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Author
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Topic: 3" exhaust??
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'69Stang
Gearhead Posts: 205
From: Detroit, MI USA
Registered: Jan 2002
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posted 03-12-2002 09:56 AM
   
I am building up a 475 - 500 horsepower 351c. Will it need 3" exhaust or is 2.5" adequate?
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blown 351
Journeyman Posts: 68
From: Seattle, Wa. 98258
Registered: Dec 2001
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posted 03-12-2002 12:03 PM
2.5" should be adequate. It depends on valve size, cylinder head port design/shape intake runner design, camshft specs, exhaust header size, etc.
I'm putting 511 HP at the rear wheels, so guess maybe 590-600 at the flywheel with 2.5" exhaust
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'69Stang
Gearhead Posts: 205
From: Detroit, MI USA
Registered: Jan 2002
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posted 03-12-2002 01:10 PM
O.K. that is re-assuring. I had to make a decision on the collector reducer size for a new set of headers i was buying for the 351c build up and the header manufacturer recommended the 2.5" size. He said that I would get better low end torque and lose virtually nothing up top. I just wasn't sure and don't want to choke my engine at all.
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Ryan Wilke
Gearhead Posts: 2494
From: Stanton, Michigan 49707
Registered: Oct 2000
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posted 03-12-2002 07:53 PM
'69Stang:
Is this a street car with mufflers and with peak HP expected at less than 5K rpms or a strip-only car, run at higher peak HP rpms and without mufflers? If you ARE planning on running mufflers, you may want to check out the recommendations at: www.flowmastermufflers.com Because with the added restriction of a pair of mufflers, your top end may be better served by stepping up to the 3" diameter system. Just my 1.5 cents worth,,,, Ryan  ------------------
The '3-Pedal Attitude' Kid
in a '69 FB w/ 306 now, but
the 460+ is coming... :D
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kid vishus
Gearhead Posts: 6590
From: middle of NC
Registered: Oct 2000
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posted 03-12-2002 08:02 PM
I agree with Steve. On my race cleveland, I run 3 1/2" Borlas, and they dont slow it down at all. And for any hot street car with a cleveland, i wouldnt run less than a 3" muffler. As for low end torque, if you're running a 4v cleveland with stock stroke, forget it, you wont have any regardless if you build the motor to make the power where those heads need to be. ------------------
member #773
'69 mustang, 351C, 9.97 @ 133 mph 1/4, 6.27 @ 108 1/8, 1.344 60'
'70 mustang, flintstone power
'93 F150 Lightning www.geocities.com/slariviere/KidV.html
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n2oMike
Gearhead Posts: 2831
From: Spencer, WV
Registered: Jan 2001
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posted 03-13-2002 07:25 AM
You'll hurt an engine's performance way more by using pipe that is too small than too large. When in doubt, go larger. Cross section of 3.0" pipe = 7.07 square in.
Cross section of 2.5" pipe = 4.91 square in. I really like the performance and deep sound of the 3" pipe on the mustang. The larger pipe doesn't really have a louder sound, but a deeper one. It sounds good. It's just hard to do tailpipes for most cars. No matter what pipe size is used, do NOT use muffler shop tailpipes. They are kinked all to hell in making those tight bends up over the axle. Flowmaster makes mandrel bent tailpipes for most cars out there, and most only cost around $99 a pair. It's the best hundred bucks you'll spend on the car. (assuming tailpipes are going to be used) Good Luck!
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Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220
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'69Stang
Gearhead Posts: 205
From: Detroit, MI USA
Registered: Jan 2002
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posted 03-13-2002 07:55 AM
Allright, 3" pipes it is......Flowmaster makes Mandrel bent pipes for a '69 Mustang? Where can I find these?
