G-Power Z4M Initial Impressions
WOW. I was expecting good top end, but I'm totally blown away by the midrange torque. Even with 265 width Michelin PSS, I can light up the tires in 95 degree weather in 2nd gear. I can't imagine needing more power for anything other than bragging rights. 3rd gear is the first opportunity to go WOT without traction control heavily interfering... which will get you over 100 mph, and jail time in some states.
The car dynoed at 405 rwhp on 93 octane, with no WMI, in the central Florida summer heat. Once I get the graph from the shop, I'll post it up here. I'm very interested in seeing the area under the curve, because it doesn't feel nearly as peaky as my non-M Z4, despite an unmodified non-M reaching max horsepower earlier in the powerband. The S54 in NA form reaches max horsepower over 7000 rpm, and I guessed that a centrifugal supercharger would exacerbate this feeling. Not so. Torque is available immediately, in large enough quantities to elicit profanity from unsuspecting passengers.
Other mods include Supersprint V1 stepped headers, Supersprint section 1 connecting pipe with HJS cats (made by Custom Performance), and Rogue Diablo mufflers. I did not get a before dyno because the car was not stock when I brought it in, and the additional modifications would have influenced the horsepower delta. FWIW, a stock Z4M dynos around 265-275 rwhp, and 405rwhp represents a 50% increase in power to the ground.
I was surprised at how much sound the headers and race cats uncorked. I thought the stock car with Diablos sounded near-perfect. Now it drones unbearably, so I'll likely be moving to sport mufflers in the future. The burbles and pops on off-throttle cruising are fantastic, however.
Any supercharger noise is drowned out by the exhaust. The bypass valve makes a nice "woosh" when letting off the throttle over 4000 rpm, similar to a turbo BOV but less obnoxious. There is no abrupt jolt when rapidly letting off the throttle, unlike my other kit. Part of this may be due to the bypass valve.
The last thing I'll mention, and probably most importantly, was the way my shop (Precision Sport Industries in Winter Park, FL) handled everything. I have NEVER in my life dealt with a business that impressed me more. I'll go into depth with a later review. Between the consultations that saved me thousands of dollars; expertise I could rely on for setting the car up to my desires; excellent communication; professional attitudes; and HONESTY... I can't recommend these guys enough. They are the only people I know of that take better care of my car than I do when I work on it. Their patriotism and personal interest in military personnel were enough for me to fly a flag in their honor while I was deployed in Afghanistan. They don't sponsor me to endorse their shop. They didn't even ask me to write a review. I was there for a supercharger install, and all they asked for was very reasonable payment for a job well done. My car looked better when I picked it up than when I dropped it off. More importantly, it truly looks and feels like an OEM install.
More to follow! Until then, here's a teaser:
Edit 8/14/2013: I got the dyno from the shop, and unfortunately don't have AFR or rpm. If the run was done in 4th, it looks like I had a little bit of rpm left to go. I also found out the 405 rwhp was done with a different correction factor, and I'm looking at about 397 rwhp (SAE corrected). Still not too shabby for a run in the Orlando summer, especially when the kit claims 450 bhp! I plan to get another dyno done in the next few weeks.
Update 3/21/2014: After 8000 miles, the kit has performed extremely well. No stalls, CEL's, or oddities while driving. Full and part throttle response is perfect. My only issues have been tightening a hose, securing a bypass valve bracket that popped off, and a mild vibration in the cast manifold at idle. Full review coming next month. Peak boost is reached by 5000 rpm. The vibration in the video is from my work laptop in the passenger seat.