I can tell you that with my old V8 truck, I drove to the exhaust shop with
open headers, and man was it a dog. Not only that I actually watched my gas
gauge moving leftward, I must have been getting like 1 mpg.....
Josh
"Jon Steiger" <jon@dakota-truck.net> wrote in message
news:998vh4$poe$1@bent.twistedbits.net...
>
> Hey, lets see if we can inject some technical discussion here. :-)
>
> I've been meaning to ask about this for a little while, and Tim Hawbaker's
> recent post reminded me of it...
>
>
> What I would like to know about is exhaust backpressure and just
general
> exhaust design as it relates to horsepower and torque. As Tim mentioned
in his
> post, he has heard from people (and we have all heard this) that some
> backpressure is needed or you will lose power. I have especially heard
this in
> relation to the V6 and there are 6ers on the list who (I think) have
> experienced losses from a 3" exhaust which was gained back when they went
to a
> 2.25-2.5". We have also heard about the folks who have installed headers
and
> driven to the exhaust shop basically with open headers (or at least an
open Y
> pipe) and have said the truck ran like a dog.
>
>
> I have several of the SA Design books, and in the "How to Build
Horsepower"
> series by David Vizard, there is a section on exhaust design. Vizard
> specifically mentions how people say that an exhaust should have some
> backpressure and he goes on to explain in no uncertain terms that this is
pure
> BS. According to his personal experiences (thousands of dyno runs),
decreasing
> exhaust backpressure also increased horsepower (99.9916030267125f the
time); something
> along those lines. Now, he DOES say that just changing a component CAN
lead to
> power loss. For example, changing to a low restriction muffler without a
> corresponding adjustment in the fuel or timing curve could cause a loss of
> power. But its not because of less backpressure, its because the system
is no
> longer tuned as a whole. Unfortunately, in the entire exhaust section, I
don't
> see any references to torque, just HP. Perhaps free flow does increase HP
but
> at the expense of low end torque? If so, this is something that the
haulers
> and offroaders need to know about. As we all know, power is more than
just a
> peak HP number; you also need to consider torque, and not just as a peak
> number, they need to be considered as a band.
>
> I guess the least backpressure would be had by open headers. The
musclecar
> and hot rod crowd will always "uncork the headers" to get the best times
at the
> strip. If this didn't work, I suspect they'd stop doing it. :-)
However, as
> I mentioned before, we have personal experiences from folks on the list
that
> show open headers on our trucks really drains the power. Is this merely
> because the system is no longer tuned as a whole, or is it really
decreasing
> the power potential?
>
> Related to this would be the whole "exhaust tuning" area. Carefully
measured
> full length headers, carefully placed H & X pipes, tri-y headers, etc.
> Obviously there are things you can do to an exhaust system beyond the
basics
> such as single or duals and pipe size. These items obviously also have an
> effect on performance. Unfortunately, except for the few formulas
available
> from the usual sources, this whole area appears to be a black art.
>
> So... Does anyone out there have any experience in this field? Any
> theories? I think it would be really cool if we could shed some light on
this
> whole situation.
>
> --
>
> -Jon-
>
> .---- Jon Steiger ----- jon@dakota-truck.net or
jon@twistedbits.net ------.
> | Affiliations: AOPA, DoD, EAA, NMA, NRA, SPA, USUA; Rec & UL Pilot -
SEL |
> | '92 Ram 150 4x4 V8, '96 Dakota V8, '96 Intruder 1400, '96 FireFly 447
|
> `------------------------------
http://www.cs.fredonia.edu/~stei0302/ ----'
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:00:18 EDT