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need to know asap about lsand vtec head

Discussion in 'Engine Building' started by 97hatch, Jan 10, 2007.

  1. 97hatch

    97hatch ?

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    im geting ready to order some weisco pistons that are 13:1 for my b20 block. My problem

    Im going to be using a LS head and the pistons i orderes are for a ls/vtec @84mm Now im told that they wont fit and the piston will hit the head is this true i didnt think so as the combustion chamber on a ls is larger than a b16 so this means that there shound be room correct




    celesta you built a b20 with like 12.5-13:1 didnt you what head did you use i forgot
     
  2. MikeBergy

    MikeBergy Blah blah blah....

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    Unless you have a jdm P8R head, your combustion chamber diameter is the same size as every other b-series head: 81mm. The only issue you would run into would be if you were running pr4 pistons with a vtec head, as the valve reliefs in the pr4 pistons are too shallow and small for the higher valve lift and larger valves that are in the vtec heads. You will be fine ordering vtec pistons for your non-vtec setup.
     
  3. 97hatch

    97hatch ?

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    im using weisco 13.2:1 shelf pistons for a crvtec
     
  4. welfare

    welfare Ancient Member

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    I would say use the pistons and then clay the engine to make sure there is clearance, like mike said, the combustion chamber is still 81mm in diameter, the problem that you may have is piston top to valve clearance.
    13.2:1 is a hefty piston (sticks up out of the bore quite a bit)
    but if it was designed for the engine you are putting it in, then you shouldn't have any clearance issues.
    I ran into a similar problem with my integra LS engine when I put some b16 pistons in, way back in the day (about 6 years ago) no one knew if they would clear the head, but I took my time, put everything together and clayed the engine to make sure there was room (which there was) I also had to do the same thing when I did a gsr head on that same engine, had to clay it to make sure there was room.
    It's time consuming, but at least you won't find out while you first crank it over that the pistons are gonna hit the head.
     
  5. welfare

    welfare Ancient Member

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    You are right and you are wrong, combustion chamber diameter does not matter where combustion chamber volume does.
    b16, b17 and b18c5 have 42.7cc chambers
    b18a, b18b, b20a, b20z all have 45cc chambers
    b18c1 is 41.6cc
    The smaller the chamber the better your chances of hitting the valves.
    Most piston manufacturers take into account the fact that people don't make their combustion chamber's larger on the head, it would defeat the purpose of making higher compression because you would effectively lower the compression by making the chamber bigger.
    I still agree that the pistons will work, but being that they are such a jump in compression, I would highly suggest claying the engine before final assembly just to make sure.
     
  6. MikeBergy

    MikeBergy Blah blah blah....

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    Just degree your cams, and you should be fine. If you are using OEM cams, you will be fine, but with that high of compression, I hope you are running at least RM M22's or Skunk 2 Pro 2's, in which I'd degree the cams regardless of which pistons you run. Claying is a thing of the past.

    I'm well aware of the fact that different heads have different volumes. The volume differeces are all made up in the quench areas, with trivial changes in chamber dimensions. The valve relief's are what you are going to need to check, as the HUGE cams that will be most effective with the amount of compression you want to run will require either very precise cam timing to avoid tapping reliefs, deeper reliefs to account for the higher lift, or both.

    Wrong, valve geometry is the same on pr3 and p72 heads.
     
  7. 97hatch

    97hatch ?

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    im using crower 404s so yes i have cams
     
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