need to run a hill. Just flat sandbars and the 350 comes close. I have been told that with an aluminum intake and headers the bb Caddy will be fairly close to the weight of the 350 Chevy. Any advise from the direct drive caddy boys would be appreciated.

Thanks again.
 
I've got a 500 Caddy in a 14' GTO hull. I just installed a 2115 Edelbrock intake. I was already runing a Edelbrock carb. If you looking for a deal on a carb look here on Ebay.
http://cgi.ebay.com/ebaymotors/ws/eBayI ... gory=33550

It's a $250.00 carb going for $150.00
I'm runing a Power Shift Prop 72X38, 2900rpm. Now I can turn 3150rpm. I need to put more pitch in it to bring the rpm down. I don't run no 65mph but it'll do close to 50mph. Thats Fast enough for me. Only down fall of a caddy is PARTS. Aluminum oil pan $250, Chevy $125. Anyway I love my caddy just wish aftermarket part where easer to find.
 
My dad has a 500 caddy on a 13ft glass hull with polymar that will go anywhere you can think of. It is 10:1 comp, has a chet herbert grind cam from Jimmy Swait, edelbrock intake with a holley economiser 400cfm 4 barrel carb. This setup swings a 74-38 wide blade sensenich at about 3100rpm and the boat will drive on an island with 6 people aboard. During a few dry seasons we have gone to the camp and back several times with out any water the entire way, about 11 miles south of alligator alley. Just keep the motor cool and you can run WFO all day long with the caddy.

Larry
 
I tried an edelbrock intake and carb on my 500, I think the only diff was the weight diference, The set up might have worked if I needed top end performance like on a gear reduction but on a direct drive I think the money might have been better served on something else. It did look better though..I think I might have even lost a little power on the low end
 
On a stock cammed low compression caddy you actually will lose up to 200 rpm with the edelbrock intake with a 650 cfm or larger carb. The intake runners are larger and you lose intake charge velocity. This is where a high comp. motor and a smaller carb come into play. I know a friend with this intake on a stock motor running a 500 2-barrel and this combo works real well.

Larry
 
Your somewhat right about running a smaller carb. It will help increase low RPM horse power by increasing the velocity of the intake plenum air and fuel charge. The best way to create bottom end torque and throttle response. Is to speed up the plenum velocity inside the intake and head ports. The easiest way to do that is to run a smaller carb. But this will limit the amount of power you can make at higher RPM’s. The cheapest and easiest way to increase intake port and plenum velocity with out limiting max power is by increasing the rocker arm ratio. When you increase this ratio the valve opens and closes much faster while creating more torque and throttle response. The higher ratio also gives you more lift at the valve thus giving more peak air flow. It is truly amazing what a high ratio rocker can do for an airboat. My recommendation is run a 600 DP with a higher rocker ratio. You will have the same port velocity as a 500 2 barrell and realy increase power over 3,000 RPM.


Waterthunder
 
The only problem with the changing the rocker arms on the caddy motor is they are already a 1.72:1 ratio. The only higher ratio rocker arm that I know of is a 1.76:1 rocker and they cost about $1,000. Gooing with an airboat specific grind cam is the only realistic way to change the lift and duration to what you need.

Larry
 
the other thing to keep in mind is that without having the caddy built for high rpm most people don't use them with reduction units so you would never turn more than 3000 rpm.
 
Running a higher ratio rocker will do more for bottom end power and throttle response below 3,000RPM over any other modification accept increasing compression. I have bought several 1.72 (higher ratio) set’s @ $499. Even higher ratios are available but in a true roller rocker. These are available in a 1.76 ratio and 1.8 ratio and cost $660. When you go with a 1.8 you need to do some valve train geometry work to clearance things for the pushrod. I would recommend the 1.72 they are cheap and bolt right on. Going from a 1.65 to a 1.72 will substantially increase plenum velocity, throttle response and increase power all across the board!
 
I currently run a 0-540 on a 13" Gilileo and can run the hill from here to there as I wish.
Several friends have direct drive Caddies on 15 - 16 foot fiberglass hulls and they run dry with two just fine and with three unless it is black mud.
The most impressive of those is running a 472 with modifications from Cadilac performance in Tampa - Buddy Branch.
 
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