Exhaust Basics 101

[Bryan Niese]

I may be the last one on this forum to know this, but I'll share it anyways. I had the exhaust replaced on my stock 1988 GW yesterday. It was the original Catalytic Converter and the muffler back had been replaced sometime ago. It seems that there are parts of the original exhaust pipe that are 2 1/4 inches, and the flange on the origianl Cat is only 2 inches http://www.ifsja.org/ubb/eek.gif I was going to go with a 3 inch system from the y-pipe back but I went with a true 2 1/2 inch and High flow Cat & Muffler becuase the increase in flow from a 2 inch or 2 1/4 inch pipe is a huge gain, something like 25 to 30 % more flow, plus that gained with a high flow cat & muffler. Results: Sounds awesome, mellow rumble at idle and only slightly louder at highway speeds, and more power when pulling hills etc (my cat was plugged pretty bad, so that was the culprit there). Best of all, it was about $150 less than running a 3 inch exhaust!

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Donzi
1988 GW
Totally Stock

[Veepster]

I ran the 3" but if I did it again I would use 2.5".......the space between the TC and the frame rail is kinda small and a 3" BARELY fits

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Peace.............BartG

the Green Flash!
78 Cherokee
360 2v, TH400 QT with low
4" skyjacker Doetsch tech shocks
33x12.50 BFG KO's 8" American Racing Baja Rims
Thorley headers, 3" exhaust, Dyno Max
Infiniti power leather seats
50%LuxuryCar,50%Tractor

[Treadted2]

Hey Brian,

I would like to do this upgrade. Where did you get all of your stuff? What kind of muffler and cat did you get? Where did you have installed? And what was the final $??

Thanks

Ted

[Bryan Niese]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Treadted2:
Hey Brian,

I would like to do this upgrade. Where did you get all of your stuff? What kind of muffler and cat did you get? Where did you have installed? And what was the final $??

Thanks

Ted<HR></BLOCKQUOTE>

Ted, I used a CatCo Catalytic converter, it is a true 2 1/2 inch high flow cat, it's about half the size of the factory one. I used a Flow-Pro muffler, not sure of the model number, but again a true 2.5 inch high flow muffler. A local muffler shop, Mission Muffler (not a chain) did the work for $265 (parts & labor), although this did not include the tailpipe because mine had been replaced recently with 2.5 inch pipe.

Veepster: I know what you mean about a tight fit. I looked under there while it was up on a rack and the clearance between the crossmember and the frame is pretty small!!



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Donzi
1988 GW
Totally Stock

[Treadted2]

Thanks brian, I will look into it.

Ted

[BobBarry]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Bryan Niese:
I may be the last one on this forum to know this, but I'll share it anyways. I had the exhaust replaced on my stock 1988 GW yesterday. It was the original Catalytic Converter and the muffler back had been replaced sometime ago. It seems that there are parts of the original exhaust pipe that are 2 1/4 inches, and the flange on the origianl Cat is only 2 inches http://www.ifsja.org/ubb/eek.gif I was going to go with a 3 inch system from the y-pipe back but I went with a true 2 1/2 inch and High flow Cat & Muffler becuase the increase in flow from a 2 inch or 2 1/4 inch pipe is a huge gain, something like 25 to 30 % more flow, plus that gained with a high flow cat & muffler. Results: Sounds awesome, mellow rumble at idle and only slightly louder at highway speeds, and more power when pulling hills etc (my cat was plugged pretty bad, so that was the culprit there). Best of all, it was about $150 less than running a 3 inch exhaust!
<HR></BLOCKQUOTE>

A 3" system would have to be custom-bent; few places around here do that kind of work, and the quote I got from the one guy whose work is worth anything was about $700!!! http://www.ifsja.org/ubb/eek.gif

The flange of my stock Y-pipe was 2.5", as was the tailpipe. I bought new Walker replacement parts for those two pieces, a Random Technology Cat, and a Flowmaster 70-series. Cost me under $400, over half of which was the cost of the converter. Dramatic increase in power; I don't think going to a 3" system would have given me another $300 worth of power.

