Designing a header for fuel economy (for a Metro G10 1.0L)
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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. http://ecomodder.com/forum/attachmen...1&d=1447946485 |
Small tubes will get you most of the way there with what you already have, triangular collector. Longer tubes better torque?
regards mech |
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? :D -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. |
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 |
header
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..... |
diverging pipe sections
Yes,if the angle of divergence is too steep you'll have flow separation and lose valuable kinetic energy,increasing pumping losses
http://i1271.photobucket.com/albums/...2/scan10_2.jpg |
Just in case you can't tell, avoid this. 2g chrysler LH cars (intrepid,comcorde, lhs, 300m)
http://thumbs2.ebaystatic.com/m/mFJb...1CL4cA/140.jpg |
Ive seen these venturi tips on all the new duramax diesels.
http://www.gmtruckhq.com/images/Dies...inatorlugs.jpg |
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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.
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My mechanical engineer friend had a cracked exhaust manifold on his 4-cyl 2.7L taco, which in Virginia means you to fail inspection.
He has fuel economy logs going back to 2005 for this truck. New dealer part was something like $800, a used one off the internet was $500. A pacesetter 4 into 1 header was $400. He put the pacesetter header on in 2010 and it is still going good. He says the header appears to have not hurt fuel economy at all, but is half the weight of the cast iron manifold and has increased low end torque and high end get up all around. For the metro header, if were going to build one I would use 1'' diameter 0.62'' wall 304 stainless. Not sure how long the tubes would be. |
1" primaries may be too big. Looking at the amount of exhaust coming out in comparison to a 350 SBC...
43.75 CID/primary. Usual* header primaries are 1.625" for street headers, 1.5" are rarer but would push the torque peak down lower. Metro 1.0 has 0.33 CID/primary, a 24.6% reduction in exhaust gas volume. 1.5" x .754 = 1.131" primaries. I stand corrected! Now I don't know if you can directly compare like this. The size I came up with seems to show that 1" is the way to go if this math checks out okay! |
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Thanks for all the tips guys, there is some good info there.
I do realize the Metro's exhaust ports are rectangular. I'll be getting to that. The initial image you saw was just me throwing together a rough draft so to say. There will be transitional pieces going from rectangular shapes to round. This will be a long tube header design, this helps low rpm power/efficiency. I'm not exactly sure on the length yet. I'm still working that out. |
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Pi(R^2) |
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Lets do step #1, selecting the primary tube size. This is no simple task, so I'm going to provide a bunch of info, and then take my best guess based on what I'm trying to design into the header. This design target is low to mid range power, 2000-3000 rpm is generally the range I'm targeting.
My info from Ed says that for the horsepower each cylinder produces (math is 55 engine horsepower / 3 cylinders = 18.3 horsepower per cylinder or tube) I should use 1.25" OD tubing. However, I'm on the very low end of the range of power for 1.25" tubing size, so its safe to say I could downsize that. Unfortunately, 1.25" tubing is the lowest on his chart, so that leaves some guessing up to me. This is also for a higher rpm producing header. I care little about that, I want more torque in the mid and low range. So, I'm going to downsize my tube. Another source of sizing exhaust tube size is found here: How To Calculate Muffler Size and Exhaust Pipe Diameter - Exhaust Videos | Exhaust Videos This chart is for exhaust piping in general, but we can use it for our header design. Again, his chart only goes down to 1.5" tube. However, I extended his chart down to 0.5" tube using his calculations in an excel document. The key when looking at this chart is each square inch of tube area gives ~115 CFM of flow. http://ecomodder.com/forum/attachmen...1&d=1448038831 According to this chart, I should be looking at 0.75" 16ga tubing. So, wait a minute! These two estimates are very different. Why is that? I believe the two designers are targetting two different flow velocities. This is the speed of the exhaust gas inside the exhaust tube. Too fast of a flow velocity and you get excessive back pressure which causes the engine to have to push harder to get the exhaust gas out. Too low a flow velocity and you don't get good scavenging effect, your exhaust gas cools and then becomes more dense and more mass to push out the exhaust tube, and a few other things. Our goal is to balance these two. To find the flow velocity of your engine and tube size, you'll need to do two calculations. 