Advice needed on exhaust pipe sizes

[The_Handier_Man1]

From: In2fire1  (Original Message)
Sent: 2/17/2004 9:36 PM

Hi, I spent the morning with the muffler guy and he suggested that I used 2 1/2 " pipe to the muffler and 3" pipe behind muffler. I have read the other messages and I am not clear if this is the right thing to do. This will be a new system from the exhaust manifold back and I want to have it done right. Because this is around $400.00 and don't want to make a mistake. The exhaust pipes on my MH are full of holes. Thanks for the help! Gil



From: Liv42dayOK
Sent: 2/18/2004 8:55 PM

I've been researching this same topic.  From headers to dual exhaust and everthing else (except turbocharging).  There are many members who have performed complete manifold back conversions with headers and dual exhaust as well. 

Personally, I want to get as much bang for the buck since there aren't a lot of bucks to work with.  I will be going with exactly the set-up you are considering.  Stock manifolds, 2 1/2" main to a series 50 big bore Flowmaster muffler to 3" tailpipe. 

In a nut shell, the cost is reasonable without having to spend big bucks for headers, etc, etc, you get increased air flow out (providing slight improvement in MPG and HP) without reducing back pressure so much as to hurt your torque power and without increasing heat around your engine's vital components and vulnerable lines, cables and wires.

If you look at the "header" and other exhaust messages, you can read the technical debate on different exhaust systems and get a more complete picture of what's available.

Nothing of my own here, this is just a synopsis and conclusion for what I feel best meets my needs based on the wealth of information shared by the techno-wizards. - Sob



From: In2fire1
Sent: 2/18/2004 10:22 PM

Thanks for the info. on the exhaust. The muffler guy recommended the series 50 big bore Flowmaster for my MH. I will get the work done this week. Thanks again I didn't want to make a mistake with this much $ involved. Hope to take pictures of the MH up on the rack so I can share them with the group. Gil



From: denison
Sent: 2/19/2004 7:02 AM

Soon I will need to replace my muffler and maybe the rest of the exhaust piping. I plan to use the stock setup, or whatever is least expensive that is equal in diameters. This is because 1. I am okay with the original sound, but no louder, and 2. my belief that a performance muffler or exhaust will not make a difference at the paltry rpms where the engine spends its working life, i.e. 3000 rpm cruising, and up to 4200 rpm towing uphills.
Now looking for new dual pipes from the manifolds back to the dual inlet muffler on my 72 indian, 413, M400 chassis. I got a price on the muffler of $99, and I will probably make up my own tailpipe using my gas torch like I did when I got it.
denison



From: UluzYarx
Sent: 2/21/2004 10:00 AM

Get your carb retuned when you've got your new exhaust for maximum benefit.

Incidentally, sounds a good bet to me.



From: Liv42dayOK
Sent: 2/21/2004 11:30 AM

Lefty,

     Is the "Y" pipe available too?  It seems that this is the one part that is difficult to get.  I had figured, in the event it couldn't be found, running 2 separate pipes back to the muffler, which would have two, 2 1/2" inlets and one 3" outlet. - Sob



From: Liv42dayOK
Sent: 2/21/2004 11:34 AM

Not knowing a lot about carbs, can you explain why the carb would need re-tuned when the exhaust is changed?  I would expect that adjustments would need to be made anytime you changed what is going into the engine but, how does what's going out affect the cycle? - Sob



From: Jim83Itasca
Sent: 2/21/2004 11:56 AM

Hello everyone
Well to answere Mark's question about the carb jetting once a exhaust change (major) is completed sometimes the engine will either go rich or lean.
Minor changes the majority of the time require nothing done to the carb (but take a plug reading).
Big block chebby's 454 & 440s only require 2 1/2 (including the header collector) straight thru and nothing else.
3" from the muffler back does nothing period and is a pain to bend if needed.
I am not a fan of "flow master" due to the noise factor but i do use them on the race cars. Good luck

