Compression and C Heads

Discussion in '96-04 - 4V Specific' started by SN90FiveOh, Jul 27, 2020.

  1. SN90FiveOh

    SN90FiveOh Active Member

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    I know, Those two do not go together. But, for science, what would it take for me to get 12:1 compression from an 04 Mach1 engine without stroking it.

    Has anyone here milled one of these heads for a compression bump? I had a set done for a 2 valve years ago but I'm not sure how much hacking I can do with these.

    What I'm seeing is that flat top pistons with valve reliefs would put me near 10.5 and then bringing the piston just above the deck could yield 10.8, but if I can get the chambers down to maybe 48cc instead of 52 I'd be in business. 45cc would be even better. Feel free to let me know how crazy I am.
     
  2. ttocs

    ttocs Legend

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    mr compression should be here shortly :)
     
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  3. SN90FiveOh

    SN90FiveOh Active Member

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    I figured Gary would be all over this.
     
  4. OLD H2S

    OLD H2S Well-Known Member SN95 Supporter

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    The fastest, cheapest way is a set of Trick Flow 38cc street heads on a stock bottom end... periodfullstopdone13enginestoprooveit!
    Do not touch the bottom end unless the cylinder walls are Really bad, they will work fine at speed.
    As soon as you start cutting heads you are down the rabbit hole... Now the chains get sloppy and tear up the rails, custom tensioner pistons are going to be made $$, The front cover will need to be milled at the top, A pain to hold to cut right.
    Going from 52cc to a 42cc is a big jump, look up my builds on welding head chambers, that is a lot of work and machine time $$
    Then there is the why did you do this without doing that? You were there and said...
    How will you know how it will run? They all come out different even when trying the same formula again..some start to detonate and you must pull timing and the power goes down fast and you wonder what changed?? It is fun and costs a lot but it is expensive and it has all been done on the 4.6, multiply 281 CID x 1.2 hp/cid and that's all you got when running NA.
    I have gone as high as 14:1 with no problem and then had lower comp. engines give me fits and run fine at low timing and HP ?
    Here is a big head scratcher for you to think about, raising the compression is not a linear scale, Just because you get 14.7 HP going from 8:1 to 9:1 you do not get the same jump going higher, 13 going to 14 is 5 HP. Higher compression can help a cam run better and make a small cam sound wicked, but much more heat and stress on all the parts and they do not last as long, look at this vid with little cams I made.

    Loved that motor but blew a rod bearing racing a Porsche.
    Call me, write me, throw a rock threw my window. High comp is not the be all end all like the old days of leaded gasoline. Running regular gas makes more power because it burns hotter and you can raise the timing more earlier. The biggest reason I can see to up the compression on a 4.6 is to get a big cam to run right and that is for drag racing and there are some good guys here in that direction.
    I road race so I am looking for torque to dig out of a corner and out pull the Japs and Eurotrash.
    Go look at the thread BLAK54 has going right now on head work..I can not think of 2 people, him and me that have done more silly shit building engines because we can with all the toy store tools you do not have. We don't care if they do not come out right we got the next idea churning in our heads.
     
  5. SN90FiveOh

    SN90FiveOh Active Member

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    I don't believe trick flow or anyone for the matter makes 4v heads. Blak54 helped a lot with the last one I put together. I had a set of 2v heads milled .030 you can see it in my last few pages of my "school me on my new 2v" thread. I fudged up elsewhere when building the engine and only put about 150 miles on it before getting frustrated and parting the car out. I definitely don't want to go that far with this engine but more wondering what .010 would bring the chambers to be.
     
  6. 96blak54

    96blak54 Legend

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    Good to know i have gained nick names!...mr compression...lol!

    If my mind serves me right, 4v heads decked .080" is right at the intake valve edge. I can confirm later.

    Going from 52 to 45 is a good bump, but every bit do-able. Hold on while i check chamber sized decked .080. Heck my last 2 builds i deck a set of npi heads .120". The 1st of the 2 builds i ran zero deck 5.4l pistons meaning the compression was 18:1. It would barely idle safe on 93octane but when flushed out for E85, the game changed! It became a normal running engine that struggled to get to operating temperature...at 18:1 static compression. I learned alot from that build!! Alot that im not disclosing too!

    The 2nd build i went with normal stock flatop pistons the yeilded 13:1. It ran well on 93, it loved a 50/50 mix with E85....which is more like 65/35 or E35.

    Keep in mind what ever you deck the heads, itll affect the front cover to valve cover surface sealing and the timing chains will get slappy. Both easily fixable

    Now dial that exhaust cam back 1 chain tooth. Thatll make the LSA 105ish making exhaust open late and giving alot more overlap.
     
  7. SN90FiveOh

    SN90FiveOh Active Member

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    @96blak54 You're absolutely nuts, I love it. If you have an idea of approximately how many cc's are removed per .010 then I may be able to decide which route I am going. Really not wanting to go too far because of timing cover/chains and intake manifold alignment but if thats what it takes then I guess thats what I will do.
     
  8. SN90FiveOh

    SN90FiveOh Active Member

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    Just looked over my old build thread. My 2v heads were milled .050 not .030.
     
  9. OLD H2S

    OLD H2S Well-Known Member SN95 Supporter

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    IIRC .006 off the head = 1cc
     
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  10. 96blak54

    96blak54 Legend

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    There you go!.... Deck .060" off to drop 10cc
     
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  11. SN90FiveOh

    SN90FiveOh Active Member

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    .060 sounds like an awful lot. How would I adjust for timing chain slack? I know my last two valve was .050" shaved but I built that on a major budget and just kind of threw it together. I dont mind doing it again but I'd like this one to last.

    Going from H2S number it looks like .048" off the head with 1.5cc valve reliefs and zero deck would net 12:1 static ratio.
     
  12. 96blak54

    96blak54 Legend

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    The mis-match surface of the valve cover on the head and front cover can have a step. The cover seal allows for some differences. Maybe not .050" different tho, im not 100% sure on that! Find a machine shop thatll cut the cover down a tad bit.

    Be sure the chain tensioner arm is new. A worn one allows more slack. Use cast iron tensioners with washers placed inside to lock it out with no more than an 1/8" tensioner arm movement. Ditch the rachet stopper. This worked great for me however i made longer tensioner piston for my tensioners. Stock ones wouldnt reach