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RPM

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speedracer

Member
Hellow all, I recently bought a airboat In fla and brought It home to kentucky to run some small rivers and streams, I have several boats but this Is my first airboat so I need a little help. When the boat Is on the trailer at full throttle It will only turn 2000 RPM. It does not miss or lag It just wont spinn up, I read some were that 3000 Was all you wanted a direct drive to spin but Im a long way from that.The motor Is a 351 ford with a direct drive 2 blade wooden prop. I am wondering If RPM will Increse When I get It moving On the water, any thoughts on this, Thanks for any help Tony.
 
You need to be turning a DD around 3000 RPM.I would check your Prop size and get back to us as well as all of your linkage to throttle body.
 
It'll typically go up a couple hundred but not 1000 like you are looking for. What is the length and pitch of the prop, there should be some numbers like 72 lxl 32 around the hub. You might simply have too much prop for that engine. When you tell us the prop specs we can let ya know if its a mis match for that engine. if it is a match then the motor might need some tuning or maybe a cam swap.
 
If it is a wide blade prop then that is what I used on my 500 Cadillac DD. I would say you are way overproped.

Try the 72/32 wide blade or 72/30 wide blade.

I ran the 72/30 on my dd350 and turned it to 3000 rpm. I tried the 72/38 on the same engine and could only get 2000 out of it with not much push.
 
speedracer":w4ud1j8r said:
I went out and looked at the prop, It Is a 72 LXL 38, Thanks again for the quick reply.
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If you have a wide blade it is to much prop, but if it is a stick prop you should be good. Cgeck you linkage to make sure you are getting full travel.
 
how wide is your blade at its widest part? That'll determine if you have a wide or narrow prop, if it's a wide blade you are over propped.
 
IMO that is way to big of a prop for that motor, more like a 72x34 would be right. Maybe somebody else has a ford DD 351 can chime in.
 
Checked the prop width today, is 8 in. wide at the widest part. I had a little time so I drained all the old fuel out, refilled with frest 93 and did a quick tune-up, new spark plugs, checked wide open throll positon (fully opened). And motor would spin up to 2200 rmp on the trailer. Idol's nice at 600 rmp, no lags or hestistation up to WOT.
 
Sounds like it's too much prop I run a 72x32 on a direct drive 350 and it spins at 2900-3000 rpms, but as others have said you might want to make sure the engine is set up right.I'm sure some of the other car motor guy's on this site that have been around these set up's a lot longer than me can give you some things to look for
 
72x32 is the ticket you got a caddy prop the best smallblock dd boats ive seen lately where runnin warpdrive props
 
8" wide? you got a stick prop, not a wide blade. you should be able to spin that prop a little higher than 2200. according to florida airboat prop you need a 72x36 stick prop. It's simple either get a smaller prop or bring up the hp on the motor. Whats the motor like: what carb and intake, do you know if it has the stock cam? if the cam is stock you can get one more suitable for this application and advane it a few degrees and throw in some higher ratio rocker arms that'll give your motor a wake up call.
 
Yes, please give details on intake and carb. Cam if you have em and where is total timing set? Initial too. It may have too much advance for that rpm as well. IMO, you'ld want a 2 bl intake with small runners for that low of an rpm.
 
Cant tell ya much about what has been done to the motor inside but It does have a edelbrock Intake with a 600 cfm holly barrel.Timing Is set at 10 degrees BTC at Idol. Found this boat In airboat trader and bought It over the phone, don't have a lot of money In It but I guess you get what ya pay for right, Any body got a 72- 32 they want to sell to a guy wanting to get started In air-boating. Thanks again all. PS I bet the 351 Is bone stock cause It Idols so smooth, No loaping at all.
 
speedracer":25bgbm1a said:
Cant tell ya much about what has been done to the motor inside but It does have a edelbrock Intake with a 600 cfm holly barrel.Timing Is set at 10 degrees BTC at Idol. Found this boat In airboat trader and bought It over the phone, don't have a lot of money In It but I guess you get what ya pay for right, Any body got a 72- 32 they want to sell to a guy wanting to get started In air-boating. Thanks again all. PS I bet the 351 Is bone stock cause It Idols so smooth, No loaping at all.
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Take your prop and send it to FLORIDA AIRBOAT PROPELLARS! Tell them to take out as much pitch as they can and balance it. This will start you off with a fresh prop and take some bite out of it so your RPMs will come up. This is your lest expensive rout. They should be able to take 3-4 degress of pitch out of that prop.
 
Found a 72-30Wide blade In airboat trader, Is a 30 pitch gona be enough If Its a wide blade, also does any one have the number for florida airboat propellers, Thanks.
 
72X30 wide blade will work great. Should put you at 3000 RPM depending on motor.Maybe a little less.
 
Hey, I've got a 72X30 wide blade for sale. It's on the trader but it's been a while since I posted it but I still have it. It was just redone before I took it off my boat so it's like brand new. PM me if you are interested. It's what I used on my DD 350.
 
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