Page 1 of 3 1 2 3 LastLast
Results 1 to 10 of 21

Thread: compression ratios with shaved head

  1. #1
    Veteran dr1ft-pig's Avatar
    Join Date
    Dec 2008
    Name
    Brendan
    State
    QLD
    Location
    NORTHSIDE YO
    Country
    Australia
    Posts
    4,116

    Default

    hey all , i have just bought a 0.5mm trd gasket, so i thought when i take the head off to put it on i may as well get it shaved,

    so
    my question is, with the stock compression ratio of a s/t 20v being 10.5:1 how much do i need to take off the head to bring it to say... 11.5:1 (stock b/t ratio) or 12:1 keeping in mine that i have a 0.5mm gasket

    or can i go higher than that safely??? coz if im gonna get it done i may as well go as far as i can

    cheers, brendan
    MY JZX83 (clicky)
    My Beams Powered AE86 SOLD (clicky)

    Quote Originally Posted by destroyer View Post
    Too bad im in the same town as dr1ft-p1g im pretty sure his mx83 is the coolest.

  2. #2
    Veteran
    Join Date
    Dec 2008
    Name
    John
    State
    TAS
    Location
    Hobart
    Country
    Australia
    Posts
    2,200

    Default

    theres alot more to it than wat uve just described.....i wouldn't be taking advice from 90% of the ppl on this forum....go straight to the ppl in the know for things like this....give terryo or similar a call and discuss it...sam q might even be able to provide some advice

  3. #3
    Veteran dr1ft-pig's Avatar
    Join Date
    Dec 2008
    Name
    Brendan
    State
    QLD
    Location
    NORTHSIDE YO
    Country
    Australia
    Posts
    4,116

    Default

    thats who i was hoping would answer (sam q) as he does all the research on that kind of shit, if its gonna cost too much i might just bar the idea and stick with standard till 3sg coems along
    MY JZX83 (clicky)
    My Beams Powered AE86 SOLD (clicky)

    Quote Originally Posted by destroyer View Post
    Too bad im in the same town as dr1ft-p1g im pretty sure his mx83 is the coolest.

  4. #4
    Senior Member shelldrake's Avatar
    Join Date
    Feb 2009
    Name
    Eddie
    State
    VIC
    Location
    Ripponlea
    Country
    Australia
    Posts
    144

    Default

    I thought the TRD gaskets to suit the 20v were .8mm, not .5mm. When changing from standard to trd gaskets without shaving the head or deacking the block you will end up pretty damn close to 11:1 .

    Sam is indeed the man - From what he told me - The blacktop and Silvertop have very different combustion chambers. You can only guess that Toyota made particular changes to the piston crown and the heads to deal with the higher compression in a certain manner. I will be shaving my s/t head the very min, and only if required. I would suss out whether that gasket is the trd 16v or 20v one too.

  5. #5
    Veteran dr1ft-pig's Avatar
    Join Date
    Dec 2008
    Name
    Brendan
    State
    QLD
    Location
    NORTHSIDE YO
    Country
    Australia
    Posts
    4,116

    Default

    its the 20v 0.5mm one
    MY JZX83 (clicky)
    My Beams Powered AE86 SOLD (clicky)

    Quote Originally Posted by destroyer View Post
    Too bad im in the same town as dr1ft-p1g im pretty sure his mx83 is the coolest.

  6. #6
    Senior Member shelldrake's Avatar
    Join Date
    Feb 2009
    Name
    Eddie
    State
    VIC
    Location
    Ripponlea
    Country
    Australia
    Posts
    144

    Default

    I wouldn't shave the head or block at all.

  7. #7
    Senior Member
    Join Date
    Jan 2009
    Name
    Eddie
    State
    NSW
    Location
    Sydney
    Country
    Australia
    Posts
    483

    Default

    In that case, prepare to take the head off again 500kms later when your headgasket starts leaking. All TRD HGs are Multi Layered Steel meaning they need a VERY flat surface in order to seal properly. You may get lucky but is that something worth risking for the sake of $100. Take the block and head to whichever engine builder you're choosing and ask them what the minimum shave would be to get both surfaces dead flat. From there, you can work out your static compression ratio with the figures he gives you. If they tell you they dont know or cant work it out... take the motor somewhere else.

    Eddie.
    4agte finally finished. 252rwkw with more to come

  8. #8
    Veteran dr1ft-pig's Avatar
    Join Date
    Dec 2008
    Name
    Brendan
    State
    QLD
    Location
    NORTHSIDE YO
    Country
    Australia
    Posts
    4,116

    Default

    thanks for your info mate
    MY JZX83 (clicky)
    My Beams Powered AE86 SOLD (clicky)

    Quote Originally Posted by destroyer View Post
    Too bad im in the same town as dr1ft-p1g im pretty sure his mx83 is the coolest.

  9. #9
    Elite rthy's Avatar
    Join Date
    Dec 2008
    Name
    Leo
    State
    VIC
    Location
    Tulla
    Country
    Australia
    Posts
    7,305

    Default

    yes I read too much

    ok standard is 10.5:1 and I have been told that a standard gasket is either 1.2mm or 1.15mm, I beleive it may be 1.15mm if so it works out to be this:

    cylender for 81mm bore = 396.8cc

    chamber size = 41.67cc

    the gasket is 0.65mm thinner so thats -3.26cc

    so the new chamber size is 38.41cc

    therfore the new compression is 11.32:1

    it might not seal though, gaskets are thick for a reason...
    30kw club

  10. #10
    Elite rthy's Avatar
    Join Date
    Dec 2008
    Name
    Leo
    State
    VIC
    Location
    Tulla
    Country
    Australia
    Posts
    7,305

    Default


    so just the gasket alone should get you to close to your intiual target but to get to 12:1 you will need a chamber volume of 36.07cc. So you will need a further 2.34cc off

    that will require 0.45mm off

    someone correct me if I am wrong on this
    30kw club

Page 1 of 3 1 2 3 LastLast

Similar Threads

  1. 7AG and compression ratios
    By Golden Circle in forum Technical - Questions
    Replies: 21
    Last Post: 28th May 2012, 06:36 PM
  2. Compression ratios
    By Jazz9 in forum Technical - Questions
    Replies: 7
    Last Post: 17th September 2007, 01:43 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •