Wha? Can you explain your explanation ? Air flow thru a restricted travel will result in higher pressure, which is why turbos create 'boost' or positive manifold pressure... according to your statement, turbos create power at atmospheric pressure, which is wholly not true... CFM has a relationship to psi, the more CFM a turbo flows is what allows a larger turbo to create more boost at lower engine speeds.

CFM per psi is important !! How do you calculate turbo sizing per displacement point ???? This is the ONLY way to correctly size a turbo to a motor ! This is why, when properly building a turbo motor, you will need to get the compressor map for the turbo you are interested in.

A greddy turbo pushing 7.5 psi does NOT make the same power as a dragIII at the same psi, Why? increased CFM from the larger turbo on a Drag kit.... ask any owner of a T3/t04 hybrid if they would rather run a smaller turbo and lower boost and they will **** themselves laughing. You know that Dustin !

Maybe you need to elaborate more on the topic.... *woo hoo !


[Modified by X2BOARD, 5:23 PM 2/28/2002]

 

I think we are playing semantics games here... but no boost would be created without the restriction of the motor. The restriction creates the pressure. For example, I can create lots of pressure at zero flow in my air compressor.. Tank reads 125psi but there is no flow... at this point the only reason that there /is/ any pressure is the fact that the air cannot escape, thus the restriction. In an environment where at least /some/ air must flow (a motor), there must be (at least some) flow to maintain positive pressure. Thus, the restriction creates /PRESSURE/ and the turbo creates /FLOW/. Flow is created by the movement of air (or whatever liquid) and pressure is created by restriction to that flow... this is why pressure and flow are inversely related. I think you would agree with me on this.

Are you talking MOTOR CFM or TURBO CFM? Turbo CFM per PSI is useless. Of course motor CFM is significant, but from context I think you have the two confused. Turbos do not know about pressure, they flow air... nothing more.

But please understand this, that at 7.5 psi of boost, both turbos are moving the EXACT SAME AMOUNT OF AIR. It is impossible for pressure to be held constant if flow is not held constant! Pressure and Flow are inversely related! You cannot change one without changing the other.

The reason the t3/t04e turbo makes more power is that it is MORE EFFICIENT. It heats the air up /much/ less. For high pressure levels, the Greddy turbo will get to the point where it CANNOT flow enough air to maintain your set boost level in the intake manifold. The turbo will be overrevving past the SURGE limit to attempt to maintain boost, but it will be unable to. The t3/t04e is able to flow more air at lower shaft speeds OVERALL, so it can maintain these boost levels. For a given amount of flow, the slower the turbo shaft is spinning, the more efficent the system is. Thus colder compressor output air, thus more dense, thus more power.

Take for example the new WRX. It comes with a miniature size turbo (a little larger than the size of your fist). The thing will maintain 15psi of boost up till about 5000rpm, at which point the turbo CANNOT FLOW ENOUGH AIR to maintain 15psi of boost, and boost drops to approximately 10psi. The FLOW of the motor changed (higher rpm = more flow), the turbo could not compensate, so PRESSURE DROPPED.

Dustin

 

I don't speak with semantics... I just simpify what is said so that everyone can understand what I am trying to explain.... just being polite ..

The pressure created by a turbo is what would be measured at the manifold wall, the pressure in your air compressor is a contained enviroment, totally different concepts.

By CFM, I am referring to the turbo's, not the motor's... if you disagree that turbo CFM has no affect on performance, I am absolutely convinced that you are DEAD WRONG.... just to make sure, because you sound convinced and I am not gonna flame anyone because they disagree with me on this... I'm going to research this and explain why this is so.... (who knows, I might be wrong, but prolly not)

A smaller turbo stops creating power at a certain point because the compressor blades cause a disruption in air flow at a particular RPM.... the same holds true for a S/C....
A larger turbo has a different trim on the blade and often a different sized blade... as an example, take a look at the compressor side of a turbo. Larger turbos have a more aggressive trim, which will result in more air flow...period, that is why one would get a larger turbo, not just to boost more, but to have a more efficient power production (read: flow of air) at said boost

As far as the WRX, which is at 13.X psi stock boost with a small turbo, the reason they chose such a small turbo was spool time, not overall CFM.... I don't know off hand, what RPM does a WRX acheive full boost ? probably really low... the smaller turbo can push the air to a particular Psi quicker than a larger, more aggressively trimmed turbo, which would have a longer spool time, yet, at boost, create more power....
no one can explain this to you better than DSM guys.... #1 upgrade ? Bigger turbo !
This explains why the DSM guys are boosting 16-18 psi on the stock turbo and get pissed and go buy a larger turbo... running an eclipse with a high boost stock turbo vs. the same boost with a... ummm

* bathroom break..... b back soon.......

 

I hope you understand what I mean by semantics. I mean we are getting caught up on the way things are phrased, but we may very well agree.