Jim



From: Im-still-Lefty
Sent: 2/22/2004 12:55 AM

I will check on the y-pipe first thing Tuesday morning when I get to work. I will borrow the book and scan the dodge section into my pc so I can send the drawings w/ part # to anyone who needs them. Lefty



From: UluzYarx
Sent: 2/22/2004 5:10 PM

In brief, what you can put in at the front, depends on what you take out at the back to make room for it.
Baffled silencers and old exhaust systems cause 'back pressure' which slows down the rate at which the exhaust gases leave the cylinder.
In turn, the back pressure slows the speed and amount of air that goes through the carb.
When you open the exhaust up, you stand a good chance of increasing the flow rate through the carb.
If the air flows through the carb faster, it may go through quicker than the petrol (gas) can keep up with.
When your engines runs lean, it runs hotter and takes out exhaust valves.
The risk , as Jim points out, is very low.

From my end of the telescope and from memory, the opened up exhaust systems discussion is linked inextricably with a quest for more miles per dollar.
So I recommended Gil to get his carb re-tuned. - Dave



From: Liv42dayOK
Sent: 8/30/2004 9:13 PM

I've spent a lot more time speaking with other members and have re-thought my choice on exhaust set-ups.  The consensus appears to be to stay with the original diameter all the way back because of the rpm and use of the engine.  A lot of "up-grades" don't show their value until you hit well over the rpms we run at and on much lighter vehicles.  I've also met a few people who had Flowmasters and said that, although they sound good, you can get the same performance (and sound) for much less money.  The main issue seems to be maintianing the back-pressure.  If I change my exhaust at all, it will be to duals with a crossover (scavenger) pipe and only slightly more open mufflers than stock.  - Sob



From: Sea Hag
Sent: 8/31/2004 10:36 AM

the PO insalled a dual exhaust system on my 76 chief  . as lefty stated , the parts are availible off the shelf .  it's 2 1/4 OD pipe , about 4 or 5 sections per side and may be a stainless alloy as they aren't rusting - they go over axel all the way out the rear . fits nicely . Mufflers aren't matched  for some reason right side has OEM Type muffler and other side a generic . I prices another OEM at NAPA $ 180.00 .  I got a quote to replace both mufflers ith matching ones at a local exhaust shop for $ 110.00 - I do that next spring .  The only time you can hear the exaust noise from inside the rig is under bridges . very quite inside . - Sea Hag 



From: DaveVa78Chieftain
Sent: 8/31/2004 2:46 PM

Ahh Sea Hag,
Far as I know and what is shown in my 72-75 Dodge chassis manual is they only built these rigs with single exhaust.  They used a Y pipe before the muffler (note I said one muffler).  The Y pipe starts out at 2 1/4 at the cast exhaust manifold and expands to 2 1/2 at the joining of the Y.  2 1/2 pipe is used from that point back.  To get dual exhaust, I cut the Y header above the Y joint and used 2 1/4 pipe from there back because that is what Dodge used above the Y joint.

Dave. 



From: Sea Hag
Sent: 9/1/2004 10:18 AM

Dave - Yes the original system was single exhaust with a cross over pipe . It has been replaced with aftermarket  parts .from manifolds ( which are also not OEM as the exit between the two rear cylinders and not in the center  )The repacement pipe that attaches to the manifold would work on the oriiginal maniflods too . the shape would allow it to be moved forward . It has a bend around starter on left so plenty of room to remove starter with out taking off pipe . then on back  with pipes running down both sides of the drive shaft over the axel and out the rear , it all fits nicely .. The right side has a muffler thats about the same size as the oem not a clue to why the left side wasn't the same . I recall the  email on your system  . thats a very good aproach modifying the existing cross over , off setting the mufflers , and running both exhaust down the same side over the axel and out the rear . well done - Sea Hag 



From: Moondisc1
Sent: 9/4/2004 4:58 PM

Size does matter!
A 2 1/2" dual exaust with truck mufflers is fine.
If I had single exaust I'd cut it off and throw it.
Flowmasters are expensive. There is a company making exact copies of Flowmasters for half the money.
If you want I'll get you the info on them.



