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Thread: LS1 T56 vs. LT1 T56 similarities/differences

  1. #1
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    LS1 T56 vs. LT1 T56 similarities/differences

    As some of you know, my build has been based on an LT1/T56 combo. When I bought all those pieces they were relatively current. But I've been so slow to complete the car they are not current at all.

    So, moving into the 21st century, I'm thinking about an LS engine. Probably an LS3 crate engine, either the 430 hp or 480 hp version.

    The question I have - are the OEM T56 transmissions for the 93-97 LT1 and the 98-02 LS1 the same dimensions, especially the tailshaft housing? What I'm wishing for is knowing whether I can use a 98-02 transmission, or convert my 94 transmission to an LS bellhousing and input shaft, and have the driveshaft and crossmember location remain the same, and with that will the engine fit the engine compartment correctly?

    I think it might be just fine - that the additional length of the LS1 bellhousing and the shorter length of the LS1 would cancel out - and the heads would clear the firewall nicely and also have good clearance between the accessory drive and radiator/fans. But I don't have much other than a gut feel.

    To be able to put that combo in the car without changing the driveshaft length, shifter hole, and have everything else fit would make the decision to do it much easier.

    The other thing I'd like to know, but this is a stretch, is what's the most likely engine mounting adapter plate to use? Stock, 1.5" forward, what?

  2. #2
    Registered Member NickP's Avatar
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    I don't recall Rick, is your engine in stock location?

  3. #3
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    It's 3/4" forward, what I'm looking for is can I use the transmission mount without moving it, and which adapter plate might work with that.

  4. #4
    Registered Member chevynut's Avatar
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    At one time I was trying to help a customer figure out which adapters were needed to install an LS engine into a frame we built with SBC mounts and I included all the dimensions for both blocks in a post here. As you know, the LS engine bellhousing face needs to be moved about 2.25" forward to clear the stock firewall, if you want to keep it stock.

    Not all T56's have the same tailshaft length:

    http://www.5speedtransmissions.com/6_speed.html

    The shifter is 1.1" further back on the LS T56 and the mounting pad is .7" further back. That actuall might be good for you since it would move the engine forward more.

    I believe the challenge for you is that the input shafts are different lengths between the LS and LT1 versions of the transmissions. Quicktime Performance makes bellhousings to adapt just about any transmission to any engine so that may be a route to go.

    I think you need to add up all the dimensions and see where everything lands, for all configurations you might want to use.
    Last edited by chevynut; 04-08-2016 at 07:08 AM.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  5. #5
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    I think it's a given that I'd need the longer LS input shaft and mid plate, along with the longer LS bellhousing. Or, just use a 98-02 LS transmission. Cost wise it's probably a toss up, and might favor the LS transmission after selling the LT one.

    I saw the dimension you posted - that seems to say the change is not just the bellhousing length.

  6. #6
    Registered Member chevynut's Avatar
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    Looking at the dimensions on the site I linked, the LT1 T56 is 5.4" long from the mount to the end of the tailshaft and the LS version is 5.3" long. So you could probably swap transmissions and not have to move the crossmember or change the driveshaft for the .1" difference.

    Looking forward, the LT version is 25.9" long, and the LS version is 26.6" long. So the LS engine bellhousing face will be .7" further forward. If your LT1 is currently .75" forward the total for the LS would be 1.45". I don't think that clears the firewall.

    The net difference in the shifter position is .4" with the LS shifter being further back that amount, with the tranny mounts in the same place.

    That all assumes the dimensions on that site are correct.
    Last edited by chevynut; 04-08-2016 at 07:27 AM.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  7. #7
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    That all assumes the dimensions on that site are correct.
    That is my concern, finding an independent verification of those numbers would be helpful, as all those little differences don't make a lot of sense to me. Why would GM have changed that stuff?

  8. #8
    Registered Member chevynut's Avatar
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    Quote Originally Posted by Rick_L View Post
    Why would GM have changed that stuff?
    Why dos GM have 10,000 alternators and 10,000 starters?
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  9. #9
    Registered Member chevynut's Avatar
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    Paul has an LS1 T56 so maybe he can verify the dimensions for you. Or perhaps there's some other sources on the internet for those dimensions. Do the dimensions match your LT1 T56?
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  10. #10
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    Just checked my transmission vs. the dimensions found on the net. The only number that matched was the length of the bellhousing. The others were off 0.3" (shifter and trans mount) - 0.75" (overall length). All those were shorter in my measurements. If one compares what I measured to what's in the chart for an LS transmission, the situation is better than using the chart for both (more like what I expected).

    The chart I had was from 5speedtransmissions.com but I saw it on another site too. I spent a fair time searching for the dimensions but will spend more.
    Last edited by Rick_L; 04-08-2016 at 04:09 PM.

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