Boost from now on means nothing unless you specify the turbo that is making said boost.

Everyone saying I can run 6 psi and be ok or the I wanna run 28 psi. Just Stop. You NEED to specify your current modifications top the vehicle, the size of the turbo. And the Modifications that will be in place when you want to Spool up 783 pounds of Boost!

i think this will clear up alot of stuff

Ok. I'm a fucking idiot.
You feel like explaing this in laymans terms, cause I am listening.

like if your gonna ask if you can run 6psi dont just say 6psi say can i run 6psi on my 14b or can i run 6psi on my 16g or can i run 6psi on my t25.
cause 6psi on a small turbo is totally different then 6psi on a large turbo

super soaker, faucet, garden hose, fire hose = t25, 14b, 16g, 50 trim



































torrential downpour = well.......lift the front of a big rig (IMG:style_emoticons/default/laugh.gif)

Ok. I think I get it now.
So it's not so much about the actual pressures, but the true volume of air flow?
Sound about right?

Yes.

WOO HOO!
You CAN teach an idiot (as in, me) new tricks! lol

yep. picture this.

You just put down 380whp on the dyno. Your car is a FWD, 4g63 2.0L with some moderate engine mods and you were flowing 40lb/min from your turbo. If you were running:

1) Evo III 16g you are almost to 30psi and close to its maximum output.
2) Garrett t3 50 trim you might be at 25psi and 2/3 of it's maximum output
3) schwitzer s300 you might be at 20psi and 1/2 of it's maximum output

same engine, same flow, same wheel horsepower rating just different boost numbers because of differences in compressor size and compressor efficiency. An example of "hybrid" turbos would be the garrett t3 baby kahuna built by slowboy. It has the design of a 67mm aggressive wheel that was squished into a 60mm wheel, then sharpened and smashed into a 60 trim housing while being mated to a t3 turbine wheel and turbine housing. Doing all of that creates a super fast spooling turbo that takes advantage of the more aggressive style wheel. Instead of just leaving it as a normal boring 60 trim turbo that spools slower and is less efficient









We can get into turbine wheels/housings later.

Then start it up damnit! lol

Ok, now that I get it, doesn' that mean, that in a way, no matter what turbo you use, you are not actually getting a proper pressure measurement?
If that is true, then what would an actual way to measure TRUE boost pressures, or volumetric air flow (is that even a word? and if it is, am I even using it correctly?), air density, etc? Some sort of guage or sensor at the throtle body inlet?
Why do I get the feeling I am being retarded?

I don't see how you are coming to this conclusion. Lol I could very well be the who is being retarded, however.

Ok, keep in mind I am still learning a lot about turbos, and I am going off of what I know at this time
A boost guage (mechanical or electronic) recieves its input from a vacumm/pressure line that feeds off of the turbo, there by giving you pressure reading. BUT, it is displaying the pressure from the turbo, not the actual airflow output of the turbo itself.
Which is why, 10psi of boost from different turbos, that are different sizes and specs, create different amounts of actual "boost" to the engine.
Does that make sense, or is my reasoning all wrong?
Now if we are going off of that scenario, then instead of actually haveing a boost guage displayng boost from the turbo, a better, and more universal way of measuring "boost" would be to actually measure the CFM (cubic feet per minute, I think) airflow rating. That way, no matter what type of turbo you were using, no matter what the specs, no matter what amount of "boost" the boost guage displayed, you could actually check your CFM reading to get a proper reading of how much air you are getting.
Is that making any sense?
Like I said, I am still learning about turbos, and their applications, so I may be totally off on all this.

you're right on track! you are thinking of pressure as just that, pressure. And thats the way you want to think of it. Like EMC mentioned 10 psi in a garden hose and 10psi in a fire hose are the same. its just that the amount of water waiting to come out is different.

Now that you have that part down forget about pressure and think about the turbos "ability to replace lost pressure." The engine uses quite a bit of the air that is in the intercooler pipes. The ability of a turbo to replace that air while supplying more air is what you want to know. Bigger turbos have the ability to replace the air being used by the engine must easier than the little turbos. IE flow.

Can you measure flow? YES, the 4g63 MAF does exactly that for the ECU to know how much air is being pumped in and thats why boost leaks and venting a bov to atmosphere is a bad idea. The OEM MAF measures density (baro sensor), temperature (IAT) and flow (lb.min). That's why when choosing a turbo it's much more important to look at its compressor map and interpret flow than it is to know its a "t3/t4," or the "trim." None of those fancy words mean shit until you know that a 60-1 flows 60lb.min, or a evo III 16g flows 46lb.min, etc. That is the proper comparison to know how much power a turbo can make and how dangerous it could be for a particular engine. compressor maps can be found at www.squirrelperformance.com (IMG:style_emoticons/default/thumbsup.gif)

