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Thread: 6.5 GEP NA or 5.9 12v NA?

  1. #21
    Colonel
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    The only thing I want to add into this brainstorming is, you cannot make a standard Cummins 12 valve a NA motor. The standard injection pump are designed to sense boost, so if you take the turbo off, the truck wont run properly and it will be a complete slug and smoke like a train. If you want a NA motor, dont get a 12 valve.
    1991 M923a2

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    2 Star General erasedhammer's Avatar
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    Quote Originally Posted by Lukes_deuce View Post
    The only thing I want to add into this brainstorming is, you cannot make a standard Cummins 12 valve a NA motor. The standard injection pump are designed to sense boost, so if you take the turbo off, the truck wont run properly and it will be a complete slug and smoke like a train. If you want a NA motor, dont get a 12 valve.
    Thats interesting. Are we talking about the p-pump? How does it 'sense' boost?
    I would want a fully mechanical engine, so converting a 24v seems harder than just starting with an already mechanical 12v.
    1986 M1028 w/ Dana 70HD Dually
    [SOLD] 1994 M998A1 w/GEP 6.5TD & 4l80e

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    The governor end of the pump has a sensing line that goes to the manifold, the manifold pressure pushes on a diaphragm which in turn moves pieces parts in the governor end to allow the pump to supply full fuel. If you delete the turbo, the engine will smoke horribly. The cylinder heads have built into the casting process, a swirl factor. Without manifold pressure, that swirl effect won't happen. Timing is designed using a turbo. The "smoke limiting" design is across the board, CAV, VE, ND and P pumps use it, it is a federal emissions thing.

    I second the shoehorn fit of a B in a GM chassis. No room for a fan, electric is needed, firewall needs "trimming", plumbing for intake and exhaust are kind of a cluster and it's heavy. Seen quite a few in my days, only 1 that I would have considered a good one or something I might consider. Think about this, in stock form, the B is governed at 2500 RPM, the Chryslers had a 2700 RPM gov cut off. What does the V8 turn? What will be the road speed loss if you go from 3000 - 3600 ish to 2500 ish?
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    2 Star General erasedhammer's Avatar
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    Quote Originally Posted by WillWagner View Post
    The governor end of the pump has a sensing line that goes to the manifold, the manifold pressure pushes on a diaphragm which in turn moves pieces parts in the governor end to allow the pump to supply full fuel. If you delete the turbo, the engine will smoke horribly. The cylinder heads have built into the casting process, a swirl factor. Without manifold pressure, that swirl effect won't happen. Timing is designed using a turbo. The "smoke limiting" design is across the board, CAV, VE, ND and P pumps use it, it is a federal emissions thing.

    I second the shoehorn fit of a B in a GM chassis. No room for a fan, electric is needed, firewall needs "trimming", plumbing for intake and exhaust are kind of a cluster and it's heavy. Seen quite a few in my days, only 1 that I would have considered a good one or something I might consider. Think about this, in stock form, the B is governed at 2500 RPM, the Chryslers had a 2700 RPM gov cut off. What does the V8 turn? What will be the road speed loss if you go from 3000 - 3600 ish to 2500 ish?
    Yeah I'm tied to NA, so looks like I'll be going with a 6.5.

    Funny enough I was looking around to try and turn down the redline rpm of the 6.5. I would never dream of putting a 5.9 with a th400. NV4500 all the way, so theoretically I wouldnt loose any top end speed.
    1986 M1028 w/ Dana 70HD Dually
    [SOLD] 1994 M998A1 w/GEP 6.5TD & 4l80e

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