The mathematics of the 8V vs16V problem

[jason at scirocco.org (Jason)]

Hey Brian,
         Good question.  Have a look again at the curves: 
http://home.netcom.com/~jdbubb/sitebuildercontent/sitebuilderpictures/Scirocco_dyno.jpg

         If you look closely, that drop is actually one side of a big bulge 
in the torque curve between 3750 and 4750rpm.  I can't know for sure, but 
that large increase in torque in a certain rpm range is most likely a 
result of a resonance in the intake.

         As air is drawn into the engine, though you would think that it's 
a steady stream, it's not.  Air gets sucked in as the valve(s)open, but 
then the flow of air stops when the valve(s) close.  This process repeats 
itself at a fast rate as the valves open and close.  As you've no doubt 
experienced while playing with yourself in the bathtub, any time there's a 
sudden stop of motion, the water (or air) will bounce back the other 
way.  At certain places in the rev range, this motion will happen just at 
the right time so that when the valve is opening, the air is bouncing back 
toward the valve... and it creates a ram-air effect pushing more air (and 
fuel) into the cylinders.  The result is an increase like you see on Dan's 
curve.

         Of course, it can also work the other way:  If it's timed right 
(or, "wrong"), it can cause a dip in the torque curve.  You can see that 
very clearly if you look at almost any 16V's torque curve.  The more tuned 
they are, the more pronounced the dip generally is.  Brett, our famous list 
host has been one of the few 16Vs to cross the 150whp mark without 
sacrifice to driveability...  He did a fantastic job designing an engine 
concept that eliminated all of those problems -- and as a result, his "dip" 
is far less severe than many.  But it's still there... check out this 
picture: http://www.scirocco16v.org/dyno/brett.jpg
You'll see a marked drop in torque from about 2750 to 4000rpm.

         Thus on Dan's 8V, there is some beneficial resonance happening 
between 3750 and 4750.  On the 16V, there's some negative resonance 
happening in the mid-range.  While I've never sought to prove that this is 
indeed the cause for the 16V's dip, that's likely the cause.

