This is a question I've always had, everybody agrees that 18psi on a k03 and 18psi on say a frankenturbo is two totally different 18's, and everybody agrees that just dropping in a larger turbo will not give you any gains without a tune for the larger turbo. So if you have a 18psi tube for your k03, put in a frankenturbo and it's still running 18psi won't you gain more power as the 18 is "different" and the larger turbo will hold boost longer than the k03. Why won't you gain power? Does it have to do with the ecu still assuming you have a k03?

This might be a stupid question haha

 

This answer is more complicated than I initially thought...

Let's start at the basics:
The MAF measures the quantity of air entering the combustion chamber. Based on how much air is measured (and maybe engine speed), the ECU delivers an appropriate amount of fuel.
And K03 tunes are typically designed to use the stock MAF sensor/housing (as well as stock injectors).

A big turbo, pushing 18psi, generally will deliver more air than can be measured by the stock MAF sensor in the stock MAF housing (about 190 g/s limit).

The stock injectors will be running at a full duty cycle (basically they will be maxed out) well before 190 g/s. I maxed out 315cc @ 3bar injectors with my FrankenTurbo on a PC-16 tune (at the highest recorded 190 g/s level). Stock injectors are 215cc @ 4bar I believe.

Conclusion: You shouldn't run an 18psi tune designed for a K03 on a big turbo - the ECU won't be able to measure the amount of air into the engine, and even if it could, it couldn't supply enough fuel. The end result could be a blown engine.

I assume most of the time when people say a BT provides no gains over the K03 on a K03 tune, they are referring to the stock 7psi K03 tune. To some extent this may be true but actual testing would be required to verify the validity of that statement.

Also keep in mind it's not all about fuel and air. BT tunes (and even aftermarket K03 tunes) typically alter the timing map to be more aggressive - and therefore gains are achieved also through spark timing.

Conclusion #2: always make sure to have an appropriate tune when upgrading your turbo (and whichever injectors/MAF the tune calls for).

 

Ok so to make it simpler, the maf can't handle the extra air getting pulled in so it acts as a bottleneck and even if you upgraded the maf housing, then the injectors can't keep up with the extra air and will therefore cause a lean condition, and when you get a lean burn nothing runs correctly let alone better...?

 

i think metal man got too far into detail. the stock ecu is set up to deliver x amount of fuel at x load with x boost. when installing a bigger turbo, the load stays the same, but you have to trick the ecu into delivering more fuel and with more boost because there is more air mass. the reason you can't run a frankenturbo at 18psi with a stock ecu is because the stock programming can't pyhsically deliver enough fuel to keep the car happy. the car keeping happy means not running the fuel/air mixture too lean. running lean does make more power, but it also creates much more heat, and too much heat is very bad.

18psi on k03 and 18psi on a frankenturbo are different. imagine this. you have a small air tank at 100 psi, and a tank the size of a semi trailer at 100psi. same pressure, but guess which one contains a larger mass of air? although not the best representation (the air isn't moving in a tank), it holds true. if 18psi were the same across turbo's, what would be the point of getting a larger turbo? larger turbos are capable of deliver a higher air mass at smaller pressure than a smaller turbo. imagine taking that 100psi out of the small air tank and putting its contents into the semi trailer size one. the same exact air mass is now contained in the big tank, but the pressure wouldnt even register on a guage. apply that to turbochargers

 

Both of these guys are spot on.

To put it another way, the air/fuel/timing maps on your ECU were written with a specific turbo in mind that moves a given amount of air at a given boost pressure. This is where compressor maps come into play like this one for the K03:



So lets say your K03 moves 275cfm (cubic feet per minute), give or take. A Frankenturbo moves roughly 540cfm. Again, estimated. YMMV. So a tune written for a K03 will be able to provide enough fuel and engine timing to keep a good A/F ratio for that much air at a given boost pressure. Trying to use that same tune/fueling on a turbo that moves almost twice as much air, you'll run very lean and risk pre-detonation which is a really good way to snap a rod or frag one of your pistons.

To answer the question in your first post, you wouldn't gain any power because 18psi through a K03 is not the same as 18psi on a FT, because the latter pushes more air at that boost level. Savvy?

 

So does this mean that if somebody replaces a blown k03 with a ft or bigger and runs the stock tune until they can afford a tune it will actually be bad for the car? Also while we are on turbos is there a difference between a k03 and a k03"s"? I know some people say it's the same turbo while others say it has a slightly larger housing

 

you could run whatever size turbo you want on the stock tune. the trick would be to not allow more air into the engine than the k03 could. this would mean keeping out of boost pretty much.