Why 1inch Set Back Mounts?

Discussion in 'High Tech Retrofits' started by cars4life, Oct 12, 2013.

  1. cars4life

    cars4life Veteran Member

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    I am in the middle of a ls1 t56 swap in my 1979 z28. I understand its best to get the motor back to the firewall as far as possible to keep the nose of the car lighter. Without 1 inch setback mounts will a f body oil pan clear the cross member and are there headers on the market that will also work without the setback? The reason I ask is because of the pooer on the t56 is future back and I really want to use the factory 4 speed console, this means with out the set back mounts I will be that much closer.
    Thanks in advance for your help.
     
  2. toddoky

    toddoky Veteran Member

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    The blocks of LS motors are about 1" shorter behind the cylinder heads than the block of an old small block Chevy, which is why you need to shift the motor back by that amount to mate up to a transmission intended to be kept in its stock location. Keeping that transmission location can allow you to reuse the stock driveshaft and crossmember, but you are not going to notice a handling improvement on anything except for maybe a purpose-built competition car. Remember that GM moved BB Chevy motors forward by 3/4" to get them into 1st-gen Camaros and you don't hear many people complaining about under-steer on their BB equipped 1st-gen.You also create clearance issues between the engine and various vehicle components when the engine is moved back 1", the most important of which seems to be the collision of the stock low-mount 4th-gen F-body alternator with the engine crossmember.

    I've swapped a couple of these cars and in my opinion it's best to mount the LS engine so that the back of the cylinder heads are in the same basic location that the old small block heads were in and move the transmission forward about 1" to mate up with it. The clearances around EVERYTHING is better with this type of positioning.

    If you are concerned with shifter positioning, the aftermarket T56 Magnum allows for more flexibility in that regard than the GM LS T56 does, although there are also offset shifters and kits available to relocate the shifter to the forward inspection cover position on an LS T56 (but you have to disassemble the transmission to perform the installation).

    Your F-body oil pan should fit with the engine located in the this position just fine and the new Hooker 2nd-gen LS swap headers will drop right in with the new Hooker engine mounts in this approximate location (other brand headers might as well).
     
  3. cars4life

    cars4life Veteran Member

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    If im understanding you correctly the set back mounts main function is to mate the ls motor to the " existing " trans without any trans modification. So if your installing a t56 or any other transmission that requires a new drive shaft and cross member the setback set back mounts are not necessarily needed unless you choose to use the headers designed for the mounts?
    Please dont feel as though im challenging you, im just trying to figure out if there was multiple reasons.
    Thanks Adam
     
  4. toddoky

    toddoky Veteran Member

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    Yes Adam that is mostly correct. The common and descrete 1" set-back typical of many swap plates was derived years ago to make up the difference between the casting length behind the cylinder heads of original small block Chevy and that of the LS engine. While that universal "live-with-the-consequences" approach works decently in some applications, it creates fitment issues and unlikeable compromises to be made in others, like 1st and 2nd gen F-bodies for example. The swap market has been maturing and producing more components of a specific-fit nature that are intended to remedy persistent fit/compatibility issues that result from using universal fit components. The new Hooker 2nd-gen engine mounts and transmission crossmembers split the difference between the common stock location (1" set-back) and 1" forward plates and move the transmission forward by about 1/2" and the rear face of the engine back 1/2" to mate up to it. Some swappers go to great lengths to get the engine back as far as possible at the cost of having to deal with the host of issues that come with that positioning as they believe there is a performance penalty associated with any forward movement made to the engine and or transmission. Believe me, you are not going to notice a performance difference with moving your transmission forward by 1/2" (remember that GM moved the heavier Big Block engine and the transmission 3/4" forward on 1st-gen Camaros compared to the lighter Small Block engine and you don't see many performance gripes from 1st-gen owners regarding the engine positioning in their cars). Some other swap mounts on the market have moved the engine forward by a couple of inches and upward to clear specific oil pans and that amount of forward/upward relocation will have a noticable affect on vehicle performance. Regardless of the engine mounts used, the headers should be matched to them to arrive at the best possible fitment geometry.
     
    Last edited: Oct 14, 2013
  5. cars4life

    cars4life Veteran Member

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    I really appreciate your prompt and professional input. I will have to do a mock up to see whats going to work for me. Im leaning in the direction of the hooker mounts and stainless steel headers but the shifter location will be the decision maker.
     
  6. toddoky

    toddoky Veteran Member

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    You have options with the shifter location as well as the market is supported with multiple offset shifters for the T56 transmission.
     
  7. Todd80Z28

    Todd80Z28 Moderator Staff Member Lifetime Gold Member

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    On my LT T56, the shifter is several inches back from the stock 4spd location. Several inches. IMO, I would switch to an auto console, as the stick will come up in the front half of the auto shifter console hole. I like the shifter in this location much better than the 4spd anyway- too far forward.
     
  8. toddoky

    toddoky Veteran Member

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    That's a good added comment Todd. Kits can also be purchased that can relocate the T56 shifter to the forward inspection cover hole, but the transmission has to be disassembled to perform the modification. The T56 Magnum offers more shifter location flexibility than the GM LS T56's but requires tunnel modifications to fit properly. It's a bit of a give and take. If someone finds the rearward shifter location of the stock T56 is preferred, I think your advice to use the auto console is a good option.
     
  9. Todd80Z28

    Todd80Z28 Moderator Staff Member Lifetime Gold Member

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    In fact, after many years of having the T56 installed, I moved the stick back another 2" to put it exactly where I wanted it.
    [​IMG]

    I wish I hadn't cut that lip all around after the fact (did that in '95, when my resources and skill set were a fraction of what they've become... I think:) ), and just notched it in the front instead to accommodate 1/3/5/R.

    Here's the finished look-

    [​IMG]
     
  10. toddoky

    toddoky Veteran Member

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    I'd say that fits in there nicely.
     

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