Announcement

Collapse
No announcement yet.

different head gaskets = 25 psi difference in compression?

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • different head gaskets = 25 psi difference in compression?

    so, we were playing on the dyno last week and apparently n/a motors with 18 psi like to run rich. leaning it out to 11.5 or so and we melted a piston. no problem, pulled everything apart slapped a new piston (read "old") and i called napa for a head gasket (thought i would give them a chance since they are cheaper and nissan usually don`t have them in stock.) so get it all back together and she runns alright. get on the dyno to set the boost and she starts pinging at ~ 4k rpm 16-17 psi. mind you i made 360 hp @ 17 psi before the "pop" and had been running like this for quite a while. so now i`m pinging at 16-17 psi and only can manage ~290 hp. hummmm....that`s a big hp loss.

    compression check showed 175 in 1,3,5 and ~150-155 in 2,4,6. ok....leak down test in 2,4,6 shows 3-4%. i can live with that. am i loosing it here or is it possible for the napa gasket (looked identical to OEM) to be thicker or not crush the same amount and cause the lower compression on that side? the right side with 175 comp is a OEM gasket. yes i followed the torqueing procedure exactly. 290 hp is no where near as fun as 360...

    suggestions?

    Exercising my constitutional right to be awesome

    1.5.2. Podium winning cars do NOT need to be running at the checkered flag
    good thing....

  • #2
    my initial guess would be the cam being off a tooth but I'd imagine you wouldn't screw that up

    Comment


    • #3
      G-E wrote: my initial guess would be the cam being off a tooth but I'd imagine you wouldn't screw that up
      I agree. Were you running the same timing for both runs? What kind of compression did the motor make before? What does the graph look like?

      P.S. A little over a week ago I found out the hard way that my boost gauge was WAY off. What I thought was 10-11 psi, was probably somewhere near 15+. Needless to say, I blew both headgaskets after one run in 4th gear. I didn't note ANY compression loss and 2 of my cylinders even showed 200 psi!
      Originally posted by Andrew84zx
      tell her your car is so fast it will make her panties fly off
      545 RWHP & 540 RWTQ
      VG30ET.com Member

      Comment


      • #4
        the boost numbers stated were taken from the dyno. i thought the cam might be off a tooth, i counted, 40 teeth. plus i thought i remembered someone saying 1 tooth was like 14 degrees (maybe more?) :?: , i would think it would run even worse than it is now...

        Exercising my constitutional right to be awesome

        1.5.2. Podium winning cars do NOT need to be running at the checkered flag
        good thing....

        Comment

        Working...
        X