1.8tScreemer

levels the same pressure is pressure, does it have to do with the density of air does the larger turbo have cooler air because it doesnt have to work hard to make that pressure, or does it have to do with efficencies of the compressor.

matt13

For example, think of keeping 15 psi of pressure flowing through a straw vs. 15 psi of pressure through a 2" pipe. Still 15 psi in each case, but you'll need more air to maintain the pressure in the pipe.

If you can find a comparison picture of our K03 vs. a T3/T4 or similar sized turbo you'll get the idea.

1.8tScreemer

push 15 psi on a 2" pipe and make a 28rs push 15 psi on a 2" pipe= same pressure however the k03 would have to work harder to maintain the pressure but end result is the same pressure.

kenny (dremel)

It puts more air through the pipes, regardless of pressure.

fusilier

It depends upon the flow.
At some flow rates(lower), the K03 will actually be more efficient than a 28RS at 15psi.

The compressor wheel's efficiency depends upon the flow rate and the pressure ratio. The efficiency effects the density which is ultimately how much air moves through a motor at a given RPM.

Generally, at high RPM on a 2 liter motor the 28RS will make more power than a K03 all other things being equal, cause the K03 will be less efficient and will be heating up the air more. At Low RPM where the air flow through the motor is less, the K03 might actually be more efficient and make more power. That is probably the case below 3000 rpm given those two turbos and say a 1.8 liter motor.

Remember Surge though.. A big compressor wheel makes power up at high RPMs but it can't make boost down low when the airflow is small, no matter how small a hotside you put on the turbo. Thats surge.

If I overlaid the Gt28R and the K03 Compressor maps there will be points where the K03 is more efficient and some points where the Garrett will be more efficient along the 15psi line. So, it completely depends upon the overall target flowrate and where you want your HP. K03 will give you power and torque down low below 3000 rpm and the Gt28R will give you power above 3000rpm because those are the compressor map sweet spots (knee) for each turbo where they are the most efficient.

f3d

the k03 being smaller and less effecient than the t28 heats up the air more when compressing it which increases the volume of x number of moles of O2 meaning youre getting less O2 to use in combustion than with a cooler intake air temp. The t28 is much more effecient at compressing air since its bigger and needs less time to create x presure..that coupled with the the main reason being higher volume of flow accounts for the power differences. change the pitch on the blades in the k03 compressor and youll make more power but youll also need more energy to create x psi. which is why that problem is solved by increasing the size of the compressor rather than changing pitch of the compressor blades. a compressor with variable pitch blades would truly rock! quicker to spool and able to reach higher PSI given the same volume and temp.

of course i could be wrong.

markbradford

The Potato does it more efficiently. The air is cooler, and thus more dense.

1.8tScreemer

yes but if your controlling variable is pressure than it does matter, your not controlling flow.

Gldnrkt(GT3076R)

I had this discussion with a DSM friend of mine when he put a 16G in his car and I still had my KO3.

Toaster29

There are many factors that influence how much "air" a turbo will flow at a certain pressure ratio. Two of the biggest reasons that bigger turbos flow more air are because of the following:

1. The hot side of the turbo is usually larger/more efficient than the smaller turbo you are replacing. We see the motor as the restriction to the cold side of the turbo, which causes a backup of air and increase in pressure in the intake mani as a result. Well, take the hot side of the turbo and apply the same logic. The hot exhaust gases are required to spin the turbo and as a result the turbine acts as a restriction. This also backs up the exhaust and causes high pressures between the turbo and the exhaust ports. Usually a well setup turbo with good efficiency will have *at least* twice the pressure on the hot side as the cold side. IE, if you are running 20 psi into the motor, you'll see at least 40 psi between the turbo and the exhaust ports. Obviously this will lower the volumetric efficiency of the motor as it must "work harder" to move the exhaust out of the cylinder.
With larger, more efficient turbines and turbine housings, the turbine is able to extract more energy to spin the shaft at the same or less pressure ratios as well as flow more as flow increases, which also helps keep pressures lower. This in turn increases the VE of the motor which will allow the "total flow" of the entire system to be higher. Basically the hot side is the last restriction (and usually largest) of the entire system. Decrease its restriction and you increase the total flow at any boost level. An example of this would be the fabled disco potato that you hear everyone talking about. The hotside of that turbo is T-25 based, but it has a new generation NSF-111 turbine which is so efficient for its size, it outflows some of the ancient T04 framed hotsides!

2. Larger turbos have larger/more efficient compressors which usually do not have to spin as quickly as the smaller ones (less frictional heating of air), or are more aerodynamically suited to high speed duty depending on the characteristcs the engineers decided to impart on said wheel (GT series turbos compressors are usually designed for high pressure ratios and as a result are designed to turn at very high speeds with relative efficiency and minimal frictional heating). They also usually physically flow more per rpm (remember the reason we put bigger hotsides on when increasing the cold side is to efficiently deal with the extra flow). It is possible to outflow the hotside with grossly imbalanced turbos. If you've even seen a compressor map, you notice that on the far left side of the graph there is a "surge line." If you exceed those parameters of flow or pressure ratio outlined there, the coldside is trying to flow more at X psi than the hotside will allow. As a result, the compressor fins loose "grip" on the air entering as the pressure is too high and the flow is not great enough. The result is a sound that sounds like surging you would hear from a car with no BOV and a rapidly self destructing turbo

Either way, the less heat generated during the compression of the charge, the greater the density of the air entering the motor which of course will allow X amount more of fuel as well. Also, the cooler the charge is, the more knock resistant it is and more timing can be run to take advantage of this. These last two facts are also the main reasons why we all run some sort of intercooler.

Sorry for the length, but those are two of the main reasons why larger OR more efficient turbos increase flow.

You only start to see huge gains when you start entering the grossly inefficient areas of the smaller turbo's maps. A properly sized GT-30R is going to usually have a compressor good for at least 2 bar and the hot side to back up that kind of flow @ those pressure ratios. Thats why you *usually* don't see a huge change in output until the pressure ratio gets on up there unless the two turbo differ very significantly in size (say you replace a k03 on the 1.8T with a GT-3071R, for example )