From: Liv42dayOK
Sent: 9/4/2004 5:51 PM

Please do post the link and any info you'd like to add, Moon!  I think Flowmasters are a bit rich for the majority of us. - Sob



From: west coast redneck
Sent: 12/2/2004 2:27 PM
My advice from my machanic was to put oversized 3 inch dual exaust .all the way from the manifolds with flowmasters I think.$850 Canadian..The main reason was to keep the exaust manifold temp down. This is an inherant problem with the 440's.It did the trick & sounds great.Obviously a little louder though.I would caution always doing things the exact ariginal way.Over the years there are persistant problems with certian aspects to these rigs and there are ways around them now.



From: Liv42dayOK
Sent: 12/20/2004 1:01 AM

I've noticed a number of people who changed over to dual exhaust and then developed a rough idle and constant popping immediately afterward.  Is there a connection?  What would cause that?  What is the remedy?

- Sob



From: Sea Hag
Sent: 12/20/2004 11:06 AM

I feal that dual set up with 3" pies may be a bit overkill and pricey . mine are dual with 2 1/4 OD pipes seam to be just fine . havent had trouble with the manifolds cracking . Sea Hag 



From: DaveVa78Chieftain
Sent: 12/20/2004 2:11 PM

You got my vote Sea Hag.  2 1/4 duals all the way back.  Works well for me.

Dave



From: west coast redneck
Sent: 12/20/2004 3:39 PM

Come on guys go big or go home.!Maytbe it's the redneck in me but bigger is better.Remember all the postings about constantly going through exaust manifold gaskets & warping manifolds.This is late 70s 440-3s You have to bring the temp down some how..It idles great with the new Elderbrock carb and that funny bubbling sound after you rev it up is called rasping.We like it up here in the north.Eh what ever works for everyone but I'd sure hate to have to go back & have to change stuff again.



From: west coast redneck
Sent: 12/20/2004 5:02 PM

Eh Sob,we should have at er in a quarter mile.Just having good fun with ya all.I love these rigs.Mine's a 78 brave ,Orange..It's had many trips to the Yukon & Mexico.Love it when people see it smile ,point & shake there head.I'm there in the Member survey camping in the snow,Vancouver Is BC.Anyway everyone have a great christmas.



From: Liv42dayOK
Sent: 12/20/2004 5:14 PM

Has anyone with a dual, 2 - 1/4" exhaust system had a manifold crack or have to change out their system?  Will having 3" pipes do anything worth the big price jump at less than 5,000 rpm that a 2 - 1/4" dual system with mild increase air flow mufflers won't?   If so, we can all go home.... if not we can stay like everyone else and have more money to spend on other things.  I found that out with the NGK Iridium IX spark plugs I bought at $8 a pop!  Almost $70 for 8 plugs and the MSD Super Conductor wires at $75!  Sure, they're really, really good but, did I need to spend that much, or could I have gotten less expensive ones which would have performed nearly as well and saved half the cost?  Sometimes bigger is just more expensive with very little, if anything, to show for it except bigger bragging rights and, I don't think that's what people who own spartan old motorhomes that mostly cost less than $3,000 are about.

When I let off the gas, the Pharaoh has a smooth, mellow growl that says, "I've got well-tuned power" and.... it's really sweet to hear but doesn't sound like a street rod... after all... it's not... and I'm not planning to drag anyone else for titles anytime soon so, I don't need an intimidation factor. 

Forgot to mention;  It's a totally stock, single exhaust with just a different muffler.  Same original manifolds for 30 years and 63,000 miles but, I would like to reduce the manifold temp if I can as well because you never know when the heat will get the better of them. 

