Critique My Exhaust Ideas

[desertPOS]

Had a plan in place for exhaust routing, and after ordering most of the parts and pieces I need, I decided to just mock the muffler up in a few different spots and see if there was another option I'm overlooking. Was planning to have the muffler next to the drivetrain, then split and shoot out in front of the rear tires on either side. Low and behold, it almost seems like the muffler fits better behind the drivetrain, and would also make everything easier to hang, easier to weld in flex pieces, better airflow around it, etc. The downside is that it would have to do a complete 180º over the rear driveshaft before it splits into tubes that kick off each side. Can't run it any further past the rear axle due to tightness and fuel cell that'll eventually be back there

I'd imagine the exhaust doesn't know or care if it's doing a 180 - what say ibb?


Top view with exhaust tube next to drivetrain

Muffler next to rear driveline, rear axle at full bump. Blue line shows 3.5" tube passing over rear driveshaft, doing a 180 and tying into the 'Y' into two 3" tubes that dump out of either side, in front of the rear tires through the orange lines. The upper links are too tight to the floor to do anything else if I have the muffler in the spot... Another added bonus to this layout is if the exhaust is just too loud, there is a little room to add a bullet style muffler up next to the drivetrain, although semi small.

Bottom view:

 

[desertPOS]

Original plan pictured below, which is a little more straight forward. Biggest problem this layout gives me is it'd be tougher to hang it next to the drivetrain (tight), as well as tougher to hang it FROM the drivetrain (plan to keep it hung or mounted to drivetrain to keep it moving together, reduce manifold cracking issues, then flex tube it after that and mount to chassis). There's also not as much room for flex tubes, and muffler is 1/2" from frame and about an inch from the tcase in this picture. I can cut out frame for clearance if needed. Also not a lot of vertical space, so belly skid within a couple inches below it, and floor/driver seat a few inches above it.

Anyway, I can make this way work, and it's how I had planned to do it in the first place, just questioning why I shouldn't do it the way I have it mocked up in the first post - which has a lot of advantages, but just seems like an odd way to do it. Few more pics of the original plan:

 

[Provience]

I think you are wasting your time going from the single to the Y and dumping in front of the tires I don't see any point or benefit to it at all, other than you've got yourself fixated on the original dump locations from the old muffler plan, which you've gotten rid of.

I also don't see the point in going from 3-1/2" to dual 3" for the exhaust after the muffler. once you hit the muffler, the exhuast pulses and velocity start changing for really the first time since leaving the cylinder. hence the reason for putting mufflers as far back as possible, if you are tight on space, drop down to 2-1/2" dual after the single 3-1/2" for more space to work with. still a ton of flow, but again the sizes don't matter as much behind the muffler.

the 180* bend will certainly change the tone a little bit, hopefully enough to kill any sharp or drone type noise. i guess that is possibly one benefit.

unless you are hard mounting the exhaust, i don't see the point in the two flex sections of tube. look like areas just to go to shit and be maint. for no reason in the future. a couple of high flex/easy to move O.E. style hangers will let you run solid exhaust, keep the weight off the exhaust manifolds, and float around as much as required.


keeping it single out from the muffler and running that over to the passanger side with 3-1/2" and then making the last ~6-12" have a bend that covers the diameter of the tube and maybe step it down to 3" or 2-3/4" right there as well should help cut down on some of the cab noise as well, still look neat with the mid chassis exhaust



critique over, it looks badass and i'm excited to see it complete as you put out great work, please keep doing you and thanks for sharing

 

[Provience]

also, probably easier to crush the tube oval that goes over the driveshaft now rather than later, more clearance is always better from spiny things

 

[crisbee1]

Nice work! Exhaust under the driver seat sucks balls in the desert.

 

[desertPOS]

I think you are wasting your time going from the single to the Y and dumping in front of the tires I don't see any point or benefit to it at all, other than you've got yourself fixated on the original dump locations from the old muffler plan, which you've gotten rid of.

