Westrock2000

I found this on searching, didn't really explain my coming question and posted over a year ago. I know what the parts do, and how its supposed to be setup, but I want to know the really deep scientific part.

Anyways tell me if this is correct and help me understand what most "how they work" website don't explain. [ <u>please feel free to direct me to any websites that explains this</u> ]

<FONT SIZE="4">Flow of engine in relation to flow of turbo</FONT>

An engine flows a certain amount of air at a certain RPM...lets say 150CFM at 3000RPM, and 300CFM at 6000RPM. This is under normal N/A conditions.

So in order for a turbo to create "boost", it has to flow some amount larger than whats being used? The turbo would have to flow &gt;150CFM while the engine is at 3000RPM? The amount that it flows extra creates a pressure on the intake tract, thus creating the boost.

So if this is correct, then lets say that <FONT COLOR="red">(all arbitrary numbers by the way...)</FONT> a turbo flowing 350 CFM while the engine is using 200 CFM would leave an excess of 150 CFM. Now I may be tempted to say that this might create a positive pressure of 6 PSI, <u>but wait</u> if the turbo is pushing with a certain force (350 CFM in this case), could it not force the engine to flow slightly higher? Say 220 CFM, since the engine not operating under its own force any more? So now we have 130 CFM left over, does this now create the "boost"? So as the turbo pushes more volume of air, the engine is forced to flow more and more? So an engine that flows normally 200 CFM, may be flowing 300 CFM when an outside force of 500 CFM is pushing on it.

So if we have an engine that flows 200 CFM @ 5000 RPM's and a turbo is put on that has no wastegate (running "full output" or whatever) and it maxes out at 500 CFM, it may create 10 PSI on said motor. So if we put larger valves or even bore the engine out and raise the normal flow of the engine to 230 CFM. Since the engine can ingest more air, but the turbo still can only put a max of 500 CFM, will the boost actually drop to like 9 PSI?

<FONT SIZE="4">Turbo</FONT>

Now moving to the turbo itself, if all my previous logic is somewhat correct, then it seems that two turbos would operate at the same PSI, if there volume (CFM) is the same at any given point. For instance a small turbo flowing 350CFM and creating 6 PSI on an engine, could be replaced by a larger turbo that would also create 6 PSI when flowing 350 CFM, the difference being that the smaller turbo will have to spin much faster due to its smaller impeller moving a smaller volume of air with each rotation....the downside being the larger turbo has larger impellers, thus it takes more flow to get it moving the same RPM as the smaller (but not always much, by messing with AR's).

<FONT SIZE="4">Different turbo's putting out different powers at same PSI</FONT>

This question would almost hint to negate everything I have just considered, because it would imply that two different turbo's are pushing out different amounts of air at the same PSI. Thus, it would say that PSI is not a relation of flow...at least not the way I explained it. So it makes me wonder why a little t25 running at 10 PSI would make less power than a t4 running at 10 PSI (on the same engines of coures).


<FONT SIZE="4">Wastegate</FONT>

Now the wastegate simply maintains a &lt;somewhat&gt; constant PSI reading by allowing the excess exhaust air volume to bypass the turbo. Thus a smaller turbo may bairly be able to stay ahead of an engine, thus the wastegate doesn't have to bypass much air to maintain the 6 PSI boost level because the turbo needs all the exhaust gases to reach the output due to a higher &lt;turbo&gt; RPM requirment, however a large turbo with its larger impellers puts out more air with each rotation, thus may only need half the exhaust gases to maintain 6 PSI, thus the wastegate bypasses half the exhaust gases around the turbo.

<FONT SIZE="4">Killing the resonance</FONT>

Also on a turbo, since its doing all the work, I'm assuming that intake manifold designs have little(er) effect on the engines powerband as they do on N/A...since you don't have any problem building "pillars" of air in the runners...its not the usual long runners for low RPM and short runners for high end type affair??

<FONT SIZE="3">Is this at all right????</FONT> I think most poeple might wonder this too, but are embarrassed to admit they they know so much about how to setup and use a turbo, but don't really understand how it work

Like poeple who have 1000W stereo's that can be heard 4 miles away, but they don't know any of Ohm's laws or how a voice coil works.


Thanks in advance


EDIT: damn thats alot of typing!

DSF

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Westrock2000 &raquo;</TD></TR><TR><TD CLASS="quote">Flow of engine in relation to flow of turbo</TD></TR></TABLE>

Basically, what you said, in a round about overly confusing way. Engines, turbo, superchargers, etc. have their own flow characteristics. Just try not to think of them in such a linear fashion. Ever seen a turbo move the same amount of air at two different pressure ratios

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Westrock2000 &raquo;</TD></TR><TR><TD CLASS="quote">Turbo</TD></TR></TABLE>

Uh...no. Pressure and flow are not linear factors and are very different for each device. Things like a.r., number of blades, blade pitch, wheel size, trim, all effect the the flow curve of the turbo. That doesn't give you a complete picture though as piping, IM, engine all change the system effect...how the turbo will really act attached.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Westrock2000 &raquo;</TD></TR><TR><TD CLASS="quote">Different turbo's putting out different powers at same PSI</TD></TR></TABLE>

See above. Pressure and flow are interrelated, but each device has it's own curve/map.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Westrock2000 &raquo;</TD></TR><TR><TD CLASS="quote">Wastegate</TD></TR></TABLE>

Basically.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Westrock2000 &raquo;</TD></TR><TR><TD CLASS="quote">Killing the resonance</TD></TR></TABLE>

Nope. All the design criteria for a N/A engine still apply to a F/I engine. Your still dealing with the properties of fluid dynamics and the physics don't change whether you run N/A or bolt on a T77. Remember, while the turbo is putting out a relativively constant flow, the engine still uses it in gulps.

Best I can do this early in the morning before breakfast. Do some reading from Corky Bell's "maximum Boost". Good primer for F/I. Also, read up on HVAC material....very related. I should know

Boltz

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Westrock2000 &raquo;</TD></TR><TR><TD CLASS="quote">Thus, it would say that PSI is not a relation of flow </TD></TR></TABLE>

Pressure is resistance to flow

DSF

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

Pressure is resistance to flow</TD></TR></TABLE>

Yes and no It's according to what pressure your measuring.

Vp = Tp - Sp

CFM = 4005 * sqrt. (Vp) * Ak