Is there any "real" performance or gas milage advantages between the single 3" vs the duals, or is it just personal preference?

The BassDean

 

Gibson tech people told me the single outlet provides more low end torque than the dual outlet. Most of my driving is 75 and below so I went with the single.

------------------
97 F-150,4.6, Reg Cab, Flareside, Air Aid Kit, TransGo Shift Kit,
Superchips, Gibson Single Cat Back, ******* Bed Cover,
EGR Bug Shield, XL Full Length Running Boards,
Hellwig Rear Sway Bar, Hellwig 2500# Overload Springs

 

Yep. A true dual system takes away some torque. But I went with the dual system because I like the look. Plus, I should have gained that torque back with the SuperChip.


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keith@myf150.com
http://www.myf150.com
Rocky Mount, NC

1999 F-150 XLT Styleside, Black On Black, SuperCab, Short Bed, 4x4, ORP, 4.6L Auto, 3.55LS

Mods: DrawTite Class III Hitch, Smittybilt Outland Grill Guard/Brush Guards, KC Daylighters, Custom Dual Exhaust-Straight Out The Back, Airaid FIPK, SuperChips Chip, Bug Deflector, Pace-Edwards Roll-Top Bed Cover

 

It really depends on the size of the pipe(s). I wouldn't go with TRUE duals that are 3". You will definitely lose some bottom-end. It's better to use a smaller pipe for minimal loss, killer looks & terrific sound.

Either way, I'd suggest you look into your local exhaust shop. They can probably install a system for far less than the mail-order companies' setup.

Neal

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1997 4x4 Expedition- 4.6L, true dual exhaust w/glass-packs, K&N air filter, SuperChip, airbox mods, Edelbrock shocks, 285/75R16 BFG ATs, Optima "T-Bone" wheels, and Clarion In-dash CD player.

1993 4x2 F150 Reg. Cab LWB- 5.0L, cat-back dual exhaust w/glass-packs, K&N air filter, Superchip, fresh paint, and Line-X bedliner.
http://members.visualcities.com/NoMo

 

Please explain the loss of torque when reducing back pressure.
I would think the less back pressure the better.
Is peak horsepower also reduced?


------------------
99 XLT 5.4l reg cab
5 star larait style wheels
Toreador red 2tone
3.55 gears
255/70/16 OWL
Delta toolbox
Eclipse cd player
Sherwood amp
subwoofer coming soon
More mods as funds become avalible.

 

No, 54, peak horsepower isn't lost w/ reduced backpressure...[usually].And, reduced backpressure is desirable for the most part. Where the low-end torque gets lost is when velocity of the exhaust gases is reduced [at least that's how it was explained to me.]

 

Personaly, I think the duals look way cool. I am having them done on Friday. Just my 02.

Dean

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99 F-150,XLT, Silver, 2WD, 4.2L, 5spd, RegCab, Shrt WB, Styleside.
Current Mods:Billet grille, Line-X bedliner, 5%window tint all the way around, Alpine CD w/2 MTX Subs & Rockford Fosgate 250w amp. K&N Airfilter.
Future Mods: Superchip, glasspacks w/dual exhaust, driving lights, & a custom paint job

 

Hey Nomo!
How does that 4.6 sound with glasspacks? I was thinking of doing the same with mine.

-Tim

 

Louder than any other new truck I've heard. I really like them. The packs are made locally (by the family of an old schoolmate) and are 36" long. Anything shorter would be too loud. The true duals sound a lot different than my F150's split pipe with the same packs.

It's 482Kb, so it takes a while to download- http://members.visualcities.com/nomo...tive/packs.wav

Neal

------------------
1997 4x4 Expedition- 4.6L, true dual exhaust w/glass-packs, K&N air filter, SuperChip, airbox mods, Edelbrock shocks, 285/75R16 BFG ATs, Optima "T-Bone" wheels, and Clarion In-dash CD player.

1993 4x2 F150 Reg. Cab LWB- 5.0L, cat-back dual exhaust w/glass-packs, K&N air filter, Superchip, fresh paint, and Line-X bedliner. http://members.visualcities.com/NoMo


[This message has been edited by nomo (edited 08-12-1999).]

 

The best explanation I've heard about the loss of bottom-end power/torque from certain
exhaust systems so far (in my own words):

How fast the exhaust gases escape (with volume=flow)
depends on a difference in pressure (makes
sense right?). Having a wide open exhaust
reduces that difference, like a water hose:
a large opening results in lower velocity,
while a smaller one increases it, thus
reducing what's called the "scavenging"
effect at certain flow levels.

The scavenging effect is what's used to
create the performance gains from exhaust
systems. Gases can be thought of like
liquids. So when a cylinder finishes its
combustion stroke and expunges its gases,
a "packet" or column of gas form (can think
of it discretely like that: 1 packet per
cylinder) that goes through the headers and
out to exhaust. Now, when that packet passes
the headers and reaches the exhaust, it forms
a vacuum (well, technically not completely..)
behind it, which allows for the next cylinder
on the exhaust stroke to expunge its gases
effecient/quickly because of the difference
in pressure created, from lots of pressure
after the combustion to almost none by the
vacuum created from the prior escaping packet
of gas. This is the scavenging effect.

Now the only constraint is how fast that
"first" packet of gas moves (since all
packets thereafter will move at that rate).
And that's determined by the amount of flow
allowed by an exhaust. Having too wide an
exhaust (either 1 really large diameter pipe
or many smaller ones) decreases the
difference in pressure between the atmosphere
outside and the exhaust so the escaping
gases will be slow. This in turn, actually
creates backpressure, a not complete
expulsion of gases from the cylinder or a
"forcing back" of escaped gases back in due
to the slowness of that moving packet, which
all of course, reduces the low rpm power and
torque. However, where the larger diameter
pipes create their gains is in the higher
rpms because using the water hose analogy,
if you have little flow by turning on the
tap just a little and want maximum range
for the water to shoot out (by increased
velocity) then you squeeze the end right?
but as you turn up the tap, you expand the
opening because there's only so much that
can flow through the small opening that
was most effecient when the flow from tap
was low--likewise with exhausts. So the most
effecient one would actually have a varying
effective diameter/end and I've only seen
this from one company.

And as far as requiring or "needing"
backpressure, from what I gather is that you
only need just a little to keep the intake
air from flowing out the end.. I presume
it must be from not precise timing of the
valves or something. But in general,
you want to reduce backpressure to increase
the scavening effect and promote flow, which
is the volume of air moving per time. And
exhausts too big decreases that for lower
rpms and actually creates backpressure.
And to reduce backpressure, you want to
increase the pressure difference between
the atmoshpere outside and within the
exhaust (from headers on).

[This message has been edited by jimveta (edited 08-13-1999).]