performance exaust, mpg increase?

[spotaneagle]

ok heres one thing i've gathered on this from high performance forums

straight pipes(less restrictive im assuming) will decrease low end torque but in crease high end horse power because the low end torque relies on backpressure and hp doesn't, I could see how this may possibly increase MPG, one guy said his straight pipes did increase mpg, but that could have been under low rpm situations, anyone think i should cut off the curve at the end of my muffler? lol

[spotaneagle]

Yeah my buddies 6.0 K2500=14mpg avg stock. After straight pipe-18.
The 5.4 turd in the F150 i rolled-12avg stock. after straightpipe-20.

from
http://forum.myspace.com/index.cfm?f...34&adTopicID=2

[spotaneagle]

hmmm mpg... I used to get 17 on the highway with my caprice... 4.11 gears, a 350 with a huge 4 barrel... lol... like 10 around town... lol

my S10 got 20-22 stock, after the straight pipe, headers, cherry bomb muffs... 25+ city 35-ish on the highway... with V6, 5 speed, and 4.10 gears. It also had a reprogrammed chip, bigger injectors, and an awesome 2 piece intake manifold. Damn thing scooted so good it would scare people and turn heads everwhere and I made the mistake of selling it instead of fixing it after the accident.

My blazer got like 15 mpg until the straight pipe now it gets almost 20... its terrible I know, but the 5 speed and fuel injection swap should change that.











i think a hi-flow cat might be a good option to achieve mpg increases

im not promoting true straight pipes or anything, i am considering if a straight through muffler may increase mpg...... or perhaps a hi-flow cat

[spotaneagle]

also this from:
http://www.saturnfans.com/forums/sho...i-flow+cat+mpg


Well, I have a 2002 L200 with about 126K miles on it and have a few "mods" if you want to call it that. I changed the factory air box to a Weapon R Secret Weapon open cone style filter that gives it a very nice "deep roar" when revved. Got it a while back so not sure if they still have anything for "L Series". I got it on special for I think $150.00 after shipping... like I said, it has been a while. I am sure you could "make" one out of the "do it yourself" stuff they have at the auto parts stores for much less. For wheels, try tirerack.com they have a nice selection of wheels and tires that have the 5x110 bolt pattern that I think our cars use. Some nice wheels that our car can fit are the 5 point stars that come on the Sky. Other cars that use our bolt pattern are the Chevy HHR, Saab (not sure the models). The exhaust situation... well, my cat got destroyed due to my ignition module dying and filled my muffler with lots of "cat fibers and burned stuff" so I replaced the cat with a large hi-flow cat that is usually installed onto trucks (smaller regular car cat caused computer errors) and had the muffler shop custom make a Y pipe that splits to 2 dual tipped "performance" (not sure of the brand but were about $150.00 each with installation) and it is a nice and deep even tone that seems to give the car a little more oomph, not to forget to mention that it looks really nice. I don't race it or anything but I do like "aggressiveness" the car seems to exude now. A benefit from the whole intake/exhaust change is that without driving like and idiot, I get better MPG than I did with normal driving before the change. I have gone as high as 400 miles on one take of gas with combined city and highway (mostly) driving. Let me know if you want some pictures or sound clips or anything as I have to do some maintenance on it anyway. Hope that helps you out...

[dkjones96]

I'm actually about to test this, but in steps. I've dialed in my normal driving mileage to within 0.02mpg over the last 3.5 tanks(short fill added to a full fill) so I'll be ordering a set of stainless headers soon. They're reported to give 20hp and 40 ftlbs over the stock manifolds but haven't heard anything about mileage.

Not exactly the most efficient of designs...

vs


The engine is out of breath by about 4100rpm, redline at 4750 and the auto shifts at 4900.

[theholycow]

Originally Posted by spotaneagle

low end torque relies on backpressure and hp doesn't, I could see how this may possibly increase MPG, one guy said his straight pipes did increase mpg, but that could have been under low rpm situations, anyone think i should cut off the curve at the end of my muffler? lol

I have no personal experience, nor a thorough understanding of the theory involved; but my understanding is that the backpressure thing is a myth that exists because people have observed the correlation without understanding it, and the torque actually comes from exhaust gas velocity (EGV), not backpressure.

Further, although some good arguments have been made that certain designs and construction techniques of exhaust system (not necessarily just more free-flowing or straight-piped) can produce more optimal fuel economy, I remain skeptical. The way I see it, if it can flow usefully at the maximum HP of the engine, a hypermiler's usage should be a tiny fraction if its flow and any system should be 100% free-flowing at that rate.