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Bob Barry<UL TYPE=SQUARE>* '78 Cherokee 4-door
* '88 Grand Wagoneer[/list]http://studentweb.providence.edu/~rbarry/wheels/

[Luperman]

Do you guys know if the stock cat had the pellets in it and when it gets old it clogs up.? 84 360

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84 Grand Wagoneer 360
86 fiero V-6

[Brazzy]

The stock cat was like a honeycomb inside like all the others I have ever seen, and when it gets cloged it also melts and breaks into chuncks, the reason it plugs the exhaust up going up hills.
I am finishing up my exhaust redo today as I had to remove the manifold to replace the gaskets at the head and found the smog pipes to be riddled with holes and broken. Wish I could get away with removeing them all together, http://www.ifsja.org/ubb/frown.gif The y pipe was 67.00 , cat from wipmy was 60.00 (generic 2.5 I.O.) another 20.00 for a generic 2.5 I.O. muffler, and I think I paid about 40.00 for the tail pipe that I reused. This setup worked great and had a very low mellow sound (not loud) I do notice a diff in power cause my cat was half cloged, The new one was about half the length of the old one but adding a section of 2.5 pipe to increase length is really simple.

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Brazzy
Formerly abused 87 G.W. 162k stock
TOW,PKG,727,229,360
The Chariot

[KENALL]

well having an older wag im lucky not to need a CAT.

but im using the 2" flexible ex tubeing from JC whipme and matching Pacesetter dual mufflers. i found it was ezr to run dual 2" pipes down the P side frame rail than one 3" pipe.

AND since the leader tubes from my SBCs OE ex manifolds are 2" OD, these 2" ID pipes slide on great and dont leak. iv had good luck with this 'bendable' stuff for 7 years...

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Ken
1966 Super Wagoneer
'The Predecessor' http://home.earthlink.net/~kenns9/index.html

[scotty]

sweet! someone else who is not afaid to run the flexi stuff http://www.ifsja.org/ubb/biggrin.gif i always tell my friends its a temp fix,but i never seem to get around to having real pipes ran.have usually got other things to spend $$$ on...



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scott
85 grand wagoneer
258 with motorcraft 2bbl/904/twin stick dana 300/dana 44/welded amc 20
38x15.5 gumbo mudders
snorkel/dual batteries/onboard air/"custom" convertable
3 inch body lift/mostly stock suspension/"modified" fender openings
custom front/rear bumpers and brushgaurd

T18/dana 20 swap very soon
searching for dana 18 to replace the 20...

[River Beast]

Here is a thought.... maybe goof for a new post but I 'll try it here.

The Back-Pressure issue.... good, bad, needed or not needed,

I understand the concept of having a free flow exhaust system on any fehicle, But I had a bad experience (non-FSJ) with a dual 2.5" system where I lost a noticable amount of power after the install. Others noticed it ,too. I changed the system from a OEM "y" pipe type setup to Flow Tech headers and 2.5" dual sytem with 2 Flow Tech Afterburner mufflers and lost power.

My concern is no wanting to lose any power in my rig. I know plenty of you run 3" singles... Can someone put my mind at ease over this back-pressure issue...

Thanks guys.... I'll wait right here for your replies in this cushy reclined black rawhide "session couch" and relax....ahhhhhhh......

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Todd
78 Wagoneer, "River Beast"
360/TH400/QT
Dana 44's locked w/ 4.89's
soon to be 38's or 42's ...not too sure yet
7" SOA in front-7" Rear Shackle Inversion Mods
4" Skyjacker Softride
3" Trailmaster Bodylift
My FSJ site: http://www.geocities.com/~spazz4life (http://www.geocities.com/~spazz4life)
My E-mail: spazz4life@yahoo.com
"If you can't stop...SMILE as you go under!"

