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Author Topic:   3" Magnaflow exhaust?
Zooki
Journeyman

Posts: 7
From:
Registered: Jul 2004

posted 11-07-2005 04:08 PM     Click Here to See the Profile for Zooki   Click Here to Email Zooki     Edit/Delete Message   Reply w/Quote
Is anyone running the complete 3" system from Magnaflow? How do you like it? How well does it fit? Any pics? How about sound clips? I'm wanting to run this on my '69 when I get the stroker in it, and was wondering how the tailpipes come out in relation to the valance panel. I have the Mach 1 style panel. Thanks for any and all replies.

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ericcasas
Journeyman

Posts: 76
From: Austin, TX
Registered: May 2005

posted 11-08-2005 10:52 AM     Click Here to See the Profile for ericcasas   Click Here to Email ericcasas     Edit/Delete Message   Reply w/Quote
I would love to be able to run 3" exhaust BUT!! Good luck finding headers that collect down to a 3" exhaust. You have to have a 3.5" collector so the reducer can get it down to 3". Everything out there that isn't custom made is a 3" collector down to a 2.5" reducer. I found a place online that will fabricate new headers with 2" pipes to a 3.5" collector for my car but they are going to set me back about $600.00. I will still do it but it's on the back burner until next year.

-E

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buening
Gearhead

Posts: 247
From: Decatur, IL
Registered: Mar 2005

posted 11-08-2005 11:43 AM     Click Here to See the Profile for buening   Click Here to Email buening     Edit/Delete Message   Reply w/Quote
3" exhaust is overkill unless you are running over 600hp. It can actually hurt performance if it is a stock motor. Also, things are pretty tight near the gas tank so getting a 3" exhaust to fit in there is a major challenge and some good $$ from an exhaust shop to make them fit.

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1970 Grabber Blue Mach 1 H-code
1970 Fastback
2003 Torch Red Mustang

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Mooney
Gearhead

Posts: 2227
From: Marietta, Ga
Registered: Oct 2003

posted 11-08-2005 12:11 PM     Click Here to See the Profile for Mooney   Click Here to Email Mooney     Edit/Delete Message   Reply w/Quote
Found this at another site.. long long read. But worth it probably won't format right when I put it in, but never the less:

Exhaust Design Comments:
The concept that maximum power is obtained by zero pressure in the exhaust is only partially true. There should be absolutely
no back-pressure from the collector rearward, but the diameter of the system beginning with the exhaust valve is a compromise. The highest efficiency for the system requires a minimum speed for good exhaust gas velocity to insure that
gas does not "back up" into the chamber during overlap at low engine speeds, and that the "suction" (negative pressure pulse) effect of a resonant (tuned length) and/or collector (overlapping exhaust pulses) system is optimized.
To predict what primary size will be best for a specific motor, you must know where you want the engine to develop peak torque. If the existing torque peak is at bit lower RPM than you prefer (typical in under-cammed or stock motors), it can be "bumped" a bit by increasing the primary diameter. If the torque peak is too high (motor is "peaky", with no range and poor recovery from
gear changes), the peak can be adjusted down by using a smaller pipe. A change of 1/8" in the primary diameter will raise or lower the peak torque RPM by 500 or so.
This factor slightly overlaps the effect of primary pipe length, but the pipe length generally will not change the peak torque or the RPM at which it occurs. A length change has the effect of improving the torque on only 1 side of the peak by "borrowing" it from the other side. A shorter pipe improves the torque after the peak (reduces it at lower RPM), preventing the curve from
flattening out so quickly as speed increases.
A longer pipe extends the torque curve backwards to improve the engine's flexibility, at the expense of after-peak torque. Less stall speed is required, and the motor will pull taller gears; this re-tunes a 4-speed motor for better operation with Torqueflite, etc.
For best effect, the gas speed in the primary tube at the peak torque RPM should be about 240 feet per second. The formula to calculate pipe size is:
Area of Primary Pipe = RPM ? Cylinder Size ? 88,200
This determines the pipe's cross-sectional area, from which we can calculate the ID. Typical exhaust pipes are 18ga. (wall thickness of .049"), so the OD will be .098" larger. From this we can construct a formula for an 8 cylinder motor, and factor in the 18ga. wall thickness:
Area of Primary Pipe = RPM ? Motor Size ? 705,600
Pipe ID2 = RPM ? Motor Size ? 705,600 ? .7854
Pipe ID2 = RPM ? Motor Size ? 554,177
ID = (RPM ? Motor Size ? 554,177).5
OD = (RPM ? Motor Size ? 554,177).5 + .098"
The following Chart shows exhaust pipe outside diameter, based on this formula, for various motor sizes and speeds. To determine if your pipe size is large enough, search across the top row for your motor size (interpolate if in between 2 sizes), and then down that column for your current pipe OD. If the peak torque RPM in the left column is high enough, your pipe is not a
restriction. If the peak torque RPM is lower than where you feel your torque peak is, look for the pipe OD on the line with your torque RPM.
If your primary pipe's wall thickness is 16ga. (.059"), add .020" to the OD figure to compensate.
LA Motors: Pipe Size @ Peak Torque RPM vs. Motor Size
Motor Size273"318"340"360"392"410"
RPMPrimary Pipe Outside Diameter, Inches
30001.311.411.451.491.551.59
32501.361.461.511.551.611.65
35001.411.521.561.611.671.71
37501.461.561.611.661.731.76
40001.501.611.661.711.781.82
42501.541.661.711.761.831.87
45001.591.701.761.811.881.92
47501.631.751.811.851.931.97
50001.671.791.851.901.982.02
52501.711.831.891.942.032.07
55001.741.871.931.992.072.12
57501.781.911.982.032.112.16
60001.821.952.022.072.162.20
Note: 392" is 340/360 block stroked with 3.79" crank; 410" is 340/360 block
stroked with 4.00" crank

B/RB Motors: Pipe Size @ Peak Torque RPM vs. Motor Size
Motor Size383"400"426"440"451"494"
RPMPrimary Pipe Outside Diameter, Inches
30001.541.571.621.641.661.73
32501.601.631.681.701.721.80
35001.651.691.741.771.791.86
37501.711.741.801.821.841.93
40001.761.801.851.881.901.99
42501.811.851.911.931.962.04
45001.861.901.961.992.012.10
47501.911.952.012.042.062.16
50001.962.002.062.092.122.21
52502.002.042.112.142.172.26
55002.052.092.152.192.212.31
57502.092.142.202.232.262.36
60002.132.182.252.282.312.41
Note: 451" is 400 block stroked with 440 crank; 494" is 400/440 block stroker
with 4.15" crank

Remember that your peak torque RPM will always be lower than your peak HP
RPM. The separation between peak torque and peak power is roughly
proportionate to your range of useable power (wider is better). Be realistic in your
estimates and plans - peak torque @ 7000 RPM sounds good, but is almost certainly
beyond the breathing ability of even a professionally-built race motor, and if
true will make the car impossible to launch. Note that 1-1/2" pipe is large
enough for a 273" motor with max torque @ 4000 RPM. A 360" only needs 1-3/4"
for 4200 RPM. A 440" is fine @ 4500 RPM with 2" primaries.
If choosing pipes for a 4WD, van, towing, etc. keep the size small to
improve torque where you need it most - the lower RPM ranges, typically 2500-3500.
One exception where use of a larger pipe (than indicated by the above
formula) will help power is, of course, motors using nitrous oxide, supercharger
or turbocharger. In these cases, size the pipe for the expected peak torque,
not the motor size.
Another instance where a slightly larger pipe may help is where the
departure angle of the pipe from the flange is very sharp (typically downward). The
added cross-sectional area immediately after the flange apparently helps
reduce the restrictive effect of a small radius after the port. This partially
explains why some header models or brands work better than others with similar
dimensions.