Originally Posted by dkjones96

The engine is out of breath by about 4100rpm, redline at 4750 and the auto shifts at 4900.

Why would they program their automatic to shift after the redline? Somebody must have been asleep at the engineering table.

[spotaneagle]

ya ya, but less resistance might prove you right even more so cow, like removing some bends?, alot of these people are removing their cats and seeing a 10mpg increase, thats why im saying a hi flow cat might do the trick, especially since i quoted one guy with a car like mine, i would think it might be different for each car

[R.I.D.E.]

In my old shop we used to install headers in customers Z cars when that is what they wanted. My observation and what I told the customer was that there was a two fold benefit to a header installation.

Power would increase above 4000 RPM.

The lack of the 30 pound cast iron heat sink that was the stock in line 6 cylinder manifold 1970-1983 240-260-280 engines would also dramatically reduce engine compartment heat levels which was especially significant in an engine where the exhaust manifold was directly under the intake manifold.

Nissan even installed an injector cooling fan to blow air on the intake manifold to reduce fuel vaporization that would make hot restarts a real pain when ambient temperatures were high on the 1979-1983 models.

I still believe that, considering the benefits of proper exhaust design that would be directly related to better mileage, that any manufacturer would be short sighted to allow the exhaust design to reduce mileage, as long as mileage was their objective. With the cost and penalties of failure to reach CAFE required fleet mileage averages, and especially considering the ease with which the redesign could be accomplished there is no incentive to poorly design any exhaust system, other than cost, which would be practically nothing.

As a direct manufacturing cost I would think the casting process would be more expensive that building a tubing header, especially from the energy consumed in casting.

As EFI systems and performance priorities became more predominant most manufacturers went to either lightweight castings or heavily shielded tubing header systems, starting in the mid to late 1980s.

The new Prius, as well as my Insight, have the manifold cast into the cylinder head. This eliminates the potential for gasket failure as well as reducing engine warm up times significantly. Not much of any way to add a performance header to one that is integral with the cylinder head. In many cases it wa necessary to electrically heat the oxygen sensor to keep it hot enough when engine on and off strategies were employed as they are in every hybrid.

02 sensors require high temperatures to function, so adding a light tubing header to your engine could actually cause the sensor to take longer to get hot enough to get into closed loop, and could also cause it to loose closed loop if you used engine off glides of significant distances in your hypermiling strategy.

My Echo has a heavily shielded stainless steel tubing header from the factory, while the Insight has the manifold cast into the cylinder head. Both have the first catalyst placed as close as possible to the exhaust valves to help with the necessary heat retention to keep the sensor in closed loop.

Additional insulation to maintain sensor heat retention may actually provide a benefit for those who do engine off glides for long periods, but you must be careful to not insulate to the point where the wiring to the sensor could be damaged. Another issue with additional insulation is the sensor has to breathe air from the atmosphere to function properly, and produce the electrical signal that depends of the difference in oxygen content between the exhaust gasses and the ambient air.

For that reason my two cars will not have any modifications to the existing system.

regards
gary

[R.I.D.E.]

Originally Posted by spotaneagle

ya ya, but less resistance might prove you right even more so cow, like removing some bends?, alot of these people are removing their cats and seeing a 10mpg increase, thats why im saying a hi flow cat might do the trick, especially since i quoted one guy with a car like mine, i would think it might be different for each car

A word to the wise about disabling any emissions component. Current fines are $2500 per offense for individuals, and $10,000 for any repair shop.

Thats Federal law.

The testing can be done with portable units in the field. I have not read about it happening at this time but it could be a part of future enforcement practices.

I know I will have nothing to do with disabling any emissions components, for two reasons.

1. Don't want to get nailed with a fine, and then have them go on a witch hunt for more examples of my disregard for the pollution it causes.

2. The fact that when you decide to disable emission components, it represents a serious disregard for the additional pollution you emit.

Also consider that enforcement personnel may be reading the post just made, and a public display of disregard for emission laws could be construed as probable cause for a warrant.

If gutting a catalytic converter was the reason for a 10 MPG increase in mileage, it would have to be due to the fact that there was something seriously wrong with the converter before it was gutted, possibly prior attempts at "enhancement" of the system without properly understanding its specific functions (just my opinion there).

regards
gary

[R.I.D.E.]

Also consider this. When I am driving down the road, I can smell a car that has a compromised emission system. Don't assume that enforcement officials could not do exactly the same thing.

regards
gary