So, I think I'd be going to 2 1/4" duals with an "H" pipe to keep that awesome tone just as it is.  I tend toward Dave, Sea Hag and Moondiscs' more conservative and less expensive options but, I'd really like to hear the significant benefits vs cost reasons why a 3" system should be selected if a less expensive dual 2 - 1/4" or 2 - 1/2" system effectively eliminates the manifold heat cracking issue!  A full spectrum of information is what us newbies really need to make a truly informed decision.  - Sob



From: Liv42dayOK
Sent: 12/20/2004 5:21 PM

Hey Moon!  Can you post the link and info for those mufflers?  I've been shivering with anticipation for it (and it's 5 degrees outside too so, maybe that has something to do with it). 

"Inquiring minds want to know!"  - Sob



From: mightybooboo
Sent: 12/20/2004 6:06 PM

Mine came with dual exhaust,dont know the size,but get this, 4 FOOT LONG GLASSPAKS!
Toooo funny,i wanted them  changed out but the Mopar mechanic said nope,wont do it(this guy is a kick,if he doesnt like something,tuff,he wont  do it,old guy),you have a really good exhaust,leave it alone.Also refused to put headers on it,said its a MH,not a race car,soo....He did tell me a place that would do it,but he 'Sure as Hell ISNT going to!'
I respect someone who will tell it like it is,even when he could make a buck on it,gives credibility in my book,FWIW.
Someday I may change em if they rust or something,and it does sound like a muscle Mopar,but not extreme,so thats what I got!
BooBoo



From: HeavyHaulTrucker
Sent: 12/20/2004 9:17 PM

Sob, it looks like you are most concerned with the risk of cracking an exhaust manifold.  Well, I will tell you a little secret that most older truck drivers know but seems to have been lost on the younger crop.

On these older engines, it is important to give them a "cool down" period at idle to allow the engine heat to dissapate through both the exhaust and the radiator/ coolant.  You see, if you just shut off the engine, there is a "heat soak" factor -- you see it most prominently when you shut off your engine and your water temp gauge goes from 190 - 200 to 210 or more.  Well, it is even worse for exhaust manifolds -- they go from a running temperature of around 600 degrees to over 1000 degrees in a matter of seconds, then cool rapidly from there.  That is when your cracking is most likely to occur -- during this rapid cool down.

It is better, and you are more likely to avoid manifold cracking, if you let the engine idle for a few minutes before shutting it off.  This allows the manifold to cool to around 300 degrees with the cooler exhaust gases of idle -- then, when you shut it off, the "heat soak" won't be so drastic.

This was an old lesson learned on the old 855 cid Cummins diesel engines, when shutting it off suddenly could crack a block, head or cylinder liner.

John



From: OldEdBrady
Sent: 12/20/2004 9:31 PM

You mean I've been doing it "wrong" all this time?  I NEVER shut down the Whiny Beggar when I get to whatever spot.  I leave 'er running until I have everything hooked up, and then shut her down.  And, I suppose that takes me five-ten minutes.  (Gee!  I've been doing it right all along and never knew it!)



From: cooneytunes
Sent: 12/20/2004 9:37 PM

John's 100% right with this especially comming in from an Interstate or High speed highway/freeway....most people only think you have to do this with a diesel....the main reason on a diesel  with a turbo charger, the turbo charger will be spinning at highway speed for up to three minutes and with out the engine running, it has no lubracation, and no way to cool off like John said, but it's also relevant in gas model engines, to let some of the metal parts disapate the high temps and cool down a little before you shup it off, cool down is also good for the valves....Also on the exaust note.... I think the main reason people also have some troubles when booting up to a larger exaust is, (Now correct me if I'm wrong) when you go larger or add headers, you change the back pressure on the engine. The engine was designed for a certain degree of back pressure, and a change, with out making outher changes,  carb asjustment, manifold, etc. will most times cause more problems. At least that is what I have been led to believe.....
Timmy



From: Liv42dayOK
Sent: 12/20/2004 10:34 PM

That tip was probrobly the very first valuable bit of information I learned from this web-group.  And it was none too soon before my first trip under mega-load going up a mega-hill on the way to the 1st NECWJ.  I let the Winnebeast run for about 15 minutes before shut-down.  Had Dave Denison and Lowell not shared that with me before hand, I very well might be sharing the pain of what it's like to change manifolds! - Sob



From: mightybooboo
Sent: 12/20/2004 11:25 PM

Very good advice about allowing a cool down,I sometimes forget that.Saw at 'Another Site' that lots of the old jockeys get off the freeway and putt-putt to the campground,actually they are doing that to cool down the rigs,and we always thought they were just ole' F@rts who couldnt get movin',not the case at all.
Thanks for the reminder.Might want to put these on a new thread Sob?

