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Thread: HTA68 7cm vs HTA68 8cm

  1. #1
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    Default HTA68 7cm vs HTA68 8cm

    Hey All,

    We had the pleasure of tuning many HTA68 powered vehicles both 2.0L and 2.5L form. While there is alot of speculation about them making power or not we've had a large enough sample pool now to draw a conclusion here. One of the conclusions is they are starved through the 7CM housing. Most will attribute a larger exhaust housing to slower spool up - but in some cases that isn't true. And a few vendors have proven this not to be true. We were lucky enough to test this theory.

    So, I had some 7CM/8CM results from nearly identical cars from the same tuning day. Fuel/timing/avcs/boost strategies were identical as were modifications. Good news is we have an 8CM on it's way for the 7CM owner. You will see why in a second:

    Cons with 7CM: Unsteady boost curve (Seen by many tuners dyno graphs) and high backpressure in the higher rpms at the boost levels the turbo naturally produces with an MBC boost curve or a moderate EBCS tuning style. I have found by tapering the boost up top (16-17ish) instead of the natural 20 psi prevented alot of potential knock and kept the intercooler at bay during our external IAT testing (while not reducing any power.) Which is a clear cut case for mis-matched wheel / exhaust housing with excessive PR pressure. As far as tuning goes at about 5800-6000rpms, regardless of the boost and motor - the power would tank naturally no matter how different the tuning style.

    Enter the 8CM: Totally manageable and predictable boost curve and less then 150rpm of spool MAX. In this case we are seeing gains everywhere and an extremely flat HP curve, all the way to redline. On the street is feels explosive to redline, similar to a TD06 20G 8CM. Full spool is seen at 3500. Peak power in this case is found at 6500.

    7CM vs 8CM



    Notice the average past 4600rpm 25whp and 25wtq to a staggering 40whp past 6500rpms. Same boost curve!

    Final graph: (Dr dabbles)




    Any questions? Let us know!

    -Bren
    Last edited by BG @ BrenTuning; 12-07-2011 at 11:29 PM.

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    8cm for 2.0 too?

  3. #3
    illesterator hiprsha666's Avatar
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    Nice write up.

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    Quote Originally Posted by -III View Post
    8cm for 2.0 too?
    EWG

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    SUPER MOD jwebsta32's Avatar
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    Great write up.

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    I like that idea.

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    Damn Son,

    That's impressive. Can't wait for that 8cm and EWG.

  8. #8
    3.0TT drdabbles's Avatar
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    Seriously, anyone wondering how this feels, let me know. If you're in my area, I'll take you for a (safe) ride.

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    Administrator Berge56's Avatar
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    Great comparison!
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    RIP Chris @EFI

  10. #10
    Stage I Donator SicRedGt's Avatar
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    Thanks for this post. I may be on the market of a turbo soon and I always assumed the 8cm would really hurt spool. Never saw a comparison like this. Keep us posted!
    I wish I was half as great as my dog thinks I am.

  11. #11
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    Very nice... Great comparison...

  12. #12
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    Quote Originally Posted by drdabbles View Post
    Seriously, anyone wondering how this feels, let me know. If you're in my area, I'll take you for a (safe) ride.
    I will def take u up on that when u can

  13. #13
    5.7L fbodydude53's Avatar
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    360 whp and 400 ft/lbs at 3800 rpm? she must move nicely I figured a 8cm would perform just as good as a 7cm, especially because its 2.5. Nice write up Bren!
    are we there yet??

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    Even sooner on the street too .

    We had the pleasure of tuning an 7cm meth'd 2.5L today. Unbelievable torque. Great midrange. Needs 8cm up top though. Stay tuned.

  15. #15
    ThePenIsMightier etaks99rs's Avatar
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    now we just need a dom 1.5xtr comparo 8cm vs 10cm (without e85)

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