model x

Is 10psi from a T3 the same as 10psi from a T25? I would think psi is psi but if all anyone wanted to run was 8 psi then a t25 would do just fine.

I'm planning on boosting my b16 and I'm leaning towards a T3 from a ford.
How would a 14b compare to this?

I want around 250whp and I do AutoX so I'd like something that's gonna spool now and is cheap.

lazerus

no, 10 psi is not 10 psi.

How much air is moving plays a huge part in how much power is developed, as well as Timing, and a slew of other things.

model x

aww yes I see now, 10psi doesn't describe the volume, only pressure per square inch.

showtymers619

but from what your saying.. its told that 10 psi from a t3 is particularly gonan produce the same about of power then a t25, correct me if im wrong.. some dude explained about the low boost difference on the turbos.

rjardy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by model x &raquo;</TD></TR><TR><TD CLASS="quote">aww yes I see now, 10psi doesn't describe the volume, only pressure per square inch.
</TD></TR></TABLE>


Now your thinking! But yes 10 psi is going to be 10 psi no matter what, NOW there is the factor of how much volume is behind that 10 psi. The physically larger turbo with a bigger cross sectional area is going to allow more volume to be put through to that 10 psi. Length x Area = volume, greater length greater area, greater volume! So in the end, your answer is well...... YEAH SORTA!


Rob

danl

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rjardy &raquo;</TD></TR><TR><TD CLASS="quote">


Now your thinking! But yes 10 psi is going to be 10 psi no matter what, NOW there is the factor of how much volume is behind that 10 psi. The physically larger turbo with a bigger cross sectional area is going to allow more volume to be put through to that 10 psi. Length x Area = volume, greater length greater area, greater volume! So in the end, your answer is well...... YEAH SORTA!


Rob</TD></TR></TABLE>


Wrong, a bigger wheel is not always more efficient at all pressure and flow levels than a smaller wheel. A bigger wheel does not usually work well at low psi, but works much better at higher pressure and flow rates. Look at a flow map and you'll see what i'm saying. If you flow 300cfm at 5 psi on a t-66, that is not a very efficient setup. A t-25 would be a much more efficient setup at those flow and pressure levels. Hence the need to choose a compressor for the desired hp.

TTWS6.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by danl &raquo;</TD></TR><TR><TD CLASS="quote">


Wrong, a bigger wheel is not always more efficient at all pressure and flow levels than a smaller wheel. A bigger wheel does not usually work well at low psi, but works much better at higher pressure and flow rates. Look at a flow map and you'll see what i'm saying. If you flow 300cfm at 5 psi on a t-66, that is not a very efficient setup. A t-25 would be a much more efficient setup at those flow and pressure levels. Hence the need to choose a compressor for the desired hp.</TD></TR></TABLE>

took the words out of my mouth

rjardy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by danl &raquo;</TD></TR><TR><TD CLASS="quote">


Wrong, a bigger wheel is not always more efficient at all pressure and flow levels than a smaller wheel. A bigger wheel does not usually work well at low psi, but works much better at higher pressure and flow rates. Look at a flow map and you'll see what i'm saying. If you flow 300cfm at 5 psi on a t-66, that is not a very efficient setup. A t-25 would be a much more efficient setup at those flow and pressure levels. Hence the need to choose a compressor for the desired hp.</TD></TR></TABLE>

When did i say anything about efficiency? I DID'NT . He asked if psi was psi, now, i dont care what compressor you have flowing 10 psi, the amount of pressure per square inch is going to be 10 psi when it is pushing 10 psi! I completely understand that a larger compresor wheel is not going to be as effecient at 10 psi as say a t25. but the fact is that if both compressors are making 10 psi, they ARE BOTH MAKING 10 PSI.

Rob

danl

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rjardy &raquo;</TD></TR><TR><TD CLASS="quote">


NOW there is the factor of how much volume is behind that 10 psi. The physically larger turbo with a bigger cross sectional area is going to allow more volume to be put through to that 10 psi.


Rob</TD></TR></TABLE>

More volume at the same PSI (in your example 10 psi) means a more efficient compressor. That is unless somehow you mean that moving more air is not more efficient.

Andrea

Compressors efficiency is either in the form of isentropic or isothermal efficiency.

Isentropic efficiency=(ideal compressor work/actual work), work meaning work from the compressor.

Isothermal efficiency=(reversible isothermal work/actual work)

The work is that of W=P(V2-V1), where P is pressure and v is volume. So the change in the volume*pressure is the work done.

If you keeping pressure the same, you are either varying volume or temperature. If you are in an "efficient" section of a compressor map you are flowing a high volume, with a low temperature. If you are outside of an "efficient" section you are flowing a lower volume or air with a higher temperature. It's simple thermodynamics.

danl

Wouldn't it be simplier to say you're flowing more O2 molecules if you are raising either volume or heating the air less LOL. Of course assuming all other variable are constant which is what is implied when you don't mention their relative change.

rjardy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by danl &raquo;</TD></TR><TR><TD CLASS="quote">Wouldn't it be simplier to say you're flowing more O2 molecules if you are raising either volume or heating the air less LOL. Of course assuming all other variable are constant which is what is implied when you don't mention their relative change.</TD></TR></TABLE>

yes it would!
hee hee, well i learned something today


Rob

model x

so does anyone have any input on the second part of my post

kpt4321

I've posted this here before, but you guys might want to read it:

http://home.comcast.net/~tarry....html

Hope this helps.

