well as we all know diesel costs have skyrocketed most of us in to poverty so in my quest to make my truck more MPG friendly i was thinking of having a 3" straight pipe exhaust installed... will this help my MPG's at all or am i wastin my money. i currently have the original exhaust and muffler on my 89 f350 crew cab 4x4. im also working on freeing up the intake with maybe a ram air system similar to what others on the forum are running to help in my quest for the elusive 20 MPG mark (im at 15mpg's currently). i know my stock 4.10 gears, even with the EO4D auto tranny, isnt helping much but thats next years project... thanks N8

 

3.5" would be better, but without a free flow muffler the noise will kill you. Turbo will chop it up though.......

 

How much does it chop it up PLC7.3? I'am thinking about taking my muffler out for the same reason as rockcrawlerdude. I'll be leaving mine at 3'' though.

 

From my own experience, I think the MPG gains from a Y-pipe back exhaust system upgrade on an NA engine as outlined above would be minimal. What's minimal? About 0.5 mpg or less (likely less) if nothing else is done. In no case I can personally document, have I seen more than 1 mpg. With headers, it could go up to 2-3 mpg (depending on how good the headers are).

I also think 3.5 inches is way too big for an NA engine that's being driven for economy. Going bigger on system size than you need is counter productive on NA engines (not much harm on a turbo engine, though). Google the term "exhaust scavenging." Bottom line, you loose more at the bottom end by going too big than you lose at the top end by being a touch too small. Why? Because you spend more time tooling around at low rpms than you do wide open at 3-grand. The rule for NA exhaust systems is 2.2 exhaust flow CFM per horsepower. For a 180 hp NA 7.3L, that rounds up to about 400 CFM. A straight section of 2.25 inch pipe flows 600 CFM (2.5-in. flows 900). If you deduct flow for bends, your stock 2.5 inch system looks pretty good. Mufflers are another matter, they are often pretty restrictive and most of the gains you see (power and MPG) come from the upgrade to a free flow unit. An unmuffled NA is pretty loud, but if you upgrade to a muffler that has the flow you need, you are 90 percent fixed (depending on how many bends your system has and if they are mandrill bends or crimped bends). I happen to have some muffler flow rates in front of me here and know that a Dynomax Ultra-Flow SS in 2.5 inch flows 1000 CFM (all flow rates at 20" HG, by the way), so you can buy a muffler that won't hurt power. Even the modest Dynomax Super Turbo flows 410 CFM. Headers would be worth a lot more MPG-wise, because they encourage better scavenging. Bottom line, a muffler upgrade (or eliminating the muffler if you want to suffer) would be your most cost-effective upgrade.

WARNING: A FWIW RANT-
Too many people out there are spending dollars to save pennies. Say you buy a $600 exhaust system that offers a 0.5 MPG increase. If you drive 15K miles per year and get 15 mpg stock paying $4 gallon, you will spend $4000 a year on fuel. At 15.5 mpg modified, you will spend $3871. That's a $129 savings. Cool, but it will then take you 4.65 years to pay off that $600 exhaust system, assuming all things stay the same. Usually, careful driving and making sure you cover the basics of vehicle setup: pumped up tires, clean air filter, traveling light, etc., is worth a half mile per gallon.

 

What are a "good" set of headers for a 7.3 NA?

 

thanks Jim for the info. the local muffler shop said thay would charge me $125 to run straight 3" pipe ( no muffler) from the "Y" back. so that alone may be worth it for $129 savings but i do more around 20k a year as my commute is 125 miles round trip plus additional local driving as well so it would be cost efective to go that route. however if my putting on a free flow muffler to replace my old stocker on woul;d yeild the same benefits then i may go with whatever option is cheapest, thus being more cost effective. and i also would like to know what headers you' recommend as even adding 2 MPG would extend my driving range roughly 72 hours so thats a half trip more per fill up....

 

Google "Stan's Headers." They are the only headers I know of for the 6.9-7.3L IDI engines. From most reports, they are good units, but some power claims seem to be a little optimistic. They were about $500 last time I looked. Combined with a dual 2.25 or single 2.5-inch system (or single 3-inch) and good mufflers, it would be a formidable system worth a coupla MPG at least. Only works on an NA engine, though.

That's a decent price to make a 3-inch system and if they are using kink bends, a 3-inch is equivalent to a mandrill 2.5 system, so it shouldn't kill your bottom end. But if your current system is good, a muffler only (which you can do at home) is the best bet to save money but buy only a brand name (Google Dynomax, Flowmaster, Thrush, Edelbrock for some very cost-effective options). Some of the no-name performance mufflers are really slightly dolled up regular mufflers that don't flow. Often made in China or India. The names shown (and others) offer proven performance and are most often available at auto parts stores or muffler shops. Good luck!

PS- Whatever you do, let us know how it worked out!

 

will do... i may just end up doing a hi low muffler for now and see how that works out. the headers are a bit steep for me right now... but thanks for all your info it probably saved me some money by just replacing the muffler...

 

Peter is dead on with this one. You really don't want a straight piped NA. At idle, it has a nice low rumble to it. But under any kind of load, it is unbearable. You can't go anywhere quietly. I ran mine with straight exhaust for about a month. It was fun at first, but became annoying pretty quick. I didn't notice any mileage change either way though.

Jason

 

hmm yea my old V8 cj7 had headers, dual exhaust with flowmasters that dumped to the side before the rear tires, at idle it was awesome sounding but man when you punched it it got LOUD! it was fine except when you ran next to those concrete dividers that got old pretty quik... i could set off car alarms 100 yds away...LOL... i figured with a straight pipe out the back it wouldbt be too bad...

 

What is a good muffler for a 2.5 in pipe? I looked for a Dynomax (which I TOTALLY loved on my Jeep) but could not find one.....well they were for the Powersmoke engines.....would they work? Or any specific suggestions?


Thanks
thad

I found one....Ultra flow welded? I am going to order it.....

 

dakotajeep: A muffler is pretty much a muffler. You gotta look at the placement of the inlets and outlets and have them match what you have. Dynomax makes a gazillion mufflers in a gazillion styles. There's one there. Don't look for kits, look at the individual mufflers.

 

I am tracking with you.....like a hound dog....

 

If you have a turbo removing the muffler makes verry litle difference in sound but seemed to improve millage greatly in my case mine was virtualy plugged with carbon as will most factory ones by now. the only sound difference is at high rpm you get a jake brake sounding cackle wich I think sounds cool and you can kinda hear the turbo. I have the ford factory turbo basicly an ATS with difernt outlet and smaller crushed down pipe.

 

my buddy claims about 18mpg with the pump turned all the way up, and 3in true duals w/ glasspacks and 4 stacks, dlp stage 1 injectors (20-40hp), k&n fatory filter. and bout 20 with it turned down and no injectors. probly the best sound ive ever heard and its really loud with tons of black smoke in warmer weather