[Diy_efi] New project- intake effect on VE on turbo car

[John Petersen]

Sorry, I thought you meant _just_ the pre-turbo effects. The turbo can
require a lot of energy to go. In the book Maximum Boost by Corky Bell
he says that exhaust manifold pressure should not exceed 3 times intake
manifold pressure... Running 3bar absolute would yield 9bar exhaust
manifold pressures (max)... _That_ will create an effect on VE, far more
than the plumbing before the turbo would.

Thanks,
John Petersen
The Underwood Group
5001 Weston Parkway
Suite 105
Cary, NC 27513
800-409-4498
919-677-1824

-----Original Message-----
From: diy_efi-admin at diy-efi.org [mailto:diy_efi-admin at diy-efi.org] On
Behalf Of Geddes, Brian J
Sent: Thursday, November 21, 2002 3:33 PM
To: diy_efi at diy-efi.org
Subject: RE: [Diy_efi] New project- intake effect on VE on turbo car

Pretty much what I was figuring.  This question stems from a technique
I'm using to generate speed density fuel maps for my car.  In order to
make tuning safer and easier, I disconnected my turbo outlets and put a
K&N air filter directly on my throttle body.  The turbos are now blowing
into the engine bay.  With the turbos disconnected, WOT is a constant
load (around 100kpa, give or take barometric pressure), which has
enabled me to generate a fuel curve at this load that holds 14.7 +/- .1
AFR points from 2000 to 7500 RPMs.  

The next step it to reconnect the turbos, and scale this curve to higher
load points (ie 200% at 200kpa, 300% at 300kpa, etc).  I'll of course
richen the curve higher than 14.7:1 at boost, but having the basic shape
of the curve should make it MUCH easier to get a consistent AFR under
boost conditions.  BTW, the idea's not mine - Derek Obanion mentioned it
to me and I decided to try it.  

Assuming my naturally aspirated VE curve stays relatively constant when
corrected for boost pressure, my tuning life will be much easier.  I
hope.  :)

- Brian

> -----Original Message-----
> From: John Petersen [mailto:john at underwoodgroup.com]
> Sent: Thursday, November 21, 2002 12:08 PM
> To: diy_efi at diy-efi.org
> Cc: Geddes, Brian J
> Subject: RE: [Diy_efi] New project- intake effect on VE on turbo car
> 
> 
> Quite a can of worms. Here's a hack at it.
> 
> Simply put, yes, the intake tract affects VE... but not a 
> heck of a lot.
> 
> Let's say that you have an EXTREMELY restrictive intake on your car,
> before the turbo. The turbo will attempt to build boost pressure, and
> will have to spin very fast to get boost to where it should 
> be (the ECU
> should do its best to get it to whatever preset boost level is
> specified, in absolute pressure terms). To spin the turbo "very fast"
> you need to provide exhaust energy. You effectively make an exhaust
> restriction by having an intake restriction. 
> 
> There are more important reasons to have an efficient intake tract.
> Primarily that you 
> a)want the turbo to be running at the lowest PR possible. PR 
> is measured
> on both the compressor inlet and outlet, not by the barometer on the
> wall and the manifold boost gauge.
> b)spinning the turbo fast generates a lot of heat on the intake, while
> it might not make a huge difference if you have an enormous 
> intercooler,
> it might cause your engine to ping-ping-ping due to excess 
> heat if your
> intercooler isn't dreadfully oversized.
> 
> Hope this helps
> -John
> 
> -----Original Message-----
> From: diy_efi-admin at diy-efi.org [mailto:diy_efi-admin at diy-efi.org] On
> Behalf Of Geddes, Brian J
> Sent: Thursday, November 21, 2002 2:41 PM
> To: diy_efi at diy-efi.org
> Subject: RE: [Diy_efi] New project
> 
> On a turbo car, is VE effected by pre-turbo intake path 
> characteristics?
> It seems to me that since the turbos are "pushing" the air at the
> throttle body, pre-turbo intake wouldn't matter to VE.  But it would
> affect maximum boost level...compressor efficiency as opposed 
> to engine
> efficiency, I guess.  Is this the way it actually works?
> 
> - Brian
> 
> > 
> > No, it's much more subtle than that.  Volumetric efficiency 
> > captures the
> > entire path of the air from the atmosphere through the air filter,
> > intake ducting, throttle body, plenum, runners, intake 
> > manifold, ports,
> > valves, cam timing/overlap, etc.  If air was incompressible and
> > inviscid, then you would be correct that simply knowing the 
> > displacement
> > of the cylinder and air's temperature and pressure would be 
> sufficient
> > to determine exactly how many air molecules entered the 
> cylinder.  In
> > fact this is the definition of 1.0 or 100% VE, the amount 
> of air that
> > would enter the cylinder if the air was some ideal fluid that has no
> > compressibilty or resistance to flow or other dynamic effects.  But
> > that's not the case, and it's not something that you can calculate
> > analytically.  You could get a rough initial map by assuming 
> > a constant
> > VE (of around .7 or so) for all spots but it will certainly 
> need some
> > refinement.
> > 
> > Brian
> > 
> > _______________________________________________
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> > 
> 
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