The only benefit to dumping in front of rear tires is that's really the only place I have to dump exhaust. Too tight to go over the rear axle anywhere, and too tight at bump to go over the upper links. There's room to go over the frame-side upper link mounts, which is where I've got it planned at currently, but no further back than that. It'd be easier to dump exhaust toward ground/rear axle inside the frame rail, but don't like the idea of exhaust collecting under the rig for slow speeds/crawling - rather have it point out the side and away from the rig as much as possible.

To your point though, which is that I don't need exhaust to exit in front of BOTH tires - could definitely just point it out the passenger side only. Or, driver side only and keep the passenger side exhaust free for running brake/fuel/electrical. Will think on it...

I also don't see the point in going from 3-1/2" to dual 3" for the exhaust after the muffler. once you hit the muffler, the exhuast pulses and velocity start changing for really the first time since leaving the cylinder. hence the reason for putting mufflers as far back as possible, if you are tight on space, drop down to 2-1/2" dual after the single 3-1/2" for more space to work with. still a ton of flow, but again the sizes don't matter as much behind the muffler.

That makes sense, and has me thinking about keeping it single 3" past the muffler. When I was initially trying to figure out what exhaust size to run, it seemed like everything's based on horsepower and rpm, so I spoke to a rep at Brodix since their higher flowing heads and intake are on this thing. Gave him part #s for heads, intake, cams, Holley EFI and they guesstimated me at 500-550 horsepower. They did not have a tube size recommendation, but referred me to a rep at Hooker Headers. After talking to him, and a rep at Holley, they both seemed to be pointing me to 3.5" off each manifold, then 4 or even 5" if converging into a single tube - which seems kind of insane - and muffler selection starts getting pretty slim past the 3.5" stuff. This isn't a drag car, talked to another person or two after that about what actually makes sense to run without being retarded, and landed on 3" converging into 3.5"

I think you're right on dual 3" being unnecessary past the muffler, so I'll look at maybe just single 3" or dual 2.5" and maybe simplify things a bit

the 180* bend will certainly change the tone a little bit, hopefully enough to kill any sharp or drone type noise. i guess that is possibly one benefit.

unless you are hard mounting the exhaust, i don't see the point in the two flex sections of tube. look like areas just to go to shit and be maint. for no reason in the future. a couple of high flex/easy to move O.E. style hangers will let you run solid exhaust, keep the weight off the exhaust manifolds, and float around as much as required.

Going to keep the 180º over the dshaft plan and see how it turns out I'm not planning on metal to metal hardmounting the exhaust, but was going to keep it pretty rigid, although still isolated through rubber exhaust mounts. It won't have much movement to it though. Based on past cracks and splits that needed to be repaired on past vehicles, I'm of the idea that hardmounting the downtubes to the drivetrain will keep any flexing or cracking issues away from the manifolds, flex tube past that, then hang off chassis after that. Obviously, the more rigidly the exhaust is mounted, the easier it is to package, so I am going to keep at least one flex rube in the mix. Worst case is undo a couple v-bands and replace in the future if need be...

keeping it single out from the muffler and running that over to the passanger side with 3-1/2" and then making the last ~6-12" have a bend that covers the diameter of the tube and maybe step it down to 3" or 2-3/4" right there as well should help cut down on some of the cab noise as well, still look neat with the mid chassis exhaust



critique over, it looks badass and i'm excited to see it complete as you put out great work, please keep doing you and thanks for sharing

Thanks for your feedback - much appreciated!

 

[desertPOS]

also, probably easier to crush the tube oval that goes over the driveshaft now rather than later, more clearance is always better from spiny things

I picked up some stainless 2x4" rectangle tube yesterday since it looks about the same volume-wise to partially crushed 3.5" tube - thinking I'll pie-cut that for my bend over the driveshaft to keep a lot of room there. Especially since the shaft I have mocked up now is smaller OD than the final shaft that was ordered over three months ago but hasn't shown up yet and 1350 yoke will be upgraded to 1410 pinion yoke when the new shaft shows up

 

[desertPOS]

Nice work! Exhaust under the driver seat sucks balls in the desert.

