[3t3p]

QUESTION seems to me is should the OTS stage 2 tunes be able to cater for inlet pipes. Could it be leveraged in any meaningful way for peak power to red line.

Could it be a tick box option or not really worth. My Dyno on stock tune showed a substantial gain towards redline of holding power.

[F87source]

Originally Posted by 3t3p

QUESTION seems to me is should the OTS stage 2 tunes be able to cater for inlet pipes. Could it be leveraged in any meaningful way for peak power to red line.

Could it be a tick box option or not really worth. My Dyno on stock tune showed a substantial gain towards redline of holding power.

it cant be a tick box option, too much in the tune has to be changed for it to be optimized. its not just a fixed few tables that need to be changed to calibrate for a new TMAP or HPFP or coils.


To make this work youd need an entirely new ots map, and no one will invest the rnd into making an ots map for such a small change + factor in all the permutation and combinations of mods one might also need.

[johnung]

Originally Posted by 3t3p

QUESTION seems to me is should the OTS stage 2 tunes be able to cater for inlet pipes. Could it be leveraged in any meaningful way for peak power to red line.

Could it be a tick box option or not really worth. My Dyno on stock tune showed a substantial gain towards redline of holding power.

You ask a very good question. IMO the addition of an upgraded Turbo Inlet Pipe isn’t adding enough air flow capacity with the stock turbo to gain much through tune modification. It’s similar to the argument of whether it’s worth $700 for a custom tune on a stock turbo running on pump gas. There’s just not much upside to justify a custom tune over an OTS tune. Now it may be a different story if you start changing those limiting factors with an aftermarket turbo, ethanol or more exotic fueling because you’re raising the overall potential performance capacity.

It’s usually helpful to look at the big picture and the development history. An engine basically combines air, fuel and spark to create combustion/power. A turbo is a big air pump that runs for free from the flow of exhaust gases exiting the engine. (Very similar to how a hydroelectric dam harnesses the free power of gravity accelerating water to convert it to electrical power.)

The turbo pumps additional air into the engine and the fuel system adds an appropriate amount of extra fuel, and more power is created from the same engine. Sometimes adjustments to the ignition system to properly ignite this extra mix of air/fuel, but I’m not going to get into spark plugs, gap, coils, etc here.

So often when discussing various aftermarket parts it’s really a discussion about three different (but related) capacities: turbo, air & fuel.

N55 TURBO CAPACITY
Turbos come in different capacities. Some current examples from smallest to largest include the Stock PWG turbo, stock EWG turbo, (new) Pure500, (old) PureStage2, (new) Pure750. Obviously there are other aftermarket turbos, but these are enough for illustration.

These can be further divided by design intent with the StockPWG, StockEWG and Pure500 being to have low end responsiveness for daily driving. It’s obvious when looking at dyno graphs. The torque curves rise sharply at a very low 2500 RPMs. That’s really why these are sometimes called Stage1 turbos. Some people use it as a slur to lump them together as small in size. But their sizes are different. What they share is low end responsiveness. IMO that’s a big deal for daily driving with a lot of stop and go.

Now the “Stage2” turbos like the older PureStage2 and the newer Pure750 are designed with power as the focus. Low end responsiveness is sacrificed for higher power. This is also obvious in the dyno graphs. Step on the gas and torque takes a lot longer to build. These designs move the torque curve from about 2500 to about 3500 RPMs. But the gain is in more horsepower at higher revs. This is great for the race track where there are no stop signs or stop lights.

Another design distinction is that the first four turbos use the stock size opening to connect the Turbo Inlet Pipe. The Pure750 is in a class of physically larger turbos that are designed to use a larger opening which means that they use a custom Inlet pipe and not the stock Inlet Pipe or any of the aftermarket turbo Inlet pipes that have been discussed here.

AIR FLOW INTO THE N55 TURBO
There are three main components that affect airflow into the turbo: air filter, intake design/tubing and the turbo Inlet pipe that connects to the opening on the turbo housing. Air filter composition and size differ in the three typical choices: stock paper filter, aftermarket drop-in filters made from better filtering materials like aFe or K&N, and the larger cone filters included with many aftermarket intakes.

We’ve already discussed Intakes in detail. Forget “cold-air intake” and various marketing terms. The most important thing is whether an intake will cause a Check Engine Light. Most intakes will provide louder turbo spool sounds from the engine. They may or may not provide a power increase from zero up to maybe as much as 5%. (~15hp on a 300hp engine). But an intake that causes a CEL will usually reduce engine power. A CEL is usually caused by a leak or a poor design of the environment around the MAF sensor which measures airflow immediately after air passes through the airfilter.

