My Corolla was the same way (well, I didn't look at the gas) when the
cat to muffler pipe rotted out. 2 miles to the shop and it seemed to
take an eternity. I had trouble just keeping up with traffic and not
being killed when turning into traffic.
Josh Stolarz wrote:
>
> 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/ ----'
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