L6 250ci with 3 Spd Manual to Big Block Conversion-Does trans need to be moved?? Help
I've been researching old threads for days about what's needed to convert to a bib block. Engine stands, bigger rad etc but I have found a few posts relating to standards transmissions that say:
1. you need a different cross member to support the standard trans 2. and you need the large hump tunnel cover cause the trans moves back a couple inches. Is this actually needed cause I've found other posts saying swapping to a BB wasn't hard but they lacked these specific transmission details. Thanks |
Re: L6 250ci with 3 Spd Manual to Big Block Conversion-Does trans need to be moved??
The 3 speed clutch and transmission are the same length as a Muncie, THM350, power-glide and 200/2004R.
Typically any/all can be interchanged without changing driveline length. Although some conversions will require the automatic cross-member. I am wondering about the 3 speed behind the BBC. This was not a factory option because the transmission was not rated for BBC torque. 1. you need a different cross member to support the standard trans. I don't see a need for changing the cross-member if you stay with the 3 speed. 2. you need the large hump tunnel cover cause the trans moves back a couple inches. The large hump was behind BBC because they had the 4 speed manual or the THM 400. If you are staying with the 3 speed no reason to change to the large hump. If you use a 700R4/4L60 they fit under the standard floor. FYI I have observed BBC installed on SBC mounts. This works but don't expect some issues like aftermarket headers will not fit. Cheers. |
Re: L6 250ci with 3 Spd Manual to Big Block Conversion-Does trans need to be moved??
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I guess the clarifying part I need is if the 3 speed standard will stay in the same spot as it is now with the BB engine stands? If I need a new cross member and have to move the tranny back then I think a BB is just too much work and cost. If it drops in with the 3 speed with no driveline changes then I'm gonna do it. |
Re: L6 250ci with 3 Spd Manual to Big Block Conversion-Does trans need to be moved??
You'll find long term that the 3 speed will complain about the big block in front of it from the added torque and horsepower. If you want to keep a manual transmission in the truck you may want to start sourcing a 5 speed that is up to the task instead of doing it twice. Big blocks ---in the stock form using factory frame stands----mount in the front holes on the frame and will push the engine forward 1-1/4'' of the small block position even though the stands bolt in the same holes. I 'm not sure of the 6 cyl placement vs big block as I have not converted from a 6 to a large V8
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Re: L6 250ci with 3 Spd Manual to Big Block Conversion-Does trans need to be moved??
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I've read many posts saying the 3 Speed Syncro Saginaw is a very tough underrated transmission, if I go small block will it hold up fine if I had something like a 325hp -350lbs of torque mouse in there. That not too far off the 402's power numbers though.. |
Re: L6 250ci with 3 Spd Manual to Big Block Conversion-Does trans need to be moved??
The Saginaw 3 speed behind a SBC will be fine and will still hang from bell housing
IMHO a very streetable 400+ HP/TQ SBC will outperform an old school BB. Weigh less and run cooler and get 15mpg all day long |
Re: L6 250ci with 3 Spd Manual to Big Block Conversion-Does trans need to be moved??
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Not sure on big blocks, but for the small block, the trans is moved forward since the engine is shorter in length than a 6 cylinder. This gets the fan closer to the radiator. Looking at the frame rail, there are 3 holes on each side for the engine mounts. The front 2 are used for V8s and the rear 2 for straight sixes.
My understanding of the V8s was that the big and small block share the same location for engine mounts. Hopefully someone can correct me if I am wrong. Attached are a couple of pics showing the 6 cylinder and 8 cylinder bracket mounting positions on the frame.. I think the actual bracket may be slightly different between the 6 and 8 cylinder. The big blocks got a beefier bracket than the small blocks or sixes. Notice how the 6 cylinder used the rear two holes while the V8 used the forward two holes. |
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