Since this is in the 420a section I have to mention speed density. The 420a engine DOES NOT use a MAF. It uses a seperate IAT sensor and a MAP sensor to know how much air is going into the engine. The MAP and IAT do NOT measure flow. They only measure temperature to estimate density and pressure at the intake manifold and therefore are not affected by boost leaks or BOV's vented to atmostphere. However, it relies heavily on the O2 sensor for feedback. Thats primarily why a 4g63 car will run ok but with bad gas mileage when the front O2 goes bad, but the 420a will pop, sputter and run like shit when the front O2 fails. Therefore, speed density takes more information to tune properly because you don't know the actual "flow" going into the engine, but if you have a slight understanding of the turbo's flow from it's compressor map and have an A/F reading from a WBO2 you can make your adjustments much easier and more accurately. And IMO makes it easier to tune because A/F is all that matters anyway.

Everyone who's watching this thread chime in when you understand all these concepts and then we can move on to the turbine side. that way it's organized and not jumping back and forth. Its going to be a great info thread.

even after all the research ive done this thread has simplified it and made it so much easier to understand

i got it!! bring on the turbine side

I'm going to pin this. It's developing into too good of a thread, with excellent info, and will really answer a lot of questions for those of us trying to REALLY understand this kind of stuff.

The turbine side plays a big role in how much top end power or low end torque a turbo can make. A/R is the most important measurement here. It is Area over Radius. Basically it is the measurement from the middle of the wheel to the center of the outlet on the compressor side and from the middle of the wheel to the center of the inlet on the turbine side.

A/R pretty much means nothing for the compressor side. It just gives you an idea of the physical size of the turbo's compressor (cold) side.

A/R on the turbine(hot) side is very different. An A/R of .42 means that it's a small turbine housing because the ratio of area to radius is small. An A/R of .85 is a much larger turbine housing because the ratio of area to radius is pretty large.

In simpler terms, the farther away the center of the wheel is from the center of the turbine inlet, the bigger amount of space there is inside the inlet. More space means it takes more exhaust gas to fill it and push the turbine wheel. More exhaust gas needed to turn the wheel = slower spool time. Less space means the exhaust gas gets to the wheel quicker. Less gas needed to turn the wheel = quick spool time. This is the first part of A/R sizing.

The second part is based on restriction. Think of it in terms of exhaust piping. OEM pipe is 2.25 inches. Installing a 2.5" or even 3" exhaust system allows more flow and more top end horse power but you lose some bottom end torque. The same rule applies to turbine housings. A .42 A/R housing (2.25" pipe) will spool quick, give lots of low end torque but won't allow enough flow for the high top end horsepower. A .85 A/R housing (2.5" pipe) will allow moderate spool time, good low end and good high horsepower to a certain RPM. A 1.25 A/R housing will have a very slow spool time, minimal low end torque but gobs of high end horsepower.

It all becomes relative when you assign racing styles to certain A/R's:
A) 1/8th mile - .42 A/R turbo because torque is better for a shorter track when the first 60 feet are absolutely critical

B0 Auto X - .85 A/R turbo because you need the torque to pull out of turns and the horsepower to take you down the straight aways but too much of each one of those can hurt traction/response/performance

C) 1/4 mile - 1.25 A/R turbo because you launch at a higher RPM and shift at super high rpm so you need the high end power to be there more than the low end torque. Sometimes a quick 1/4 mile pass also has a bad 60 foot time on the time slip.

It also might make you say, "oh yea," when you think about OEM A/R sizing for different vehicles:
A) .42 A/R on the smaller displacement compact cars that are driven primarily in city traffic. Stop go. (torque to start out from lights, stop signs, crosswalks etc)

(IMG:style_emoticons/default/cool.gif) .85 A/R on the medium sized delivery trucks that are primarily driven in city and highway traffic. Stop go, distance. (torque to start out from lights, stop signs, crosswalks and then horsepower to maintain highway speeds)

C) 1.25 A/R on the big rigs that are primarily driven on the highways. distance (horsepower to maintain highway speeds)

Ok Ok I know someone is going to argue, "big rigs have gobs of low end torque." That is true, but forget about that for now and focus on the example. Diesel engines are a whole different world.

**** A/R numbers were ONLY numbers I picked off the top of my head for example. They in no way reflect actual A/R numbers specific to any manufacterer or specific to any kind of performance. Please don't reply saying, " My .42 A/R turbo makes more horsepower than torque." Good for you, but I don't care. They are just examples to show size differences.****

So lets say hypothetically I wanted a turbo that would give me the quickest Nuremberg lap time. What A/R would you recommend? Lets assume our 420a has a built bottom end.

depends on how it is built

+1 need to know more about the engine: compression ratio, head work, tubular or cast turbo manifold, stock intake manifold or aftermarket, size of IC piping, size of FMIC, etc