Re: Adding some pep- LONG.

On Sun, 2 Apr 2006 18:59:29 -0400, "RCE" <rce@xxxxxxxxxxx> wrote:


"Will Sill" <will@xxxxxxxxx> wrote in message
news:fqj032l6aavkcsck5n54hspcr7d74p0n50@xxxxxxxxxx
I see where "Bro***" wrote:

In order to market a vehicle which is affordable to the masses,
compromises
are inevitable.

True but irrelevant to the issue of whether exhaust mods alone boost
low-rpm performance enough to be noticed.

The accountants are running the Big 3, not the engineers.
In the case of headers, they are definitely more expensive than a cast
iron
manifold. Take this differential in cost times the number of vehicles
produced and you very quickly get your answer that trumps "gas flow
dynamics". Now take part of this saving and spend it to install fake
wood
grain in the interior and you have a much greater appeal to Mr. and Mrs.
Joe
Q. Public, who for the most part, wouldn't know the difference in engine
efficiency if it bit them in the ***. It would be interesting to know
how
many motorists do not know where to find their hood release! If you want
to buy a vehicle that is engineering driven, you will need to open your
wallet VERY wide and that car might not have his and her cup holders.

Interesting and even partly true, but also irrelevant.

Disclaimer: have no engineering degrees, real or imaginary. But, when I
installed headers and dual exhaust on a 350 cu in Chev C class, the
quadrajet carb also had to be changed so as to richen the mixture. Why?
Because the engine was now running lean - the throttle response was
sagging
and the spark plugs were showing white rather than the desired tan color.
Since more air was leaving the engine (maybe due to the better exhaust??),
this allowed more air to enter through the carb. Since the engine
requires
a certain ratio of atomized fuel to air to operate efficiently, the fuel
portion needed to be increased.

Without realizing it, you just presented one of several reasons why
bolting on aftermarket pipes won't do the job all by itself - and is
also irrelevant to the issue of whether exhaust mods alone boost
low-rpm performance enough to be noticed.

Will Sill
Law of Logical Argument: Anything is possible if you don't know what
you are talking about.


I tried finding some actual, measured data that shows significant gains in
low RPM torque by simply changing the exhaust system and adding custom
performance headers. Can't find any yet, other than advertisements. There
is data on horsepower gains at a specific RPM .... all high RPM's BTW. I
did find an obscure note that in some cases (this happened to be BMW), the
higher horsepower gains achieved with expensive headers and custom exhaust
came at the expense of lowering low end torque, not raising it. Another
technical article also said that a custom exhaust/header is tuned for a
specific performance range and typically low end torque is achieved with
small diameter exhausts and high end horsepower is achieved with large
diameter exhausts.

I see it like this. Forget about fuel injection for a moment and think
carburetors. A big block engine might have a 650-750 cfm carb. That's the
amount of air it would suck in wide open at high RPM.
Any throttle setting less than pedal to the metal at 5000 RPM will suck less
air. So, the exhaust system has to be big enough to get rid of , say 650
cfm. At 1500 or 2000 RPM the amount of air moving through the engine is
less than that. Assuming the car/truck/RV was reasonably well designed, I
just can't imagine the exhaust system being a torque limiting issue at 1500
to 2000 RPM, assuming it can handle at least most of the 650 cfm potential.

RCE

Hi,
You are right, nobody I know tows at max RPM with a gas engine. There
are a few places I've seen where they give what the pipe diameter
should be for X amount of engine horsepower. Putting larger pipes on
aren't going to help much even at max HP and could hurt at lower ranges.
For the reason you said. The pipes are already big enough to handle the
max air flow and you could hurt the scavenging properties of the exhaust
at lower RPM's with to big an exhaust.

Take care and Happy Campin...

--
RichA
"We Get Too Soon Olde and Too Late Smart"
.

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