which i doubt unless its a rebuilded turbo....for the price range they can't be using somethign too big ....or that its even ballbearing

 

So that might be a plan for limiting lag in one of these STS units... Although it would be weird to swap for a smaller exhaust to increase backpressure...

 

atleast some one here thinks with their brain and not their right foot........

 

This is cut and paste off the FAQ page at www.ststurbo.com

Doesn't heat create the velocity in the exhaust gasses to spool the turbo?
No, heat doesn't create velocity. Heat creates volume. If you look at any of the physics laws for gasses, you will find that pressure and volume and heat are related. PV=NRT is a popular one, The V isn't for velocity, it is for Volume.
The turbine housing is what creates the velocity. The scrolling design that reduces the volume of the exhaust chamber as it scrolls around causes the gasses to have to increase in velocity and pressure to maintain the same flow rate.

Hotter gasses have more volume, thus requiring a higher A/R which in effect means that it starts at say 3" and scrolls down to approximately 1". Lower temperature gasses are denser and have less volume, so they require a lower A/R housing which would start at the same 3" volume, as the turbine housings use standard flanges, and scroll down to say 3/4".

Now if you were to reverse the housings in application, the conventional turbo would spool up extremely quick, at say around 1500 rpm but would cause too much backpressure at higher rpms because the higher volume of gas couldn't squeeze through the 3/4" hole without requiring a lot of pressure to force it through. On the reverse side, the remote mounted turbo with its cooler denser gasses, wouldn't spool up till say around 4000 rpms but once spooled up would make efficient power because it doesn't require hardly any backpressure to push the lower volume of gas through the larger 1" hole.

 

Heres another FAQ answer I thought made sense.


Don't turbos have to be really hot to work properly?
Putting a torch to your turbo and getting it hot doesn't produce boost. What produces boost is airflow across the turbine which causes the turbine to spin. If turbochargers required very high temperatures to produce boost, Diesel trucks and Methanol Race cars wouldn't be able to run turbos. However, each of these "Low Exhaust Temperature" vehicles work very well with turbochargers when, like any turbo application, the turbocharger is sized correctly.
In a conventional, exhaust manifold mounted turbocharger system, the extra heat causes the air molecules to separate and the gas becomes "thinner" because of the extra space between the molecules. This extra space increases the volume of air but doesn't increase the mass of the air. Because the volume is higher, the velocity of the gas has to be higher to get it out in the same amount of time.

By mounting the turbo further downstream, the gasses do lose heat energy and velocity, however, there is just as much mass (the amount of air) coming out of the tailpipe as there is coming out of the heads. So you are driving the turbine with a "denser" gas charge. The same number of molecules per second are striking the turbine and flowing across the turbine at 1200F as there is at 1700F.

Front mounted turbos typically run an A/R ratio turbine housing about 2 sizes larger because the velocity is already in the gasses and the volume is so big that the turbine housing must be larger to not cause a major restriction in the exhaust system which would cause more backpressure. With the remote mounted turbo, the gasses have condensed and the volume is less, so a smaller A/R ratio turbine housing can be used which increases the velocity of the gasses while not causing any extra backpressure because the gas volume is smaller and denser.

Sizing is everything with turbos. There is more to sizing a turbo for an application than cubic inches, Volumetric Efficiency, and RPM ranges. A turbo must also be sized for the exhaust temperatures. A turbine housing sized for 1700F gasses would have lag if the gasses were 1200F. This is why turbo cars have lag when they are cold and not warmed up yet. Both systems work well if sized correctly

 

I disagree!!! She said size doesn't matter, it's how you use it !!!

Oops, sorry, I thought you said "size"....

 

Any girl will tell you its not how long it is, its how long its long....

 

So are you going to tell me something I don't know? But really, pressure loss over the cold side piping is going to mean more lag at that. The undersized turbo they're using is going to have to spool that much longer to overcome the drop in pressure accross the 12 or so feet of piping and intercooler that appears to be involved.