Agreed! All stainless should help, and definitely going to get some heat shields in critical spots. Past that, may consider Jet Hot coating later on, or wrap in some of the tight spots. This stuff seems promising: HD Heatshield Armor

I've spent enough time in boat engine rooms to appreciate the thicker exhaust insulation - makes the thin stuff most people use seem like kind of a joke...

 

[Provience]

That makes sense, and has me thinking about keeping it single 3" past the muffler. When I was initially trying to figure out what exhaust size to run, it seemed like everything's based on horsepower and rpm, so I spoke to a rep at Brodix since their higher flowing heads and intake are on this thing. Gave him part #s for heads, intake, cams, Holley EFI and they guesstimated me at 500-550 horsepower. They did not have a tube size recommendation, but referred me to a rep at Hooker Headers. After talking to him, and a rep at Holley, they both seemed to be pointing me to 3.5" off each manifold, then 4 or even 5" if converging into a single tube - which seems kind of insane - and muffler selection starts getting pretty slim past the 3.5" stuff. This isn't a drag car, talked to another person or two after that about what actually makes sense to run without being retarded, and landed on 3" converging into 3.5"

I think you're right on dual 3" being unnecessary past the muffler, so I'll look at maybe just single 3" or dual 2.5" and maybe simplify things a bit

well that sounds kind of odd for their estimating, they are pretty far off from everything that i've come across or managed to find as "standard or expected" flow numbers


short google to turn up 3.5" tube flow rate

exhaust diameter CFM rate hmmmm

exhaust diameter CFM rate hmmmm

www.kappaperformance.com

2.25 dia. flows 457 cfm
2.50 ............. 564
3.00 ............. 813
3.50 ............. 1106
4.00 ............. 1445

4" x 7" x 15" (ish) muffler recommendations for LS3?

I need a muffler that'll fit under the tub but above the skid. Any recommendations that are quiet?

irate4x4.com

and then borrowing the math from this post

550 hp (estimated) * 0.625 * 1.10 = ~380 CFM demanded.

exhaust runs 1.5-2x intake airflow just for the sake of low restriction, cuz running on the push side rather than the vacuum side of the motor

570-760 CFM for the max exhaust flow, if 3" will flow 813 CFM on a straight pipe section, then it should be more than enough for 550 hp on a single system, then figure in the especially considering you aren't likely spending much time at redline/WOT

4" by comparison would support like 1k horsepower basically dual 3", which anybody would say dual 3" is pretty excessive for a 500hp system.

but yeah, it all goes off power because that is an easy way to convert to CFM airflow.

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racingcalcs.com

instead of guessing your HP, you can put in your engine size and known or typical RPM and guess at your V.E. to get an equally close range for CFM to size the exhaust tubing with.

 

[desertPOS]

well that sounds kind of odd for their estimating, they are pretty far off from everything that i've come across or managed to find as "standard or expected" flow numbers

I agree, and there are charts like these that seem way overblown on their sizing:

How To Determine Proper Exhaust Tubing Size

A guide for exhaust-pipe tube size needed to balance prevention of excessive back-pressure while maintaining adequate exhaust-gas velocity...

m.roadkillcustoms.com

How To Calculate Muffler Size and Exhaust Pipe Diameter | Exhaust Videos

If you're a math wiz and/or an engineer, you're probably going to like this article and the resources we've linked to. However, if you find yourself getting stuck (or bored) with the info below, here are the key take-aways: 1. The factory exhaust pipe diameter is usually a good choice for most...

www.exhaustvideos.com

instead of guessing your HP, you can put in your engine size and known or typical RPM and guess at your V.E. to get an equally close range for CFM to size the exhaust tubing with.

