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85mm b20b vtec bore/ CTR cams and compression

Discussion in 'Engine Building' started by khai_tuan_nguyen, Aug 30, 2004.

  1. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    I had the 13.5:1 compression pistons in a swap i just bought. I can not tune the motor with this compression and pump gas so I will be taking the pistons out and putting in lower cr pistons. I will be running ctr cams.I heard that higher compression does not necessarily mean more power. It depends on what cams you have also.

    My question is:

    What is the best compression to make the most power to run with ctr cams only to 8k rpm?

    The b20b block will be machined to 85mm bore so will the walls hold up or is it really necessary to sleeve (only 8 k rpm max).

    What will that bore net me in terms of liters? (b20b block 85mm and b16 head)

    Thanks
    KHai
     
  2. xj0hnx

    xj0hnx I wanna be sedated VIP

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    Higher compression needs to breath more, hence taller lobes producing more power. CTR cams aren't very wild, so you'd do best sticking to a stockish (slight bump up) CR.
     
  3. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    Since CTR cams are not wild and you suggest a little higher than stock, what is stock? and how much higher? Also what about the bore and sleeve ordeal. lol

    Khai
     
  4. exospeed*com

    exospeed*com Member

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    Building a motor isnt just slapping on high comp pistons and getting a big cam. you have to match the piston to the type of cam you are using. while most cams can work with different compression setups. its best to plan a good combo of cam and piston setup. CTR cams would most likely work with either CTR pistons or a 12:1 compression Aftermarket piston.
    keep in mind that valve clearances will be a factor in choosing the right piston. This is the case, when you are going with higher lift cams and off the shelf pistons.

    if you are the CTR cams, I assume you arent looking for something crazy like a big bore block. sticking with an 81.5mm CTR piston is good enough. There is no need to go 85mm bore or 84mm bore sleeved block if you are just on a CTR cam. when you are putting money into a hardcore setup like that, look into bigger cams such as skunk2 stg2 to match with that block.
     
  5. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    Thanks for the help exo on this and other threads, but what i am saying is taht i already have a b20 block and it came with 13-13.5 pistons as stated in my other thread. So since I am swapping them out for lower compression pistons and having to clean the block to spec, which is 85mm.

    My question was will the b20b be ok bored to 85mm with only ctr valvetrain (springs, cams, retainers) up to 8k

    Khai
     
  6. exospeed*com

    exospeed*com Member

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    My question was will the b20b be ok bored to 85mm with only ctr valvetrain (springs, cams, retainers) up to 8k

    Khai


    Mah bad Khai, iteh ctr valvetrain and cams should be fine for what you are using it for. 8K is not that high anyways.

    Wil
     
  7. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    Umm I know the ctr valvetrain is fine, but will an 85mm bore be ok on a b20b with no sleeves and higher compression for the ctrs?
     
  8. exospeed*com

    exospeed*com Member

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    oh, I wouldnt go big bore at all on a b20 block. Before my picture archives got deleted, I had pictures of cut b20 sleeves and b18A sleeves. the b20 are thinner and have a webbing in the foundation that makes it weaker than the b18A. The most i'd bore on a stock b20 sleeve is 84.5mm 85mm is going to the limits. I personally wouldnt do it. the concern is more on the cylinder wall thickness rather than its compatibility with the CTR setup.
     
  9. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    That is the problem, since this is the second time the motor has been torn apart it has to be machined and the next size off the shelf piston is 85mm.

    I don't have money to sleeve.

    What to do what to do?

    ............
    Khai
     
  10. phunky.buddha

    phunky.buddha Admin with a big stick Admin VIP

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    Sre you sure you need to bore the engine again? Unless you need some serious cleanup inside the bore, you could probably make do with another hone job and continue to use 84.5mm pistons.
     
  11. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    I am assuming I will need some serious work, because it has been pining bad and I can see some piston shards on the top of the pistons when i look through the spark plig holes.

    Khai
     
  12. phunky.buddha

    phunky.buddha Admin with a big stick Admin VIP

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    Ooh... ok. Well, you're going to have to pull it apart anyway, so get the head off and pistons out so you can see just how much sleeve repair you're going to need.
     
  13. khai_tuan_nguyen

    khai_tuan_nguyen Senior Member

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    NO matter how much I need to shave off, the next size up (shelf wise) is 85mm, does anyone have any other opinions on 85mm bore on a b20b block revved to 8k or some cheap insurance.

    Khai
     
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