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post #4 of (permalink) Old 12-25-2016, 04:40 PM Thread Starter
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Thanks guys.

Originally Posted by SaturnSkyRedline2015 View Post
Troy, nicely written. Thank you for doing this.
A couple of questions:

1). Often when one describes the size of a turbo, it is referenced by millimetres. How big is the K04?
I know someone mentioned once the size of the K04...but I cannot remember for the life of me what that size is...that said...

When they talk in mms, it usually is talking about the diameter of the compressor wheel though it can be in reference to the turbine wheel as well. I'm still relatively new to the world of turbos (writing stuff like this helps me organize my thoughts and get the information down in my head better) but from what I can understand so far, the bigger the wheel the greater the volume of air you can compress and thus your airflow rises even when boost pressure stays the same.

There are also TWO wheels on one Inducer and an Exducer. So usually mms refers to one of these wheels.

Think of it this way (and mind you, these numbers I'm just pulling out of thin air...). Lets say you have a 45mm compressor wheel and it moves 30,000 cfm of air at 25psi. Now you upgrade to a 50mm compressor wheel and now you move 35,000 cfm of air at 25 psi. While your boost pressure hasn't changed, you're moving 5,000 cfm more of air and thus can inject a bit more fuel to make a bit more power off that larger compressor wheel. This is overly simplified but the general premise. Keep in mind though that moving that extra air usually comes at a price of a slightly longer "lag" time when spooling up. There are doctorates written on lag, compressor wheel size, turbine wheel size, housing design, and how all these things affect boost levels and spool time.

2). So the system from the factory vents back internally. I see some on here venting to atmosphere via blow off valves. How does this affect the operation/ecm/life/dependability of the car. Is it an easy conversion. Does it throw off the computer?

Good question and it all depends on where the blow off valve is in relation to the Mass Air Flow (MAF) sensor. In the stock LNF, the MAF is in the air intake before the turbo. Thus by using a recirculating system, the air entering the engine has already been measured and feeding it back into the system before the turbo (but after the MAF) keeps the measurements accurate.

In my setup, the MAF is in the cold side charge pipe between the intercooler and throttle body. If I changed my bypass valve to a blow off valve it would have no affect on the ECM settings since the measurement of air entering the engine is being done well after the turbo and where the bypass or blow off valve is doing it's thing. So long as I keep the blow off valve before the MAF, I'm golden.

Now this is in a MAF based Electronic Fuel Injection (EFI) system. Some cars don't use a MAF like my girlfriend's Veloster Turbo. It is on a Manifold Air Pressure (MAP) system. In her car, the stock bypass valve is on the Intercooler just before the charge pipe that connects the IC to the throttle body. The stock bypass valve has a hose connecting it to the intake tube before the turbo. Veloster owners can make their bypass valve a blow off valve just by removing this connection tube and capping off the attachment point on the intake tube. Since their ECM uses a MAP based fueling system, this modification doesn't affect the ECM programming at all.

In either case, if properly set up converting a Bypass Valve system to a Blow Off Valve system isn't going to hurt anything or affect engine longevity since all we're doing is changing where this excess air goes. Even if we have a MAF based system and don't change the ECM programming the worst that will happen is, for a split second, the Air/Fuel mixture is going to be rich because less air is coming into the engine than the ECM believes it should. I don't think the amount or the longevity of the incident is enough to cause any reliability issues.

Originally Posted by wspohn View Post
Good question. In any case, small as the engine size doesn't warrant a larger turbo.

The big wheel Werks mod only takes it up to around 46 mm compressor.

Robo - excellent write up - you should pin it somewhere as a reference!
It is pinned in Sky Technical Discussion...or it should be.

The size of the engine doesn't necessarily dictate the size of the turbo. Remember, the turbo's job is to cram more air into the engine than the engine could normally draw in NA in an effort to add more fuel to get more power. The limiting factor is how much extra air/fuel can the engine take before one of two things happen:

  • You push too much air into the cylinder and the head/head bolts can't keep the head on the engine to maintain the seal between the head and the block causing you to pop something.

  • You start to see detonation or your other bottom end parts can't handle the extra combustion pressure and you pop something.

For the record, popping something is bad.

But you can build the engine to take the extra air.

Setting a lift or duration of your intake and exhaust valve timing and/or increasing valve size can allow the engine to draw in a bigger gulp of air without raising boost pressure and with it, air charge temperature.

Bigger intercoolers can reduce the intake charge temp to near ambient levels to reduce the chances of knock.

Higher octane levels can let you run more boost. This can be achieved by fuel octane level or meth injection.

Harder head studs and forged internals can all strengthen the block to allow it to withstand higher pressures.

All these modifications would allow you to run a larger turbo on the 2.0 LNF.

V.A.L. (#1108)
2007 2.4 Base
MagnaFlow dual outlet, quad tip exhaust test car

Max (#1547)
2007 TURBO 2.4
Too much to list here. See my Garage for details.

Last edited by Robotech; 12-27-2016 at 11:55 AM.
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