Knucklehead97 Posted December 27, 2014 Share Posted December 27, 2014 So I just wanna ask some questions I've been wondering for a bit about exhausts. Currently I have no cat because my original one exploded. I have a Thrush Welded muffler connected in probably the most unreliable way possible because I can't weld. But I plan to redo my exhaust from the header back as soon as I get the truck running good. I want to have a nice sound on it. Loud enough to be noticed but not obnoxious. I think the Thrush can provide that once I get the entire exhaust system worked out. I found Walker replacement piping for a really good price. 56$ for the tailpipe and from the header to the cat is like 30$ and they both have free shipping. I want to keep stock 2 1/4" pipe because of airflow and backpressure. Being in Alabama I don't have emissions checks and all that so the cat isnt NEEDED but like I said I want the right backpressure so either I want to get one or do something to correct the backpressure. My questions are how could I correct the backpressure without a cat? Because they are pricey. And I've heard of people using Glasspacks in front of mufflers, why? Can that correct the backpressure and add a good sound? And also I wanted to cut the tailpipe at the bend and run the pipe straight back under the rear bumper with a 3" tip to hopefully add a deeper sound. Would the 3" tip change the sound at all or would it just look obnoxious? Another goal I want to complete with this is as little interior sound as possible. No drone on the highway hopefully. I know this is a bunch of typing for such little questions but I felt the need to explain everything. Exhausts are important to me because I love good sounding trucks and would love for my I6 to sound even more like a deep toned V8. Thanks guys :D Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 27, 2014 Share Posted December 27, 2014 Works fine, nice sound. Stainless Cherry Bomb Link to comment Share on other sites More sharing options...
Knucklehead97 Posted December 27, 2014 Author Share Posted December 27, 2014 Does it actually add enough backpressure? And are you running it with another muffler or just a Cherrybomb? Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 27, 2014 Share Posted December 27, 2014 How much back pressure is enough - no idea. But yes, it adds some back pressure because of the louvers on the inner tube create turbulence. And glass packs are great for reducing droning at certain RPMs. Glasspacks are an old, simple, and relatively inexpensive muffler design that effective at reducing back pressure, but not very effective at muffling noise. A longer glasspack will reduce noise to a greater extent than a shorter one. Sound is also dissipated into the fiberglass damping material. Other glasspack mufflers utilize perforated louvers punched into the center core. This can adversely affect total flow capacity. How much it lowers total flow capacity will vary depending on how far the louvers protrude into the airstream and which direction the louvers face. The turbulence created by the perforated louvers therefore achieves greater muffling capacity at the expense of total volume of air flow. The more turbulence created, the greater the muffling & less total air flow / power production capacity. Depending on the directionality of the louvers, once can choose between slightly higher flow capacity or slightly greater muffling. This lower flow but slightly quieter design approach is commonly used in glasspack mufflers. Link to comment Share on other sites More sharing options...
Stacks Posted December 27, 2014 Share Posted December 27, 2014 +1 on Hornbrod's comment on the back pressure. Here's a link to my MJ exhaust sound, dual outlet Clifford headers and an 18" glasspack going to each stack. With a single exhaust you won't get the crackle I have. http:// Link to build thread. http://comancheclub.com/topic/33955-89-mj-work-truckdd-to-dd-and-4-wheeling-whenever/ Link to comment Share on other sites More sharing options...
Knucklehead97 Posted December 27, 2014 Author Share Posted December 27, 2014 I've already read through your build thread, Stacks. And gosh... I love the sound and look of those stacks all around. Creative to do to a Comanche. I'm thinking when it comes down to it I'm going to experiment with a Glasspack and Thrush Welded. From what I've seen Glasspacks are amazingly inexpensive. Way better than the $60-90 for a cat. Link to comment Share on other sites More sharing options...
gogmorgo Posted December 27, 2014 Share Posted December 27, 2014 Cats really don't add all that much restriction. A cat is basically a bunch of small tubes that flow the same amount of air as the open pipe does. Sure, there's some turbulence entering and exiting the small tubes, but it's still an unobstructed straight shot through. Pulling a clean (not plugged) cat off a car and replacing with a straight section of pipe won't cause a noticeable change in power. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted December 27, 2014 Author Share Posted December 27, 2014 I've just heard that running with to low backpressure can cause valves to go out quicker and give worse gas mileage with less low end torque. Which all of those things are something I want to keep lol Link to comment Share on other sites More sharing options...
