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Thread: St4s based engines, seeking advice on pistons and heads

  1. #1
    Join Date
    Feb 2011
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    Default St4s based engines, seeking advice on pistons and heads

    I’m working on another 2 st4s based engines for the track.
    Engine 1
    Left side dual pick ups, RS flywheel and generator
    Crank 996RS w rods and primary gear
    Heads T1 w T1 cams (from 2000 SPS)
    Throttles from 996 SPS
    Question ; What pistons/CR should I look for

    Engine 2 Less exotic
    Left side dual pick ups, RS flywheel and generator
    Crank : std, rods from SP5, std primary gear
    Cams ; T1
    Heads ?!
    Throttles from 996 SPS

    Question: I have only 1 set of T1 heads, but 2 sets of T1 cams .. does the drop head from ST4s vs a normal 996 make a Big difference ( valve size bring the same ) ?
    Should I change the pistons or just give a squeze for higher CR?

    Now ; Engine experts ; any advice to above ?
    Last edited by stiglarsenDK; 06-05-2019 at 03:12 PM.

  2. #2
    Join Date
    Aug 2008
    Location
    Calne UK
    Posts
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    Default

    I did enquire about putting T1 cams into a Drop Head 99 unit but was advised that the intakes on the Drop Head just do not tune well, hence I shall not be bothering.
    I continue to look for 996 Superbike heads.
    celeresracing.blogspot looking-back-at-2016-classic-tt
    Power tends to corrupt and absolute power corrupts absolutely.

  3. #3
    Join Date
    Jan 2015
    Location
    Chicago
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    Default

    Yes, just use regular 996 heads. I'm actually not aware of any differences between them and the SPS. Same valve size, just different cams.

    Mine has a pretty similar spec except I kept the ST4S throttle bodies but upped the single injectors to 450 cc/min, but I do not know the CR--I'd guess 12.5 or 13:1. It's even tougher since different companies can measure differently. I just wanted it to be able to run on normal pump premium without detonation.
    '01 996R, '94 888 SPO Ltd, '88 851 Adamo racebike, '91 ZX-7R K1 homologation, '89 NSR250 MC18r5k, '01 Derbi GPR50/75, '71 CB450/500 café.

  4. #4
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    Jun 2007
    Location
    Melbourne, Australia
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    Default

    if you set the squish with std pistons you get 12:1 from memory. if you want more there's a pistal that gives 14 or so.

    the drop cam heads have poorer exhaust ports, but they can be fixed. inlet is the same.

    the 97-98 sps head is a different #, but all 996/996sps heads 99> are the same part #.
    Brad The Bike Boy

    www.bikeboy.org

  5. #5
    Join Date
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    Default Thabks for comments...

    Have an eye on some 996 heads...

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