Jason





At 04:57 PM 10/20/2003, Brian Wagner wrote:
>Why does it fall off between 4 and 5k?
>
>Brian
>
>Jason <jason@scirocco.org> wrote:
>At 02:07 PM 10/20/2003, Dan Bubb wrote:
> >This dyno reflects my current state of tune although the mixture has been
> >richened up some since then since it's alittle lean here.
> >http://home.netcom.com/~jdbubb/sitebuildercontent/sitebuilderpictures/Sci 
> roc
> >co_dyno.jpg
>
>Now that, ladies and gentlemen, is a beautiful curve. Dan, I assume it
>took a lot of work to get to that point -- and congrats, that is by far the
>best example of a high-performance 8V I've seen.
>
>It's interesting to compare to the 16V curve I posted earlier... You
>obviously have a quite aggressive cam in there - your HP peak is around
>6000rpm; which is where you'll find it on cammed 16Vs. You have a nice
>torque curve. It's only slightly less torquey at low rpms than a 16V of
>comparable HP output would be -- so not only does it breathe well, but it's
>also not miserable down low.
>
>
>
> >Micropenis!! Ouch!
>
>lol -- a medical term, not an insult. :)
>Jason
>
>
>
>
>
>
>
>
>
> >----- Original Message -----
> >From: "Jason"
> >To:
> >Sent: Monday, October 20, 2003 12:27 PM
> >Subject: RE: The mathematics of the 8Vvs16V problem
> >
> >
> > > Heya Patrick,
> > > Thanks for posting that graph. Your torque curve illustrates
> > > exactly what I pointed out in my last mail:
> > >
> > > Even though your engine pushes out a very, very healthy peak of 
> around 118
> > > lb-ft of torque to the wheels, it manages only 98hp. Exactly as I said,
> > > the 8V concentrates its torque output down low in the rpm range - yours
> > > peaks at around 2700rpm. This is ideal for a daily driver -- around town
> > > at leisurely rpms, your car is at its happiest. It'll squirt off the 
> line
> > > like a beast...
> > >
> > > As you can see though, the torque curve peaks early and then falls off
> > > gradually as you approach redline. Horsepower is nothing more than 
> torque
> > > at high rpms. Since your car is making relatively little torque at high
> > > rpms, its Horsepower number is so much smaller. Horsepower isn't my
> > > favorite number when used to gauge the overall driveability and feel 
> of an
> > > engine, but it's the only number you need when you're talking about
> >all-out
> > > acceleration. At full-tilt, if geared correctly, a 240hp, 3000lb Honda
> > > with 180 lb-ft of torque will still be even with a 240hp, 3000lb V8 with
> > > double the torque.
> > >
> > > The reason why is simple: Under full acceleration, you're between, say,
> > > 4000rpm and redline all the time... save for the initial launch, which
> > > admittedly, if done properly, will be in that range, too. Ignore what
> > > happens at low revs on your chart, and you'll see why a stock 1.8 16V 
> with
> > > the same gearing will outrun your car... it puts more torque down at 
> those
> > > speeds and can rev 1000rpm more.
> > >
> > > Now, with that said: Driving your car and driving that stock 1.8 16V 
> will
> > > feel completely different. Let's say you and the 16V are puttering along
> > > in 2nd gear at 2500rpm next to each other, and you both realize that 
> your
> > > two lanes are about to turn into one, and you both gun it. The 16V will
> >be
> > > eating your hard-earned 8-Valve dust.
> > >
> > > Now, if you both kept your foot in it, the 16V would eventually catch up
> > > and walk away from you. But your subjective impression from the short
> >race
> > > will be of course, that your car is faster than a 16V.
> > >
> > > This is why I say quite clearly that the 8V is certainly not without its
> > > merits. The 8V versus 16V war is certainly akin to the V8 and big
> > > displacement versus VTEC and revs debate, albeit on a lesser scale. Flat
> > > out at the 1/4 mile, the VTEC Honda can keep up with the V8s. The reason
> > > is because the high revving motor will let you take advantage of 
> gearing,
> > > where the big V8 just pulls and pulls from low revs. You have to work
> > > harder to keep up in the Honda, but if you do, you'll be rewarded 
> with the
> > > same acceleration times as the big boys.
> > >
> > > So yes, your car will, without a shred of doubt in my mind, be a 
> whole lot
> > > more fun around town than a 1.8 16V would. Low-end torque is what the
> > > American public wants -- that's why we have Buicks with pushrod 3800
> > > V6s. They give fantastic acceleration off idle and feel powerful, 
> smooth,
> > > and fun -- until it's time to really get moving. When it comes to the
> > > stoplight race - or racetrack - or 1/4 mile track - or high speed race -
> >or
> > > Autobahn cruise, all of that advantage is lost, and indeed a stock 16V
> > > would be faster than your fun-to-drive, torquey and happy built 8V. It's
> > > just a matter of physics... not me trying to diss ya!
> > >
> > > Jason
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > At 10:40 AM 10/20/2003, ATS - Patrick Bureau wrote:
> > > >jason how about this 8v (mine) I think my torque curve is quite broad,
> >you
> > > >got 133ft'lbs, I got 118ft'lbs torque and in the same manner of the 16v
> >it
> > > >instersecs the HP curve. stock JH head and 2L bottom end with only a g
> >Grind
> > > >in it.
> > > >
> > > >
> > > >
> > > >is this what you where looking for ? or perhaps I did not understand 
> the
> > > >question.
> > > >
> > > >
> > > >
> > > >ATS - Patrick Bureau - txrocco@sbcglobal.net
> > > >----------------------------------------------
> > > >MSN:ATSGTX@hotmail.com |YAHOO:ATSGTX@yahoo.com
> > > >ICQ:32918816 |AIM:Texasscirocco
> > > >----------------------------------------------
> > > >
> > > >
> > > >=>-----Original Message-----
> > > >=>Case in point, please see the following curve:
> > > >=>http://www.scirocco16v.org/dyno/16V.jpg
> > > >=>This is a dyno plot from one of our veteran list members. It's a 2.0
> >16V
> > > >=>with a slightly P+P and shaved head; Schrick 260/276 cams, and an
> > > >=>exhaust. That's a relatively stock motor in my book -- the entire
> >bottom
> > > >=>end is completely stock.
> > > >=>
> > > >=>You'll see that not only does it peak out at 144whp and almost 133
> >lb-ft
> > > >of torque, but the torque curve itself is tremendously broad and
> > > >=>beefy: This engine puts more than 120 lb-ft of torque to the wheels
> >from
> > > >3000 until 6250rpm. That is a simply awesome number from a 2-liter
> > > >engine... and
> > > >=>flies directly in the face of any complaints of the 16V being a dog
> >down
> > > >low. And further, this particular motor puts down about the same torque
> > > >=>at 2000rpm that the 1.8 16V does at its peak -- just under 100 to the
> > > >wheels -- which is, as we know, more torque than any VW 8V motor
> > > >=>(including the ABA) did from the factory. So there's monumental
> >high-rpm
> > > >power (VR6 territory) with low rev torque besting all other VW
> >4-cylinders.
> > > >=>You just can't do that in an 8V VW motor.
> > > >=>
> > > >=>http://neubayern.net/mailman/listinfo/scirocco-l
> > >
> > >
> > > _______________________________________________
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>
>
>
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