Driftomagnifico

My headgasket is fine, and this engine has seen over 600whp.

Oh, and I also tuned this engine since day one myself.

Driftomagnifico

I will make a post to back up my perspective tomorrow. Feel free to get your points in.

Porschefile

14psi = 14psi, regardless of the size of your compressor wheel. The actual volume of airflow does not change. The size of compressor wheels are restricted by the laws of physics. 14 pounds per square inch does NOT equal 16 pounds per square inch. This is physically impossible! The difference is due to the EFFICIENCY of the compressor wheel. With tuned chips on a maf car, technically you do not need to have them retuned when going to a different turbo. Though, the limiting factor is your fuel system, so it will only work to a certain point before you are pushing past your fuel system's capabilities. This doesn't mean that your fuel maps will be properly optimized for the new turbo, though it will still run within the capabilities of the fuel system and your fuel maps. You will probably have to adjust your boost accordingly, because at 14psi for example, if you switched from a k26 to a T66 then you might have such a huge improvement in compressor efficiency that you are pushing your fuel system and seeing lean spots in the fuel map.

The only issue I can think of is if you installed a significantly smaller turbo. A much smaller turbo could spool up so much earlier that the fuel maps could be too lean when it is coming on.

If you want optimized maps for your new turbo, then yes of course you need the chips retuned for the different power curve.

Uhhhh....... yes a MAF or AFM is what determines fuel control. So what if much of the work is done in the DME, the airflow signal is what determines the outcome. You are talking semantics and both of you are right. One can't work without the other, though the maf/afm is an integral electrical component in fuel control.

Porschefile

Lets work with an example here, and please feel free to post any questions. Lets take a fairly stock setup with a k26/6 and switch to a 27/6. What will the effects be from doing this? First of all, the 26/6 and 27/6 spool similar enough that there won't be too much of a difference in the boost threshold and rpm that full boost is acheived. So where is the extra power coming from by doing this? The difference in power is acheived by an increase in compressor efficiency. In short, the k27 compressor wheel is more efficient then the k26 wheel at certain boost levels. On a stock fuel system, if you are running a good amount of boost (14psi+) then you are most likely going to be pushing the fuel system close to it's limits with a 27/6. Theoretically, if you have a properly sized fuel system (lets say 55# injectors and a 3bar fpr for this example), the airflow signal from the afm or maf will automatically change according to the amount of airflow detected. The end result being that the maf/afm detects this increase in airflow and the dme in turn determines the proper injector duty cycle to compensate and maintain the programmed a/f ratio. Again, the laws of diminshing returns apply here. This will not work if you run a k26 at 1bar, and then switch to a T67 at 1bar because the increase in efficiency will net such a huge increase in power that you would be well past your stock fuel system's capabilities.

I do not have the charts for each KKK compressor to show this, so lets compare a few Garrett T04E series wheels.



Okay, here you have a 46 trim and a 50 trim T04E wheel. Lets do this comparison at .8bar, which is visible on the X axis (it's in absolute pressure, so 1.8bar). At 3000rpm both compressors are within the 72% efficiency island. Up to 4000rpm we see that both compressors are in the 76% efficiency island. So far, there hasn't been any significant change in efficiency. What does this mean? At the same .8 bar boost level on the same motor you're not really going to see any significant difference in power output at these rpm levels. Now lets move on to 5000rpm. The 46 trim is only at 74% while the 50 trim jumped up to 78%. Continuing on to 6000rpm we see 70% from the 46 trim and 76% from the 50 trim. We'll stop there and analyze what's just happened. To put that into real world terms, we can get a general idea that the 50 trim compressor on the same motor is going to generate more power above ~4000rpm, and it will hold longer to redline compared to the smaller 46 trim. Also, if you notice, the actual airflow did not change between the 2 compressors. The only actual change was in efficiency. I realize this is a generalization, and there are a ton of factors that play into the operation of a turbocharger. However, this should give everyone a general idea how different sized compressor wheels change things. The same laws apply to turbine wheels.

As far as an optimized fuel curve, you are going to need to retune if you want a 100% perfectly optimized fuel curve for your new turbo. However, this isn't always necessary unless the spool characteristics of your turbo are significantly different. What does that mean? Well if you throw on a large turbo that doesn't begin to spool until 4000rpm in place of your setup tuned for a k26/6 (lets say it starts to spool ~2k rpm), then your a/f's are going to be too rich between 2-4k rpm, so you will be loosing some power. With a k26/6 and 27/6, you have the same exhaust turbine/housing, so the same turbine efficiency. The spool characteristics are similar enough that you could get away without retuning, though you'd need to be careful of how much boost you run on a stock fuel system. I, for example, have VR maf chips, 3 bar fpr and 55# injectors. If I could find a 27/6 for sale, I would throw it on and show you guys what I mean. I have the proper fuel system to support the max power of a 27/6. Technically I could throw on a 27/6, run the same 1bar of boost and the effect would be more power although a/f's would stay very similar as the 27/6 spools similar enough to the 26/6. Most people don't seem to upgrade their fuel system first on the stock turbo, though. Because of this, it only makes sense that most 951 tuners recommend a retune, as you really need an upgraded fuel system with most of the upgrade turbos for our cars. You can't exactly throw in larger injectors and a higher pressure fpr and expect it to run properly without retuning.

Someone sell me a k27/6 so I can prove this with dyno sheets!

streckfu's

So if two different sizes of turbos flow the same volume of air at 14psi, that would explain why a VR stIII makes the same power as a K26/6 at 14psi while using the fuel map of the K26..... Gotcha.

What I don't get is why all these people are wasting money on upgrading turbos if they are not running more than stock boost.

streckfu's

Only in the sense that it provides airflow data. That's it. It's the 0-5v signal that's important. The DME doesn't care if it's a MAF, AFM, or MAP that sends it.

Please search this forum for "MAF" and "chips" to see what you come up with.

pk951

>>You might trim fuel and ignition timing to optimize the setup (cooler boost temps), but the actual airflow to the engine at 1 BAR is the same with any turbo<<

So what your saying is to4-E turbo will flow the same amount as a k26/6 at 1BAR even tho it has a bigger com-wheel, and housing interesting.

To some it up you saying slap on any turbo with MAF run stock chips, and the AFR will take care by it's self.

Hope John can jump in here.

streckfu's

On a 951?

lart951

Tony, wth 600hp is it a 951? I call that BBS=Big bull ****, please post dyno sheets, motor specs and pictures.

pk951

Lart- I don't think he is making that on a 951.

lart951

I see, he is probably refering to a JDM engine.

black944 turbo

So then why do you upgrade injectors, cuz what you are saying is everything is the same!!!! YEAH RIGHT, with an upgraded turbo you need upgraded injectors and a way to control timing and fuel end of story. The new turbo will require different things than a stock one.

WesM951

Because 15psi on a T04E isn't even into its effiency range yet.

pk951

>>Because 15psi on a T04E isn't even into its effiency range yet.<<

Correct at 15-psi it's probably on in the best range.

But what
Driftomagnifico is saying is k26/6 or a k27/6 or to4/e is sucking in the same amount of air at 15-psi ?
So there is no meed to change chips ?

streckfu's

Correct. That is what he is asserting.