Dual Exhaust MPG gains

[95busa]

ALCON-
I am contemplating installing a Walker factory police style dual system (no resonators with H pipe) on my Grand Marquis. In the factory rating this was good for about 15HP if I recall correctly 239HP vs 224HP with single pipe. I am trying to figure how much of a MPG bump I would get. I am guessing about 5% given the 7% increase in horsepower. If so, I would think a 1.5MPG increase would be in order. Any thoughts? Observations? Remarks? Trying to determine if the MPG increase will justify the duals. I -THINK- in the long run it would since I plan on driving this car another 100K or so.

 

[simple_gifts]

Approach from a different angle. Figure out what the mpg increase needs to be over the life of the vehicle to recover the cost of the install, assuming $4 gas and X miles/year.

If it is wildly high (which I expect it to be) then any mpg investigation is irrelevant. JMO.

 

[rpn453]

Tuning the exhaust for top end power is diametrically opposed to tuning for efficiency at moderate engine speeds. If you remove restrictions due to minor losses - improve flow smoothness - you can improve both fuel economy and power, but don't necessarily expect anything by simply increasing the capacity.

There's no way to guess what the effect will be. You'll probably have a slight loss in fuel economy from the larger capacity but slight gains from smoother flow through the mufflers, if they're less restrictive than the regular one. It's probably a wash so you'll have to justify it on sound and power. But there's nothing wrong with that!

 

[mpvue]

I think you'll get less mpgs, because you're going to be whooping on it more often since it'll sound better

 

[troyb43]

Originally Posted By: mpvue
I think you'll get less mpgs, because you're going to be whooping on it more often since it'll sound better

+1 Same thing my dad told me in the late 70's with the Chevelle I had

 

[Loobed]

Originally Posted By: mpvue
I think you'll get less mpgs, because you're going to be whooping on it more often since it'll sound better

+1

 

[jetmech1]

Quote:
I think you'll get less mpgs, because you're going to be whooping on it more often since it'll sound better


+3

You'll most likely take a slight MPG hit. Less back pressure means greater volumetric efficiency which translates into better cylinder filling. More exhaust out = more fuel/air in. Hopefully, the power gain will translate into less throttle needed in cruise and balance out (maybe). But, like the other poster said, It'll sound great and run better. As has been mentioned: "Nothing wrong with that"!

 

[Colt45ws]

I got a big fat nothing from going duals. Nothing lost though either. However! My system is not factory style. Its way more than I need; Dual 2.5" mandrel bent stainless with X-pipe. I plan on doing more with the engine though, so its future proofed.

 

[The_Jeff]

On a throttled, normally aspirated engine... I don't think so.

Peak HP would be at WOT, which you aren't at, much.

Something is going to keep the air from going through the engine, either on the intake or exhaust side. It would be an interesting exercise in where the throttling occurs and how it affects your specific motor/ cam/ computer programming. But I would not expect anything. A diesel or a turbo, maybe.

 

[95busa]

Originally Posted By: jetmech1
You'll most likely take a slight MPG hit. Less back pressure means greater volumetric efficiency which translates into better cylinder filling. More exhaust out = more fuel/air in. Hopefully, the power gain will translate into less throttle needed in cruise and balance out (maybe). But, like the other poster said, It'll sound great and run better. As has been mentioned: "Nothing wrong with that"!

More fuel/air in = less throttle needed to achieve a given speed though....With a 1.5 MPG increase and $4.00 a gallon gas it would save me about $200 or so a year. I think if I sell my SiG I am going to hook it up.

 

[95busa]

Originally Posted By: jetmech1
You'll most likely take a slight MPG hit. Less back pressure means greater volumetric efficiency which translates into better cylinder filling. More exhaust out = more fuel/air in. Hopefully, the power gain will translate into less throttle needed in cruise and balance out (maybe). But, like the other poster said, It'll sound great and run better. As has been mentioned: "Nothing wrong with that"!

Yeah....I am thinking more HP=Good and duals are cool anyway. Plus with a 2.73-1 rear end 15 more HP is a REALLY good thing.