Jeep Driver Posted December 27, 2014 Share Posted December 27, 2014 I made up this exhaust for a project that I was working on a few years ago. Before I clamped the tubes onto the manifolds I started the engine up and attempted to hold the tubes on by hand, I was all I could do to hold them on and I'm no sissy. The point is- it doesn't take much to create back-pressure, anyone who says otherwise is full of $#!&. I'm no expert and I don't claim to be but I do know this- there are intake pulses and exhaust pulses, disrupt one side or the other and you will lose performance, horsepower, torque, or both. A full exhaust, all the way to the rear bumper, will have back-pressure, cat or no cat. Link to comment Share on other sites More sharing options...
Jeep Driver Posted December 27, 2014 Share Posted December 27, 2014 Also wanted to add this- Motorcycle days....way back then...... I went to a full exhaust and K&N intake. The guys I rode with told me- "lean makes horsepower, leave the carbs alone". My power band completely changed, 6K rpm on through 9K rmp....grab a handful and hang on..... but above 9K? complete fade....nothing. Re-jet my carbs and even though I lost that quick twist....I regained my pull right on through 12K. There is a member here who claims that he had a 2.5" full exhaust installed on his MJ, he says that his power loss was so significant that he immediately turned around and had the new exhaust removed and another new 2.25 exhaust installed. If you free-flow the exhaust side and do nothing to increase your intake side....give no consideration to fuel supply....what the hell does one expect? Free-flow the exhaust and restrict the intake, starve it of fuel.....yeah, sure you'll lose power. Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 27, 2014 Share Posted December 27, 2014 Gotta balance the suck and blow. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted December 27, 2014 Author Share Posted December 27, 2014 Thats the exact reason I want to try to keep it the same but still be able to get a good sound. don't wanna take away from performance just for sound Link to comment Share on other sites More sharing options...
Tommy Posted December 27, 2014 Share Posted December 27, 2014 Back pressure isn't really a thing you want. It's all about velocity. Link to comment Share on other sites More sharing options...
gogmorgo Posted December 27, 2014 Share Posted December 27, 2014 Back pressure isn't really a thing. It's all about velocity. Fixed that for you. Backpressure is a made-up term to explain several phenomena that most people don't understand. Basically what's going on is that a specific exhaust system will flow the largest volume of air at a certain RPM. At that RPM, the air is flowing down the pipe at an ideal velocity that leads to the moving gasses "pulling" the exhaust out of the enigne — the engine doesn't need to work (as hard) to pump the exhaust out. There's also some really cool stuff going on with the gasses cooling off and venturi effects, but that's above the scope of this thread. If you're below that RPM, you don't fill the entire volume of the exhaust with moving gasses and you start getting turbulence which slows it down. You lose the pull, and the engine is now pumping exhaust out. Above that RPM, then you're starting to need to compress the air to get it all down the tube... the engine's pumping again. The other major thing that comes into play is called wave-tuning. Basically the concept is that your engine doesn't emit a constant flow of exhaust like a turbine would, but rather a bunch of pulses. In layman's terms, If they don't sync up, they can run into each other which will slow things down. You don't need to worry about this if you're not looking into doing anything with headers or manifolds, because this mostly has to do with header pipe lengths. What does this mean for the average Joe Schmoe with a pretty well stock motor? Stick to the manufacturer's exhaust diameter. You can play around with mufflers and routing for sound quality and/or looks, because they're not really changing things all that much so long as you don't add anything overly constrictive (i.e. "squish" bending), but frankly the manufacturer picked what they did for a reason. If you spend a good amount of time at higher rpm, it might benifit a small increase in exhaust diameter, but mostly that'll just manifest itself as reduced torque at lower rpm. That said, when/if I ever get around to getting my MJ going again, I'm thinking of doing straight pipe down to just before the rear axle, maybe with a glasspack in there, minimal bends over the axle, and then a Flowmaster 50 series with a single pipe going straight out the back. Not sure yet if I want to do the crossover or keep it all on the driver's side, not sure how it'll work in proximity to the gas tank. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted December 29, 2014 Author Share Posted December 29, 2014 Well I think this all just proves I should try a glasspack and all that and see if I like it. Which I'm sure I will. Thanks guys. Link to comment Share on other sites More sharing options...