'93 3/4 ton 4x4 Suburban...a.k.a. "FSJ Hauler"

[Veepster]

Todd I know your concern.......I have a 3" BUT I also have a Cat, the cat is what keeps my back pressure up.

dual exhaust is NOT a good thing on any vehicle without a crossover. and the setup you explained is GREAT for top end power but would kill your low end.

back pressure...hhm how to explain? back pressure and scavenging work hand in hand... you need back pressure to assist in scavenging....scavenging is when an exhaust pulse creates a low pressure area behind the pulse which helps suck the next exhaust pulse out of the combustion chamber....

does this make sense....???

free flowing is good but too much of a good thing is not good.

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Peace.............BartG

the Green Flash!
78 Cherokee
360 2v, TH400 QT with low
4" skyjacker Doetsch tech shocks
33x12.50 BFG KO's 8" American Racing Baja Rims
Thorley headers, 3" exhaust, Dyno Max
Infiniti power leather seats
50%LuxuryCar,50%Tractor

[River Beast]

thanks Bart.... i thought I was the only one who worried qbout this... I feel a 2.25" dual 2-chamber Flowmasters with an "H" pipe will be just fine for my rig... of course 18" 3" tips will be added to resonation purposes (hehe) http://www.ifsja.org/ubb/biggrin.gif

As soon as I get my 33 gal tank in and working properly, the exhasut will be done.


Thanks again, Bart

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Todd
78 Wagoneer, "River Beast"
360/TH400/QT
Dana 44's locked w/ 4.89's
soon to be 38's or 42's ...not too sure yet
7" SOA in front-7" Rear Shackle Inversion Mods
4" Skyjacker Softride
3" Trailmaster Bodylift
My FSJ site: http://www.geocities.com/~spazz4life (http://www.geocities.com/~spazz4life)
My E-mail: spazz4life@yahoo.com
"If you can't stop...SMILE as you go under!"

'93 3/4 ton 4x4 Suburban...a.k.a. "FSJ Hauler"

[Veepster]

that is a good choice for you!.....you need all the low end you can get, those tires are huge!...even though you compensate with gearing, the rotating mass is incredible.

------------------
Peace.............BartG

the Green Flash!
78 Cherokee
360 2v, TH400 QT with low
4" skyjacker Doetsch tech shocks
33x12.50 BFG KO's 8" American Racing Baja Rims
Thorley headers, 3" exhaust, Dyno Max
Infiniti power leather seats
50%LuxuryCar,50%Tractor

[Dave _S]

Hey Todd,

Are you runing those twin pipes side by side past the QT and over the rear axle or along each frame rail and out in front of the rear wheels?

Dave


<BLOCKQUOTE>quote:</font><HR>Originally posted by River Beast:
thanks Bart.... i thought I was the only one who worried qbout this... I feel a 2.25" dual 2-chamber Flowmasters with an "H" pipe will be just fine for my rig... of course 18" 3" tips will be added to resonation purposes (hehe) http://www.ifsja.org/ubb/biggrin.gif

As soon as I get my 33 gal tank in and working properly, the exhasut will be done.


Thanks again, Bart

<HR></BLOCKQUOTE>

[River Beast]

Dave_S,
Right now I have straight headers... I am retro-fitting a 33 gal fuel cell from a donor mid 80's full-size Bronco in the rear center between the frame rails. When this is complete, the 21 gal OEM tank that is mounted on the driver's side wil be removed to make dual exhaust real simple. The only bends I will require is over the x-member, then straight back and 45 degree angle out the sides behind the rear tires. I am high enuf to not need a bend to go over the axle... it's 12" from the axle with a straight pipe. My 'H' pipe will be just after the QT over the top of the drive shaft 6" back from the yoke... my driveline will never hit it cuz it's at 15 degrees.

PS. Test fit 39.5 Swampers tonight and they fit PERFECT!!! Picking up 4 for $350.... what a blessing!!! http://www.ifsja.org/ubb/biggrin.gif

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Todd
78 Wagoneer, "River Beast"
360/TH400/QT
Dana 44's locked w/ 4.89's
soon to be 38's or 42's ...not too sure yet
7" SOA in front-7" Rear Shackle Inversion Mods
4" Skyjacker Softride
3" Trailmaster Bodylift
My FSJ site: http://www.geocities.com/~spazz4life (http://www.geocities.com/~spazz4life)
My E-mail: spazz4life@yahoo.com
"If you can't stop...SMILE as you go under!"