The short answer is, yes, 10 psi is 10 psi. However, 10 psi is not necesarily the same amount of MASS flow. This depends on a large number of factors, such as compressor efficiency, IC efficiency, VE, etc, etc.

Andrea

If you are comparing the same psi of two compressors, you are keeping the pressure variable constant. The main difference between the two compressors is the point at which the volume is the greatest and the temperature is the lowest, thereby increasing the density of air. If the density is increasing, you are essentially increasing the mass of oxygen being moved per unit volume flow. The real comparison between two compressors is the quantity and the quality of the air being moved into the engine.

nigel

the bottom line is... If you have more cfm's you are going to make alot more power. for instance, ryan autry. he has a good sized turbo, precision sc 34, he will make around 275-300 on a stock b16 after its tuned on high boost.

boosted hybrid

CFM doesnt mean much if the air behind it is hot, aka out of its compressor efficiency. The Garret GT compressor technology is able to have a broader efficiency range, thereby giving greater cfm AND lower temperatures over a larger part of the compressor map as with the sc61, sc63, pt67, etc wheels.

Beanbooger

Many of the responses in this thread are on the right track, let me try to put it together and add a few more things.

Number 1 is ALWAYS: Increasing air (or more correctly, oxygen) DENSITY is the goal for increasing horsepower. This means increasing the number of air (oxygen) molecules in the cylinder. This is the ultimate goal because this means you can add more fuel, make a bigger boom, and make more power! Turbocharging and supercharging do this by increasing the intake pressure, packing the molecules more tightly together. NOx does this by adding oxygen in a different form, and normally aspirated engines do this by reducing restrictions and "tuning" the intake and exhaust systems to improve scavenging (improving volumetric efficiency).

2. For forced induction systems, as stated above, the density improvement is obtained by raising intake pressure. One of the side effects of raising the pressure is an accompanying increase in temperature. This increase in temperature is undesireable and negatively impacts density. How much of an increase you see is based on the compressor's efficiency. Higher efficiency doesn't heat the air as much and requires less work from the turbine wheel. Every compressor has an operating range that is plotted on a "compressor map". You can go to http://www.turbobygarrett.com and download the catalog to see a variety of the modern GT-series maps. On every compressor map there are regions of higher and lower efficiency, with the highest region usually being in or near the center of the map. A properly matched compressor puts as much as possible of the engine operating points into the higher efficiency regions. You can bias towards upper rpm range or lower rpm range by choosing larger or smaller wheel trims or wheel sizes.

3. For a given amout of boost (like 10 psi) a compressor is only going to flow as much as the engine can breath. This is a result of the engine's displacement and volumetric efficiency. If we ignore compressor efficiency and turbine size effects for a moment, a big compressor or a small compressor will flow the exact same amount of air. The bigger compressor won't "force" or "flow" more air into the engine and make more power at the same 10 psi. Now lets add in the effects of compressor efficiency. As stated earlier we can bias the engine operating range to high rpm by choosing a larger compressor. This will put have the high rpm engine operating points on the high effciency region of the map, but at the expense of low rpm performance. Since the engine is now operating at higher compressor efficiency at the high engine rpm range, the intake air is at higher DENSITY, and thus, at the same pressure, will make more power!!!!

4. I've alluded to this a couple of times, and now we'll include turbine effects. Actually, these turbine effects can be more important to peak power output than the compressor differences mentioned above. As with the case of a T25 VS. a T3, the T3 turbine wheel is considerably larger. This definitely allows lower back pressure which improves peak power, but greatly increases the rpm at which the turbo is spinning fast enough to make useable boost, hurting drivability. The smaller turbine will come up on boost earlier, which improves drivability, but then must be wastegated more to maintain the 10 psi boost and prevent overboosting. As it sounds, wastegating wastes exhaust energy by diverting gas flow around the turbine wheel. This hurts overall engine efficiency and increases backpressure. This backpressure hurts the engine's ability to breathe at higher rpms. The larger turbine does not come up on boost as fast, but since it flows more, it has less backpressure and it does not need to be wastegated as much, using more of the exhaust energy to drive the turbo and make boost, improving overall engine efficiency and resulting in more engine power. There are limits, of course, in how big you can go on turbine and still have the car be driveable.

5. Finally, you must decide what you really want from your engine. If you are drag racing and ET and trap speeds are the most important thing, then choose a larger turbo. If the car is your daily driver and you don't want to wait until 4000-5000rpm for the turbo to spool up, then choose a smaller turbo.

Hope this helps,

Brian

TraKtioN

you guys know your stuff, I will post the formula for determing the right turbo for your engine and the amount of psi you want to run as soon as I find it, its big but fairly straightforward.