What hung me up on the formulas I found were inputting your rpm, and I didn't really see it addressed anywhere how to determine what rpm to put in for that. Max rpm? Average rpm I think this thing will be at? If I put in the average rpm I believe it'll be running at, does that mean it will be restricted at any rpm over that? I don't expect this thing to be at WOT much, if ever, but it'd be cool if it could maintain some speed in the desert or on the street, and it's got a TH350.

Ultimately, I based the tubing size more on the multitude of data points I collected from various build threads and people I spoke with, and less on the #s I got out of a formula. I do think there is a decent amount of conflicting information on the web about this. If you remember K5Runner from pirate, I have some screenshots I took when going through his build, since he seemed pretty similar with a Chevy-based tube buggy and big block, although he was racing KOH and other events. I think he was 3" off the manifolds to 4" single tube, 4" in/out bullet style muffler.

So anyway, I would prefer to base it strictly off the numbers, since that seems to make more sense - but that's how I derived at my tube sizes. And I'm thinking I'm set on single 3" out the tailpipe instead of dual like before...

Thanks for the in-depth reply

 

[Provience]

for RPM, that would be the Max WOT RPM at your peak horsepower.

basically, even the drag racers shift just a couple hundred RPM above peak HP because there is nothing to gain afterwards and if you HP is dropping off, then your VE is dropping off and your airflow is dropping off.

Peak HP, WOT RPM is going to be your peak CFM airflow pumping into the engine, so as long as you are sized to flow that much on the exhuast side easily then you aren't hurting your performance. this is where the 1.5 or 2 x that CFM comes in, because you want the exhaust to be no restriction so you get some room to play.

if you want to say that you will never have a long enough WOT max RPM to care about and max power isn't the name of the game anyways, then stick closer to the 1.5" factor and pick a peak useable RPM. If you are running a TH350, do you happen to know what RPM it shifts at? Without trying, i'm not running over 4,500 rpm personally, and that puts me over 75mph in second gear. what the heck do i need 6,500 rpm for?

so if you run a tighter ratio AND you pick a lower RPM for your max (and above that, who cares if you have some power loss due to restriction) then you can confidently say "below xyz power level, my exhuast is no restriciton" while making it much easier to package. working with an estimate of 500-550 hp, do you really care if your exhaust knocks your peak from 550 hp to 525 hp? probably not

the flip side is that there is almost nothing wrong with running too large of an exhaust size (and it's almost difficult to run too small of tube, muffler/cat failures/impact are the things that cause problems). even in a racecar, a 4" straight exhaust with a bullet muffler sounds like a way to make a long day longer, but it probably sounded bad-ass on the short course

single out curving up and around and back out in front of the tire is going to look wicked

 

[mobil1syn]

id do this, single 3" the whole way. pink box is the muffler

 

[desertPOS]

id do this, single 3" the whole way. pink box is the muffler

I'm positive there's no way I can fit that, but I'll double check anyway...



Btw, we had to redo the exhaust on two of the engines on a boat I worked on back in '13 and that was all 5 or 6" exhaust behind a HO 454, so it didn't seem completely out of line to be thinking about 3.5 to 4.5" range Marine exhaust insulation that got laced up on everything made it so you could work in the engine bay while it was running without cooking the second you dropped down there

 

[Provience]

well yeah, and a boat is running high load, high RPM all day long while trying to keep the temperatures down. 5 or 6" seems pretty extreme, but is a bit more justifiable there.

wrapped 4" would likely have been just as good

 

[Gdogg]

What are you using for hangers?

