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Discussion Starter · #1 ·
I am helping a friend build a new 427 cu in SBC to go racing. It has a alky digger tunnel ram with 2 1050 carbs and planning on running a 400hp shot of nitrous so it should be pretty stout. The boat is a TR3 and from what he tells me it used to be a blown gas boat and has been over 140 MPH. I would have to assume this boat is dialed in as it has been raced for many years.

I was talking to another friend who has a blown gas flatty and he has had to lower his motor because of drivability issues. This was an unrigged boat so there were no existing motor plates or "starting point". This got me thinking about this boat that is going from a BBC to a SBC and with less power. I have no experience with v-drive drag boats so I have been reading a lot, but wanted to ask your opinions before we set the motor plates.

Should we keep the rear motor plate in the same spot to start?
Will the weight/HP reduction require the engine to be moved forward or backwards/up or down?

Question for anyone using nitrous.
Does a large shot of nitrous affect the boat? Does it need to come in before the starting line, after it sets or right off the line?

Should anything else need to changed/modified going to a SBC that we should look at?

Thanks
 

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Just another Wannabe
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First of all, motor placement doesn't mean that much. You can move the motor four inches back or forward and see very little change in a v-drive boat. Also, the height of the engine doesn't mean that much unless you are turning left. Plus, changing height means adding u-joints to a driveshaft and re-making motor plates, and no one wants that when the boat is set up nice already.
If the boat were mine, I would leave the rear (of the engine) motor plate the same and just adjust the front (of engine) motorplate to fit the SBC. That SBC isn't much of an SBC. That is more like a big block of the 80's. The movement of the strut is way more critical than engine placement. If I were you I would make sure the prop was nice and close to the strut (as a smaller torque engine will want the prop under the boat a little more than higher torque to kep the nose up.) Just make sure it isn't spaced away from the strut. Then I would make adjustments to the prop to get everything perfect.
What we have learned through time is that if a boat works, it will always work. And a boat that doesn't work needs an act of deity to make it work. Boats that worked with blown big blocks make the best single carb boats. Etc. If the boat and prop like each other, start there with the engine you have and make small prop adjustments and small plate adjustments. The plates will want to come up a click from where they were before. If the thing set nice before, it will set nice now.
 

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Village Idiot
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I would imagine if the boat was well setup I would leave the rear engine mount that is on the flywheel end of the engine right where it was for big block. Moving an inch or so would not make a huge difference. Now, 8 inches is another story. Also, moving the prop forward or back 1/8” makes a difference. Keep that in mind. Also, having a prop guy work your prop will also make a difference to fine tune it.

Paul
 

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Discussion Starter · #5 ·
Thanks for responses. He is bringing the boat over tomorrow to place the motor and we will leave the rear motor plate in the same position.
I did not know about the importance of the placement of the prop on the shaft. This is why I am asking questions. I have been reading posts on this site to try and educate myself. Great people and great information being shared.
My experience is from nostalgia drag racing and it has been fun learning about what makes these boats work and the different types of hulls.

The boat will be fitted with a 400HP shot of nitrous. Would this added power upset the boat if it is already set or would you want it to come in during the launch?
 

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Just another Wannabe
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The width of a nickle between the prop shaft and the v-drive shaft will do more to the boat set up than moving the engine 2 inches. Where the prop sits is the most important measurement in these boats. When you look at the way the prop and shaft are set up now, see how much clearance the prop has to the strut. If it is spaced away from the strut too much, you will want to start it a little closer to the strut. But not too close. If the prop hits the strut, very bad things happen. And don't be fooled. These v-drives and plates shift and flex. 100% of the thrust is all going to the bottom of that v-drive. So don't think an 1/8" between the prop and the strut is enough. That will probably crash the prop and strut. Most people will perfectly set up a boat to just barely get a prop puller between the prop and the strut. But, once we get them wet and find out what it wants, we are sometimes on one side or the other from that measurement to make it happy.
Once you get the boat set up with the small block, you are going to find it may want more down pedal and a bit more to the plates during a launch to not let the nose fly away and set the hull with the added power of the nitrous. But everything else should want to be about the same.
I would not be surprised to find that the difference between the 400 shot and without will all be in the driver's left leg.

Good luck and let us know how it goes.
 
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