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Same old block issues, need answers please?

This is a discussion on Same old block issues, need answers please? within the Internal Engine forums, part of the LSx Technical Help Section category; I am preparing for the worse case scenario in regards to my second 5.7 aluminum block and need answers in ...

  1. #1
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    1986 Turbo 944

    Same old block issues, need answers please?

    I am preparing for the worse case scenario in regards to my second 5.7 aluminum block and need answers in regards to it please.

    I have a set of probe forged rods and scat crank that are for stock bore. I would hate to get rid of those. I am running LS6 heads with ls2 timing chain along with custom short headers to fit my car.

    In my build the weight ratio of my car has been an issue, but it may be coming down to a ratio of weight to the money wasted on others mistakes.

    I am looking into the possibility of an iron block and just sacrifice the weight in front and redistribute the excess weight with other items like a battery relocation.

    I need to know if the iron blocks will run the ls6 heads, cam and valve train. Do they run the same crank and mains? Pretty much I need to know besides weight what the differences between the aluminum blocks are compared to the iron.

    I want to make sure that the stuff I have now will work either way.

    Thanks for the info. I did a search and found info on lt1 vs ls1, but nothing in this specific question.

  2. #2
    cutting and welding mark21742's Avatar
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    hugger orange
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    Bore size, 87 lbs and the aluminum block has a bolt hole in the front for the alt bracket...those are the only differences...and the iron block is stronger.

  3. #3
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    how does the alternator attach to an iron block if it is missing the bolt hole that the aluminum one has?

  4. #4
    cutting and welding mark21742's Avatar
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    hugger orange
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    The iron block still has the two bolt holes in the side of it, just not the one on the front...you could drill and tap a hole...but I just left the bolt out, and so do most other people

  5. #5
    Moderator Firebirdjones's Avatar
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    I'm am unclear on your probe pistons for a stock bore....

    Are you talking about a 5.7 stock bore or the cast iron 6.0 block stock bore??

    The 6.0 cast iron blocks are a 4"bore, the aluminum 5.7's are 3.898 bore.

    If you are stuck with a 3.898 bore piston that you have to use, you could do a 5.3 cast iron block, which is 3.780 bore, and they can be taken to the stock 5.7 3.898 bore.

    The aluminum 5.7's are hit and miss on the bore. Some get away with a hone, usually oversized to a max of .010 is about all you have to play with,,,,others won't clean up enough. Depends on mileage, maintanance, and how they were abused.

    I would personally start with a 6.0 block, not worry about the minor weight penalty. They have much more to offer, the biggest of which is a nice overbore with room for a refresh later down the road. Not to mention the 4" bore is considered the industry standard starting point for a foundation of making horsepower. Then throw your LS6 heads on it if that's what you want.

    You can find other ways to remove the weight you added, and not just shift it to the rear of the car. A tubular K-member along with tubular control arms will remove nearly all the weight you added with the iron block.

  6. #6
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    I should mention this is not for a domestic car, so weight and size is an issue. It is in my 944 porsche.

    I know about the maximum recommended over bore on the ls1 and had a perfect block going that I bought rebuilt and ready to go with the forged lower end. Some where along the line of the previous owner the valley got painted along with the block with a aluminum color paint to make the block look descent. The problem was the paint in the valley came off and went into the oil pickup and dropped pressure, this wore the cylinders fresh home out pretty quickly.

    So I am looking at my options. I have forged probe pistons 3.89 bore with scat rods. I would like to keep those. So may be looking at the iron block for less pricey cost.

  7. #7
    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by cfgioja View Post
    I should mention this is not for a domestic car, so weight and size is an issue. It is in my 944 porsche.
    That makes a little difference


    Well then if you are set on using your stock bore 5.7 piston/rod assembly, You are either stuck with using the 5.7 aluminum block that has a servicable bore,,,or grabbing the cast iron 5.3 block and boring that to your desired 3.9 size.

    Unless there is another option I'm missing here, I think it's the only way to arrive at that oddball bore diameter. Everything else is a 4" bore I believe.

  8. #8
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    I will have to do some debating.

  9. #9
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    Just got the call from the Machine shop, my Probe SRS pistons are a 3.92 bore instead of the 3.89 stock bore that I thought they were.

    They managed to get a home in there leaving a little of the scuff in there they assured me it was not enough to cause any engine problems. I will get this motor rebuilt soon and hopefully get numbers off of it finally.

    I also realized if I go to iron block later, I will have to up my front suspension again to compensate for the additional weight. So I am keeping my fingers crossed on this build. Third time is a charm..... I hope.

    Thanks for the info I will keep it in mind if I need to tear it apart again.

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