setzep

I'm sorry I started talking about straws!

AJatx

iTrader: (1)

The straw example is not the most accurate, but it gives a person a picture to see how the flow of air is important and that restriction of any sort is what reduces the efficiency (heat, port, turbine, runner, manifold design).

Actually, the straw example isn't too far off considering the engine could be your body and the straw could be the turbo. You have to inhale air to help your muscles convert ATP and work. Work creates heat. Heat has too be cooled be means of fluids and air (breathing included) otherwise efficiency and reliability of the body can be compromised. The body exhausts energy (heat, for example) partly through breathing, exhaling.

You can knickpick all you want, but the big picture is illustrated. I'm also glad that you guys corrected the details that could've been taken away as inaccurate.

10psi is 10psi. It's pressure per square inch . The volume or mass may be different with some influence from temperature, but the pressure remains the same.

So talking about relative atmospheric pressure isn't the best way of talking about power resulting from a given turbocharger unless you're trying to discern low boost from high boost.

J

Piranha

I think you're still missing the point that the ports aren't open all the time.

A turbo isn't a restriction when it is the start of the system. if seperates ambient air from pressurized air. the throttle plates at half throttle=restriction.

pianoprodigy

I think I opened up a can of worms! This is interesting reading though. The reason I asked was that I bought my FD (first FD, last car was 90 Vert) with a T-66 and basically every other modification already done. I'm supposed to pick up my car tomorrow (crosses fingers) with it tuned and boostin' about 10 psi. In one of my other posts, someone told me that I would be wasting my time if I only ran 10 psi on an upgraded turbo. I was just thinking about that and that's what spurred on my question.

Does anybody care to guess what kind of numbers I'll have at 10 psi? I know what my mechanic told me, but I want to hear from you guys.

rwhp?
1/4 et?

Most all the significant mods are in the sig. I'm sure that I've missed some. Basically, everything is done except a lightened flywheel and an electronic boost controller (manual currently).

Thanks for the input guys!

Alan

HWO

thats where you are looking at it wrong though, the turbo isn't the start of the system, the important part of the turbo is the last piece of the system, the exhuast side of the turbo, restricts how much CFM the motor can exhale, by exhaling more, it can inturn inhale more (higher VE)

then the compressor side starts to play a part which is the start of the system.

When the end of the system isn't limiting flow, then you can worry about opening up the start of the system

I'd honestly like to see how much Hp could be made from a Std S2 compressor with a T04 exhuast housing/P trim wheel on the back

rotarygod

iTrader: (1)

If the throttle plates are half closed then you probably have little or no boost anyways so where's the problem?

As a general rule (but there is always an exception!) for every 1 psi of backpressure you can free up on the turbo exhaust side, it is equivalent to 2 psi more on the intake side! HWO hit a good point. Too many people try to upgrade to a really large compressor when half of their problem is a really small exhaust side. The T-II compressor is still too small for really high numbers though but there would be an improvement.

Marshall

~300 rw SAE on a dynojet, same as stock twins. At 10 psi, these "huge restrictions" don't show up. I still stand by the only gains you'll see if you otherwise leave the motor untouched will be from better exhaust flow and lower charge temps. Dyno and draw your own conclusions.

little rotor

Personally on a 13B I don't think a T66 compressor will be more efficient than the stock twins at 10psi. The compressor map doesn't look too good until you start running some real boost. Therefore, I think any gains you'll see will be the result of the better exhaust flow.
If you only want to run 10psi I bet you could gain power by going to a smaller compressor which is effiecient under the operating conditions. It's not just a case of bigger compressor = cooler intake temps.

HWO

Hence i am not a fan of hybrid turbo's, the exhuast side of the factory turbo is the MAIN thing limiting the Hp output, by putting a larger compressor into it, all you are doing is forcing more air in, this is great for the people who think PSI = HP, but for the people who know that CFM = HP its not a nice equation

I believe a hybrid at 15psi making 330HP, is probably putting more strain on engine components than a Full T04 at 10 psi making 400HP

fatboy7

Big turbos have big compressors that are designed to flow big CFM. This has come up in this thread several times. But the compressor size increase's effect is not one of increased CFM, it just compresses the air. Its up to everything down stream to change the CFM. Here's my example of this:

Suppose for a minute that you could take the T66 compressor, and power it with the stock TII turbine -obviously not possible, but humor me. The T66 spools up and makes for this example 15psi. Because this compressor is more efficent at this pressure than the stock turbo it makes a cooler charge. Thats it though, every thing is still the same because the "straw" that the compressor sees is still the same size. But a cooler charge is only going to give you 10-20% maybe. So at 15psi you make 320-350 vs 280-290, hmm sounds like what the typical compressor upgrades would give, go figure. Like RICE has pointed out, the biggest restriction in this "straw" is not the porting, but the turbine. On the stock turbo I'd bet the inlet pressure is at least twice the boost pressure at any given time. Thats a worse restriction than the worst possible NA OEM exhaust. The T66 makes bigger power because it's turbine flows much more efficently, lowering the turbine inlet pressure considerably.

