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Need advise on either cam selection or possibly new pistons.

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  • Need advise on either cam selection or possibly new pistons.

    Here's my dilemma,
    I have a GMPP 454 mark VI crate engine. A while back, I followed an Chevy High Performance article on the same engine where they did a cam swap and some minor head work, trying to reach 500hp.
    I did the same to mine but added MPFI.
    Now I'm in the process of doing some detail work with the engine out. Not real happy with my chassis dyno numbers, I was thinking of changing cams again. But in doing research, I found out why my dyno numbers are not what I expected.
    Seems the 8.75:1 compression my engine has is not high enough for the Crane cam I'm using (#168731).
    I talked to Crane, they suggested going to a smaller cam.
    I like an aggressive idle so I'm not really interested in going smaller.
    I don't have a lot of money to spend, so I was trying to figure out, Do I bite the bullet and raise the compression? Or do I use a different cam.
    So now here are a couple of more questions.
    How high of compression can I go and still use 92-93 octane fuel? 10:1 -10.5:1?
    The heads are 118cc's.
    Also GM recommends 93 octane for my engine. Why so high of octane if the CR is only 8.75:1?
    I hate to spend money on new pistons when I need money to address some other issues with the car, but I also want it to be right.
    The car doesn't run bad now the way it is, I just expected more.
    So I either leave it alone, change pistons, go to a smaller cam. Or possibly have a custom grind done with a LSA of 108* instead of 112*. What I learned from that is I'll lose top end and vacuum, so I guess that wouldn't be a good idea.
    Any thoughts on my issue?
    Thanks guys.

  • #2
    Re: Need advise on either cam selection or possibly new pistons.

    Honestly I don't care for either the cam or the compression ratio. The cam is 226/234* @ .050 on a 112* LSA. That's a big motor for that cam.

    I would consider going with a small dome piston (like a +17-18cc piston) that bumps your compression to around 11:1. Then a cam with 250* @ .050 duration on a 108-110* LSA. That would be my choice -- you would still have enough vacuum for power brakes, but it would thump at idle and pick a lot of HP.

    Changing just the compression ratio OR the cam would not make much difference IMO.

    Hope that helps

    Comment


    • #3
      Re: Need advise on either cam selection or possibly new pistons.

      You wont get there with your current set up if you follow what Eric has said you will have over your HP target and be very happy with it in the end.
      2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
      First to run in the .90s .80s and .70's in SBN/A
      2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
      2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

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      • #4
        Re: Need advise on either cam selection or possibly new pistons.

        or angle mill the heads and use shim gaskets to bump the compression.

        Comment


        • #5
          Re: Need advise on either cam selection or possibly new pistons.

          With 11:1 would I still be able to run pump gas?

          And thanks for the advise. 8) 8)

          BTW, If it makes any difference, the heads are iron rectangular port with 2.25 intake valves and 1.88 exhaust with some minor porting from Indy Cylinder Head.

          Comment


          • #6
            Re: Need advise on either cam selection or possibly new pistons.

            With the correct cam, pump premium would not be a problem. You need 290-295* on the seat and at least mid-24x* @ .050 to make it work.

            I did it on a 468 -- it was a low budget build and rattled like a can of bolts with 11:1 compression and an XE256 RV cam. I put a Magnum 292H in it and it ran fine on pump premium (and picked up probably 100 HP in the process). The car went from a low 13 second quarter mile at 102 MPH to low 12's at 114 MPH (spinning the tires)

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            • #7
              Re: Need advise on either cam selection or possibly new pistons.

              How about just a head swap to a closed chamber head?

              Comment


              • #8
                Re: Need advise on either cam selection or possibly new pistons.

                how about picking up a set of .010 cometics for $100 and boosting the compression to 9.2:1 assuming you're running a minor dome in the piston with a .040 gasket to get to 8.75:1

                Comment


                • #9
                  Re: Need advise on either cam selection or possibly new pistons.

                  Originally posted by Green Junk
                  how about picking up a set of .010 cometics for $100 and boosting the compression to 9.2:1 assuming you're running a minor dome in the piston with a .040 gasket to get to 8.75:1
                  I'm not that familiar with those. How do you think they would hold up for a street driven car? I've done two Power Tours. Last thing I would hate is if I was stuck in the middle of nowhere with a bad head gasket.
                  It is a tempting idea though.. Thanks.

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                  • #10
                    Re: Need advise on either cam selection or possibly new pistons.

                    Originally posted by efi-diy
                    How about just a head swap to a closed chamber head?
                    I like that idea, but I'm trying to spend the least amount of $ possible. Unless I have no choice. I have to have rect ports because of my Holley MPFI intake.

                    I know a guy that's been trying to convince me of having a custom cam made the same as the one I'm using only with a 108* LSA instead of 112*. I did bring up the idea with the tech dept at Holley and because of the EFI, he didn't think it would work.

                    I noticed that a 572 crate has 9.6:1 compression. The specs are listed as:

                    Camshaft duration (@.050 in)
                    254 degree intake / 264 degree exhaust

                    Camshaft lift (in):
                    .632 intake / .632 exhaust

                    Lobe Centerline- 112

                    Camshaft Part Number:
                    88961557

                    Camshaft type:
                    Hydraulic roller

                    I could probably get that cam at a good price since my shop has an account with the local dealership.

                    Comment


                    • #11
                      Re: Need advise on either cam selection or possibly new pistons.

                      I know you dont want to spend much money, but it seems to me you are looking at a pretty good start to a mild supercharger build.

                      Comment


                      • #12
                        Re: Need advise on either cam selection or possibly new pistons.

                        you can't blow cometic gasket, espcially on a mild street motor. they're awesome. You buy them in increments of .010 so if you get a .040 gasket from them its 4 .010 stacked up. just about every performance motor runs these.

                        Comment


                        • #13
                          Re: Need advise on either cam selection or possibly new pistons.

                          Here is what I'm thinking of using:

                          have found SRP pistons that will get me 9.9:1 compression.
                          I can get a 572 cam for about $250 which is less expensive than one from Crane. A 572 uses 9.6:1 compression. So I figure this cam may be a good fit.
                          Here is info on the cam:
                          We are sorry, but the page you are looking for cannot be found. If you have any questions or can't find what you are looking for, please contact us . About Us Customer Service Resources How To's References


                          Steel Hydraulic Roller Camshaft GM 572-620 H.P. Crate Engine
                          Intake duration @ .050"- 254
                          Exhaust Duration @ .050"- 264
                          Intake Lift- .632"
                          Exhaust Lift- .632"
                          Lobe Centerline- 112
                          Pace Price $249.95

                          And here is info on the pistons I'm looking at:


                          Manufacturer: SRP
                          Mfg part #: 212135
                          Our price: $ 548.00
                          Cubic Inch Bore Size Stroke Rod Length 118cc
                          460 4.280 4.000 6.135 9.9:1

                          Is there anything I should be concerned with this set up?
                          Thanks.

                          Comment


                          • #14
                            Re: Need advise on either cam selection or possibly new pistons.

                            What were the chassis dyno numbers you got and with what tranny?

                            Comment


                            • #15
                              Re: Need advise on either cam selection or possibly new pistons.

                              The best chassis dyno I got was 365hp, I don't remember the rpm. Torque I believe was around 411 ft lbs. The guy that did the dyno test didn't give me a print out, so my memory may not be exact.
                              The trans is a 4L60E with a 2800 stall and 3.42 gears in the diff.

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