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Adding Ls/gear reduction to a dd rigging

12ftgso480

12ftgso480

Well-known member
So we had a dd sbc 350 with a 72" blade. With swapping to a Ls with 79" blade and gear box we have to compensate 12" somewhere. I've never built a boat or adjusted rigging. I know we are going to have to modify our cage but my main questions. The boat set level in the water with old setup. I have about 12" I can scoot all the rigging and front seat forward. There will be room to move the gas tank toward the rear to help compensate some of the weight. Thoughts?
 

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Also not sure how much I can gain lowering the motor for I'm not sure what is too low for the prop at the back of the boat. I would think at some point I would start to lose trust the lower I go.
 
The output hub on the gear box is higher than the engine crank. I made that same move but with a caddy on my old boat. I slid my rigging forward 12" and added new legs for the gear box. Your prop can go below the transom lip some without any affect on push. I believe the racers props are only a few inches above the stringers. New cage will be needed for sure, but on my boat anyway it didn't ride any different in the water. It will be a different boat though LOL.
 
Would be alot of help if I can get an answer on just how low that prop can be below the transom. For the weight subject I'm sure it will be trial and error
 
Rule of thumb for prop spacing is a beer below the transom lip and a beer can away from the transom.

All of my setup have been this way or very close.

I did the same some time back went from a DD caddy to a 5.3 with gearbox.
Slide my rigging forward to added back 2 legs with radiator support.
My cage was close to big enough so I opted to use 1" solid aluminum blocks to rise the cage.
 
One Eyed Gator said:
Rule of thumb for prop spacing is a beer below the transom lip and a beer can away from the transom.

All of my setup have been this way or very close.

I did the same some time back went from a DD caddy to a 5.3 with gearbox.
Slide my rigging forward to added back 2 legs with radiator support.
My cage was close to big enough so I opted to use 1" solid aluminum blocks to rise the cage.
Click to expand...
Thanks for reply one eyed. Still scratching my head on my next move 😑
 
One Eyed Gator said:
Rule of thumb for prop spacing is a beer below the transom lip and a beer can away from the transom.

All of my setup have been this way or very close.

I did the same some time back went from a DD caddy to a 5.3 with gearbox.
Slide my rigging forward to added back 2 legs with radiator support.
My cage was close to big enough so I opted to use 1" solid aluminum blocks to rise the cage.
Click to expand...
Did you have to shim angle of motor any with sliding rigging forward.
 
No

My setup had gas tank under rear passenger seat as a DD (was in a 14x7-6 Alumitec) when I moved the rigging forward I moved the tank to under the motor.
 
Little update on the panther guys. Things got pulled on hold when noodling season showed up. Cage is modified, putting some seals in the 6.0 before we order headers. One step closer.
 

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If you are going to do the seals I would replace timing set and Oil pump (polish the bypass and shim the spring) and rear barbel

I would also replace the stock rocker bearing with trunion setup.
 
12ftgso480 said:
One eyed you got a picture of your maf setup?
Click to expand...
Unlikely you have a MAF (Manifold Air Flow) sensor. What injection system are you using? Most likely you have a MAP (Manifold Air Pressure0 Sensor.

IMG_4496.jpg

Aftermarket injection systems like the Holley also use an IAT (Intake Air Temp) sensor to correct the MAP sensor for temperature variations. You can install the IAT on either side of the throttle body, but the software needs to know where you put it. I drilled and tapped out an existing boss on my intake manifold for the IAT sensor.

IMG_4497.jpg


Add throttle position sensor and she is running.
 
One Eyed Gator said:
If you are going to do the seals I would replace timing set and Oil pump (polish the bypass and shim the spring) and rear barbel

I would also replace the stock rocker bearing with trunion setup.
Click to expand...
I'm on it dude
 

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I run a Holley HP system without a MAF mass air sensor I do run a MAP and an IAT in the location shown by sliding gator.

If you a going to run a GM PCM and harness and no boost then yes you can run MAF.
 
Last edited:
Slidin Gator said:
Unlikely you have a MAF (Manifold Air Flow) sensor. What injection system are you using? Most likely you have a MAP (Manifold Air Pressure0 Sensor.

View attachment 98372

Aftermarket injection systems like the Holley also use an IAT (Intake Air Temp) sensor to correct the MAP sensor for temperature variations. You can install the IAT on either side of the throttle body, but the software needs to know where you put it. I drilled and tapped out an existing boss on my intake manifold for the IAT sensor.

View attachment 98373


Add throttle position sensor and she is running.
Click to expand...
Slidin what water pump is that
 
12ftgso480 said:
Slidin what water pump is that
Click to expand...
The LS product line has 3 different accessory offsets, I went with the Corvette setup that pulls everything as close to the engine as possible, which is probably what you need to do given your rigging issues. The Truck is the farthest out and the Camaro is in between. Honestly, I have no idea why they didn't just keep everything at the Corvette offset??

The water pump itself is a 2008 and earlier Corvette LS3 pump. The 2009 and up use a different thermostat setup, which I figured out after the purchase but stuck with what I had.

It's still a work in progress, I'm close to putting it on the dyno but people keep calling me to go to the woods, so I do that instead :)

Here is the thread on my engine build, jump to page 6 and 7 for coverage of the accessories. One Eye has been very helpful on this build, he has been down this path for a while now.

Looks Like I'ma gonna be a Caddy Guy - Now What?
 
480, try to find a TBSS intake (it has longer runners) for your heads either cathedral port or Square.
You may need an injector adapter depending on the harness you run

Glenns Performance has takeoffs at a great price and offers larger injectors if you need them.
www.glennsautoperformance.com

Glenn's Auto Performance

Glenn's Auto Performance is an online automotive retailer based out of Clearwater, Florida that specializes in LSX and LTX performance products.
www.glennsautoperformance.com www.glennsautoperformance.com
 
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