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

[Ecky]

Sorry to derail, but what is the gearing in your Metro, Daox? What RPM = what MPH in 5th, specifically?

I would imagine it's probably shorter than the G1 Insight, and I'm able to drop mine in 5th at 30mph/1000rpm and either cruise there or take it up to highway speeds with no issue (though that's not the most efficient way to accelerate). Downshifting is not necessary for climbing shallow grades either.

[iveyjh]

Originally Posted by Old Tele man

If the Geo engine TORQUE peak is ~3500 rpm, I'd "tune" the headers for nothing lower than ~ 2,500 rpm. What road speeds would 2,500 rpm be in 4th and 5th gears?

In 5th 2500 rpm with 4.39 diff is right at 50mph.

[Daox]

Here is a gear/speed/rpm chart for the Metro with its current transmission (4.390 differential ratio). I say current transmission because my 4th gear grinds and if I find another one at a good price I will probably nab it up. Who knows what ratios it may be, but this is the highest (aka worst for mileage) transmission that came with the Metro. All the other ones are geared taller.





For comparison, here is the tallest trans (3.524 differential ratio) you can put in the Metro.

The difference between the two at 45 mph (my typical cruising speed) is pretty huge. The 4.39 gives me 2219 rpm, and the 3.524 gives me 1779 rpm, a 440 rpm difference.

I'm not looking to design a header that is perfectly designed for 2200 rpm @ 45 mph. I'm just not that good, plus I think it would really choke the high end like Darcane said. I'm really looking to design something that gives better fuel economy than stock without absolutely murdering the max power output. I'm fine with sacrificing some high end.

For future reference here are the gear ratios:

95-01 1.0L hatch and convertible
3.420
1.890
1.280
0.910
0.760
4.390

89-94 base, lsi, gti
3.420
1.890
1.280
0.910
0.760
4.110

XFI & 1.3l
3.580
1.890
1.280
0.910
0.760
3.790

89-94 swift 1.3l
3.580
1.890
1.280
0.910
0.760
3.524

Tire diameter is 22.76"

[arcosine]

A guy told me that running long pipes on his BMW hurt gas mileage. I don't remember the reason, I think it was sucking the mixture out the exhaust port.

[oil pan 4]

Originally Posted by arcosine

A guy told me that running long pipes on his BMW hurt gas mileage. I don't remember the reason, I think it was sucking the mixture out the exhaust port.

That will only happen if there is valve over lap or if the valves are floating.

[iveyjh]

Originally Posted by Old Tele man

The best/conservative approach would be to 'tune' the headers to coincide with the engine's torque peak...ie: striving to improve it's existing torque output rather than shift or move the torque peak, which would be about 62" length header pipes before the collector.

However, *IF* you use Freebeards idea and put a small motorcycle muffler on each pipe, the 'total' length (valve to atmosphere) would now INCLUDE the muffler length, since it's now all one-continuous length (no joining of gas flows from other cylinders).

torque peak = 3300rpm or 65mph in 5th gear

[freebeard]

This just showed up on Just A Car Guy:


http://justacarguy.blogspot.com/2015/11/original-owner-boss-429-mustang-not.html

This is on a 429 Mustang, but scaled down, it could allow pneumatic control of the volume and/or length of the pipes.

[Daox]

I haven't set anything in stone yet. I've actually been out of state for the past week so I haven't thought about it at all. Playing catch up at this point, but I will get back to it.

[Shawn D.]

I'm late to the conversation, but here are a couple of comments.

1) For a collector with good transition & design, contact Burns Stainless (yes, they also work in regular mild steel). Their collectors are a work of art and have great internal flow, without tubes crudely inserted.




Unfortunately, this appears to be the smallest they normally offer. You'll need to call to see about a smaller collector. Nope, they ain't cheap!

2)

Originally Posted by ksa8907

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

That (or a variation) tip is on all new diesel trucks. It's not for economy or power, but is for when trucks go in to "regen" to burn carbon out of their particulate filter. When doing so, the exhaust gets extremely hot, and the tip causes entrainment of cool air around the hot core flow, helping to prevent fires caused by the exhaust.

[TimRogers]

Originally Posted by Old Tele man

Obviously, 108" header pipes are both impractical and physically too long to fit, but the "longer-is-better" approach could be compromised to "fit" by making them as long as practically possible, and then transitioning directly from the header pipes directly into the obligatory muffler...thus eliminating more piping.

What engine RPM do you want the pipes to "tune" to? I don't know where the torque peak is for the that engine...I just guessed at 2,000 RPM for highway cruising.

One of the things to know about header design is that due to packaging concerns, headers are often shorter than they need to be. This is not as bad as it sounds because the pulses traveling down the tube reflect off the "open" end at the collector and again at the closed valve. So, if you find that you "need" a length of 108", a length of 54" will also have good effect at your chosen RPM (and at double that RPM as well of course.) If you can make the length of the "midpipe" from the collector to the muffler that same 54", that will help to reinforce the pulses at your chosen RPM as well.

Additionally, the idea of running individual pipes with their own mufflers will also be disadvantageous. Having them come together in a collector will let the pulses from the other two cylinders affect the cylinder that is in it's exhaust stroke. As the other cylinders are operating 120* off of the cylinder in question, the effects come in at different RPM but they do help to balance out the entire torque (and therefore FE) curve of the motor.