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Hemikiller
Gearhead Posts: 667
From: Killingworth, CT
Registered: Feb 2002
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posted 03-13-2002 12:24 PM
Flowmaster make 2.5" tailpipes for 65-73 Mustang/Cougar. Part # 15807. They also just introduced a complete kit for 64-66 Stang, Pt # 17273. I don't know of anyone who makes 3" tailpipes for a Mustang, I think a company called TorqueTech makes 3" pipes for GMs and Mopars. The Roadrunner/GTX tailpipes possibly could be made to fit. I used a set many years ago from one of my brother's cars on my first Mustang, a '73 Grande'. Might have to do some adjusting because of the 3" pipes. You can get the Flowmaster pipes from your local speed shop or order them from Summit or Jegs or whoever....http://www.torquetechexh.com/users/kblythe/Torque_Tech_Sh/Page_1x.html
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kid vishus
Gearhead Posts: 6590
From: middle of NC
Registered: Oct 2000
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posted 03-13-2002 04:15 PM
There is a local muffler shop here that madrel bends 3" pipe. Since you are in Detroit (or there abouts), you might want to look around and see if any of the better custom shops can mandrel bend pipe that big. You might be suprised and find someone local that can do it for you.
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n2oMike
Gearhead Posts: 2831
From: Spencer, WV
Registered: Jan 2001
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posted 03-13-2002 04:33 PM
Just be careful, the VAST majority of muffler shops have the standard hydraulic benders.... and most of the guys working in those shops don't even know what "mandrel" bending refers to. If you ask them if they do mandrel bending, they will often answer 'yes'.Mandrel benders are big, complicated machines that use a 'snake' that goes into the pipe during the bending process. This mandrel keeps the pipe from being crushed as the bend takes place. Be informed, and be careful. You may be able to get flowmaster 3" tailpipes for another vehicle, and modify them to fit your car. Check their website for applications. Of course, I don't even run tailpipes. Asphault Jungle makes 3" kits for Fox bodied mustangs, but they aren't cheap. Be informed! Good Luck! ------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220
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mvierow
Gearhead Posts: 209
From: Bay Area, Ca
Registered: Apr 2001
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posted 03-13-2002 04:35 PM
What about with an AOD with a custom cross member? Is that kit customizable enough to spread the pipes a little further apart to fit that cross member?I took a look at their charts and the tail pipe exit location is 'DOR'. I'd like the pipes to come out the trumpet holes - do you guys know if this will work? Here's the page I was looking at:
http://www.flowmastermufflers.com/web10/pages37-38.pdf
http://www.flowmastermufflers.com/web10/openrd/showthread.php?s=91c8ea62eb7f4a5ed2f47bb1ce3f8744&threadid=201&highlight=17273
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kid vishus
Gearhead Posts: 6590
From: middle of NC
Registered: Oct 2000
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posted 03-13-2002 04:47 PM
I dont run tailpipes on my street car either, just straight back to the rear-end housing, then dump them. I know the local shop has one, and it is a complicated looking piece of equipment, not your typical pipe bender.
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n2oMike
Gearhead Posts: 2831
From: Spencer, WV
Registered: Jan 2001
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posted 03-13-2002 05:43 PM
MAC also offers mandrel bent tailpipes for early mustangs. They offer a non-GT and a GT model. I suppose the GT model exits out those holes in the rear valence.Find their website, and it's on p. 18 or 19 of their .pdf catalog. Good Luck! ------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 03-14-2002 06:27 AM
I picked up 40RWLBS across the midrange (~3000-5000) by changing from a 2 1/2" full system to a 3" dumping at the rear axle.Paul
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'69Stang
Gearhead Posts: 205
From: Detroit, MI USA
Registered: Jan 2002
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posted 03-14-2002 08:07 AM
I found a local shop that will do a 3' mandrell bent exhaust system for the following:
pipes back to muffler w/h-pipe - $175
each tail pipe - $125
total = $425 + mufflersClevo377: that is an impressive gain!
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Clevo377
Gearhead Posts: 312
From: Blackburn, Victoria, Australia
Registered: Nov 2000
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posted 03-15-2002 04:57 AM
Yeh, I was surprised too. Power was leveling off at around 6200 and I thought it was the exhaust. So I pulled out the old 2 1/2" full system and made my own 3" with a H pipe. The H pipe is also 3" and scalloped into the the adjoining pipes. There are no bends, just straight to a pair of 3" Magnaflows.I didn't pick up any more top end, (I now believe the manifold was the culprit) but it sure made a difference to the midrange. Paul
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