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Small block questions

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Old 03-08-2008, 12:41 PM
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Default Small block questions

I have a friend who has a Small block with 10.5 to 1 compression built for a car. He wants to put it in his pleasure boat and it has aprox 425hp. The cam specs are 292 duration and 501 lift. Whats the max cam duration and lift that can be used before you get water reversion. He also wants to use his stock exhaust. Will this work and can a alpha handle it?
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Old 03-08-2008, 12:44 PM
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the cam is close the drive is real iffee i dont think the drive will last unless he babys the hell out of it my 3cents
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Old 03-08-2008, 03:12 PM
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if its a heavy boat or he will be in and out of the water a lot, I don't think the drive will take it......also, he needs to change the freeze plugs to brass
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Old 03-08-2008, 03:35 PM
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Alpha......be very gentle.
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Old 03-08-2008, 04:06 PM
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It is a heavy cruiser. Just wants a little more cruising speed. Can 425hp small block motors run OK with the stock exhaust or will it just kill it? Not looking to do a lot of modifications just swap out a simple motor change.
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Old 03-08-2008, 05:25 PM
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Would even bother the stock exhaust will choke it down , as far as the Alpha is concerned you would be ok, Hp doesn't kill a drive Torque does . Change out the cam and put in something a little more designed at towing, something with a wider torque range .
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Old 03-08-2008, 06:13 PM
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StraightJacket,

I have to ask you a question, not being a smart azz. But when you make a statement like "Hp doesn't kill a drive Torque does " - what exactly do you mean? The reason I ask is, Hp is relative to rpm & torque. So, why or how do you think torque tears up a drive and not the Hp since torque for equal Hp is lessen as rpm increases? You can't have high torque without high Hp for the same rpm?

I'm a little bored and depressed with all the rain in NJ today so I want to hear you reasoning - maybe I'm missing something here about drives?
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Old 03-08-2008, 06:53 PM
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Yeah I'm just sitting around myself when I should be working in my garage.

You've been around this game for a while and well lets face it everyone talks about how much H.P. their motors make and such, but its really the torque that we all should be talking about. People don't build blower motors because the make alot of HP, they make alot of torque and thats what moves the boat not the hp. Hp is what keeps it moving . Torque is made on the lower end of the rpm range and thats what gets the boat on plane, at some point they hp/tq will be equal and then in the higher rpm the Hp will peak. I know alot of motors that make great hp at 7000 rpm but the way they set there boats up they run at a max of 5500 rpm , just outside of the torque range and into the hp range.

This could start a great debate on here and quite frankly everyone has there own opinions on what they like or works . We have been doing this stuff for years and like how it works for us. I run our boats outside the into the Hp range and we don't break drives.
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Old 03-08-2008, 08:19 PM
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I agree with you that is better to run the engine faster and up in the Hp curve, you make alot less torque and I always think high prop speed small dia compared to slower and more dia is better and I agree less strain on the drive - whenever I get into that debate on here people then to clam up. Anyway, thanks for the response.......................................and the debate wages on!!!
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Old 03-08-2008, 08:40 PM
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Randy,
Can you post exact cam specs? 292* duration sounds like advertised , dont think it can be @ .050" . When considering a possible reversion problem, equally as important to duration is lobe seperation. Most likely, your friends car cam is set too tight to work in a wet marine exhaust system, especially a stock one. If that thing sucks up water as fast as I think it will, he wont have to be worried about the alpha holding up.
Another problem is 10.5 compression. A bit too high for todays gas dock fuels. What heads are on the engne? Steel or aluminum?

Last edited by Vinny P; 03-08-2008 at 08:43 PM.
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