Unfortunately, pressure is pressure.

Of course Turbo CFM affects performance! That is what I have been trying to tell you! Turbo CFM has NO RELATION to pressure though! The only way you can relate TURBO FLOW to INTAKE MANIFOLD PRESSURE is if you know the FLOW of the motor. Trying to say that XX turbo has XX CFM at XX psi of boost is absolutely worthless. It depends on how much air is flowing through the motor!

What is this about "disruption in air flow"? A/R and blade design determine overall CFM and spool time. Unfortunately your "compressor blades cause a disruption in flow" theory holds no water.

Didn't I just tell you this in my last post?

I just explained this entire thing to you in my last post!

I still think you misunderstand several things, though.

Dustin

 

Dustin, this is a discussion, you don't need to get rowdy...heh heh...


Actually, your prior posts are against this, which is why I said what I did in my previous posts... I don't think I am going to get thru to you judging by your reaction to what I am saying, From my experience as a teacher, I know when no to argue a point with certain people, so I won't bother with these sections of the post....


but I gotta go for the day, but you seem to be completely confused with what you are saying, or you are not relating your point properly.... maybe I'll check you tomorrow..... right now, my fingers are tired....

BTW, We are WAAAAAAYYY off topic.....

Laters, going back to my hotel....

 

My posts are consistent. Max turbo CFM and PSI mean nothing without the flow rate of the motor. I have explained this twice now (make that 3 times).

Manifold pressure is a relation of compressor flow to engine flow (cfm). The more air a compressor can flow than the motor can, the more pressure! You cannot rate a turbo by flow and /pressure/ alone, This is why compressor maps show engine flow on the X axis.

Well, I already understand how it all works. I'm just relating this for your education. I think maybe you are not relating your ideas properly or you misunderstand me... because I think we are saying the same thing.

But you are right, we are way off topic.


Dustin

 

This train of thought would lead to an assumption that any given turbo, regardless of trim or A/R housing size would generate the same Hp per psi of boost on the same motor all else being equal..... and this is not so, but, anyway....


Cool, we are way off topic, so maybe one of us is hard-headed, ok, maybe both of us.... Let's agree to disagree before FI mod decides to lock this post and make me feel all guilty.

Cheerz on a somewhat educated discussion, they have to happen sometime.


[Modified by X2BOARD, 8:01 AM 3/2/2002]

 

Id like to throw in a few things..

Boost: a measured amount of pressure due to a restriction in the flow path of air.

Volumetric Efficiency.

quote: dustin

"What is lost through higher shaft speed is efficency, in that the air is heated up. This is what you may be referring to... as the air is hotter and makes the motor more susceptible to preignition (and thus detonation)."

this is the biggest reason why larger turbos make more power for a given boost level. The larger compressor doesnt have to spin as fast and doesnt heat the air up as much.

CFM per PSI is hard to use when describing anything dealing with turbos. The CFM per PSI can be changed by changing the volume of the chamber being boosted. ex. 500CFM @ 20psi with X turbo through 4 inch piping and X motor is not going to be the same CFM per PSI if you change the piping to 2 inch and run it on twice the motor. Volumetric Efficiency.

jason

 

You guys always say "with proper tuning". With average tuning, like an AFC or even a FMU, the B engines can take 9-10 psi, if you baby the hell outta them. 6-8 if you're gonna put your foot in it. Does anybody remember 5 years ago when noone had standalone management?


[Modified by ZCTURBO, 2:55 PM 3/2/2002]

 

I have to agree with dustin that the turbo does not create pressure, but flow. The key is for it to try to flow more than the engine can ingest, thereby creating pressure. The turbo will never actually flow more than the engine, as that is impossible. Flow rate has to be the same throughout the system. Instead, it will try to flow more, and that's what causes pressure.

It's like trying to push a car. If you can't run (flow) as fast as the car, you will not be pushing it (0 pressure). If you can just barely keep up with the car, you will not be pushing on it either. If you can actually run faster then the car is moving, only then can you push on it. The car has to be there as a restriction to you running. If there's no car, hence no restriction, you can run as fast as you want but you won't be pushing on anything. I hope this makes sense, I'm known for bad analogies.

Anyway, if the engine was stopped and the turbo kept on spinning, flow would be 0 and pressure would go through the roof. Same if you blocked off the pipe by closing the throttle, hence a blow off valve. If there was no motor, just a straight pipe with no restriction, there would be no pressure. All the air would just flow through the pipe at atmospheric.

I really don't know how this relates to any other part of this thread, I didn't pay attention closely enough.


[Modified by Lsos, 11:02 PM 3/2/2002]

 

I have some for sale brand new..... check it out
https://honda-tech.com/zerothread?id=134945

By the bye, I ran 15 psi with stock pistons for a while - no problems at all.