Lazy BooBoo <----who always has something for SOB to do



From: Liv42dayOK
Sent: 12/20/2004 11:30 PM

Aint' that just like you, BooBoo!  If you're not tipping off the general public, you're coming up with more things to do! - Sob



From: Jupp318
Sent: 12/30/2004 6:30 AM

Hi Guys,

  I have now found one of my reference books which tells all about exhausts for RV's.  The suggestion is for engines 400" or less the pipes should be 2" and the larger engines 400"+ should be 2-2.25" with 40 inch glasspack mufflers with 2 inch cores.  There is a recommendation NOT to take the pipes all the way to the back but to take then out the sides either just in front or just behind the rear wheels. Personally I favour just in front to save the hassle of getting over the rear axle.  The book also says that if you are using headers the maximum size of primaries should be is 1 7/8" with the outlet not exceeding 2 1/2".

The book BTW is RX for RV performance and mileage by John Geraghty & Bill Estes ISBN 0-934798-06-0 not currently in print but I manged to find a copy 2nd hand on Amazon.

Cheers Ian...



From: denison
Sent: 12/30/2004 7:58 AM

My winny still has its original dual pipes from the manifolds back to the original dual inlet muffler - which I recall is 7 inch dia. by over 3 ft long.  The size of my tailpipe was determined by the output from that muffler.  I think it was 2-1/4 i.d. so my tailpipe is 2-1/4 o.d.    I welded up my own tailpipe, bringing it over the axle and out behind the passenger side rear wheels.  I routed that pipe to leave room behind the axle for a spare tire to be carried under the frame.    I didnt want any extra exhaust heat on those tires, hence running it out behind the axle.   To my surprise that tailpipe has lasted nicely for 13 years, even where my welding burned away its galvanized coating.  Dumb luck!<o:p></o:p>
    Now Im facing buying a new muffler - my original one looks scabrous.  I expect to use the original type of course.  I had thought of trying to make one from stainless steel - but I dont have a mig or tig welder to do decent looking welds, and besides; the original one has lasted 32 years!  As it is I will probably need to make up new pipes from the manifold to the muffler, since I havent found anyone selling them.  I can probably buy a tig welder for what the original pipes would cost me anyway, and I would make them up from stainless  -- definitely in the original diameter.  <o:p></o:p>

    Anyone know the best alloy number for stainless exhaust pipes?



From: Liv42dayOK
Sent: 12/30/2004 8:28 AM

"Now Im facing buying a new muffler - my original one looks scabrous".

Scabrous (def): A word that only Denison knows the meaning of but
                       sounds real nasty.

Daniel Webster



From: olivereaman
Sent: 12/30/2004 11:14 AM

Dennison,  I'm sure if this'll help you, but you can take a look at the different properties of different alloys of stainless steel.

                      www.qualitykingdom.com/stainless_steel.html



From: olivereaman
Sent: 12/30/2004 11:17 AM

Post above should have read      NOT  SURE          Sorry!



From: olivereaman
Sent: 12/30/2004 11:23 AM

Dennison, here's another link that lists advantages and disadvantages of different alloys.

   www.burnsstainless.com



From: west coast redneck
Sent: 1/5/2005 2:53 PM

Eh 42day.Didn't mean to say your deficient as far as your skinny exaust goes.I tend to do things maybe alittle overkill.I've seen way to much in the past people cheaping out getting the cheapest price & just addiquat stuff to do the job.It more often than not comes back to bite you.It's worth a little extra for my peace of mind to know for sure it's better than it really needs to be.See ya on the road.I'm the groovy Orange 78 brave 21 ft.