When I do a custom exhaust it probably take me more time to do the hangers than the pipe work and I have a complete exhaust bender.
I like to use the rods with the mushroom heads and then the rubber isolators (factory Ford type), I heat the rods to bend where I want then weld to the pipe.
The parts stores only have that cheap universal junk that breaks after a few bumps.
The only place I find the stuff I like is ebay

4X HEADED 1/2"x 10" 90° EXHAUST ROD HANGER WELD-ON MILD STEEL | eBay

1/2" HEADED ROD 1/2" DIAMETER ROD 2" x 10" MILD STEEL WELDABLE 4 PCS.

www.ebay.com

Yonaka Exhaust Hanger Rods Polished 304 Stainless Steel 10 Pack 1/2" x 9.5" | eBay

Find many great new & used options and get the best deals for Yonaka Exhaust Hanger Rods Polished 304 Stainless Steel 10 Pack 1/2" x 9.5" at the best online prices at eBay! Free shipping for many products!

www.ebay.com

6x PACK RHR1 Exhaust Mount Rubber Insulator Grommet Hanger Bushing 1/2" Support | eBay

Find many great new & used options and get the best deals for 6x PACK RHR1 Exhaust Mount Rubber Insulator Grommet Hanger Bushing 1/2" Support at the best online prices at eBay! Free shipping for many products!

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I just did a custom exhaust on a 6.7 Ford and used that stuff for the hangers.
Since you'll be bouncing around you need good hangers.

 

[arse_sidewards]

Bear River on eBay tends to have the best or close to the best prices on hangers, flex pipes and all the other little hardware that goes into a system.

 

[desertPOS]

What are you using for hangers?

When I do a custom exhaust it probably take me more time to do the hangers than the pipe work and I have a complete exhaust bender.
I like to use the rods with the mushroom heads and then the rubber isolators (factory Ford type), I heat the rods to bend where I want then weld to the pipe.
The parts stores only have that cheap universal junk that breaks after a few bumps.
The only place I find the stuff I like is ebay

4X HEADED 1/2"x 10" 90° EXHAUST ROD HANGER WELD-ON MILD STEEL | eBay

1/2" HEADED ROD 1/2" DIAMETER ROD 2" x 10" MILD STEEL WELDABLE 4 PCS.

www.ebay.com

Yonaka Exhaust Hanger Rods Polished 304 Stainless Steel 10 Pack 1/2" x 9.5" | eBay

Find many great new & used options and get the best deals for Yonaka Exhaust Hanger Rods Polished 304 Stainless Steel 10 Pack 1/2" x 9.5" at the best online prices at eBay! Free shipping for many products!

www.ebay.com

6x PACK RHR1 Exhaust Mount Rubber Insulator Grommet Hanger Bushing 1/2" Support | eBay

Find many great new & used options and get the best deals for 6x PACK RHR1 Exhaust Mount Rubber Insulator Grommet Hanger Bushing 1/2" Support at the best online prices at eBay! Free shipping for many products!

www.ebay.com

I just did a custom exhaust on a 6.7 Ford and used that stuff for the hangers.
Since you'll be bouncing around you need good hangers.

I picked up a bunch of these:

Jones Exhaust JSH3890AH: Exhaust Hanger 3/8" Arrowhead End - JEGS

Get the Best Performance with Jones Exhaust Exhaust Hanger 3/8" Arrowhead End JSH3890AH parts at JEGS. Shop Now at the Guaranteed Lowest Price!

www.jegs.com

but I wasn't seeing them in stainless, so I basically got them for the rubber bolt-on portion and picked up 5 or 6 feet of 3/8 stainless to bend up the hangers. Going to try and allow for some movement up near the drivetrain, but get more rigid as it goes back.

Got a little done today with the '180' where it passes over the driveshaft - went with ss 2x4 tube and a few pie cuts. Won't be mounting it against the tube like that, but just clamped it there for my own temp visual

Going to repurpose the 'Y' I tacked up and move it to the front for where the passenger side comes over the top of the trans and ties in, and got the d side cat tacked in. Planning to put the o2 bung right behind the cat

 

[desertPOS]

Bear River on eBay tends to have the best or close to the best prices on hangers, flex pipes and all the other little hardware that goes into a system.

I'll have to check that out

 

[Wendle]

I've been using these jiggers strategically located so they are loaded in compression. Pretty bulletproof.

