Most Efficient Header and Exhaust Design

[rh77]

OK, so there's an age-old debate on which header and exhaust makes the most horsepower, but what about fuel economy? I have an exhaust leak and all but the Cat must go. 80/20 Highway/City driving. What is the opinion:

* For the Integra, should I go for the 4-into-1 header, or the 4-into-2-into-1 header?

*Backpressure: leave the stock exhaust diameter
or go larger (or smaller, for that matter).

*The RS-R Ex-Mod may be the muffler of choice (instead of a stock replacement) for sound preference and free-flow.

The CO is getting to me at stops, so everything must go (but the Cat seems to be doing the job for now).

I'm willing to take a sacrifice in power for better economy.

RH77

[SVOboy]

Unfortunately, this question is not age old, and you will get a different answer from everyone, and you'll end up figuring I'll just have to go for a shot in the dark and see what the hell happens. I'd try more restrictive, but that's just my shot in the dark. The economy models from honda all came with super restrictive exhausts and intakes.

[Matt Timion]

The economy models from honda all came with super restrictive exhausts and intakes.

he's right. The honda economy models have restrictive intakes and exhausts. It kind of flys inthe face of what everyone has been saying to me for the last year.

More power equals better fuel economy.

See, they just did it again.

Seriously though, I'd start researching the smallest possible diameter you can put on.

I wish we could get a Honda engineer here to talk about why certain choices were made and how fuel economy was considered in the process.

[rh77]

Yeah, I figured that "more restrictive" might yield better economy, but too much backpressure could be counter-productive. Since the '06 Civic get's awesome mileage, I'd figure I'd start there with some research. It turns out that it doesn't even have an exhaust header (http://hondanews.com/CatID2013?mid=2005083043340&mime=asc). It has an exhaust manifold integrated into the cylinder head, and a Cat right off of the outlet for quick burn-off, etc. It's a tidy design, but doesn't help my cause.

Further research shows a direct correlation between more backpressure and decreased fuel economy. So...perhaps leave the header and diamater the same, but add a free-flow muffler.

RH77

[rh77]

The economy models from honda all came with super restrictive exhausts and intakes.

he's right. The honda economy models have restrictive intakes and exhausts. It kind of flys inthe face of what everyone has been saying to me for the last year.

More power equals better fuel economy.

See, they just did it again.

Seriously though, I'd start researching the smallest possible diameter you can put on.

I wish we could get a Honda engineer here to talk about why certain choices were made and how fuel economy was considered in the process.


Everything I read keeps saying more flow = more power/economy. But more power doesn't seem to relate to economy -- seems like the opposite. I remember when I replaced the muffler on my old civic DX with a free-flow model, the torque went through the floor. After damaging it in a "Winter incident", I put the stock muffler back on, and it felt like it had a turbo installed. Hondas must thrive on that backpressure. We could certainly use the help of Honda engineer.

RH77

[kickflipjr]

Yeah, I think: Bigger Exaust Pipes=more air flow=more fuel to keep an even ratio.

The best setup would be free flowing but small (stock size maybee smaller). Manderal Bends and a free flowing muffler would help.

I assume, Bigger pipes also have less air velocity at lower rpm (were most economy driving is done).

[SVOboy]

My stock size is 1.5 inches I think, so think about that. What else...No point in having a high flow muffler with a stock exhaust, defeats the purpose. I think you want to be able to strike a balance between exhaust velocity and backpressure. Not enough velocity and it kind of stews around there.

[rh77]

I think the diameter is 1.8" -- I'm not sure of the different sizes of tubing, but I can see trying to go down to 1.5" as a solution and find a close-to-stock muffler replacement. Does anyone know what diameter the late-90's Civic HX Coupe exhaust system is? That may be a good starting point...

RH77

[SVOboy]

I dunno for sure, but I'll be damned if it ain't smaller than either of your cars'.

[kickflipjr]

what do you guys think of the turbolator

http://www.jcwhitney.com/wcsstore/jcwhitney/images/imagecache/10014575.gif

They claim it save gas up to 8.3% (which dosen't mean anything).

