motor placement in a 520 Ib runner bottom
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motor placement in a 520 Ib runner bottom

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    Senior Member tkriley13's Avatar
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    Default motor placement in a 520 Ib runner bottom

    If a guy goes from a all iron BG BBC to a all Aluminum BA BBC how much further forward should he put the new motor in at?
    Im guessing it would need to move forward 3" or 4" since its probably 150 to 300 Ibs lighter and with the potential to have 300 to 500 more HP than the current motor or is it one of those things by adding nickles to the prop shaft for lenght can cure?
    The current measurement is 37 1/4" to the block from the inside of the transom.. thanks

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    Senior Member stix818's Avatar
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    Quote Originally Posted by tkriley13 View Post
    If a guy goes from a all iron BG BBC to a all Aluminum BA BBC how much further forward should he put the new motor in at?
    Im guessing it would need to move forward 3" or 4" since its probably 150 to 300 Ibs lighter and with the potential to have 300 to 500 more HP than the current motor or is it one of those things by adding nickles to the prop shaft for lenght can cure?
    The current measurement is 37 1/4" to the block from the inside of the transom.. thanks
    Tom, give Jim Lange a call.. He's the man and if you need his number PM me.. Not sure if he wants it broadcasted.. Seems like your motor is pretty far back already.. Where's the strut at?
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    Distinguished Member David 519's Avatar
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    Quote Originally Posted by tkriley13 View Post
    If a guy goes from a all iron BG BBC to a all Aluminum BA BBC how much further forward should he put the new motor in at?
    Im guessing it would need to move forward 3" or 4" since its probably 150 to 300 Ibs lighter and with the potential to have 300 to 500 more HP than the current motor or is it one of those things by adding nickles to the prop shaft for lenght can cure?
    The current measurement is 37 1/4" to the block from the inside of the transom.. thanks
    Tom, I know what you're thinking and all I can say is don't do it. Fix your engine, put it on alky and have a blast making laps!! If you're gonna put that motor in anyway, talk to Lange and do what he says and ONLY what he says. When you're running a deal like that, it's better not to run it by commitee. Have one guy you trust and do what he says... Good luck bro, drop a dime sometime!!
    Quote Originally Posted by gn7 View Post
    ....... David 519 is 100% correct........

    Quote Originally Posted by fuelinmyveins82 View Post
    .....I think people forget that racing is supposed to fun. Losing shouldn't be discouraging it should motivate you work on your pile to make it faster.....

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    Member TomV's Avatar
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    Jim Lange set my Howard Runner bottom up for me. He was recommended by some of the best out there. He knows his stuff and was a pleasure to deal with. When I picked up my boat he had done more than what I asked and he told me dont worry about it. If your looking for advice on setting something up so it runs hit him up.

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    Senior Member LiquidDan's Avatar
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    Tom,
    When I was running the Comp/ProGas combo I moved the motor back and forth 3-4 inches trying to find the "sweet" spot. I found out that moving it didnt affect the gravity center that much. If it was me I would leave it where it is and run it.....and listen to it..it will talk to you and tell you what it wants. I will assume since you are jumping up in power it will drive the nose over and you will be moving the propellor a bit forward.
    Jim is one of the best in this business and I agree listen to one person......but remember you can listen to the boat as well
    Just my .02 cents
    Dan

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    Senior Member Billy-B's Avatar
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    Quote Originally Posted by LiquidDan View Post
    Tom,
    When I was running the Comp/ProGas combo I moved the motor back and forth 3-4 inches trying to find the "sweet" spot. I found out that moving it didnt affect the gravity center that much. If it was me I would leave it where it is and run it.....and listen to it..it will talk to you and tell you what it wants. I will assume since you are jumping up in power it will drive the nose over and you will be moving the propellor a bit forward.
    Jim is one of the best in this business and I agree listen to one person......but remember you can listen to the boat as well
    Just my .02 cents
    Dan
    Well said Dan. Jim does know his stuff if you need more backup. 37.5 to the back of the block from the inside of the transom seems far enough to start. But then were talking "Drag [email protected]%" stuff here...
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    Old Timer LeE ss13's Avatar
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    Quote Originally Posted by tkriley13 View Post
    If a guy goes from a all iron BG BBC to a all Aluminum BA BBC how much further forward should he put the new motor in at?
    Im guessing it would need to move forward 3" or 4" since its probably 150 to 300 Ibs lighter and with the potential to have 300 to 500 more HP than the current motor or is it one of those things by adding nickles to the prop shaft for lenght can cure?
    The current measurement is 37 1/4" to the block from the inside of the transom.. thanks
    Be very very careful with this. I know it sounds logical to think to move it forward, but can lead to a dangerous problem. Check with Rick King on this. He did that once and when he crossed the finish line at Firebird, it blew the tail out of the water and he went though the lights sideways. The photos were pretty scary. It cracked open the boat along the runner. You need weight to hold the back end in the water. Maybe moving the motor back would be the ticket, but like everyone says, check with the experts. Just my $.02
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    Senior Member Hi Tech Marine's Avatar
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    Quote Originally Posted by LiquidDan View Post
    Tom,
    When I was running the Comp/ProGas combo I moved the motor back and forth 3-4 inches trying to find the "sweet" spot. I found out that moving it didnt affect the gravity center that much. If it was me I would leave it where it is and run it.....and listen to it..it will talk to you and tell you what it wants. I will assume since you are jumping up in power it will drive the nose over and you will be moving the propellor a bit forward.
    Jim is one of the best in this business and I agree listen to one person......but remember you can listen to the boat as well
    Just my .02 cents
    Dan
    Motor location is not an exact science. There a far too many variables for it to be. My general rule of thumb has always been: The more power it has, the farther back the motor placement to help avoid tail blow. But one has to remember that when we where building boats for specific classes, the hull weight was what we considered (at the time) correct for that class. A typical TAF weighed between 800-900lbs bare hull not 520! Things a very different today than in the 70's. Prop technology, and the standing start really changed the game and the way we think about whats correct or not. Like Dan mentioned, motor location is a fine tuning aid and sliding it back and forth can help compliment the lift charactristics of a propeller. If I was you, I'd put it in at 36" make a bunch of laps, study the videos, then decide if it needs to go forward or back. This takes into consideration that the strut placement and relief is correct for the power you have (and it's probably not). I'd be more conserned about that then placement of the engine.

