Another GM MAFT thread Options

[KOU In3]

Ok, I'll be upfront that I'm just being a bit of a Devil's Advocate here. I like the MAFT and from what I hear, I'll probably end up owning one. I've plowed through most of the DSMtalk threads on it too. But, just to cause trouble I'll ask the following from those of you that have it.

Anyone have any concrete dyno numbers or even track numbers and actual gains from this mod? Before and after improvements?

I know the 3.5 in flows like the Mississipi in and of itself but when you neck down to the throttle body is all that flow lost and even disturbed by all the steps to get it to mate up? The 2G MAS looks to be pretty close to a 3" MAS flowing more or less straight through.

Although tuneable, can it match the increments of the SAFC in terms of fine tuning?

Granted, everyone who's bought one seems to love it. I'm just wondering if anyone's truly dialed it in on the Dyno and done a side by side with the 'old' SAFC 2G mas combo.

OK, flame suit is on. Time to endure the punishment of the translators.

[awd4kicks]

Currently I have to disagree, but there is no hard evidence.

There are a number of people on DSMtalk that claim a 10th or two in the quarter simply by adding the dump tube. A tenth or two is a lot in the quarter, but may not be nearly as noticeable on the butt-O-meter.

The only crude logic I can come up with to make sense of this is backpressure and combustion charges not being in sink. What I mean is, when an internally plumbed waste gate opens it re-routes a portion of the exhaust gasses around the turbo and then back into the exhaust stream in a different location. This may get a bit complex, but the gasses coming out of the pre-turbo exhaust stream released some 'pressure/flow' between the engine and the turbo - hence cutting back on the turbo's driven output. This batch of gasses has force, displacement and it has not expanded as it travels through the wastegate tubing. Once it reaches the exhaust piping 'post turbo' this pressurized gas is interjected into another part of an already flowing exhaust stream. Besides adding volume, and force on the wrong side of the turbo, both of these are multiplied as the waste gate gasses expand in the large exhaust piping, thus raising the average pressure on the back side of the turbo. With that said I understand that we're are not talking about forces that will break off turbine blades or slow the turbo down. The key is efficiency, and if your adding pressures on the wrong side of the turbo the efficiency could be better.

So when you have an external dump pipe the exhaust gasses flow un-interupted through the turbo and exhaust piping while the re-routed waste gate gasses have the open atmosphere to expand into (almost like a vacuum compared to the exhaust piping), releasing the force and volume that drive the turbo that much quicker.

The only proof I have of this is that the external dump O2 housing is the only major change that I had on my car when I ran the 12.67. I hope I have this wrong, because I'd like to go back to a more stealthy exhaust. I just don't see how right now.

BTW - This same efficiency theme should hold true for the intake piping as well. It's not a matter of whether the turbo can make the pressure, it's how much air in volume can you make that engine pump through. The difference between pressurizing a 2" diameter pipe to 15psi and a 2.5" pipe to 15psi is a substantial volume increase. That is where your performance gains come from.