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  • 284 Schrick exhaust cam query

    Hi Guys,

    I appreciate this topic has been covered alot, but I spent a couple of hours reading the threads brought up by a search regarding this and could not find a conclusive answer to my question - maybe one doesn't exist?

    I am in the process of planning the rebuild of my 2.3 S14. The engine will be mostly rebuilt with new, stock parts, but I do have a pair of 284 Schrick cams to be fitted on both the inlet and exhaust side.

    I'm aware of the more popular combination of 284/276, but I have a pair of 284's that arrived to me at the right price shall we say. It was too good an opportunity to pass up on.

    Would you be concerned about valve to piston contact using a 284 on the exhaust side on a standard engine. This is my only concern.

    Thanks in advance for any advice given.

    Ollie

  • #2
    284 on the exhaust is said to touch original pistons specially if it has been skimmed.

    Comment


    • #3
      Bugger, thanks Kiko.

      I shall sell one 284 and replace it with a milder cam for the exhaust.

      Thanks,

      Ollie

      Comment


      • #4
        Nigel at BMSport for instance says in some cases he found the 276 dangerously close on some engines (probably where the head was skimmed at some point).

        But even then you're still very close which makes an over-rev a sure kill...

        Sent you a PM.

        Comment


        • #5
          A 276 will also have PV contact if one attempts to install according to Schrick specs, even on a non-skimmed head.

          Using a 284 would be that much worse, even if advancing it the proper amount to avoid pv contact. unless you want your engine to not run for very long....I can't see it not having other issues.

          My advice, sell the second 284 and buy a 276. However, I do hope you install them properly with slotted cam gears and measuring the clearances if you are using stock piston valve reliefs.


          Nick

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          • #6
            I've managed 20,000kms with my 284's -works for me.

            Comment


            • #7
              Like I said, some get away with it just by dialing them in slightly advanced other cars dont seem to tolerate them even advancing them. Eiter way Dave, if you're on original pistons be very careful when downshifting to avoid any overring, also keeping that timimng chain well tensioned is a must.
              Last edited by kiko; 03-06-2010, 02:10 PM.

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              • #8
                Thank you for the advice guys, much appreciated.

                I don't think I will risk running the 284 on the exhaust.

                Ollie

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                • #9
                  Kiko, yes - Piston to Valve clearance is something I think about but the engine was fully rebuilt, rebored w new pistons (stock oversize), E3 valve springs etc and it was all done properly and mapped by Paul Shep who had it steady state at 7,600 with power runs to 7,800 and I've done 20,000 kms since - all good.

                  Piston to Valve contact will be bad, but I dread the wife finding the invoice for last year's engine build even more !!

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                  • #10
                    Today I met a a chap running 284's on both inlet and exhaust on an otherwise standard engine for some time with no issues.

                    Has anyone personally experienced problems with this setup?

                    Thanks,

                    Ollie

                    Comment


                    • #11
                      I always find this discussion interesting... US owners say that 284/284 is not possible, yet somehow across the pond people are saying they run this setup with no issues on a stock motor.


                      Originally posted by -Ollie- View Post
                      Today I met a a chap running 284's on both inlet and exhaust on an otherwise standard engine for some time with no issues.

                      Has anyone personally experienced problems with this setup?

                      Thanks,

                      Ollie
                      Mark Williams
                      Dallas, TX

                      Nothing says "welcome to the neighborhood" like a search... oh wait... looks like they are all gone! :rastajake:

                      sigpic

                      Comment


                      • #12
                        Clearances are very tight, so if you're building an engine and planning to install cams (any cams) where contact could happen if not done correctly; then the first thing you have to do is use an engine builder with experience in checking and measuring such things.

                        Put some plasticine or blu-tak type putty on the piston, dry fit the head with an old gasket, torque it down, move the cam by hand, let the valve leave an impression in the putty, remove the head and see what happened.