"Patented self-adjusting internal control valve responds to RPM load and temperature to equalize pressure and regulate exhaust flow. During high exhaust flow, the internal valve opens to let engine gasses escape freely. At lower RPM, the internal valve closes to regulate exhaust flow and improve engine performance. The result is increased horsepower and torque, improved fuel economy and less harmful emissions—without having to modify original engine specifications. Must be welded to exhaust pipe. "




I would like to try one out if it wasn't $64

[DaX]

The result is increased horsepower and torque, improved fuel economy and less harmful emissions—without having to modify original engine specifications.

Sounds like you get everything - mileage, power, torque, less emssions... Generally when they offer a solution to all problems (i.e. - if it sounds too good to be true), it IS too good to be true, and I'm going with my gut instinct on this one.

Plus, who wants to ride around with that ricey fat *** chrome tip on their exhaust, haha.

[rh77]

The result is increased horsepower and torque, improved fuel economy and less harmful emissions—without having to modify original engine specifications.

Sounds like you get everything - mileage, power, torque, less emssions... Generally when they offer a solution to all problems (i.e. - if it sounds too good to be true), it IS too good to be true, and I'm going with my gut instinct on this one.

Plus, who wants to ride around with that ricey fat *** chrome tip on their exhaust, haha.

D-Money, that phat bling would pimp my ride hella badd. In all seriousness, I was thinking of this concept. Compaq888 may be able to confirm this, but I think the Altima muffler has a similar device to maintain backpressure at low RPM, then it opens up at higher RPM for the maximum free-flow (my '03 Evo had a simlarly valved muffler -- it sounded cool from behind, once the turbo spooled-up and you hit about 5000 RPM+ it sounded like a jet engine -- another side point :-) ) Basically backpressure for torque and free-flow for when you need it (so you're not stuck with a choked-off exhaust at 6500 RPM). I might give it a shot.

RH77

[DaX]

D-Money

HAHAHA, I haven't laughed that hard in a while...

[CruiseControl]

When a buddy of mine from work was into drag racing motorcycles, I was looking for a header to put on my Kawasaki GPZ, also. The 4/2 designs gave better mid range power, and lower red line power. While the 4/1 designs gave better red line power and less mid range power. The ratioal behind this was that the 4/1 designs could take advantage of tuning all of the cylinders in one acoustic chamber. So one big fat pipe was the answer, for peak red line performance. Headers seemed to be designed like air craft wings, with a super-critical RPM or speed in mind.

[MetroMPG]

can someone explain the relationship between backpressure and torque? it seems counter-intuitive that more backpressure = better low end torque.

my brain says, "how could backpressure help if the engine has to work harder to expel exhaust from the cylinders?"

[dkjones96]

Digging up an old thread, but everyone is doing it.

But this question was never answered. Backpressure doesn't increase torque. Backpressure is ALWAYS counter-intuitive of fuel economy and power.

It used to be thought that bigger pipes reduced backpressure and you lost torque and economy. That is only half true. The bigger pipes did reduce torque and economy but not because of backpressure, it was the result of less exhaust gas velocity resulting in less scavenging and more waste.

[skale7]

I am no expert, but my understanding is this: Backpressure is always bad, as it increases pumping losses. The problem with large pipes, however, is an exhaust velocity that is too slow, especially at low RPM, when there is not much gas to be pushed out. The factory-equipped exhaust is small because most street driving involves RPM < 3000. At these speeds, a larger pipe would have very slow exhaust gases, and because of the low volume of exhaust, backpressure is not an issue. Upgrading to a larger pipe would increase power at higher rpms at the expense of some torque at the low end. If you like to drive to the redline, it will help, otherwise it would hurt. You want the smallest pipe that would have minimal backpressure at the target RPM. As a hypermiler, you would probably want to stick with the smaller exhaust.

[Pete]

rh77,
I would start with working out your RPM for your highway driving then tune the exhaust to match the highest level of efficiency you can find for that RPM.

The debate about power/ economy is about the choice of either/ or but not both at the same time.

Pete.