Just switched my Cobb Stage 2/2+ E70 35i over to MHD. So far have tried both stage 2 and 2+. I have been running stage 2 for about 300mi. Did some logs when I first put the tunes on, need to log again now that I have driven for a while on it.
So far, I can say a few things comparing the tunes.
MHD Stage 2 vs Cobb Stage 2
MHD has slightly more boost but we are talking 1psi or less along the curve.
MHD has better throttle response
Cobb has more refined downshifting when the trans kicks down automatically (manual mode feels the same).
MHD has cold start noise reduction. This is EXCELLENT and the main reason I switched.
Downpipes
With a catless or even high flow catted downpipe, the cold start is very loud. I really didnt like the fact that I was waking up the neighbors when starting my car daily driver late at night. Going catless DP didnt last long for me. I almost switched back to stock because of the noise. I added a 3" 200cell metal spun cat right after the downpipe. This helped the noise some and the smell alot. I wouldnt really recommend a catless downpipe. I am sure that most of these are daily drivers, I dont want to arrive at work with my clothes smelling like catless exhaust (girls dont particularly like the smell either). I also want to keep it reasonably quiet since its a daily. Magnaflow high flow solved my issues and this MHD solved my other issue with the downpipe.
The pros of the downpipe are the exhaust sounds awesome. There is a factory vacuum controlled flap on the passenger exhaust exit. Above 3k rpm and mid-high throttle the flap opens. The OEM exhaust is straight back from the downpipe to the muffler with no secondary cats or resonator (the OEM cat is actually 2 cats separated by 2-3" inside the same shell). So when that flap opens, its almost a straight exhaust. Without the high flow cat, it was RAW. Guaranteed to make you smile. With the high flow cat, the tone is the same just quieter. With the flap open, its on par with my BMW Performance Exhaust on my other car. With the flap closed, its stock like.
I like the duality of the quiet normal driving vs aggressive tone when getting on it. I will have to post up a video.
The only downside is that with a downpipe, you no longer get the S54 intake sound that the stock N55 has.
Second benifit of MHD.
On the cobb running the stage 2+ there is an abrupt spike of tq and boost. It in some ways makes the car worse to drive because it is so sharp. If I was loaning out my car, I would switch it back to stage 2 because I wouldnt want someone else driving it like that.
On all the Cobb tunes, in any gear above 3rd (4,5,6,7,8), full boost was limited to above 4k rpm. Even on stage 2+, if you floor it at 3k, it will only do 9-10psi, but keep it floored and at 4k, it jumps up to full boost (18psi) and you get a surge of power. Only really noticeable on the + FMIC tunes where peak boost is much higher. Because of the limited boost in upper gears, highway driving retains the 7-8th hunting of gears with terrain.
MHD is much better in this regard. If you put it in 8th and floor it at 2k, it will go up to 13psi. Same for every other gear. I like having that extra tq down low and the suv seems to hunt less.
Stage 2+
I have not run more than a few miles on MHD stage 2+. My experience with Cobb Stage 2+ is the following.
Stage 2+ will heat soak the intercooler in very hot temps. You can get away with a single gear pull, but anything long or multiple gears will get the IATs up 50deg above ambient. This isnt an issue if its cold out, but on a 90-100deg day, the car will pull boost through throttle closures and the fun with it.
Gobs of tq when at full boost. This 5000lb suv moves. I easily pulled away from a E70 50i on the highway. I also clocked 5.4sec 0-60 without launching it. The 35i can walk away from most cars too. Video Cobb 2+ 0-80
I dont recommend trying to hard launch these suvs. I wont launch the car beyond just flooring it because brake boosting is really hard on the trans and will burn out your TC fast.
More about our trans. Our 35i have the ZF 8HP45. Its published tq rating is 450nm (330lbft). Now its has been known that they are underrated as even the Dinan tunes put down 300-360lbft to the ground (so nearly 400lbft crank). I spoke in person with a few ZF engineers and they said that they have a race 8HP45 that uses the same internals minus a torque converter and is rated to 550nm in racing applications. Another words, our trans is unofficially rated for 550nm (405lbft). They also told me that it will handle more tq, but at the expense of wearing the clutches out faster. They said that the hard parts inside (gears and such) are all really strong.
After alot of research and talking with ZF, I think that for a daily driver we should keep the tq below 400ftlb at the wheels. When you combine the additional traction of xdrive and the extra weight (5000lb) of an SUV it will be more strain the trans. In a RWD car, the extra stress and tq breaks the tires loose and lowers the actual torque transferred to the ground. The E70 will never break loose and has alot of load with its extra weight plus cargo and the potential of towing 7000lb. So these are my reasons I want to keep the tq limited. HP wont hurt anything, so we should tune our cars for more top end but keep the midrange and peak tq at or below 400lbft at the wheels. Stage 2+ puts us right above that.
Most people dont have issues with the 6AT trans (rated the same as the 8AT) until running meth and thats normally 500-550lbft territory, so 400ftlb should be ok for a reasonable trans life.
I have monitored trans temps with my scan tool and they stayed the same running either stage 2 and 2+ as stock. I monitored trans temps towing 2000lb with stage 2 through the mountains and they were also normal. I tow driving very conservatively though and never hit more than 10psi.
I think we need to either stick with stage 2 or have something between stage 2 and 2+. Probably target around 16psi and taper down to 12 up top. Our OEM intercooler should be able to handle that and it will keep us in a safe range of tq for the trans.