Most Efficient Header and Exhaust Design

[GasSavers_DaX]

Originally Posted by They

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]

Originally Posted by DaX

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

[GasSavers_DaX]

Originally Posted by rh77

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.

[GasSavers_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.

[kakaroto_ss4]

ok i have a d13b engine 1.3l what if i change the header to a d15b stock one ?

[hondaguy72]

The d15b header should work well on your 1.3.

Honda does have somewhat restrictive exhaust manifolds, but they've moved on recently to longer runners. Smaller, longer primaries and a well designed collector help exhaust air move with better velocity, improving engine breathing and power production. The size of the primaries (smaller= lower) is probably the most important factor in determining what rpms power is available. More torque at lower engine rpms will allow you to drive in a lower range thus improving mileage. It's all about driving in the most efficient rpm range that maximizes economy!