high flow exhaust = 3-5% mpg gain?

[California98Civic]

Originally Posted by Ladogaboy

California98Civic brought up a good point about pulsing and gliding, which I have seen is proven to be more efficient, but P&G isn't an option for me. I can't turn off AWD, and I can only fix so much of my ~.33 cd. Unless I can figure out a better way, cruising at constant speed at low loads seems to be my best bet for highway mileage. On the aside, targeted mpg on hills seems to garner fantastic gains in mpg.

I hear you. Most important thing is to figure out the enjoyable way to make your car more efficient, mile-for-mile, on fuel. You can P&G one of these cars, with the engine ON. I did pretty well with my wife's Subaru Forester once, which is an auto AWD too. I squeezed maybe 5 mpg more over the long haul on the highway. I can't fully recall. I posted about it here somewhere. My technique was probably quite sub-optimal, though.

[RH77]

Likely due to the liquid road salt introduced to the region not long ago, the old Integra is being eaten alive (first brake calipers, now an exhaust pipe and other surfaces).

Most of the stainless exhaust is fully intact, except for the common A-Pipe and muffler buzz, except for now, a leak.

Between the Cat and Resonator, a simple straight pipe has developed a significant leak between its heat shield and the pipe itself (the rest of the heat shields have rusted and fallen off or were removed due to imminent failure or nasty "clanking").

So where is all of this going? Perhaps it's the CO leaking into the cabin since it's right below the driver's seat, but I've noted that highway economy has significantly improved. Highway RPMs are 2500-3000 RPM, so the engine is moving quite a bit of air. After charting the data, the SGII has displayed lower loads, higher FE, and and the ability to hold more constant hill speeds with similar throttle input. This is good, but keep reading...

It could all be the change in Weather, but it got cooler and milder before the pipe blew out, so that variable is out. I used the A/C during this observation. I would call it significant because exhaust can be smelled and heard as a loud air pumping sound. The problem -- FE is lower around town, and the butt dyno calls it "sluggish off the line".

So, I need to take the vehicle to the exhaust shop to get it repaired, since occupant safety (and vehicle inspection failure) is important. The question becomes, when big parts fail on this system, should I go for the stock setup, or look into something custom? There has to be a compromise between city and highway. The transmission is holding out (and engine design demands) higher RPM at highway speeds.

Food for thought...

-RH77

[SiVX]

Originally Posted by 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.

This calculator is really complicated. I'm new to EcoModding. I just got a VX that has a 3" aftermarket intake. The exhuast pipe was replace from the engine back and has a 2007 Si muffler. I guess tomorrow I'll take some diameter measurments n figure out what else I need.

[Blu3Z3rg]

Originally Posted by SiVX

This calculator is really complicated. I'm new to EcoModding. I just got a VX that has a 3" aftermarket intake. The exhuast pipe was replace from the engine back and has a 2007 Si muffler. I guess tomorrow I'll take some diameter measurments n figure out what else I need.

Once it gives you a length, if you go for a 3" fart can after that length, it's probably just like dumping it in the air anyways. That calculator is a bit on the tricky side, and isn't very descriptive of the measurements, but it's pretty accurate when you put more and more info in it.

[SiVX]

Originally Posted by Blu3Z3rg

Once it gives you a length, if you go for a 3" fart can after that length, it's probably just like dumping it in the air anyways. That calculator is a bit on the tricky side, and isn't very descriptive of the measurements, but it's pretty accurate when you put more and more info in it.

I'm definitely trying to EcoMod this car. If that means taking the previous owners ehaust and intake off I'll do it. Gaaaah! Just gonna keep reading and re-reading.

[mcrews]

that is a great attitude to bring to the table!
you may not get a PhD here.....but you could get a great college education!!

I find myself reading and re-reading often!

[niky]

Originally Posted by Blu3Z3rg

Once it gives you a length, if you go for a 3" fart can after that length, it's probably just like dumping it in the air anyways. That calculator is a bit on the tricky side, and isn't very descriptive of the measurements, but it's pretty accurate when you put more and more info in it.

A 3" fart can will still cause turbulence at the end of a much narrower (typically 2 - 2.25" ) tube. For all the sound muffling qualities it gives you (probably none), it's better to just dump to atmo. Been there, done that... really bad idea.

Honda stock mufflers from higher displacement variants are an excellent way to improve engine efficiency, gain a little bit of power, and keep the vehicle sounding sweet.

[SiVX]

Can someone with a stock vx please crawl under the car and give me a pipe diameter? or circumference if thats easier for u... the vx I bought recently has an aftermarket pipe from the exhaust manifold/cat. then it has a 2007 SI muffler added. and yes i have googled and tried to look up replacement parts for the sizing but they dont give me all that info wherever i find parts.
I've read all the stuff about less back pressure at higher RPMs. I plan on maintening those lower RPMs for lean burn and FE. Seems to me trading it off for a stock would be the thing to do??? I'm confused lol
I still don't have enough info for the pipe calculator. Dont know where to find valve opening BTDC or closing ATDC or duration...
Thanks!

[niky]

If it drives okay, then it's probably not suffering from the larger pipe size. What economy are you getting?

[anotherls]

I thought this might be a good place to ask this question, but I was under my 03 civic ex last weekend hunting down an exhaust leak. Found it, it was from the exhaust manifold to the (b-pipe), I replaced to donut gasket in there and no more exhaust leak. While I was under there I noticed from the exhaust manifold to the rear of the cat (b-pipe) the piping diameter is around 2". But out of the cat, the diameter drops down to like 1.5''. I have read many exhuast threads but none with a question like this, so what is the reasoning behind the bottleneck in my exhaust or did someone do a bad job matching up pipe diameters? It looks factory, therefore there must be a reason for it.