IMO based on experience and from what I’ve heard, the MST Intake is one of the best and the BMS Intake is one of the worst.

The Intake tubing is probably not something that will differentiate on a dyno but in general smooth airflow is best.

TURBO INLET PIPE
It’s important to understand the history. BMW designed the stock Inlet Pipe probably around 2010 to work with the stock N55 PWG turbo. It provided sufficient air to the 300hp turbo engine. Several years later when BMW decided to upgrade to a larger N55 EWG stock turbo, they used the same stock Inlet Pipe. Both engines were tuned to provide 300hp. A larger Inlet pipe wasn’t necessary.

To my knowledge, it was Pure Turbos who recognized probably 6+ years ago that the stock Inlet Pipe was too restrictive. Pure was selling turbo upgrades with larger capacity BUT the stock Inlet Pipe was restricting the performance that could have been obtained from their product.

So Pure created a new fitting for the end of the stock Turbo Inlet Pipe. The outer diameter fit the stock Turbo opening size, but the inside diameter was larger allowing up to 40+% more airflow than the stock pipe. The Pure Turbo Inlet went through four interations that I know of.

First the fitting that would be attached to the end of a stock plastic pipe that had been hacksawed off, then a full sized aluminum pipe that also eliminated stock flow issues, then the next generation of that aluminum pipe that could be fastened at the turbo opening stud, then finally the current style that copies the MST design of maybe 3-4 years ago. Although Pure also made an improvement to the end fitting that now includes two o-rings to better seal the end entering the turbo housing. There’s been discussion of some Inlet pipes allowing air to escape. That air isn’t boosted yet but it has already been measured by the MAF so it could throw off air/fuel mixtures. I don’t know if any of the latest aftermarket pipes have this feature.

So Pure was selling the improved Inlet pipe as a component for its aftermarket turbos. But the prevailing opinion 5 years ago was that it would only help the higher capacity aftermarket turbos. Everyone who I spoke with who was knowledgeable about aftermarket turbos thought that the N55 EWG turbo was maxed out to its power capacity with the amount of air provided by the stock Inlet Pipe.

About 2-3 years ago several of us with N55 EWG turbos thought that this may not be true if the car had been upgraded with Stage2 hardware and a Stage2 level tune, which meant higher than stock boost levels. We tested by taking “before” engine logs with the stock Inlet Pipe, and “after” logs with several aftermarket Inlet Pipes. We all got the same reproducible result. The MAF sensor values that measure airflow into the turbo tracked exactly the same until the engine hit 5000 RPMs. Then the “after” MAF values increased and continued to increase towards redline.

This proved that the Stock N55 EWG turbo was NOT at its capacity. It was actually being limited by the maximum airflow that it could receive through the stock Inlet Pipe. All this was posted at the time.

If I remember correctly the MAF numbers increased up by roughly 10% at the high end. Since the aftermarket Inlets increased flow potential by 40+% and the MAF increased by roughly 10%, it was logical to conclude the stock N55 EWG turbo was now being limited by its own capacity and not by the air Inlet Pipe. Driving it definitely felt like a bump up in power.

A few people claim that a Stage2 tuned N55 PWG turbo would also benefit from an upgraded Turbo Inlet Pipe. I haven’t seen anyone actually do before/after logs using a Stage2 tune with a stock PWG turbo. If there is a difference it would have to be less that the difference found with the larger N55 EWG turbo.

Hope this helps someone!

[AmuroRay]

Originally Posted by 3t3p

QUESTION seems to me is should the OTS stage 2 tunes be able to cater for inlet pipes. Could it be leveraged in any meaningful way for peak power to red line.

Could it be a tick box option or not really worth. My Dyno on stock tune showed a substantial gain towards redline of holding power.

OTS tunes are a one size fits all solution that isn't meant to give you the best - it's just meant to give you something.

They surely aren't bothering to adjust for the additional airflow via Cam retard at higher rpm, or overlap, or Valve lift, etc. You want to do better, build your car how you want and get a good tuner to adjust your car on the dyno.

All these OTS tunes are is removing the power class limiter, increasing the load and adjusting the fueling.

[F87source]

I have a BMS inlet in my possession now, so if anyone needs measurements let me know (it might take me a bit of time to reply since I'm flying out for work in a few days). Otherwise they'll be in my full review that I'll do during the summer.


After a really brief hands on look I can say the BMS Inlet looks amazing, the tube is made very well and all curves are gentle and organic which will help ensure air flow doesn't separate and is as smooth as possible to the turbo. This is good because smooth laminar air flow is more efficient flow for the compressor blades.

Silicone is also very thick and durable so no worries there either. It's also sealed in a plastic bag, so it won't get dusty and dirty.