Minor Improvements
If possible, slightly enlarge the inside of the flange opening in the
header itself to produce a sharp step (be careful of grinding off the tube weld).
Do not radius the edge. A 1/16" bevel is generally possible and will help. If
there is not much room, don't grind all the way into the flange - a 45? angle
is fine. This has a minor anti-reversion effect, helping to prevent back-flow
at low engine speeds; helps clean up idle quality, etc.

If the primary pipe inside diameter is more than 1/8" larger than the
actual port opening in the head, the header flange bolt pattern can be slotted
slightly to raise the centerline of the primary pipe above the center of the
port, until the bottom of the pipe just matches. This puts the pipe's effective
center closer to the most active area of gas flow, and the mis-alignment at the
roof allows the highest-pressure gas an easier path away from the port; also
adds some degree of anti-reversion.
If controlling reversion is more important than maximum port flow (e.g.
primary diameter is very large), Vizard suggests the mis-match should be at the
bottom of the port where gas flow is slowest, and therefore most likely to
reverse-flow at low engine speed.

An easy way to effect a small increase in exhaust efficiency, if space
permits, is to move the header out away from the port by 1/2" or more (using an
extra gasket and longer studs or bolts). This moves the restrictive angle
farther away from the port - every little bit helps here. It also reduces local
exhaust port temperature in the head slightly. An easy spacer is an extra header
flange or 2, but be sure that the transition from the extra flange to the
header is not restricted. The extra flange may be slightly larger than the port
opening in the head, but must not step down entering the header. Do not taper,
blend, or bevel the extra flange to act as a transition between the port and
the header.

Anti-Reversion Plate
If the header in use is substantially larger than other available choices
for the same motor (i.e., you're using 2" OD, but headers are also available
in 1-5/8", etc.), an inexpensive anti-reversion plate can be made from a bare
flange with the smaller size (1-5/8"). Do these steps in order:
? Match the extra flange openings to the exhaust ports.
? Lay it over your actual 2" header flange.
? Spray paint, mark etc. the 2" openings around the 1-5/8" openings (they
will
be concentric circles).
? Remove the marked area as shown, using ball end carbide, etc.

I would suggest the following rules for best effect:
? The extra, smaller flange be no smaller than your motor's exhaust port.
? The extra flange be at least 1/4" smaller than the header in use (if
using a
header with 2" primaries, the extra flange should be 1-3/4" maximum).
? Make sure there's enough room to move both sides of the header away
from the motor by 3/8" or so (the header flange thickness).
? You may need an extra gasket between the flanges, or sealer may do
(Vizard uses silicone here)
? Longer bolts or studs will probably be needed; remember to use sealant on
B/RB motors due to water in holes.
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Fastymz
Moderator

Posts: 21741
From: Reno Nv USA M&M#1240
Registered: Apr 2001

posted 11-08-2005 02:00 PM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by ericcasas:
I would love to be able to run 3" exhaust BUT!! Good luck finding headers that collect down to a 3" exhaust. You have to have a 3.5" collector so the reducer can get it down to 3". Everything out there that isn't custom made is a 3" collector down to a 2.5" reducer. I found a place online that will fabricate new headers with 2" pipes to a 3.5" collector for my car but they are going to set me back about $600.00. I will still do it but it's on the back burner until next year.

-E


Hooker header makes a 3" collector to a 3" exhaust pipe reducer/conector.
www.Summitracing.com
sells it for $25 or so.

http://store.summitracing.com/default.asp?Ntt=11032HKR&Ntk=KeywordSearch&DDS=1&searchinresults=false&N=0&target=egnsearch.asp&x=46&y=7


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oddly obsessed with big scoops on little Mustangs

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If your parents never had children, chances are you won't either.