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    Distinguished Member David 519's Avatar
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    Quote Originally Posted by LiquidDan View Post
    Tom,
    When I was running the Comp/ProGas combo I moved the motor back and forth 3-4 inches trying to find the "sweet" spot. I found out that moving it didnt affect the gravity center that much. If it was me I would leave it where it is and run it.....and listen to it..it will talk to you and tell you what it wants. I will assume since you are jumping up in power it will drive the nose over and you will be moving the propellor a bit forward.
    Jim is one of the best in this business and I agree listen to one person......but remember you can listen to the boat as well
    Just my .02 cents
    Dan

    This right here!!! The boat will tell you what it wants, just takes laps to learn to listen....


    Quote Originally Posted by Hi Tech Marine View Post
    Motor location is not an exact science. There a far too many variables for it to be. My general rule of thumb has always been: The more power it has, the farther back the motor placement to help avoid tail blow. But one has to remember that when we where building boats for specific classes, the hull weight was what we considered (at the time) correct for that class. A typical TAF weighed between 800-900lbs bare hull not 520! Things a very different today than in the 70's. Prop technology, and the standing start really changed the game and the way we think about whats correct or not. Like Dan mentioned, motor location is a fine tuning aid and sliding it back and forth can help compliment the lift charactristics of a propeller. If I was you, I'd put it in at 36" make a bunch of laps, study the videos, then decide if it needs to go forward or back. This takes into consideration that the strut placement and relief is correct for the power you have (and it's probably not). I'd be more conserned about that then placement of the engine.
    Jim, what do you mean by the term "relief". I think I have an idea but would like the opinion from an expert. Thanks!!
    Quote Originally Posted by gn7 View Post
    ....... David 519 is 100% correct........

    Quote Originally Posted by fuelinmyveins82 View Post
    .....I think people forget that racing is supposed to fun. Losing shouldn't be discouraging it should motivate you work on your pile to make it faster.....

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    Senior Member stix818's Avatar
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    Sorry, meant pretty far forward.
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    Senior Member Hi Tech Marine's Avatar
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    Quote Originally Posted by David 519 View Post
    This right here!!! The boat will tell you what it wants, just takes laps to learn to listen....




    Jim, what do you mean by the term "relief". I think I have an idea but would like the opinion from an expert. Thanks!!
    David, "Relief" is referred to as the differance between the angle of the cav plate and the angle of the bottom just forward of the cav plate.

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    Distinguished Member David 519's Avatar
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    Quote Originally Posted by Hi Tech Marine View Post
    David, "Relief" is referred to as the differance between the angle of the cav plate and the angle of the bottom just forward of the cav plate.
    Thanks Jim. As always, I appreciate your experience.
    Quote Originally Posted by gn7 View Post
    ....... David 519 is 100% correct........

    Quote Originally Posted by fuelinmyveins82 View Post
    .....I think people forget that racing is supposed to fun. Losing shouldn't be discouraging it should motivate you work on your pile to make it faster.....

  15. #13
    Senior Member tkriley13's Avatar
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    Sorry for the late response but I was at the river and I forgot to bring the computer but as usual I appreciate opinions and the advice!!!
    time well / points this season tell if we go this route or it will be next season before I try it.. I think when I get my BG engine stuff back from the shop and the head gaskets are sealing 100% I think she is gonna run way faster than she ever has...

    I like trying to wrap my head around why/how these things work set up wise...especially when I look at the pictures/videos after a pass and wonder what if I did this? what would it do I think sometimes I should try somethng but I need a little more seat time in case she does something unexpected so I can keep from getting wet..

    David - I`ll give you a buzz tomorrow evening..

    Again Gentleman I appreciate the information... Tom

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