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

[Geddes, Brian J]

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. =20

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. =20

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
>=20
>=20
> Quite a can of worms. Here's a hack at it.
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> Simply put, yes, the intake tract affects VE... but not a=20
> heck of a lot.
>=20
> 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=20
> 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.=20
>=20
> There are more important reasons to have an efficient intake tract.
> Primarily that you=20
> a)want the turbo to be running at the lowest PR possible. PR=20
> 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=20
> intercooler,
> it might cause your engine to ping-ping-ping due to excess=20
> heat if your
> intercooler isn't dreadfully oversized.
>=20
> Hope this helps
> -John
>=20
> -----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
>=20
> On a turbo car, is VE effected by pre-turbo intake path=20
> 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=20
> to engine
> efficiency, I guess.  Is this the way it actually works?
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> - Brian
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> >=20
> > No, it's much more subtle than that.  Volumetric efficiency=20
> > captures the
> > entire path of the air from the atmosphere through the air filter,
> > intake ducting, throttle body, plenum, runners, intake=20
> > manifold, ports,
> > valves, cam timing/overlap, etc.  If air was incompressible and
> > inviscid, then you would be correct that simply knowing the=20
> > displacement
> > of the cylinder and air's temperature and pressure would be=20
> sufficient
> > to determine exactly how many air molecules entered the=20
> cylinder.  In
> > fact this is the definition of 1.0 or 100% VE, the amount=20
> 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=20
> > a constant
> > VE (of around .7 or so) for all spots but it will certainly=20
> need some
> > refinement.
> >=20
> > Brian
> >=20
> > _______________________________________________
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> >=20
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