When you spend the time and money on a car as I have done with this one you want it right and it has never been so. The first tuner was SS and a bit of me, obviously we are not tuners. Second tuner recommended to me but the original Cyborg was just not enough power so had the EFR setup built and tuned by them but it had horrible lag, far worse than expected. I swapped to the GT2560R in hopes of making my power goals and getting rid of the lag, a different tuner recommended, work a long time with him and simply gave up, way to much lag and said that was all he could do. Now on the last tuner and he has made huge improvements but keeping my eye on the Gen II GTX as it seems to spool better and makes more power. If he had tuned the original Cyborg I would of likely stayed with it and made the upgrades as they came out. If he had tuned the EFR I would of stayed with it, now he is tuning the GT2560R and I might stay with it unless is just cannot do what I want. Cool thing is the cost is only around $1k to swap to the GTX and I have all the supporting mods in place and easy to do, what is another $1k when I have already spent well over $50k on the car
I have been driving it quite a bit lately, up to 13,800 miles now, it was at 9,500 last fall and I do not drive it in the snow and live in northern NV.
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Anyway, looked at the different turbos available and by far the best deal for real power in a wide band, meaning more power where and when you need it the most often is the C39. If I lived in CA and was starting over I would have one with ported manifold, modded the stock DP to flow much better which I have recommended to many but none have done it, and everything stealthy so it passed inspection and ran really clean.
I would swap to the C39 now but would just be wasting all the money on the DHM kit as selling at a loss, buying all the parts needed as having nothing stock to do the C39, I would end up about even so just keeping the DHM and swapping to the GTX if needed.
I have been modding cars for 49 years, this car is a drop in the bucket compared to some I have built and in many ways the most fun