slay2k

Okay, I'm aware that at ~4.5 psi the PE puts down about the same HP as the Greddy does at 5.8psi.

Question is, where is this PSI measured ? At the turbo INLET ? Because if that's the PSI going to the MOTOR.... then it should be the same HP output, correct ?

Also if it's at the inlet, then that means at that lower PSI the PE is putting the same stress on the engine as the Greddy at the higher PSI, true ?

Thanks boys

scz

iTrader: (1)

That is absolutely true, I am sure PE used their own dyno and for some reason got more hp from the same amount of boost. In case you didnt know, it is impossible to get actual dyno numbers from an everyday dyno. You have to go to go to a government standard for weights and measures to accurately read horsepower to the wheels. It is also impossible to get more hp from the same amount of pressure. The engine has no idea what kind of turbos or intercooler you are running. All it knows is that there is 6psi of manifold pressure and it guages how much fuel to give it based on that. You can have a very small non ball bearing turbo vs. a monster aircraft quality ball bearing turbo both running at 6psi, and you will get equal horsepower. The only difference one turbo kit makes from another is quality (how long it will last and the material its made out of), how large of an intercooler (allows you to run more boost, which is the only way to get more power), or better tuning.

PE is feeding everyone a load of ******** and if they truly believe that their kit produces more hp from the same amount of manifold pressure, I would not trust them with a matchbox car let alone a very sophistocated and tempermental engine.

Feel free to PM me for more info.

Stephen

slay2k

Well if they measure that PSI at the turbo inlet... not the outlet, then I suppose that can make sense, being more efficient and all. Because if it takes 4psi of exhaust gas to produce the same OUTPUT psi at the outlet of the turbo as the 5psi of the Greddy turbo, then that makes sense. But the other way around isn't really possible.

SKiDaZZLe

slay:

i still have not seen a dyno from any PE TT user... i think this would be a good starting point... as opposied to believing that 4.5# from this kit makes the same HP as 5.8# from the greddy.

my turbos are bigger than the greddy, and the greddy are bigger than PE.

given identical a/f ratios... my kit makes the same power as the greddy at any PSI... (this has been tested between t32gzz and myself)... only difference is my torque and power come quicker because of the ball bearings.

i have not raced or driven a PE TT equipped car... so i really do not have a comparison.

this is turning into rambling, so i will cut it off here

m

slay2k

Mike,

I'm contemplating an upgrade to PE because I might have a good deal lined up. The primary reason would be for the simplicity of running 8psi... the Greddy's a pain in the *** when it comes to that.

Rest assured, I will not only dyno the car if I go that route, but you'll have 11-sec slips from me in a matter of days =)

THX723

iTrader: (3)

Folks,
When disccussing forced induction, it's the 'flow rate' that really counts rather than boost (psi). It is in fact easier to accumulate higher boost for a system that flows less. Imagine trying to cram air through a pin-sized hole with 100psi of boost behind it versus 10 psi through a 2" hole. Rather than thinking in terms of air 'compressor', view turbo charger (or super charger for that matter) as air mover/shover. The one that's able to sustain a higher rate of air flow wins. I hope that clears up the fluid dynamic aspect.

I've yet had a chance to go through the differences between the PE and Greddy designs, so I can't say whether one's actually more efficient than the other with respect to flow. But, if the claims are true, then the PE TT simply flows better ... that's what the deal is.

Speaking of Dyno for PE ... didn't Cheston dyno 420+ to the wheel a while back?

Sharif@Forged

iTrader: (92)

Turbo efficiency is exactly what THX said. It is the peak CFM that the turbo is operating at its best level...meaning....coolest intake charge to the manifold. If the flow is too low, or too high, intake temp will increase. This is counterintuitive...but true.

A better matched turbo, runnning at 6psi, CAN in fact, produce more power than a mis-matched turbo at the same 6psi. So it wouldnt surprise me if the PE turbos, which are smaller and better sized for our application, produce more power than the larger Greddy TT at 6psi. Now, at 20psi, the Greddy turbos will be more efficient thatn the PE's at 20psi...all things being equal.

