Exhaust header: help or hurt f/e - Fuel Economy, Hypermiling, EcoModding News and Forum

Chalupa102 · 12-22-2009, 07:59 PM

A while back when i was into quicker acceleration i installed an exhaust header (4-1 style) in place of the stock manifold. Since hypermiling i almost never exceed 2500rpms, so clearly i don't care how fast my car accelerates now. There's a person with a Corolla who is willing to buy my header and give me his stock manifold. Do u guys think the header helps or hurts f/e, and should i do the swap?

mcrews · 12-23-2009, 02:12 AM

your getting pretty decent mpg right now....

I had a 66 mustang back in college) with a 200ci inline 6 cyl. I intalled headers and dual exhaust but used 1 3/4 pipe to provide some backpresure. going back and forth to shool on the freeway it worked great. When I graduated, I went to a single pipe and single muffler to get the backpresure up even more. I was doing mainly intown driving.

moral of the story is that you need some backpresure for the engine to work effecveintly....in my opinion.

Daox · 12-23-2009, 06:51 AM

A properly designed header will improve mileage. Pretty much all aftermarket mufflers are designed to shift your powerband to higher rpms. This of course is the opposite of what we want. So, short of making your own custom header, I'd say it won't help.

SVOboy · 12-23-2009, 09:11 AM

Quote:

Originally Posted by Daox

A properly designed header will improve mileage. Pretty much all aftermarket mufflers are designed to shift your powerband to higher rpms. This of course is the opposite of what we want. So, short of making your own custom header, I'd say it won't help.

I'll just chime in to confirm this. If you want a header to increase FE you need to do custom design keeping in mind troublesome things like resonance blah blah. Seems more effort than it is worth.

Christ · 12-23-2009, 09:32 AM

Unfortunately, I have to stick a word in here.

I did two mods in the interest of power to my Civic that also increased efficiency to a point where my economy improved noticeably.

#1 MPFI swap. Started with DPFI, and with my (then) driving style, this wasn't working out well. No torque on the bottom of the revs at all, so I was always revving up to keep the car moving. I seldom used 4th or 5th gear. After the MPFI swap, more low-end, so I used the lower gears more.

#2 eBay header. Yep. $32 shipped, and (no scientific data here) about 3MPG increase. Of course, again, I was also driving much differently then than I do now. Also, there was a marked increase in low-end again, header vs OE exhaust. I did not remove the cat or install an open muffler. I had a thrush turbo muffler on the back, in the OE configuration. Later, I installed a fart can, but left the baffle in it. I never noticed a decrease in torque until I removed the baffle.

Both of these are non-conventional mods in the terms of the way we (the majority of people on this site) drive, but if you don't drive like us, they may make a difference for you.

In all honesty, I'd probably do both mods again, except change my transmission to longer gears to accommodate the increase in torque. This is where I wish I'd kept my Civic and the HF transmission that I sold.

Daox · 12-23-2009, 09:47 AM

I agree, if the header increases low rpm torque, it will most likely increase mileage.

It has been my experience that most headers are not designed this way though.

Christ · 12-23-2009, 09:49 AM

I think in the case with the early D-series engines, the OE exhausts were so inefficient at doing their job, and the added scavenging from the header made it run easier on the lower ranges.

Again, never really tested it, though.

rgathright · 12-23-2009, 10:21 AM

Increasing torque is good. Keep the headers man.

rgathright · 12-23-2009, 10:23 AM

Quote:

Originally Posted by Christ

Unfortunately, I have to stick a word in here.

I did two mods in the interest of power to my Civic that also increased efficiency to a point where my economy improved noticeably.

#1 MPFI swap. Started with DPFI, and with my (then) driving style, this wasn't working out well. No torque on the bottom of the revs at all, so I was always revving up to keep the car moving. I seldom used 4th or 5th gear. After the MPFI swap, more low-end, so I used the lower gears more.

#2 eBay header. Yep. $32 shipped, and (no scientific data here) about 3MPG increase. Of course, again, I was also driving much differently then than I do now. Also, there was a marked increase in low-end again, header vs OE exhaust. I did not remove the cat or install an open muffler. I had a thrush turbo muffler on the back, in the OE configuration. Later, I installed a fart can, but left the baffle in it. I never noticed a decrease in torque until I removed the baffle.

Both of these are non-conventional mods in the terms of the way we (the majority of people on this site) drive, but if you don't drive like us, they may make a difference for you.

In all honesty, I'd probably do both mods again, except change my transmission to longer gears to accommodate the increase in torque. This is where I wish I'd kept my Civic and the HF transmission that I sold.

I have a Mopar hot rodding magazine that detailed the same changes to a Dodge Neon. They were able to find an additional 37lbs of torque by doing this to the 2.4L engine. I have since dreamed of this doing this to make a FE NEON.

SVOboy · 12-23-2009, 10:40 AM

Quote:

Originally Posted by rgathright

I have a Mopar hot rodding magazine that detailed the same changes to a Dodge Neon. They were able to find an additional 37lbs of torque by doing this to the 2.4L engine. I have since dreamed of this doing this to make a FE NEON.

Can you scan and post this article? Would be interesting