                        I'm not an engine builder but can follow the logical steps in my head and know such things must be measured so there is confidence that things are not going to contact.

                        Fit decent valve springs - at high revs you don't want bounce - make sure your big end bearings are good as you don't want pistons moving further up the cylinder, don't try it with a skimmed head (brings the valves closer and could alter the timing) etc; all common sense stuff. But ultimately, if you're nervous, don't do it yourself but get an expert to do it for you.

                        It worked for me, I'm careful not to over rev - my down shifts are controlled so I don't slot the wrong gear etc and with a new chain and tensioner assembly I'd like to think I'm being responsible in my approach and don't take chances.

                        Cheers,

                        Dave.

                        Comment


                        • #13
                          M3 Adjuster has quite rightly asked for me to bring some closure to this thread by updating it with my findings.

                          My S14 is now being rebuilt at LH Owen Automotive. I hope to have the engine re-installed in the car in the next 2/3 months.

                          LH Owen at not in the slightest bit concerned RE the fitment of a 284 cam on the exhaust side, as clearance will all be checked, and double checked in the "dummy build" stage.

                          Since purchasing the 284's, I have seen first hand an S14 running a pair of 284's on an otherwise standard car. The car had been running the 284's for several years (and gets driven hard) with no issues whatsoever. It seems that this is quite a common choice in the UK, and no one I have spoken to has heard of issues arising from this.

                          So, it is possible to run a 284 on the exhaust of an otherwise standard road car.

                          Once the "dummy build" is complete, I will try to remember to post up the exhaust valve to piston clearnace measurements for future reference.

                          Thanks guys,

                          Ollie

                          Comment


                          • #14
                            Originally posted by -Ollie- View Post
                            M3 Adjuster has quite rightly asked for me to bring some closure to this thread by updating it with my findings.

                            My S14 is now being rebuilt at LH Owen Automotive. I hope to have the engine re-installed in the car in the next 2/3 months.

                            LH Owen at not in the slightest bit concerned RE the fitment of a 284 cam on the exhaust side, as clearance will all be checked, and double checked in the "dummy build" stage.

                            Since purchasing the 284's, I have seen first hand an S14 running a pair of 284's on an otherwise standard car. The car had been running the 284's for several years (and gets driven hard) with no issues whatsoever. It seems that this is quite a common choice in the UK, and no one I have spoken to has heard of issues arising from this.

                            So, it is possible to run a 284 on the exhaust of an otherwise standard road car.

                            Once the "dummy build" is complete, I will try to remember to post up the exhaust valve to piston clearnace measurements for future reference.

                            Thanks guys,

                            Ollie
                            Actually it never was a common choice in the UK till somebody started to run 290/290 cams......
                            That person even got told what a rubbish decision it is to run symetrical cams on a 4 cylinder....(but after seeing dynographs it was sudden the right choice)

                            However, the above person also found the exhaust valve pockets (stock pistons)polished by the exhaust valves after tearing down the engine 25k miles later.

                            Personally I don't think it's a good idea to build and engine which doesn't tolerate the occasional overrev on a mis-shift if there is the easy solution of fitting the right piston.

                            You are going to rebuild the endgine anyway, so why not fit the right pistons? This will give you the CR you need for these cams AND the PV clearance.

                            just my p


                            Goodbye M3, you served me well.

                            Comment


                            • #15
                              In the interest of making this a thread about what is right or not, as opposed to another internet rumor, I kindly request that if possible you (or the engine builder) provide us with some measurements of the fitment.

                              If you are using stock pistons I'd like to know the following so we can compare to the Schrick specs:

                              EO, EC, deg BTDC of max lift, valve lift at TDC, and finally what your builder is using for p-v clearance.

                              If you are going aftermarket pistons with big valve reliefs, then the numbers are not needed as you should be able to match Schrick's specs and adjust easily for a custom tune.

                              Good luck with the build and let us know how she runs!


                              Nick

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