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maximumken
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Joined: April 13, 2012
Posts: 2
Location: Austin, Texas
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 Posted: Wed May 30, 2012 10:57 am Post subject: Type 4 airboat |
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This will be direct drive. To move the boat I need 140 ft/lb of torque at 2800 rpm or less. I'd like wide open throttle at no more than 3200 rpm so I can keep the prop diameter big. (Faster prop means the tips get inefficient)
I'd like to keep the costs down. I'm thinking about a single two-barrel carb and new spanish heads redone by Rimco or one of the other good shops. 42/36 valves should be plenty for those rpms. And I like Raby's Camper Special cam. 8/1 compression is about all I can do.
Any recommendations on stroke x bore? It would be great if I can stay small enough (2.0) not to need expensive aluminum cylinders. But it may be impossible to make that much torque at that low rpm without more cubes.
Thoughts? |
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brettsvw
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Joined: November 22, 2007
Posts: 2145
Location: Florida
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BL3Manx
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Joined: August 29, 2006
Posts: 6767
Location: Northern California
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maximumken
Samba Member
Joined: April 13, 2012
Posts: 2
Location: Austin, Texas
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| Posted: Fri Nov 02, 2012 11:02 am Post subject: t4 airboat |
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Read down that link and you'll see he's on his third crank.
Now I'm thinking a 2332 with single-port heads might work and be a bit cheaper than the t4. I'll clean up the ports and build a long intake manifold.
Any thoughts on what the cam should look like to put out peak torque at about 2800 rpm or less?
Looks like Jake Raby liked the FK-41 but I need much fewer rpms (and peak torque much lower) than his engines. |
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BL3Manx
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Joined: August 29, 2006
Posts: 6767
Location: Northern California
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| Posted: Mon Nov 19, 2012 8:48 am Post subject: Re: t4 airboat |
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| maximumken wrote: |
| Read down that link and you'll see he's on his third crank. . |
You say you're building a boat. The worst thing that would happen to you if the crank breaks is it will get quiet, the boat won't sink. The engines he broke the crank on were overbored to 3100cc and he did some fairly serious yanking and banking putting extra gyroscopic forces on the crank, stuff you just can't do in an air boat. The stock 110hp Corvair got 145 lbs torque at 2800 RPM and the crank/engine would out last any VW of equivalent power you could build for thousands of $. Even if you snap a crank you can buy Corvair engines all day long for a couple hundred dollars.
http://www.n56ml.com/corvair/110curve.jpg |
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trik3r
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Joined: April 18, 2013
Posts: 4
Location: Miami (Cuba) Fl
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brettsvw
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Joined: November 22, 2007
Posts: 2145
Location: Florida
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