Date registered: Aug 2010
Vehicle: '84 Euro 500SE, '85 Euro 2.3-16, '51 Euro 170S, '97 Jeep Wrangler Sport, '15 G63 AMG
Location: San Antonio, Texas/Gulf Breeze, Florida/Neustadt a.d. Aisch, Deutschland
Mentioned: 5 Post(s)
Quoted: 712 Post(s)
Looked around the web for anything, but nothing so far.
Stock HP for a 2015 S550 is listed at around 449HP, so $1500 nets you an additional 91HP, which runs you about $16.48 per 1HP. Relatively speaking, that's not all that expensive.
Given base HP of 449, and we'll say you got the car from the dealer for $91,000 out the door before taxes (you may have done better, you may have done worse, this is just an example) which is around $202.67 per 1HP.
RENNTech has a tune as well, for $2700, claiming the same 540HP, but reduced torque at 705lb-ft.
They state the factory numbers are underrated (they list 429HP and 516lb-ft, to the crank, as the stock ratings from MB) and actually got 474HP @5500RPM and 566lb-ft @ 2800-3900RPM when measured at the crank for a stock 4.7 BiTurbo V8.
At the crank, RENNTech measures 540HP @5500RPM and 705lb-ft @3700RPM with their ECU tune. According to them, this translates to 448HP @5500RPM and 585lb-ft to the wheels for 4Matic models. Based on the difference between crank and at the wheels, this is a 17% loss due to the 4Matic drivetrain. I'd imagine the loss to be less to a RWD car, but not by much.
At any rate, this translates to 66HP gained with the RENNTech tune, which translates to $40.90 per 1HP. Still reasonable compared to what you payed per HP for the base car, but almost double (I know I said it's ~$16 per 1HP for the Weistec tune, but I'll get to the real cost per HP for the Weistec unit down below) the cost per HP when compared to the Weistec unit. That said, RENNTech is a very well-known name and intimately familiar with MBs. I would trust their dyno sheets and their product. However, Weistec is also well-known, and if you're currently in CA with the car, local to you. They could do the install for you, even.
Using the stock crank numbers from RENNTech, we'll say your car makes 474HP at the crank, and you get the 540HP tune. That's an increase of 66HP, which when you figure in $1500 for the tune, comes out to $22.73 per 1HP from the Weistec tune. $4 more than the $16.48 that was calculated at a 91HP gain based on a 449 stock HP rating at the crank, but still almost half the cost of RENNTech.
There are other tuners out there who provide tunes, but both of these are big names that are local here in the US, one of which is even local to you.
I'd give the Weistec tune a try and post up your results. Know many who have used their tunes in BMWs who are happy with the results.
I hope all of this made sense.
'85 Euro 190E 2.3-16
'84 Euro 500SE
'51 Euro 170S
'15 G63 AMG
'97 Jeep Wrangler Sport
'98 Dodge Durango SLT+ 5.9L Magnum V8
'96 Ford F350 7.3 PSD