RE: Re: RE: Exhaust backpressure (TECH!)

From: Bernd D. Ratsch (bernd@texas.net)
Date: Tue Mar 20 2001 - 22:00:15 EST


They told me that the system I have may be a little but too much for the V6
on bottom end. It actually improved it with the 10psi boost from my
Powerdyne.

- Bernd

-----Original Message-----
From: owner-dakota-truck@BUFFNET.NET
[mailto:owner-dakota-truck@BUFFNET.NET]On Behalf Of Chris Spotts
Sent: Tuesday, March 20, 2001 8:57 PM
To: dakota-truck@BUFFNET.NET
Subject: DML: Re: RE: Exhaust backpressure (TECH!)

OK, one more question to add to that list. If one were to turbocharge ( a
v6 for example) would the turbos provide the necessary back pressure with
huge pipes out the back? In other words, turbos from what I hear, need free
flowing exhaust, but the same free flowing exhaust will kill the torque on
the low end. Does the turbo being there help keep some of that back
pressure in check? (I hope this makes sense)
Best of both words, low end torque with a screaming high end?

-Chris

----- Original Message -----
From: "Bernd D. Ratsch" <bernd@texas.net>
To: <dakota-truck@BUFFNET.NET>
Sent: Tuesday, March 20, 2001 8:32 PM
Subject: DML: RE: Exhaust backpressure (TECH!)

>
> If it helps...here's what I just (finally) had done today.
>
> 2.5" Intermediate Pipe (from Cat) to 2.5" IN on Muffler into Dual 2.5" Out
> and 2.5" Pipes out to behind the rear wheels (3" Megs Slant Cut Tips).
> HOLY FREEKIN' CHIHUAHUAS!! What a difference. (This was coming from a
2.5"
> IN on the muffler into dual 2.25" outlets and then into 2" pipes out the
> rear.)
>
> Now granted, this is a Supercharged application...but this is a hot setup
> for the V6's (with S/C's.)
>
> - Bernd
>
> -----Original Message-----
> From: owner-dakota-truck@BUFFNET.NET
> [mailto:owner-dakota-truck@BUFFNET.NET]On Behalf Of Jon Steiger
> Sent: Tuesday, March 20, 2001 7:18 PM
> To: dakota-truck-moderator@bent.twistedbits.net
> Subject: DML: Exhaust backpressure (TECH!)
>
>
>
> 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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