Someone once posted a cool website that listed all the common turbos, and their efficiency islands..it was pretty neat. At 6psi, the Greddy TD05;s are barely on the shore...let alone..on the island. This is all the more reason to build your motor and turn up the boost to 18psi...all for the sake of "efficiency".

lacartus

As THX and GQ said, the turbo efficiency can affect HP at a given psi. As an example, on another car I went from a Mitsu 14B turbo to a 16G turbo and still running 18psi I increased my 1/4 MPH by nearly 4 MPH. That's about a 35 WHP gain using the standard forumula HP = (MPH / 234) cubed x Weight.

A good way to see this, as GQ mentioned is with a compressor map. I've attached an 18G map that I pirated from http://www.stealth316.com/2-3s-compflowmaps.htm. Great site by the way...
As you can see, there is a plateau in the graph, that is where the turbo is most efficient. As you move away from the plateau you still generate power, but it is less efficient (hotter air).

Now, for the Greddy kit. If you are running 7.4 psi, that is about half atmospheric pressure (14.7 at sea-level), so your pressure ratio on the map is 0.5. You'll note that is so far from the "plateau" that it's not even on the map. pun intended! :-)

Beyond this basic analysis it gets a bit more complicated, since you'll have to determine the target CFM. Roughly:

theoretical cfm = rpm x displacement / 3456

volumetric efficiency = actual cfm / theoretical cfm x 100

Giving us roughly 400 CFM at 6500 RPMs (theoretical), cut in half for two turbos and the the 18G map plateau is clipped at 1.2 pressure ratio or about 18psi. Caveats: these are real rough approximations, a lot more goes into it as the guys at Greddy, APS, etc. could go on for pages about this stuff. Also quite possible I screwed this up since I don't have my required level of caffeine yet. :P

spazpilot

iTrader: (2)

I would have to agree with SKiDaZZLe on this. Even though everyone has made good points about turbo efficiency. I also have still not seen dynos on the pe kit proving that it makes more power at lower boost. It seems to me that no matter weather you get a custom kit, greddy, ultimate racing or any other they all seem to put down same numbers. Buy what you like the end result will be about the same.

Sharif@Forged

iTrader: (92)

lacartus, good post.

At atmospheric pressure at sea level is 14.7psi or 1 BAR, so adding 7.4psi to your example...would give you over 23psi of total pressure. Maybe I misunderstood your post...but can you clarify? I am somwhat challened in reading these maps..I just think they look pretty.

AmarilloMike

Hi scz:

You wrote:

"All it knows is that there is 6psi of manifold pressure and it guages how much fuel to give it based on that."

6 psi air at 100 degrees has more power potential than 6psi at 200 degrees. The hundred degree air is denser. I think the efficiency on the map posted by lacartus has to do with how much heating of the air is done to get it up to a given psi, in your example 6 psi. If you have an ecu/fcu that adjusts for manifold air pressure boost and manifold air temperature you can get more power with a more efficient blower and the same boost psi. It would also seem if your system just worked on boost (no temperature adjustment) and that you were watching air/fuel and detonation when you tuned that you could get more power from the more efficient blower at the same 6 psi boost. The stock Mass air flow sensors also measure air temperature and the ecu adjusts the airflow calculations for the temperature. Even though this is for non boost it is still the same principal.

Thanks

Mike

lacartus

You're right GQ,

Not enough caffeine this morning... PR for 7.4psi should be 1.5 not 0.5--too bad I can't fix my previous post so I don't confuse people. Doh!

The Y-axis is the pressure ratio which is the outlet pressure divided by the inlet pressure, e.g., a PR of 1 = 14.7psi/14.7psi as you might see on a non-boosted motor ingesting air at atmospheric pressure. So for 7.4 psi of boost you have PR = 14.7 + 7.4psi / 14.7 psi = 1.5.

Now, what was my point...Oh yeah, if we are running 7.4psi (PR of 1.5) on twin 18Gs, the map shows that we're off the plateau below about 250CFM. Previously we calculated that at 6500RPM the VQ35 is at 400 CFM, which is 200 CFM dividing for both turbos, so even near redline we've not yet reached the plateau.

