Re: engine decision's...)

[Shawn C Meze <skerocdriver@juno.com>]

On Mon, 6 Aug 2001 21:41:41 -0400 "Scott F. Williams"
<sfwilliams@home.com> writes:

>That's all very well. You may have made the bends to restrict the flow,
but
>what you were really doing was altering the timing of the exhaust shock
wave
>to coincide with the exhaust valves opening. By timing the wave to
impact
>the freshly expelled (and unburnt) fuel/air mixture while the valve is
open,
>you force the charge back into the cylinder and thusly make more power 
>in the process.


Ummm. dude. I think you just described a backfire. LOL!!

Well, in this example of the Chevy 460 CI alcohol burning funnycar, the
headers were as I said, Zoomie headers meaning, each cylinder had its own
exhaust pipe. No 4 into 2 stuff here. real racing stuff.

Ill try and express the effects of port scavenging with back pressure
like this:
its like syphoning water with a tube from a tank of water to a little
bucket. (The tank and buckets are not important, just for a visual. Pick
the colors you want them to be. be happy. I want you to be happy. Keep
the colors to yourself. -K-?)

OK, once you get the water to start flowing out of the tank into the
bucket thru the hose, what maintains the water flowing is the water that
is in the hose. It draws out more water and will do so until the tank is
empty. This is how a slight restriction in an exhaust system helps draw
out more of the exhaust gasses thusly allowing the refreshment of
air/fuel to flow into the cylinder without having to share space with the
icky burnt fuel. 

Too much restriction is just that, a restriction and hurts power. Just
enough and its free power. That's why the tube we used was only brought
down 3% from its original size. On a 14-1 race motor That's not a huge
difference. If you look at some of the top fuel cars, check out he header
where it bends under the body. Look at how small it gets there. its not
because they couldn't mandrel bend it. Its because they intentionally
build into the system a specific amount of restriction.

Other racing bodies that have recently been forced to use mufflers and
even Catalytic converters have discovered that the cars make more power
now than when they were completely uncapped. 

Trans Am
Sprint cars
Mid level Drag Racing
Mostly roundy round V8 stuff. 




>Incorrect. Timing the shockwave was your elusive quest. If it were 
>just a
>matter of adding restriction then you would have just plugged the 
>existing exhaust tubing.


Its not just a matter of adding a restriction. Its the size and shape of
the restriction. A simple plug, as you suggest would gain nothing. 

Ive looked at the shockwave theory and also have imputed its use on a few
systems. I think its safe to say that the typical VW motor doesn't flow
enough to make use of the mathematics available for decent power gains.

Have you ever cut a small section off the exhaust tip to break the
shockwave as it exits the exhaust? its reported to make more power as
well. (less restriction for the wave to penetrate.) Ive never noticed a
difference. 


>You'd still make better power all around if you could find a
high-flowing
>and less restrictive exhaust. 


Absolutely. As an example, if a stock system was say, 20% restrictive
then the ultimate system would be less than 5%. 

Here was mine at the dyno: 
Eurosport race header with Eurosport 2" mandrel bent to a dynomax
muffler. No mid pipe. It flows.

Its an 1835cc 8v with lots of detail work done. It revs strong up to a
7200 redline. The loss of torque and hp can be directly linked to the
header. The primaries are way too big for this motor. I will put the dual
outlet manifold and eurosport downpipe back on it and re-dyno the car.
This should be most interesting. 


>Often you won't get one without the 
>other, but
>pipe diameter and flow are not necessarily linked. 


See, I disagree. The size of the primaries are absolute KEY to making
great power. Large ass primaries (bigger than the exhaust ports flow)
will do more to restrict flow than allow flow. As the exhaust pulse
exits, it swirls into a confused vortex of lost power. A smaller matched
primary will guide the exhaust pulse out of the cylinder and power is
made. This is why I believe that the header I have on my car is better
suited for the massive P&P head and CR That's on my 84. The head on my
82, as per the rules of FSP can not be ported. The dual outlet manifold 
has already been port matched for this motor and when I got the header,
the dual outlet manifold we delegated to the 84. Not smart planning on my
part but I wasn't planning on building a 150hp motor just so the wife can
drive to work. Me now thinks this will make a good weekend track car and
I might just take to for the road race at dubwar.
I digress.....


>For instance, you could
>take a bigger diameter pipe and then ceramic coat it to retain more 
>heat.


Yes, but this is a small gain in comparison. if the primaries are larger
than the exhaust port it cant flow more than what can exit the port, no? 




>You upset the acoustic tuning and/or the scavenging effect. The
restriction
>in the exhaust may have been lowered (good!) but the positive effect 
>was offset by the aformentioned negative conditions.


The acoustic tuning has never been better! (Yeehaww!!
BRAAAAAAAAPPPPPPPP!!!) 
Seriously. it was nothing more than an open exhaust right off the header.
How could anything of been "hurt". If anything, according to your
theories, it should of been better since it was much less restrictive. 



>Think about it, Shawn. If an engine is a glorified air pump, and exhaust
>volume/velocity is inextricably linked to operating efficiency, then how
can
>a restriction of that said exhaust increase the power? It can not and 
>it does not.


Yes it can and it does. Pbbbbbbbbbbbbthhhhhhhhhhh!!


>-not even in sunny San Diego. ;^)


Uh-huh. so there. :)


Shawn Méze
86' Jetta GLi 8V       84' Scirocco 8V           88' Corvette -SS 30-
82' Scirocco GTi -FSP 54-     79' "Project FSP Scirocco"
The Fastest, Quickest, Cleanest and best looking Scirocco in all of San
Diego!
http://www.Geocities.com/MotorCity/Speedway/1308/index.htm

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