Thus big turbos flow big cfm because they pose less restriction to the system

fatboy7

And I forgot to read the second page.... you already covered it!!

Piranha

After talking to my friend, he explained the same thing. It does make sense too, I'm running a S5 hybrid with a T04E wheel and housing, and I know I'm not near 300 HP.

Marshall

Yes, the exhaust is a big restriction and will allow the engine to breathe much better. The gray area is whether or not the compressor section can flow more in addition to what you get from the cooler charge temp. I say no, if the compressor is compressing and can maintain your desired boost, then it isn't a restriction -it may be inefficient and blowing alot of heat, thus lowering flow, but the flow isn't restricted at the compressor other than by the temp.

mass flow = density * cross section area * velocity

Keeping the engine the same, at the intake port at a certain rpm, the CSA and velocity will be constant, the only thing that can move is the density. Density can change with pressure or temperature. We've already said pressure is constant, so the only thing making a difference on the compressor side is the temp. What did I miss?

This is why I bet money that 10 psi on the T-66 makes no more power than 10 psi with healthy stock twins. Higher boost and the T-66 will make more power because of less exhaust restriction and cooler charge air.

SPOautos

If you have the same engine and same IC pipe system you have the same amount of space to fill up with air. The difference in how much o2 is in that air. The larger compressor wheel grabs more air and compresses it into the same space, but since it grabed more air it got more o2.

Say you have a box that holds 100 cubic feet of air, you can have a small turbo grab 150cubic feet of air and compress it down to 100 or you have have a big turbo grab 200 cubic feet of air and compress it down to 100.

The size and design of the wheel determine how much and how efficiently it grabs the air. Then that air is compressed into the IC/engine system.

STEPHEN

Marshall

??? In that example, if you keep temp the same, the pressure HAS to rise and the wastegate won't allow that. If temp is constant, and you compress 150 ft^3 of air to 100 ft^3. you will need to compress it 50%. Likewise, 200 ft^3 to 100 ft^3 will require a 100% increase in pressure.

SPOautos

Who said the temps would be the same??? Large turbo's temps are generally lower. You system doesnt create o2 the only way to get more o2 in the system is to take in more air

Also, the pressure inside the compressor housing of a turbo where all the air is actually being compressed is not the same as the pressure in your IC system.

STEPHEN

Marshall

And I'm saying that the only way for it to get more air in for a given pressure is to reduce temp. What other way is there?

And you're right the temps of course won't be the same, the amount they rise will be proportional to how much the air is compressed and how efficient the compressor is -I just used that as an example to show that you can't just "fit" more air somewhere without something budging (pressure or temp). We've established that lower temp will get more 02 molecules into your motor, the question is:
If you're already reaching and sustaining desired boost, what can a more efficient compressor do besides lower temp?

Will it give less losses through the compression? Sure, but that shows up in the efficiency which shows up in the outlet temp.

Now, if you've got a free flowing turbine section and a compressor so small that it cannot reach your desired boost level, even with the wastegate fully closed, THEN it would seem the compressor is a restriction.

SPOautos

The compressor wheel grabs the air and compresses against the housing creating a huge amount of pressure then as the compressed air travels thru the "snail" to cools off and expands. The amount that it cools and exands is dependant on the size and length of the "snail". Then at that point you'd basically come out with a certain volume of air that has more O2 in it then that air would pass into your IC system.

The difference in the stock twins and a T78 at 15psi cant be explained soley off of charge temps. The temps arent THAT much lower to make a 100hp difference. If you take a T78 in the summer it would have hotter charge temps than stock twins in the winter.....however the T78 would still make more power.

STEPHEN

Marshall

If the system was open, yes. ...but it isn't. Other than lowering temp or raising pressure, how else can you pack more 02 between your turbo outlet and your combustion chamber?

I'd love to see a T-78 put 100 hp over a good set of stock twins at 15 psi.

But true, it would make more power, because of the exhaust section.

j9fd3s

iTrader: (3)

dumb question: simplistically is the spooling of the turbo the difference in pressure between both sides of the turbine wheel?

mike

HWO

the difference in pressure between both sides is what equates to HP in a way.

the less pressure on the exhuast side the more HP it'll make

stock T2 turbo at 15psi generally has 40-60psi exhuast manifold pressure ............................ VERY BAD

maxcooper

For a given set of ports at a given boost pressure, reducing backpressure will increase the amount of air that flows through the engine. Temp is very important, too, of course, but it isn't the only factor in the amount of flow (quantity of air molecules) that you get.

-Max

Marshall

True, but is that not a contribution from the exhaust side?