People still make good power off the plateau of compessor maps, but it's not as efficient as possible. It's tough to extrapolate this theoretical stuff to expected results. Based on my 14B vs. 16G experience and this theory, I'll assume that smaller turbos on the VQ35 will also lead to better efficiencies and more horsepower at a given psi. Your mileage may vary ...it would be interesting to see dyno results of Greddy vs. PE or JWT or APS (all else being equal--dyno, supporting mods, etc.).

I should note that the 18G map I attached is Stealth316's extrapolation for an 18G map using a 20G map, so my point is more theoretical than absolute.

lacartus

Right, that's how I interpret the maps. The efficient plateau is where the turbo produces the coolest charge. As an example, on some factory turbo cars with smaller capacity turbos (e.g., WRX, 95-99 Eclipse) high psi (high pressure ratio) puts the turbo in such an inefficient part of the compressor map that it is not even worth running higher psi.

scz

iTrader: (1)

Amarillo,

I see what your saying, but if the air is more dense at a cooler temperature, then the manifold pressure would be higher. 6psi measured at the turbo outlet at a higher temperature would produce less manifold pressure than if it was cooler. That is what I am saying, if you have the same manifold pressure, you cant vary the power produced. Anyone can add a better intercooler and produce more manifold pressure with the same turbo outlet pressure. I think we are just running around in circles. Let me know if I am just totally wrong.

DaveO

I don't think it really matters in your application, but...

1 atmosphere = 14.696 PSI

1 bar = 14.503 PSI


DaveO

AmarilloMike

Hi scz:

You wrote:

"I see what your saying, but if the air is more dense at a cooler temperature, then the manifold pressure would be higher. 6psi measured at the turbo outlet at a higher temperature would produce less manifold pressure than if it was cooler" <snip>

It is possible to have (in the manifold) boost of 6 psi at 100 degrees, 6 psi of boost @ 200 degrees, 6psi of boost at 300 degrees, and so on.

The type of efficiency that is referred to in lacartus' map post is a measure of how much you heat the air while compressing it to a given psi. So if you have a 50% efficient blower making 6psi the air from it will be hotter and less dense that the air from an 77% efficient blower making 6psi. You can therefore tune the 77% efficent blower setup for more power because you have more pounds per minute of air, even though both the 50% and the 77% are putting out 6 psi.

I am assuming the same size intercooler.

Trivial technicalites are for the techies:

An intercooler will take more degrees out of hotter air than cooler air. The 77%/6psi setup will still provide more much power potential than the 50%/6psi setup. (log mean delta T)

The assertions I made are based on intake air temps, pressure, moisture content, engine, and airflow across the intercooler all being the same.

I hope I don't sound like a know-it-all. I have learned many things from reading this forum and others. I learn new things every day and am wrong quite often.

Thanks

Mike

GurgenPB

iTrader: (2)

I agree with Clint (THX723) and Mike. THere is another way of looking at it too. Assuming ideal gas behavior, which is certainly FAR from reality yet valid for qualitatively comparison, PV=nRT will describe the gas behavior (not its dynamics as Clint desrcibed).

Solving for pressure you will see that P=nRT/V. Where R, V are constants in our application, while n (moles of gas) and T (temp) are the variables (again, just for our application). The same P (say 7psi of boost - around 21.6 psi of gauge pressure) can be achieved by having a relatively low n and high T (not preffered as you obviously have fewer O2 molecules to react at higher nad unfavorable temperature), OR high n and low T (the flipside of the other scenario - MUCH, MUCH better). That's where efficiency comes in - which is why PE is better suited for our engines at lower psi setting, while near 20 psi of boost or so, Greddy's will be more efficient than the PE 1420s.

Sharif@Forged

iTrader: (92)

very true.

SKiDaZZLe

can someone compare the greddy kit to my kit (via compressor maps, etc?) i was wondering how my turbo sizing compares and how theoretical max power output compares.

Assuming the rest of the Turbo kit is identical (i/c efficiency, etc)... how do these match up?

I have twin Garrett GT28R Ball bearing turbos...
here is the map:



eagerly awaiting your analysis!

m

edit:
i noticed that the x-axis is a different metric... is there an easy conversion?

also... here are the specs of the compressor and turbine housings (2nd line down):

http://www.turbofast.com.au/GTseries.html

Chebosto

iTrader: (43)

Hey Mike-


i think the conversion is 10 lb/min is equal to 144.72 cfm

--cheston