'93 3/4 ton 4x4 Suburban...a.k.a. "FSJ Hauler"

[This message has been edited by River Beast (edited October 23, 2000).]

[scotty]

according to the book "how to build and modify intake and exhaust systems" it is a common misconception that a slight amount of bacpressure is needed for the engine to run properly.the headers can be tuned to the rest of the engine and increase the volumetric effeciency by altering the primary tube length and diameter. the scavenging effect takes place as the exhaust pulses flow past the other tubes in the collector,creating a vaccum that helps pull the gasses out as the exhaust valve opens.in a really well designed system,the gasses rushing out can actually help pull the air/fuel mixture in as the intake valve opens.

RB-i dont think that your power loss was because of less back pressure.prolly the factory Y pipe actually was having some sort of scavenging affect as the pulses flowed past the Y. with a dual system you now no longer have the scavenging affect. that and maybe carb or timing adjustments needed to be made to be able to take advantage of the new ability to breath.

you cant get the air/fuel mixture in if theres still exhaust in the way.backpressure creates a hindrance to getting the new mixture in. a well thought out exhaust system should have a header that optimizes power in the bandwidth the engine will run in,and the most restriction free,free flowing path possible away from the engine,and safely out from under the car and away from the occupants.if backpressure was good,then you wouldnt hear the cars at the race track-everyone would be putting on mufflers to add power.

as far as the CAT goes,this is another misconception.in the cat is in good shape,it should flow well enough to handle any amount of power a streetable engine can make. the cross section of the cat is usually many time larger than the cross section of the pipe that runs to it.if its in good shape and not clogged,it should not provide any restricitons. those of us forced to run them on daily driven rigs can benefit from installing a larger one,and/or using 2.

im by no means an expert,and it has been awhile simce ive read the book,but riverbeast,rest assured that a 3 inch dual system will not cost you any power loss over a 1 inch,2 inch,or whatever,identical system using the same headers.if youve got a good header for your powerband,youll be in good shape.

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scott
85 grand wagoneer
258 with motorcraft 2bbl/904/twin stick dana 300/dana 44/welded amc 20
38x15.5 gumbo mudders
snorkel/dual batteries/onboard air/"custom" convertable
3 inch body lift/mostly stock suspension/"modified" fender openings
custom front/rear bumpers and brushgaurd

T18/dana 20 swap very soon
searching for dana 18 to replace the 20...

[This message has been edited by scotty (edited October 24, 2000).]

[River Beast]

Scotty,

Thanks for the very informative reply... it explained alot in detail to issues i have heard about but never had explained to me or understood. You have opend my eyes to a couple of things but the cost effectiveness of a what I would like to do, plus space and noise level (not really an isuue to me but my neighbors) I feel I will have to "settle" with a max fo a 2.5" dual "H" pipe system.

I will see if anything can be done otherwise.. but I doubt I have room on the T-case side to go bigger....

BTW... picking of a set of Swampers today http://www.ifsja.org/ubb/biggrin.gif
(check my sig)


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Todd
78 Wagoneer, "River Beast"
360/TH400/QT
Dana 44's locked w/ 4.89's
39.50x15x15 Super Swamper TSL's
7" SOA in front-7" Rear Shackle Inversion Mods
4" Skyjacker Softride
3" Trailmaster Bodylift
My FSJ site: http://www.geocities.com/~spazz4life (http://www.geocities.com/~spazz4life)
My E-mail: spazz4life@yahoo.com
"If you can't stop...SMILE as you go under!"

'93 3/4 ton 4x4 Suburban...a.k.a. "FSJ Hauler"

[Treadted2]

Yo Todd,

I can't believe those tires! What motivated you to go so huge?? I mean, doesn't your wag have a performance issue now? How does it handle? Just sounds like it would be really shady and sluggish. Not trying to rip on your rig, just kinda curious. You gonna put some pictures up after you get it together? I would like to see that.