 

[arse_sidewards]

I've been using these jiggers strategically located so they are loaded in compression. Pretty bulletproof.

How are they holding up?

I've contemplated that on every shitbox I've done an exhaust on but talked myself out of it on the basis that the rubber would instantly fall apart from the heat

 

[Wendle]

How are they holding up?

I've contemplated that on every shitbox I've done an exhaust on but talked myself out of it on the basis that the rubber would instantly fall apart from the heat

Yeah, they're ok as long as you outboard them a little.

They do break down pretty quick if you tuck them in too tight.

 

[pennsylvaniaboy]

I still dont understand the duals, a single 3" exhaust would be sufficient for just about anything. i am running a single 3 in from the trans back, 3" x18" glasspack ran in reverse, exits at the back. I cant imagine a louder system like yours for all day.

 

[mobil1syn]

Got a little done today with the '180' where it passes over the driveshaft - went with ss 2x4 tube and a few pie cuts. Won't be mounting it against the tube like that, but just clamped it there for my own temp visual

you need more pie cuts bro

 

[Lilyota]

You shouldn't use that brillow pad for your lines....





You should use something smooth and flat.

 

[desertPOS]

I still dont understand the duals, a single 3" exhaust would be sufficient for just about anything. i am running a single 3 in from the trans back, 3" x18" glasspack ran in reverse, exits at the back. I cant imagine a louder system like yours for all day.

Despite what your woman tells you, that extra 1/2" matters We're going 3.5" with this one, because 3" isn't enough to contain all the awesome, but I'm going to drop it down to single 3" after the muffler... I wish I could exit out the back, but it's too tight to get back there

you need more pie cuts bro

Always need more pie cuts!

You shouldn't use that brillow pad for your lines....





You should use something smooth and flat.

Good eye. I'll work on that



Got a little more done - tacked up the front portion back to the end of the trans, then pulled to purge and finish weld

 

[gt1guy]

We're going 3.5" with this one, because 3" isn't enough to contain all the awesome, but I'm going to drop it down to single 3" after the muffler...

Pretty sure if you're going to drop down to a single 3", then there's your limit on flow and running two 3.5's to it isn't gaining anything.

 

[desertPOS]

Pretty sure if you're going to drop down to a single 3", then there's your limit on flow and running two 3.5's to it isn't gaining anything.

I'm not running two 3.5s anywhere - 3" off each manifold. I don't think the tailpipe diameter indicates size limit for the whole exhaust - it seems pretty common for tube size to drop after the muffler, which I didn't understand at first, but I've gotten the impression that cooling exhaust gasses and something or other about turbulence lends itself to larger exhaust tube size ----> muffler ----> smaller tube size so that's what I'm going with.

I ordered a muffler with 3.5" in/out so that's what we're running, and we'll see how it works out. If it creates the perfect tone that makes the shop implode and create a black hole that swallows the universe, so be it I think it'll be ok...


Thanks Wendle for the suggestion - I ended up liking that idea better then what I was planning, and found these at McMaster that are good up to 300º so I ordered some and going to see how they work

Haven't gotten quite as much done with the exhaust lately, but got a hanger made with the new sandwhich mounts. Hopefully they stay cool enough at that distance - hanger material is 3/8 ss solid round and 3/16 plate for the tabs

Also, had some last parts to order and bought from Ace Race Parts — V-Bands, Flex Bellows, Weld Els, Intercooler Cores and wish I would have known of them sooner. Seems like a great business to order from and much easier to look for exhaust parts based on size then Jegs or Summit, which is where I got most of the stuff I ordered previously...

 

[desertPOS]

Thought I'd post a few finished shots -thanks again for all of the replies. I'm happy with how it turned out, looking forward to hearing it run someday soon

 

[1Sinner]

Turned out slick.

 

[gt1guy]

Ya, that came out really nice.

That had to be a head scratcher at times.