I don't see how this kit could possibly spool up before 3500 rpms, and even if it did whichever turbo they were using would probably be almost past effciency by the time it flowed enough cfms to make 400whp. Oh well, who knows... Prove me wrong...

 

What exhaust? No backpressure is the only plus I see in this setup. It's basically a direct dump from the wastegate/turbo back...

 

Except for the backpressure built up before the turbine. Remember as the exhaust gas cools its going to expand only this time instead of having a free exit its going to hit the turbine. While this should help keep the turbo spooled the pressure drop across the piping is going to hurt that AND we haven't taken into account the fact that the exhaust gas volume is going to be much higher once you start feeding boost into the motor..

 

Doesn't the gas expand as it heats up?

 

yeah, i'm not sure what you were trying to say here....especially in the "a the exhaust gas cools its going to expand"...that's not true at all....

 

The major pressure drop in an aftercooler is going to be across the heat exchanger. So adding 5-6 feet of straight pipe is not going to increase head loss that drastically.

As for spool time, its all about the pressure differential, and with a properly matched turbine wheel and compressor wheel, there shouldn't be a problem.

The main factor that might induce lag in this setup is lack of heat in the journal oil in the turbos, increasing viscosity and lag. But I'm assuming that the people at STS took that into account when designing thier turbos. (all they would have to do is redesign the journal to compensate for the increase in viscosity)

I have my concerns, but I'm open minded and eager to hear some dyno numbers and track times on this kit.

 

I don't agree with this theory.

If you take in 1000 molocules of air through the intake, have combustion and expel 1000 molocules out of the heads into the exhaust into an exhaust pipe that can only handle 500 molocules worth of air at a given temperature you will create pressure obviously (what drives the turbine since the turbine is the path of least resistance). If the temperature gets lower, the density increases. Thats great! You can push more dense air into the turbine which means you can fit more air molocules in a given volume. The only problem is that the exhaust is not connected to an unlimited source of air such as an air filter and therefore it cannot take in any more molocules of exhaust gas then is expelled from the head. So if the density increases that means that you may be able to fit 750 molocules in the volume that could only fit 500 molocules at a higher temperature. This means that there will be less pressure against the turbine therefore increasing lag.

Again, I think they are trying to hype this up in the FAQ's with some physics laws that don't make sense. They are not reinventing the wheel here. They are making an economy kit that offers good performance but trying to state that this will have an increased benefit is somewhat ludicrous.

They stated that you would not want to put a torch to your turbo to increase horsepower. You are correct. However, it would seem that they are stating that cooler exhaust gases will be better in which case we should make some aluminum heatsink turbo manifolds for our TT's so that we can have super duper spool up.

Plain and simple. This kit will be a great kit and it will work great for the money you are going to pay for it. I am sure that the quality is great and that those who just want more horsepower via boost will be very pleased. This kit is not going to be the best kit out there. It is just nice to see another option for Z owners.

 

They can increase the pressure by decreasing the volume. There is going to be a trade off, but there may be as much of a benefit due to reduced pressure after the turbo as there will be loss from reduced pressure (or volume/velocity) before the turbine. If you think about it, the STS will be very close to an ideal 0 psi backpressure after the turbine.

 

Your also forgeting the benifiet of keeping the HOT turbo out of the engine compartment. This does wonders for EGT's, oil temps and coolant temps, as well as engine efficiency..

 

Yeah, as we saw from the Turbonetics vs APS ST dyno comparisons. Besides, neither company or person is going to get test figures on a heat soaked car.

They're making this STS setup out to be a magic can of beans. Lets stop playing the "garage physicist" game and get some real world info on it.

 

That's what heatwrapping is for...

 

Wow, I'm glad they meke perfectly insulating heat wrap now... Lets get some of that to nasa!

There will still be added heat under the hood from a turbo, even a well wrapped turbo.

I'm sorry... I had to edit that... to was too sarcastic.

 

Not too sarcastic. But it does alleviate (sp?) the problem with heat to a certain degree, plus, there are so many kits for other cars with top mount turbos.