Ted

[River Beast]

Ted,

Did you ever want to do something you had never seen done, or seen but would would like to...I'm sure many of us have... I have built many Ch*vy rigs in the past, either mine or friends and never thought it possible to achieve what I have today... A MONSTER FSJ with 11" of pure suspension lift... NO BLOCKS... and 3" body to give me room for the 39's. I have spent several months in the planning of this latest episode of my project. The feeling of accomplishment I get to have gone as far as I have with all the mods I have done gives me great pleasure and satisfaction. there are few of us here that have dove into the realm of mods that it takes... Mark is one of them with his W/T Cherokee aka "Above the Law". He runs 42's on his rig. I guess it's just personal preference. I realize now that my off-roading abilities are going to be degraded... but that may be a good thing. I was too extreme before, launching my rig in the air (just twice..once by accident and once I had to) and breaking stuff just about everytime I went out to "play". I will still push my new limits a abilities with the height concerns... but I will definitely have to "learn" those limits as experience of trails and terrian with trial and error will dictate.

I know others probably feel the way you do as well and there are no "ill" feelings to be had. It's just a journey thru a FSJ lover's dream to build a rig that is so personalized that it would be hard to duplicate.

As for being sluggish... hardly... 4.89 gears pull the rig w/ 39's down the road like a set of 3.54's on 29" tires... with a little more wieght of course.

As for pics... check out my site (link below) to see the whole story.. my SOA page will show/explain the latest suspension mods (7" rear shackle inversion...these pics were the prototypes, I have the final design completed on my rig at this point) but with 31's used to fit in my carport by 1/2" http://www.ifsja.org/ubb/biggrin.gif

I did take pics of the 39's mounted and will post them soon.. after developing them... sorry no dig cam yet... need the $$$ for the River Beast http://www.ifsja.org/ubb/biggrin.gif!

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Todd
78 Wagoneer, "River Beast"
360/TH400/QT
Dana 44's locked w/ 4.89's
39.50x15x15 Super Swamper TSL's
7" SOA in front-7" Rear Shackle Inversion Mods
4" Skyjacker Softride
3" Trailmaster Bodylift
My FSJ site: http://www.geocities.com/~spazz4life (http://www.geocities.com/~spazz4life)
My E-mail: spazz4life@yahoo.com
"If you can't stop...SMILE as you go under!"

'93 3/4 ton 4x4 Suburban...a.k.a. "FSJ Hauler"

[Treadted2]

Hey dude, that's cool! I commend you for attempting the unknown, and down right achieving it. I can say that I will never have the desire to modify my fsj the way you have, but I will enjoy telling people that I know of a guy that has a wagoneer lifted 11" when they are looking at 3" lift in awe! That's cool man, keep on jeepin'!!

Ted

[Veepster]

Well said Scotty!

That is definitely another theory. As I recall Ed of "Headers by Ed" agrees with you. It is fun to progress to the area of automotives where there is no one right answer. These are all theories......Doug Thorley swears by the Tri-Y theory....Ed of "Headers by Ed" completely disagrees with with Thorley. I have known winning racers that swear by equal length primary headers and other winning racers who don't care......they are all winning races so who is right??
Exhaust design is also so affected by cam design, head design, gearing etc etc etc....so what works for someone may not work for someone else.....Over the last 10 years I have spent humdreds of hours in the dyno room and the one thing I have learned is sometimes two plus two equals five....

and I may disagree with Scotty on this issue but there is one thing we have in common... reading!...I have an entire book shelf in my garage dedicated to automotive books...... Do I understand them all? heck no! but I keep reading them over and over...there is some awesome books out there and there are some cr*ppy ones. so take some of the FSJ budget every once in a while and pick up a book, your FSJ will thank you!..OK off my soapbox!

again....Great job on the explanation Scotty!

------------------
Peace.............BartG

the Green Flash!
78 Cherokee
360 2v, TH400 QT with low
4" skyjacker Doetsch tech shocks
33x12.50 BFG KO's 8" American Racing Baja Rims
Thorley headers, 3" exhaust, Dyno Max
Infiniti power leather seats
50%LuxuryCar,50%Tractor