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4.125 bore questions

This is a discussion on 4.125 bore questions within the Internal Engine forums, part of the LSx Technical Help Section category; Well I have a 1994 b4c m6 with an lt1 and its on its last leg and I want to ...

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    4.125 bore questions

    Well I have a 1994 b4c m6 with an lt1 and its on its last leg and I want to build a 350 ls style motor for it (7.0's bore 4.125 and 4.8's stroke 3.27)

    My question is, i have a 6.0 LQ9 out of a 2001 denali and a few 5.3's and I was woundering if i can bore the blocks out and sleeve them with 4.125 inch sleeves? I'm pretty sure it can be done with the aluminum blocks but I dont know about the cast blocks.

    Also does anyone make a forged 3.27in crank? I looked and i cant find one

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    Moderator Firebirdjones's Avatar
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    The 6.0 LS motors have a 4.00 inch bore. Taking them another .125 over is a huge stretch and not possible on a stock block.
    You may need to look into the aftermarket LSX blocks for something of that nature, or step up to an LS7 block.

    Sleeving is extremely expensive to do, about $100-150 per sleeve. Only worth doing to save a rare block to put back into service. To spend that much on all 8 cylinders to gain 1/8th inch in bore size?? I'll leave that up to you.


    However I like your thinking of the large bore/short stroke combo. Makes HP and turns alot of rpm, reminds me of a certain little 302

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    I know it cost a lot but the cheapest 4.125 inch block i could find is $2600 and if i sleeved all 8 cylinders it would only be about $1200...less $$$

    I was woundering if it is possible to bore and sleeve a 6.0, 5.3 or an ls1 out to 4.125?


    lol yea thats where i got the idea from i was going to build a 302 i even have the cross drilled forged steel 3inch crank to do it. i have the one that is same casting number as the dz 302 out of a 1967 Z/28 camaro.... but then I looked at the flow charts on the lsx heads and decided to go with a lsx motor because they flow way better especially at high rpms

    I even thought about putting a 3in stroke in a 4.125in lsx block, but i thought the 3.27in in stroke would be easier to find because it actually came in an lsx style motor but i cant even find a forged 3.27in crank
    Last edited by smokinz28lt1; 12-25-2010 at 05:55 PM.

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    Quote Originally Posted by smokinz28lt1 View Post
    I know it cost a lot but the cheapest 4.125 inch block i could find is $2600 and if i sleeved all 8 cylinders it would only be about $1200...less $$$

    I was woundering if it is possible to bore and sleeve a 6.0, 5.3 or an ls1 out to 4.125?


    lol yea thats where i got the idea from i was going to build a 302 i even have the cross drilled forged steel 3inch crank to do it. i have the one that is same casting number as the dz 302 out of a 1967 Z/28 camaro.... but then I looked at the flow charts on the lsx heads and decided to go with a lsx motor because they flow way better especially at high rpms

    I even thought about putting a 3in stroke in a 4.125in lsx block, but i thought the 3.27in in stroke would be easier to find because it actually came in an lsx style motor but i cant even find a forged 3.27in crank
    If the cheapest you can find a block with a 4.125" bore is $2600 just buy that because the only way you would be able to reliably resleeve the block and bore out to 4.125 is with MID wet sleeves. I know people are going to disagree with me about the reliability of MID wet sleeves but if you get a reliable shop to do them they are reliable. To resleeve a block with MID wet sleeves it is going to cost about $2600 so it would be better to just buy the block with a 4.125 bore.

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by smokinz28lt1 View Post
    I know it cost a lot but the cheapest 4.125 inch block i could find is $2600 and if i sleeved all 8 cylinders it would only be about $1200...less $$$

    I was woundering if it is possible to bore and sleeve a 6.0, 5.3 or an ls1 out to 4.125?


    lol yea thats where i got the idea from i was going to build a 302 i even have the cross drilled forged steel 3inch crank to do it. i have the one that is same casting number as the dz 302 out of a 1967 Z/28 camaro.... but then I looked at the flow charts on the lsx heads and decided to go with a lsx motor because they flow way better especially at high rpms

    I even thought about putting a 3in stroke in a 4.125in lsx block, but i thought the 3.27in in stroke would be easier to find because it actually came in an lsx style motor but i cant even find a forged 3.27in crank

    If it were possible and the cheapest way to go, I would think more people out there would be doing it. You have a good idea with parts that are already production pieces, I just don't see it as cost effective since your best block option is the LSx.

    I wouldn't let the heads be the deciding factor. Considering the LS flow numbers are based from 12 degree up to 15 degree valve angles, that's why they work so well. You can always build a gen 1 302 with an 18 degree gen 1 head and make nearly identical power numbers. In the end it would be cheaper. Gen 1 parts are much more wallet friendly. Just throwing it out there.

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    Member Jay37's Avatar
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    Sounds like a sweat biuld!

    In my opinion, For large bore, short stroke, revv to moon the combos... THE 352, 4.155 400ci block w/ a 3.25 large journal 327ci crank. They use to own the drag strips, and sound like a indy car on steroids.

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    Just crunchin' some more numbers, on bore/stroke combos...


    The classic, hell hound hunter 302=1.3 bore/stroke
    the 7.0 block to 4.8 combo ls350=1.26 bore/stroke
    the 400ci block w/327 crank 352=1.26 bore/stoke
    a 4.250 LSX block w/4.8 crank 371=1.29 bore/stroke

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