Designing a header for fuel economy (for a Metro G10 1.0L)

[Daox]

We've talked a fair amount about a header for fuel economy. I think its safe to say that almost no aftermarket header is going to be designed for that purpose. So, I'd like to step through the process of designing a header for the Metro's G10 1.0L 55 hp engine as an example of how you would go about designing a header for your own car.

Now, lets keep in mind that this probably is not worth it cost wise. Even with the Metro being a 3 cylinder, and materials being very cheap (under $100 for a stainless header), the fuel economy gains are just not going to justify that cost. That being said, I'm not sure I'll actually make a header for the Metro, but I do want to run through the design for those who are interested.

To run through the design, I'm going to pull info from multiple different places, but the bulk of my info is from:

Header's by Ed - Infopak

It is a paid for product, so I can't divulge too much from it. However, I will refer back to it as we go along.

I've also tried to get in contact with mwebb as he seems to know a good amount about engine and header design.

So, Ed says the keys to a good header are (links go to the steps in this thread):
1) tube diameter
2) tube length
3) collector size
4) collector length
5) equal length tubes
6) efficient collector shaping
7) efficient port matching

In my next post, I'll start going through these 7 steps to design a fuel economy header for my Metro.

As a teaser, I have started drawing up a header for the Metro in SolidWorks. Its just roughed in thus far and will definitely change as I haven't taken any real measurements of the engine. But, here is a sneak peak.

[user removed]

Small tubes will get you most of the way there with what you already have, triangular collector. Longer tubes better torque?

regards
mech

[BabyDiesel]

I'm looking forward to what you come up with, Tim. The best I can recall from what I know about small block Chevy engines:

-Decreasing tube diameter increases low-rpm exhaust speed, which in turn helps low-end torque through more efficient cylinder scavenging. This *may* lower upper rpm power, but how bad could it be on a 1.0?

-Longtubes are better than shorty or block hugger headers for low-rpm situations (towing, economy).

-Thicker material and/or header wrap will keep heat inside the collector tubes, keeping exhaust speed up for better scavenging. This is for all rpms.

-Port match!

All dyno test I have seen are at WOT. Since we rarely go past 1/2 - 2/3 throttle for short periods and spend a lot of time at part-throttle, this seems to indicate smaller tubes than usual? I think you could go down to ~1" on the collector tubes, since each cylinder is only 0.33 liters of displacement, versus 0.713 liters/cylinder on a 350 SBC.

[spacemanspif]

I've seen headers with a choke point or venturi built into the collector. I'm not sure if it's a race application thing or if it helps throughout the RPM range but it might be another feature to explore.

Formed Collectors, hand built Custom Collectors, Street Exhaust Hookup Cones, Megaphones

[aerohead]

In Todd Howard's,HOT ROD Magazine' article,'HEADER SCHOOL', he mentions:
*primary tubes determine peak torque (mpg)
*primary diameter affects the rpm at which peak torque occurs
*small primaries offer a low end peak
*large primaries offer a high end peak
*"In most applications you should always opt for the smaller primaries."
*"... header length is a second factor in torque peak:
.......long = low rpm
....... short = high rpm"
*equal-length primaries if you can
*collectors must be tuned for diameter and length
*up to a point,the larger the collector the more low end torque
*Tri-Y's are good but they're not for 3-banger
*primaries need to be paired with cylinders 180-degrees out of firing order,so one's rarifaction can help scavenge the others' flow as it passes.Makes for steadier pulse train as well.Good for mid-range
*If the engine has much valve overlap,anti-reversion pipe stepping needs to be incorprated,otherwise exhaust will flow into the open exhaust valve during overlap event,spoiling the new charge.(Mr. Gasket's Cyclone and Blackjack headers can be studied for this feature.)
*EFI and CPU will automatically recalibrate ignition timing and mixture,which headers will tend to lean out.....

[aerohead]

Yes,if the angle of divergence is too steep you'll have flow separation and lose valuable kinetic energy,increasing pumping losses

[ksa8907]

Just in case you can't tell, avoid this. 2g chrysler LH cars (intrepid,comcorde, lhs, 300m)

[ksa8907]

Ive seen these venturi tips on all the new duramax diesels.

[Gasoline Fumes]

Originally Posted by ksa8907

Just in case you can't tell, avoid this. 2g chrysler LH cars (intrepid,comcorde, lhs, 300m)

Displacement is the replacement for engineering!

[Gasoline Fumes]

The G10 head has square exhaust ports, roughly equivalent to a 1"-1.25" diameter round pipe. I'm guessing you'll want primaries smaller than that. Suprf1y on TeamSwift or GeoMetroForum knows a lot about these engines too, I'd ask him for recommendations as well.