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What REALLY is my compression ratio?

Discussion in 'Engine Building' started by GSRCIVICTN, Mar 28, 2007.

  1. GSRCIVICTN

    GSRCIVICTN Lost in a sea of rednecks

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    I just got my new pistons in the mail today. They are SRP (PN 149237) and they are supposed to have a 9.5:1 compression ratio. They are .50mm overbore. I called SRP just to make sure I got the right ones and I asked them what the cc's were supposed to be. They told me -8.4cc's. That seemed like too much of a dish, so I entered all of the info in the Zealautowerks.com compression calculator only to find that I would have closer to 8.85:1 compression. The engine is a B18c(JDM), basically a GSR. So I want to know who is right. Anybody know for sure??
     
  2. jlicrx

    jlicrx Senior Member

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    i also get slightly under 8.85:1
     
  3. GSRCIVICTN

    GSRCIVICTN Lost in a sea of rednecks

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    I put that the head had been milled .002" and I get 8.85:1. Still, even with a little help from me, that doesn't put it anywhere close to the claimed 9.5:1. Anybody know if the Zealwerks calculator is accurate? I thought it was.:huh:
     
  4. GSRCRXsi

    GSRCRXsi Super Moderator Moderator VIP

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    whats the compression height of the pistons? what size? 81.50mm? what head?

    zeal is fairly accurate.
     
  5. GSRCIVICTN

    GSRCIVICTN Lost in a sea of rednecks

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    I called SRP and talked to their technical dept. The guy at SRP came up with 9.5:1 when he did his calculation. We walked through every measurement and then it was figured out. We had different deck height measurements. When I asked him where he got his measurement from he said that it was assumed that a used block would have a shorter deck height and that it was also assumed that I would have to deck my block. In the past I have always cleaned the deck and checked it with a straight edge, but I have never had to have one decked.

    Why would they assume all of this and not advertise it? I'm not 100% sure what to do now. 8.85:1 seems a little too low. I don't plan on running 25 lbs. of boost or anything high like that.
     
  6. MikeBergy

    MikeBergy Blah blah blah....

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  7. GSRCIVICTN

    GSRCIVICTN Lost in a sea of rednecks

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    Yeah, I know. They told me that information was wrong. They said 9.5:1 and that the dish was -8.4cc. The messed up thing is that they claim it's 9.5:1 with that much of a dish. They want me to shave 0.035" off the top of my block. Seems excessive.
     
  8. dbone_vtec

    dbone_vtec HONDA 4 LIFE

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    More Boost

    More Boost Would Be Allowed With Lower Commpression Pistons

    Does'nt Seem Too Bad
     
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