Stacks Posted December 29, 2014 Share Posted December 29, 2014 A 3" tip wouldn't alter the sound at all. If you want to do that make that 3" section about a 36" section of 3" pipe and it will deepen the exhaust note very noticeablly!! Link to comment Share on other sites More sharing options...
big66440 Posted December 30, 2014 Share Posted December 30, 2014 Back pressure isn't really a thing you want. It's all about velocity. :agree: :agree: :agree: :agree: 100% Link to comment Share on other sites More sharing options...
Knucklehead97 Posted December 30, 2014 Author Share Posted December 30, 2014 Would making it a 36" section change the flow to much, if any? I mean of course it's going to be after the glasspack and muffler. I don't mind cutting out the idea of doing a 3" section. Just really wanting the deep sound Link to comment Share on other sites More sharing options...
Knucklehead97 Posted December 31, 2014 Author Share Posted December 31, 2014 Another couple questions. Do you guys think I could do all of this successfully without welding? And I may try and make a Cherokees tailpipe work so I don't have to pay a shop to build me one or buy an original off Ebay and cut it to add the 3" length on.. I think I could cut out the section that goes over the axle with enough to clamp some pipe on, and then piece the rest together. Like with everything I do on this truck I want to do it as cheap as possible (and preferably by myself) while still maintaining quality. May have someone that could weld it up for me if clamps couldn't do it. But I'd like to do it all myself :D Link to comment Share on other sites More sharing options...
gogmorgo Posted December 31, 2014 Share Posted December 31, 2014 When the cobbled-together nastiness that was on my Lada when I bought it finally fell apart (about 1000 miles after I bought the Lada) I pieced together a system with pieces of tubing from the parts store, and clamped it all together. It leaked from about half the connections. I mashed down the clamps with only marginal improvement. I doubled up the clamps for the worst spots, and that helped, but the leaks are slowly getting worse again. I have seen professional shops successfully clamp on mufflers and stuff, so it's possible that I just suck, but there you go. Welding is nearly always better, the exception of course being if your weld looks like this: I mean really? What was even the point of that? ALL the welds on the Niva's exhaust looked like that... any wonder why it fell apart? :doh: So yeah, that exhaust was total junk. I honestly picked up 3 mpg when it fell off. 3! I was also trying to do things on the cheap. :D I'm thinking ditching that... thing... in the middle is why performance improved. Running with only a glasspack makes it sound pretty hillariously awful, and it's pretty loud, but at least I don't need earplugs to drive it any more... Link to comment Share on other sites More sharing options...
Jeep Driver Posted December 31, 2014 Share Posted December 31, 2014 From the x-member back, no cat, local shop charged me $180 labor and material- how much more freakn' cheap do you want?????? All WELDED! I don't like it and it will get replaced after I get the new engine installed but that's a different matter, still, it was well done.......and CHEAP! Image Not Found Link to comment Share on other sites More sharing options...
Knucklehead97 Posted December 31, 2014 Author Share Posted December 31, 2014 Lord. May just have to bug a guy I used to work for and see if he'd mind helping me piece it together. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted December 31, 2014 Author Share Posted December 31, 2014 And I'll check with local shops beforehand. From internet research I was hearing 300+ for an install and materials... Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 31, 2014 Share Posted December 31, 2014 A few years ago in a local muffler shop just up the road from you, I had a new 2.5 exhaust system installed from the header collector pipe all the way back for a bit less than $200. This included a stainless glasspack to replace the cat, new Walker performance muffler w. one inlet / two outlets, and dual tailpipes exiting under the rear bumper. With new hangers and all welded. Would probably be less than $300 today. So yes, check with your local shop. Link to comment Share on other sites More sharing options...
MuddFoot Posted December 31, 2014 Share Posted December 31, 2014 around here you can get glasspack catback duals for 125 with turbo tube 135 with fake flowmaster 175 stock tail pipe and muffler 80. my true dual on my 2010 dakota was around 380 but thats 2 flowmasters all stainless pipe and tips Link to comment Share on other sites More sharing options...
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