 

[pcoxe]

I agree with less mpg. Reduction of back pressure will help mostly at WOT, not part throttle cruising. You'll burn more extra fuel during acceleration than you will ever save during cruise conditions.

 

[JHZR2]

Originally Posted By: jetmech1
Quote:
I think you'll get less mpgs, because you're going to be whooping on it more often since it'll sound better

+3

You'll most likely take a slight MPG hit. Less back pressure means greater volumetric efficiency which translates into better cylinder filling. More exhaust out = more fuel/air in. Hopefully, the power gain will translate into less throttle needed in cruise and balance out (maybe). But, like the other poster said, It'll sound great and run better. As has been mentioned: "Nothing wrong with that"!


This.

 

[expat]

Remember the HP gain is at the Top end (6k rpm or whatever)
Depending how you drive your car, you might only be using 25% of the engine's potential HP in normal use.
There will be very little restriction through even the standard exhaust at that output.
There are other considerations, like having a 'Tuned Exhaust' can boost Torque at specific RPM, But in general, everyday use, you are unlikely to see much change, one way or the other.

 

[user52165]

Originally Posted By: 95busa
More fuel/air in = less throttle needed to achieve a given speed though....With a 1.5 MPG increase and $4.00 a gallon gas it would save me about $200 or so a year. I think if I sell my SiG I am going to hook it up.

Who says you will get a 1.5 mpg increase? Very unlikely. No evidence, just your wishful conclusion.

+4 to the above comments.

FWIW - if you do it, an X pipe is generally preferred over an H pipe, and resonators are non restrictive - no effect on economy, just sound.

 

[Hokiefyd]

Originally Posted By: 95busa
More fuel/air in = less throttle needed to achieve a given speed though....With a 1.5 MPG increase and $4.00 a gallon gas it would save me about $200 or so a year. I think if I sell my SiG I am going to hook it up.


Either way, it takes X amount of horsepower to move your car through the air at speed. And changing the exhaust doesn't significantly change the inherent efficiency of the engine. You may get slightly less backpressure with the additional exhaust system volume (physical volume, not auditory volume), but I don't think it would be significant. I'd say your mileage will be unaffected (or slightly worse due to you running the car harder to hear the duals).

 

[95busa]

Originally Posted By: user52165
Originally Posted By: 95busa
More fuel/air in = less throttle needed to achieve a given speed though....With a 1.5 MPG increase and $4.00 a gallon gas it would save me about $200 or so a year. I think if I sell my SiG I am going to hook it up.

Who says you will get a 1.5 mpg increase? Very unlikely. No evidence, just your wishful conclusion.

+4 to the above comments.

FWIW - if you do it, an X pipe is generally preferred over an H pipe, and resonators are non restrictive - no effect on economy, just sound.

Sir,
Just FYI- your post is kind of [censored]

 

[SteveSRT8]

Typically there is a slight movement up the rev range in the torque peak with a bigger exhaust volume.

That can be really bad in a huge sled with a small displacement V-8 with tall gears. I'd be very careful about this, as it could make the car a bit slower off the line and not really be much difference in power at all.

 

[mechtech2]

You will have more power with the dual set up.
But velocity will be lost in cruising conditions, which are NOT full throttle.
Depending on the speeds, I guess a loss at low/med speeds, and maybe a gain at high cruising speeds.
Losses will be more in cold weather , as the gas cools down and gets more dense. Then, the engine is actually fighting harder to pump the larger volume out the tailpipe. the larger pipes actually have MORE restriction [at low RPM/throttle].]

 

[Colt45ws]

Oh, one thing I noticed with duals is it downshifts less often. I have the same gears you do. There are a couple hills Ive tested this on. One on a 50mph highway would normally take a TC unlock in order to pull it. No longer.
On the interstate (75mph) a particular hill used to cause a unlock, then shortly after a kickdown to 3rd. Now it will just unlock but remain in OD.
This is all with cruise control on.
I call that a win in my book.