Lifting Stains... and Gains

[JShadzi at aol.com]

Rob, in a supercharged application which is getting boost from crank speed not exhaust speed, greater overlap will cause power loss due to lost boost.  So yes, no need to go to a more aggressive cam really unless you are looking to take some power off the bottom and add it up top for greater peak power.

In a turbo applicaiton, however, increased overlap isn't quite *as* bad of a thing.  Unlike a supercharger where boost out the exhaust heads down the exhaust, in a turbo application boost heads back through the exh turbine, thus creating more boost energy on the intake side.

I'm more of a proponent for agressive overlap (relatively speaking) in turbo applications than most since unlike a supercharger, a turbo can actually help spool itself up with a little overlap.

Javad

> Good conversation fellows...But I have been wondering this now....
> I run a 2.8 30 v V6.  It is aftermarket supercharged....
> SOOO....would I gain anything by adding a cam, or would I be blowing too
> much boost out through valve overlap?
>
> > -----Original Message-----
> > From: quattro-admin at audifans.com [mailto:quattro-admin at audifans.com]On
> > Behalf Of QSHIPQ at aol.com
> > Sent: Monday, January 28, 2002 9:24 AM
> > To: mlped at qwest.net; quattro at audifans.com; 200q20v at audifans.com;
> > s-car-list at yahoogroups.com
> > Subject: RE: Lifting Stains... and Gains
> >
> >
> > --
> > [ Picked text/plain from multipart/alternative ]
> > Michael:
> > Comments inserted below:
> >
> > >"Early AAN Head Stock Bench Flow Baseline"
> > >INTAKE - measured in Inches (") of lift / cfm
> > >Lift      Cyl1    Cyl2    Cyl3      Cyl4    Cyl5
> > >.050       39.9    39.9    41.5       40.7    37.6
> > >.100       74.0    72.2    75.5       74.5    72.2
> > >.150      100.2   102.4    103.3      100.3    99.2
> > >.200      132.6   128.9    130.9      131.6    132.0
> > >.250      159        155.1    161      158.4    157.5
> > >.300      177.2   175.5    178.8      178.4    175.3
> > >.350      185.8   185.7    188.8      190        184
> > >.400      188.2   190.3    193.6      194.4    188.2
> > >Total 1,056.9 1,050.0 1,073.4 1,068.3   1,046.0
> >
> > Mike:  you are adding the wrong way.  Totals are not lift cfm
> > vs duration,
> > it's total cfm AT a given lift.  So your total for .400lift
> > is 954.7....
> >
> > >EXHAUST - measured in Inches (") of lift / cfm
> > >Lift      Cyl1    Cyl2    Cyl3      Cyl4    Cyl5
> > >050       31.8    32.9    33.1       31.8    31.7
> > >.100       61.2    61.2    62.5       61.4    60.4
> > >.150       85.5    84.8    85.9       84.1    84.8
> > >.200      109.1   111.3    110.6      108.9    108
> > >.250      120.3   123    123.5      120.9    119.8
> > >.300      126.5   128.4    129.5      127.3    125.2
> > >.350      129.5   132    132.7      129.7    128.2
> > >.400      131.4   133.7    134.8      131.4    129.5
> > >Total   795.3   807.3   812.6   795.5     787.6
> >
> > See above: at .400 lift you have a total flow out of 5
> > exhaust valves of
> > 660.8.   IMO, it would be interesting to compare these
> > numbers with the RS2
> > exhaust cam.  Looking at the above (as I'm sure porsche did),
> > I'd want better
> > exhaust numbers.  This would also reflect the pretty
> > impressive gains in
> > torque just adding a RS2 cam to the AAN delivers.
> >
> > Current theory on the turbo heads is almost opposite the N/A
> > heads.  Since
> > you have boost pressure as a variable, that really is
> > "effective" valve area.
> >  IOW, you can change the size or lift of the intake valve, OR
> > add boost, both
> > do the same thing.  In N/A cars you can ONLY add valve size
> > or lift for
> > effective valve area.
> >
> > >Last, I offer for free beer conversation the following
> > hypothesis regarding
> > >heads, valves & "pressurized" operations thrown at me by one
> > porting maven
> > >confronted by the question, "Well, if all that polishing and
> > grinding you
> > >are doing isn't generating a number better than anything
> > above, what the
> > >hell are you doing?"
> >
> > Well here's where the magic starts...  Javad is right that
> > these numbers all
> > give you the theoretical amount of flow, and that reducing
> > the restrictions
> > TO a valve is key.  This includes a bunch of variables to
> > make it optimal:
> > temp, pressure and flow.  The smoother the flow TO a valve,
> > the closer you
> > are to the ideal flow the valve generated.  These numbers
> > also don't include
> > engine volumetric effieciency, which then includes cam
> > overlap, exhaust pulse
> > theory etc....
> >
> > >Bleary eyed hypothesis/theory/defense (??), "Well, A**H**,
> > it don' make no
> > >difference in a pressurized car.  Pressurized {editorial
> > clarification here,
> > >i.e. super & turbocharged applications) cars don't need to
> > worry about all
> > >that flow bench B*S* (s/he'd had more than a few beers, and I believe
> > >his/her SO had recently tossed them out of the house, or
> > something like
> > >that.)  If'n its pressurized, all you want to be go'n fur is
> > SIZE!  S/he
> > >told me "SIZE matters.""
> >
> > Vixen; it does, but the caveat is it's EFFECTIVE size that
> > matters (insert
> > all inuendos here).  In a pressurized car, size is created by
> > boost pressure
> > or a bigger valve or more lift, in a N/A car, size can only
> > be created by a
> > bigger valve, or more lift.  That's why many of us turbo
> > tweeksters (me
> > included, 2.5mm larger EV) leave the intake valves stock, go
> > (physically) big
> > on the exhaust valve.   The side benefit, is more exhaust
> > energy to spin the
> > turbine.
> >
> > I'm hoping you can buy me those Fat Tire Ales after I
> > terrorize Steamboat
> > this weekend.  Monday?
> >
> > HTH
> >
> > Scott Justusson
> >
> >
> >