 Red is SlickTTop - stock TT block with full breathers (except 2.5in Stillen) standard compression, stock TT heads Blue is XtraVerTT - stock NA block with full breather (except 2.5in Stillen) NA compression, stock NA heads Same gt28rs turbos (although they have a vband connector on SlickTTop). 94 octane IIRC As you can see, XtraVerTT "might" be slightly ahead due to its higher compression below 3200 rpm. It is hard to say because of where the chart for SlickTTop starts. After that XtraVerTT is behind until 4700 rpm, where it essentially ties SlickTTop briefly. Looking at the boost response - XtraVerTT is always behind. XtraVerTT always makes more power with less boost on a relative basis. XtraVerTT is boost limited by the onset of detonation. I suspect that substituting the TT heads "might" alleviate this problem but I haven't tried it yet. (but frankly that begs the following question: If I go to all the trouble to find and swap in a set of TT heads and then have the car retuned, why wouldn't I simply buy the whole TT block, drop it in and retune?) On the street, the difference between the two cars in most noticeable at the top end. Practically speaking below about 80 mph it is hard to tell the difference between the two cars. in and around 80-100 mph SlickTTop takes off. If you drive a similarly modded factory TT I suspect the difference that you would notice jumping into either of these cars is predominantly due to the 4.08 gearing. So I think Ash actually got it right in the post that someone linked the other day: Higher compression means more efficient conversion of energy in the NA motor relative to the TT. However this also means that there is less "waste" energy available in the exhaust to spin up your turbos. Conversely lower compression means less efficient conversion of energy in the TT motor relative to the NA. All things being equal this means more energy available in the TT exhaust to spool those turbos. Each configuration can be optimized and tuned to run at peak efficiency for its configuration, but that is basically the bottom line. And finally, IMO, as the overall power level of the engine increases, any benefits to the higher compression actually decrease. (As I said earlier, my original "stockish" black convertible with stock piping, injectors, manis, turbos makes 350/350 and is a fun little street car and is cheap to build) Hopes this helps
 CLOSED For The SEASON :-( |
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