BMW 135i N54 vs. BMW 135i N55: Round 2

I feel as though this debate will rage on with 1 and 3 series owners for years to come. N54 vs. N55. In a previous post 2009 BMW 135i N54 vs. 2011 BMW 135i N55: Round 1 I gave some background and showed a dyno comparison plus a first blood street race result. The information I'm about to spew forth muddies the waters just a tad.

The last time that we, may or may not have, put our engines to the test my lowly N55 lost even though it was modded to a slightly higher level. I lost by about half of a car length up to 110 mph. About a quarter mile. The N54 had a Berk Race axle back exhaust. I was running the stock axle back with the purdy anodized tail pipes. The big difference was that I had a cat-less down pipe. The down pipes on the twin turbo N54 were both catted. That's good for at least 15 hp and 30 lb ft. Some people will say more like 30 hp and 50 lb ft but that's BS. Something also needs to be noted. At the time I had the N54, catted mid pipe installed on my car. With no cats at all it made my BMW smell like a 77' Charger Daytona going down on a septic tank. To fix that problem I made a swap deal with a real nice guy that drove a couple hundred miles to take my cat-less mid pipe off my hands.

Now let's get to the meat and potatoes of this post. The curiously awesome dyno chart above...Is it marketing slight of hand or are the tuning Gods on to something that'll tighten the power gap? You'll notice in the graph that the tune is referred to as JB4 ISO. Also it's a G5 board. I'll try to explain this nomenclature. JB4 is a piggy back module that intercepts and modifies the signals processed by the engine management computers that tell the car how much power to make and when to make it. G5 means that he is using a Generation 5 JB4 unit. The G5 unit has the correct circuit board to allow for ISO firmware, given that you take apart the case and cut a specific diode. ISO mean Isolated Boost. What the hell does isolated boost mean? Well it means that this unit is capable of completely bypassing the engine management computer regarding the amount of boost that's generated by the turbo(s). Before we read the DME (Digital Motor Electronics). Let's say based on conditions and throttle position the DME wanted 10psi. The tuner would change that target to 14psi then stuff that response back into the computers forcing the boost to be made. Now there is complete control of this which should increase total power output, smoothness of delivery, and lag time. The N54 engines also have this new ISO tune available to them via BMS.

At the moment my plans are to get migrate to the ISO firmware as it transitions from Alpha to Beta to production. Also I'm researching front mount inter coolers to death trying to find the best option. Currently I'm deciding between ETS, VRSF, and AMS based on pressure drop, and overall efficiency while allowing for minimal modification. Anything over 5" deep requires some plastic removal but all is good in the pursuit of more power.

Mr. Andree and his N54 will also be getting an intercooler, suspension modifications, and down pipes before Spring. Should be fun next year when we run them. In addition to the drag strip there may be some good road course results too. SCCA style.

In the end us N55 guys are still down but not out. Nothing is settled just yet but in the end I'll bet with a turbo swap we'll kick the pants off the old N54ers.