high flow exhaust = 3-5% mpg gain?

[Frank Lee]

Originally Posted by justjohn

Cool. So my takeway from that was that adding backpressure (the silencer) won't help, I need the correct sized tubing. Probably better to take the silencer off.

Sound right?

No.

Leave it on. Even if... IF... it helped fe, it would be by fractions of an mpg, and nobody wants to listen to something that sounds like crap blatting around anyway.

[user removed]

Look at the 92-95 Civic VX, smaller intake runner diameter and smaller diameter exhaust system. Bought mine salvage in 08 with 27,492 actual miles.

Mine would cruise easily at 1000 RPM at 30 MPH, because it was purposefully designed with several system modifications incorporated to work together properly.

On one trip of 300 miles I got it to 68 MPG in the early summer of 2008, carrying two people and other stuff that totalled 500 pounds. Speeds averaging 60 MPH on the 15 year old original tires made in March of 1993.

You can search the web and find what they did to the VX to make it one of the all time mileage champs, and none of it was for performance. Compare the mileage to a standard DX or an SI model of the same body style to understand the cost of performance over economy.

regards
Mech

[incautious]

WILL NOT LET POST LINK TOO FUNNY Search aero turbine exhaust mpg chart
on google

I no longer have my IRS mandated log book( sold the business), but I used a 1990 5.0 Lincoln town car for business putting about 40,000/year on it. Just by installing 225 75 15 tires on the rear in place of the stock 205 70 15 and installing a 2" dual exhaust( in place of single) with Police issue "h" pipe , 18" magnaflow low restriction mufflers and factory tail pipes my MPG went from 19-20 to 23-24. total cost of the exhaust system $200(parts only) went from using 2000+ gals in one year to 1700 gals at $3.50 that's $1200 savings/year Speedometer was corrected for the taller tires. So mileage results were accurate.

[MetroMPG]

Unfortunately, by making 2 changes at once (tire size + exhaust), it's not possible to say which one caused the fuel economy change (assuming the change was caused by one of the pair).

FYI, you might like to read this thread: http://ecomodder.com/forum/showthrea...ery-11445.html

BTW, a change from 19 to 23 mpg is a 21% increase.

[cleanspeed1]

Originally Posted by incautious

WILL NOT LET POST LINK TOO FUNNY Search aero turbine exhaust mpg chart
on google

I no longer have my IRS mandated log book( sold the business), but I used a 1990 5.0 Lincoln town car for business putting about 40,000/year on it. Just by installing 225 75 15 tires on the rear in place of the stock 205 70 15 and installing a 2" dual exhaust( in place of single) with Police issue "h" pipe , 18" magnaflow low restriction mufflers and factory tail pipes my MPG went from 19-20 to 23-24. total cost of the exhaust system $200(parts only) went from using 2000+ gals in one year to 1700 gals at $3.50 that's $1200 savings/year Speedometer was corrected for the taller tires. So mileage results were accurate.

The Ford 5.0 has always had bad heads for performance use, but those small ports and valves have high velocity, which is great for bottom end torque. One of the reasons that a 5.0 with the tuned port style manifold can mpg like crazy in the right chassis. The Honda is the same. Small ports, high velocity, mild cam timing, lean burn, big mpg.

[comptiger5000]

Keep in mind, under light load at cruise, this won't make any significant gains. The gains would be had in city driving where the engine is under more load when accelerating, or when towing (or climbing a steep hill). In those situations, more low end torque means you can keep it in the good part of the BSFC curve (low rpm, high throttle) more easily, as you don't have to rev it as high to accelerate, and don't have to downshift as much when pulling.

[NHRABill]

Lots of exhaust advice but please keep in mind there is no general rule across the board. Every car and engine setup is different. Exhaust tubing size and length varies dependent on how your engine is tuned.

I changed the leaking exhaust on my truck and noticed the previous owner went from the factory single 3" pipe behind the cat to a 2.25" pipe with goes of weld into a 2.25" muffler with a 2" single out tailpipe ... Yeah it was a mess..

It was replaced behind the factory cat leaving the stock exhaust manifold and the stock catalytic converter that still functions properly. I extended the 3" pipe to the stock muffler location where I ran a single 3" inlet and Dual 2.5" outlets exiting stock location. Muffler is hi flow... result is no gain or loss in MPG but noticeable increase in torque. I do tow once a month and it is is easy to feel when pulling the trailer.

point is not all recipes will be the same for each vehicle as a few pointed out driving style city to highway also plays a role into the equation. best of luck figuring out what is best for your application.

[Blu3Z3rg]

Pipe Sizing Calculator
Use this for a VERY accurate calculation of your diameter size.

You don't need HP for fuel efficiency. You DO want a properly sized exhaust, with a SMOOTH flow in your exhaust.
Mandrel bends, straight flow mufflers, high-flow cats. THAT's what will give you the benefit.

For example, I had a turbocharged mustang that many people suggested I went with dual 3" exhaust. When I ran it through the calculator, I found that a SINGLE turbo with SINGLE 3" exhaust, would be enough to reach 600hp (remember, turbocharged changes the dynamics). I saw an increase in HP, AND I was getting 22 mpg if i could keep my foot out of the boost. All this and it was about 550hp.

[robertwb70]

I ran some numbers through one of the on-line calculators before my last exhaust mods to my Geo Metro, results are posted here- Robertwb70: Exhaust size

[markweatherill]

A 'high flow' air filter, by itself, makes no difference to the amount of air passing through an engine unless that engine is running at such high output that the intake becomes a restriction to it.

In short, exhausts are similar.
Except that the exhaust gases are under pressure and 'therefore' it's considered a good thing to reduce the 'restriction', to help them escape. But then it's important to consider cam timing, valve overlap, which is designed around certain exhaust characteristics.