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Piston to valve clearance?

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  • Piston to valve clearance?

    What would you guys say is the minimum p2v clearance on an sr with solid lifters?

    The setup I’m working on is Sr20det with flat top 11:1 cp pistons, block decked even with pistons, 1.1mm hg, stock valves, 260 pro cams and eagle rods. I did a half ass clay job (don't have the correct rod bearings on hand) and came up with about .090-.095 on exh side.

    I feel like it’s close enough that I need to redo the clay in a more precise manner to be sure once the correct bearings get in. Just not sure what would be the minimum clearance as I think it's going to be pretty close.
    Last edited by ericb382; 01-01-2018, 03:02 PM.

  • #2
    Is that measured with or without a headgasket? If I remember correctly I think exhaust side needs .100

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    • #3
      That’s with hg. My machine shop told me .100 is considered safe for v8 stuff but there’s more valve train slop there so he said I may be able to go tighter. He’s not positive for this motor though. I’d relly prefer to not bring the pistons back to be cut because that’ll put my completion date past my next race that I really don’t want to miss. Once I have the right bearings in I’m thinking i’ll be closer to .085-.090, can’t say for sure yet though.

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      • #4
        You could buy a thicker head gasket if you need to. But first I would redo and check the clearance again if you felt you did a half ass job

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        • #5
          Yeah, definitely need to redo it, just thought it would be worth halfassing it while I was waiting on the bearings Incase there was miles of clearance (figured there wouldn’t be though). I thought about the thicker hg but didn’t want to lower compression too much. I should probably cc the head before I decide though, thicker hg could be a better option depending on how high the compression comes out. I won’t be running a ton of power through it due to power to weight restrictions, that’s why I figured the higher compression is better.

          Just for the record incase anyone has more insight based on the setup...It’s 2871r, e85. . I’m in Nasa so we go off “average power”. My max average power allowed is 342 so I plan to run high boost at low rpm and taper to lower boost to keep power right around 335 through the whole power band. Most tracks around here are smaller, tighter tracks where focusing on low weight is beneficial. We’re allowed 250lbs of ballast so I’m considering having a second setup that’ll allow 381 average whp with ballast for the few higher speed tracks we run where power/drag ratio becomes more important than power/weight. In that case I’d be shooting for about 375 whp, same tapering boost scenario but obviously a smaller flat portion of the power. So being that I’ll likely run the higher power setup at some point what compression ratio do you guys think will be too high for that, to where I’d be better going with a thicker hg? I know the 2871r will be struggling to keep up on the top end so that plus super high compression is probably a bad combo. But at what point?

          I know I’m asking for definitive numbers on non definitive topics but all input is appreciated!

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          • #6
            I suggested a thicker headgasket because of your limited time.


            Have you degreed your motor? If you did and end up putting a thicker head gasket, your going to have to go over it again

            Another option is adjust your cam gears and retard the exhaust cam to get more p2v clearance. But you will be increasing overlap which isn't good for Turbo setups.

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            • #7
              Turns out the compression is right about 10.5:1, so I definitely don’t want to go thicker with head gasket. I definitely agree that hg would be the quicker option though.

              I don’t have adjustable cam gears...

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              • #8
                Is your valve to valve clearance okay? If not, you're going to need adjustable cam gears. Personally I always got them to set the cams to match the cam card.

                The only options I can think of at the moment are

                1. Thicker headgasket
                2. Cam gears and adjust as needed within reason
                3. Purchase another set of cams with less lift

                I've never had any pistons cut but it's something I would avoid only because machine shops out here take forever and you'll end up dropping your compression ratio just like a thicker head gasket

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                • #9
                  I haven’t been on the board for a bit (life got in the way) but I just wanted to say thanks for all the replies! I missed the race I was gunning for so I’m now on the slow path of doing things right instead of the rush job with a deadline. I’m sure i’ll have more questions on the new setup but I just felt like a thanks was in order!

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