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Dual exhaust vs. single exhaust, fuel mileage.
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Normk1
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Jan 26, 2009, 3:39 AM
Post #1 of 9
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Dual exhaust vs. single exhaust, fuel mileage.
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I just bought a 1995 Chevy Silverado ext cab. It has the 5.7L V8 (350) and auto trans. I am going to have to replace a good portion of the exhaust system and was considering paying the extra amount for true dual exhaust with a crossover. I do not care for loud exhaust, I just want to improve the mileage. Gas is about $1.70 now, but if it goes back above $2.50 I am thinking 2-3 more MPG may pay for the exhaust in the long run. I assume I will have to have 2 cats, although my state has NO vehichle inspections whatsoever.
Any thoughts?
Thanks!
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 26, 2009, 5:42 AM
Post #2 of 9
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Re: Dual exhaust vs. single exhaust, fuel mileage.
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IMO:
Leave it as OE as you can. I seriously doubt you'll gain much of anything except looks and tone. These use large diameter single pipe. Just a glance suggests that true duals are 2.5" I.D. and Single is 3" I.D which ONE 3" is about the same CFM or would create the same approx backpressure (a needed thing)
If you think you can gain 3mpg (20%) then it would be a no brainer. You won't get any such results - IMO.
There was a day you really did add some power and potential effeciency by using duals. The engine doesn't really care so much that it remains TWO all the way but need adequate and proper flow if ONE or if you used EIGHT!
There's more to this than meets the eye. There's balance. That's achieved by using crossovers, "H" pipe and sometimes counter weights to keep in balance. This stuff get some serious engineering for OE.
Consider that if you did double up all the items that you later have double the stuff to replace as it almost certainly won't last as well as real OE parts - if this is a keeper I'd probably pay for that.
Again - IMO,
T
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Loren Champlain Sr
Veteran
/ Moderator
Jan 26, 2009, 3:51 PM
Post #3 of 9
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Re: Dual exhaust vs. single exhaust, fuel mileage.
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I agree with Tom 100%. On the other hand, I love the sound of dual exhaust. (nope, I refuse to grow up) Keeping your tires inflated properly, the engine tuned, injection cleaned, synthectic fluids, ect. are the best ways to get optimum fuel economy. A tonneau cover or canopy will help, but would probably take 54 years  to pay back the savings you'd see.
Loren
SW Washington
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way2old
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Jan 26, 2009, 3:53 PM
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Re: Dual exhaust vs. single exhaust, fuel mileage.
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Now we know how old you are 
Being way2old is why I need help from younger minds
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Loren Champlain Sr
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Jan 26, 2009, 4:00 PM
Post #5 of 9
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Re: Dual exhaust vs. single exhaust, fuel mileage.
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LOL, Way2. 57 and counting!
Loren
SW Washington
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Normk1
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Jan 26, 2009, 5:44 PM
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Re: Dual exhaust vs. single exhaust, fuel mileage.
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Thanks so much for the thoughts opinions and insights.
I belive I will keep it OE (at least for now).
I may go all out at some point with tube headers X pipe crossover and flowmasters, but not for now at least...
I like the sound of duals too, but then tend to encourage one to keep their foot in the pedal.
I will go with the tuneup, synthetic fluids etc.. for now...
Any thoughts on oil additives such as slick 50, Lucas and Duralube?
I have seen most of the commercials. What do you guys think?
Thanks again.
Norm
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 26, 2009, 7:00 PM
Post #7 of 9
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Re: Dual exhaust vs. single exhaust, fuel mileage.
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Norm,
I actually own a 97 C/K 2500 4X4 5.7 (it's a damn 350 - I'm old too!) and the exhaust is huge compared to older 350s used in everything made out there by GM for ions now.
Can't speak for model year 95 but 96, 97, and 99 all in the family stable do about the same for power and economy. I plow show with my own truck and we've had a bit this year and I leave the damn plow on if there's a chance of more which kills economy to just go errands. Twice have measured about 6mpg! Hey - keep in mind that's driving back and forth pushing tons of snow in a driveway and 2mi trips to a store each way - forgive it.
All use synthetic motor oils and synthetic trans fluid and in great shape. Actual mpg can be 10 or carefully checked on highway runs of some distance I've seen them brush 18 or so. Never heard of one actually breaking the 20 mark yet in these years but they have nice power again after a decade of being lame in the 80s anyway.
I really don't find exhaust to be the magic bullet for power or mpgs with some exceptions but it's less than you really expect.
#1 for MPG is how you drive followed by keeping tire pressure proper. You may ave 15 and probably won't notice a percent or two increases. I've clearly noted and so have the others that this 10% ethanol mixed in drops the mpgs by about that much which kinda defeats the point IMO as for these it just acts as a "filler" so you get the gallons right but they aren't as effective??
It's a truck and the nature of it is utility. If it was too aerodynamic or too light it wouldn't serve its purpose too well!
Like Loren and others I love duals and just last year put them on my own 89 Town Car. They do make a difference which still doesn't justify the cost but it's cool AND the car was designed for duals as an option. These are real duals, not just dual tail pipes. In that application they don't add tone much as the car was designed to be quiet. Those are gutless wonders for OE HP but do get decent mileage for a large car. Trade off for that exact vintage.
I'd forget the additives as just using quality oils to begin with is enough.
Headers and other modifications may show some improvements but factor the costs and the day they actually were cost effective is far down the road - again IMO. Do anything you want when it's a love affair with the vehicle.
Fuel cost prediction - my guess only: We are cheap right now and still sore from the $4+ costs not long ago. Bet ya $ this will be the opportunity for state and federal fuel tax increases to further encourage conservation and to line the pockets of someone out there under the guise of fixing up the roads (can you tell I'm from Massachusetts?)
If you do a ton of plain driving with the truck also it may be worth getting a car with tons more mpgs for just non utility use,
T
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Normk1
Novice
Jan 26, 2009, 7:43 PM
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Re: Dual exhaust vs. single exhaust, fuel mileage.
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Thanks for the insight and info. Once again, I appreciate it.
I lived in Vermont for 18 mos. I know a bit about what you are talking about.
I am 41 and live here in Southern Alabama with my Wife, stepdaughter (14 going on 24) and our 22 mo. old son.
We had been using my 1990 Nissan ext cab as primary transportation for the last couple of years. I have a company vehicle for work, so I had not seen the need to get another vehicle, until recently. We decided to use income tax refund to get a full sized truck. While waiting on the refund check, the transmission in the 1990 nissan went ka-put. I don't understand it. It only has 250,000 + some odd miles on it. Gee wizz. Japanese junk! LOL... Anyway, I have had that thing since Sept. of 1995 and it is a member of the family. It isn't going anywhere as long as it can carry people and roll. It gets 24 mpg on the highway and best of all is paid for...
I had always wished it had a 5 spd man. transmission in it. Any thoughts on this conversion? I have heard horror stories. Taking the dash out to install the pedals doesn't bother me... Changing wiring harness, computer, crossmember and driveshaft however does. I do not know if I will have to do all those things, but I have heard that I will.
Anyway, wondering why you got a 3/4 ton with a 350 (gas engine) instead of going with a Duramax? Those diesels seem to be a lot more popular down here in the south...
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Loren Champlain Sr
Veteran
/ Moderator
Jan 26, 2009, 7:53 PM
Post #9 of 9
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Re: Dual exhaust vs. single exhaust, fuel mileage.
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PMJIH; The diesels are popular down in the south, because you guys got lots of mosquitos. Diesels are great for killing mosquitos.
Loren
SW Washington
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