Re: Correcting for 80% VE - just more questions then

[QSHIPQ@aol.com]

In a message dated 97-10-31 01:44:32 EST, you write:

<< 1. Why?  Are you saying that a larger turbo is less efficient at
> producing boost than a smaller turbo?  Correct me if I am wrong, but I
> thought that larger turbos were more efficient at making large
 >quantities of boost and smaller turbos spool up faster at the loss of
 >top end boost.  One might make the assumption that if a smaller turbo is
 >better then smallest is better yet.  I know that is not true.  SO why
 >would a smaller RS2 make more dense air than a larger more efficient at
> generating high boost turbo?
Glad to see you are reading up on this Randall.  No, I'm not saying that at
all.  Larger turbos "can" create larger amounts of boost than a smaller one,
but at what CE?  Remember CE is the ability of the exhaust gasses to
translate the chosen turbo to boost pressure at the highest efficiency>lowest
outlet temps.  2.79 @ 500CFM is a really high PR for a relatively low CFM...
 That is a good indicator that something ain't right.  Specifically it takes
massive exhaust velocity to produce a very low flow.  Wrong turbo.  A
3.0Liter porsche motor only needs 2.08PR to produce that same 500CFM, so
efficiency, by definition is WAY down.  Again, since I don't know what Eric
has, I'm giving an example here, but regardless, if it takes 2.79PR to get
500CFM, you have the wrong turbo.  Why?  Cuz if another turbo can get that at
a lower PR, then the DR is higher as well, so is the CE, by extension.  
  >>
>2.  Why compare a 20v motor with the RS2 to a 10v motor with the hybrid
>turbo?
>173*2.5=432.5CFM.  By my calculations that is an 11% drop in CFM and HP.
You assume a CE map to be pretty small.  As a general rule 20-25% variations
from the "given" point are easily within the same CE.  I also assumed a
higher VE for Eric, giving him the B.O.D. that all his mods got him the
efficiency of the 20v crossflow head.  Some called me crazy.   Forget that it
goes on a 20v car.  Look at it in terms of PR vs Flow only. Good question
tho.

>3.  Ask those who programmed the box.  The other car has seen over 80in of
>boost out of one chip.  Therefore, the boost has been governed by the
>chip.  I do not happen to be privy to such details of the program.
NO you don't.  Cuz if you did, you would know that controlling 2.79PR with a
2.5PT is not possible, not without dividing down the voltage (not the claim).
 A 2.5bar PT will give a max voltage out at 2.5bar (usually a little less
than that actually).  So with a stock spring, what is keeping the boost at
2.79 Randall?  Couldn't it just as easily be 3.0?  Not without dividing down
the voltage.  But why?  You could divide down the voltage of a 2.0bar PT to
do the same thing.  Remember 80 Hg of boost at sea level is 35psi.   Are you
sure you have that right?  Let me know before I respond to that part.

>4.  What I still do not understand is how you differentiate the turbos
>from one another  in your equations.  Lets say I have the Joe Schmoe
>brand turbo that can just barely blow 2.50PR does the efficiency of the
>turbo hold equal to the RS2 or is the DR lower because of the air being
>hotter due to la ess efficient turbo?  I think any assumptions you are
>making about the density of the air to the engine is just that an
>assumption.  I think the bigger turbo works less to make the boost and
>therefore has a higher air density than the RS2.  
Well, the claims presented don't let you make the assumption here.  IF the
question is, can a larger turbo flow more air than a smaller turbo at a
higher DR?  YOU BET, but not in the case of Erics turbo, and why I won't call
Ned and tell him he is wrong either.  2.79PR at the intake manifold can be
backed upstream and TELL you what the ICE and VE have to be.  In this case
it's a little incredulous.  You need to increase the DR with the PR if you
are going to a 2.79PR turbo vs a 2.50PR RS2.  If we take Eric's claim of
2.79PR, given the motor size and VE, the RS2 will flow the same amount of air
at a lower outlet temp = lower DR.  For me to evaluate the J.S. turbo, you
need to give me a number.  "just Barely" indicates that the PR is higher to
achieve the same output, so CE  would be less, if that's what you are trying
to say> higher heat.

Air Density is figure into the MAP in CE Randall.  I don't have to Assume
anything.  It can TELL you what the IC efficiency has to be.  The more
efficient the IC efficiency, the higher actually is the turbo outlet temp.
 Look hard at what Dave did in the math section of his post.  He did it
assuming 2.79 is at the turbo outlet.  That is NOT the claim.  The claim is
that 2.79 PR is at the MANIFOLD.  Backing that up, really shows that the
claim and turbo is prolly even that much further off.  

Thanks for taking the time to really think on this.

Scott Justusson, RS2 wannabe