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!