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Mooney
Gearhead

Posts: 2227
From: Marietta, Ga
Registered: Oct 2003

posted 11-08-2005 02:25 PM     Click Here to See the Profile for Mooney   Click Here to Email Mooney     Edit/Delete Message   Reply w/Quote
LOL Nice sig addition Scoop

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ericcasas
Journeyman

Posts: 76
From: Austin, TX
Registered: May 2005

posted 11-08-2005 05:02 PM     Click Here to See the Profile for ericcasas   Click Here to Email ericcasas     Edit/Delete Message   Reply w/Quote
I've heard that you should always use a reducer to accelerate the discharge of the exhaust. If you run 3" to 3" it's not a reducer at all. I've heard that this can cause a big loss of horse power and a harmonics/backpressure nightmare (with backpressure actually effecting the flow of exhaust in the combustion chambers. Anyone know about running this 3" header to 3" exhuast pipe connector? I'd like to have 3" exhaust and can probably reach that 600 HP level w/ the help of baby bottle. >8)

-E

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Fastymz
Moderator

Posts: 21741
From: Reno Nv USA M&M#1240
Registered: Apr 2001

posted 11-08-2005 05:11 PM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
I was under the impression the reducer was there to reduce the pipe to fit the exhaust. I don't know about what your asking. Just if you want to run a 3" exhaust and hook it to the collector that part will do it. I wouldn't worry about back pressure with 600hp and rpm's above 5000.

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oddly obsessed with big scoops on little Mustangs

HOOD HACKERS DELIGHT!
My Pics

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ericcasas
Journeyman

Posts: 76
From: Austin, TX
Registered: May 2005

posted 11-08-2005 05:14 PM     Click Here to See the Profile for ericcasas   Click Here to Email ericcasas     Edit/Delete Message   Reply w/Quote
I guess I should have read that long post before I posted! =\ Definitely must run a reducer.

-E

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Fastymz
Moderator

Posts: 21741
From: Reno Nv USA M&M#1240
Registered: Apr 2001

posted 11-08-2005 05:30 PM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by ericcasas:
I guess I should have read that long post before I posted! =\ Definitely must run a reducer.

-E


"There should be absolutely
no back-pressure from the collector rearward, but the diameter of the system beginning with the exhaust valve is a compromise."

Read this too,

http://www.torquetechexh.com/whichsize.htm


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oddly obsessed with big scoops on little Mustangs

HOOD HACKERS DELIGHT!
My Pics

[This message has been edited by Fastymz (edited 11-08-2005).]

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ericcasas
Journeyman

Posts: 76
From: Austin, TX
Registered: May 2005

posted 11-08-2005 06:02 PM     Click Here to See the Profile for ericcasas   Click Here to Email ericcasas     Edit/Delete Message   Reply w/Quote
That was a good site to give you an idea as to what diameter you should run. I didn't like the negative part about the 'loud' open headers. Loud open headers are the shizzle!! I always run open headers at the track just like back in da ol' school.

-E

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Fastymz
Moderator

Posts: 21741
From: Reno Nv USA M&M#1240
Registered: Apr 2001

posted 11-08-2005 06:13 PM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
If you always run open headers at the track,then it doesn't matter size exhaust you run. And why would you worry about collector reducers if you have open headers anyways?

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oddly obsessed with big scoops on little Mustangs

HOOD HACKERS DELIGHT!
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Jake11
Gearhead

Posts: 207
From: Banning,Ca,USA
Registered: Oct 2005

posted 11-08-2005 08:34 PM     Click Here to See the Profile for Jake11   Click Here to Email Jake11     Edit/Delete Message   Reply w/Quote

Run quiet muff's and cutouts like in the
old days. More fun

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Jake11
Gearhead

Posts: 207
From: Banning,Ca,USA
Registered: Oct 2005

posted 11-08-2005 08:42 PM     Click Here to See the Profile for Jake11   Click Here to Email Jake11     Edit/Delete Message   Reply w/Quote

All engineering talk aside, want to know how the car factory engineers used to measure
exhaust system performance?

The hooked a pressure gauge in the ext. outlet. 1 to 2 psi or less was good to go.
Your gonna have back pressure no matter what, unless you shut off the engine.Kinda
simple, huh?

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