1) Find your flow rate for each cylinder. This is roughly equal to 2.2 CFM per engine horsepower (per exhaustvideos). Now divide by the number of cylinders. 2) Find your velocity. Velocity calculator here. Directions: solve for velocity, put your CFM in from the above calculation and your tube inner diameter in the other field. Most articles say to target ~250 feet per second (FPS) for peak torque. Using Ed's sizing, our flow rate is around 200 FPS. Using the exhaustvideos calculation, its around 275 FPS. But, these are values at max rpm and wide open throttle (WOT). The thing is, for a fuel economy header, we're again tuning for a lower rpm, roughly half of peak rpm. This translates into roughly half the flow, and thus half the flow velocity. So, I could probably go with 5/8" OD 16ga tubing and call it good. http://ecomodder.com/forum/attachmen...1&d=1448038808 (Yes, my name is Timothy :)) This seems ridiculously small, but if I measure the exhaust tube on my 1981 Honda CM400 which has a 42 horsepower 2 cylinder engine, the outlet's inner diameter is 9/16" (there are two exhaust tubes), so I don't think I'm too far off. Sadly, I haven't been able to find any information that says "don't exceed this velocity", or "after X FPS you start getting Y psi of back pressure". So, I can't really design to that factor. Now, when searching for actual parts for the header, I was only actually able to find 3/4" OD 16ga mandrel bent 304 stainless tube. This gives me 320 FPS at max power output (5700 rpm). So I should have ~250 FPS around 4450 rpm. That is pretty high for me, but since I haven't been able to find smaller tube it'll have to be good enough, and its certainly smaller than the stock setup. So, that is pretty much that... 3/4" 16 gauge stainless it is. Also, please keep in mind that these are very rough calculations. This is by no means a super specific guide. Real header builders calculate tons more stuff like valve diameter, cam lift and duration, bore and stroke, and lots more stuff. This is by comparison very rough. |
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The math worked like this for me - A 1.5" primary SBC Header will have a primary cross section of 1.767". 25% of this would be 1.325". Since there is a greater focus on low-end, I believe Tim could go slightly smaller. A 1.25" primary gives ((0.625" x 0.625")3.14), which equates to a 1.227" cross section, a 30.6% decrease. So 1.25" seems to be the front runner:confused: unless there is some specific exhaust information that we are missing... Edit: Tim posted right before me. Throw all this malarky out the window! :p |
Haha, good shot at giving it a try. I had to dig pretty hard for a lot of this info, and the rest is really my best guess. There isn't a massive amount of info out there on header design to begin with and ALL of it is for 'performance' and/or racing applications. You have to take that data and try to wrangle it into some form that we can use for fuel efficiency. I hope I'm in the ballpark. :)
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Lol you're welcome Tim! I enjoy bouncing ideas around and trying to help :) excellent work on deducing the info down to what you need!
That does seem ridiculously small, even for a 1.0! If you do not mind ordering pipe, I found this site - Order Stainless 316 Tube in Small Quantities at OnlineMetals.com Where you can get 8' of 5/8" OD, 0.495" ID 316/316L tubing for around $80 after shipping and a 10% discount. That would be more appropriately sized for what you need, but it would not be mandrel bent. You would have to find an exhaust shop to do it for you, and I doubt you want to do that. |
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Designing a header for a small displacement Geo engine running at low RPMs, and part throttle will need a very different design since the CFM is so low. If this header ever gets built, be aware it will significantly restrict high RPM performance. |
From: https://en.wikipedia.org/wiki/Suzuki_G_engine#G10
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Tubing lengths and diameters will be whatever they turn out to be. The three things I'm wondering about are:
http://i.imgur.com/oNvuDko.jpg |
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http://geometroforum.com/pages/3tech/ Also check this out: http://geometroforum.com/pages/maas http://geometroforum.com/topic/4569879/1/ I'm not sure if he's still making headers, but there's good info there. |
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Ahhh, you deleted your posts, thats why I couldn't see it.
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Daox, have you condsidered a water jacket? You'll need to open up your grille block a little, but it will significantly improve warmup times.
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Three straight pipes, each with a small SuperTrapp™ motorcycle muffler?
SuperTrapp: Performance Exhaust |
Not necessarily on topic to this thread but has anyone ever considered variable displacement headers?
AKA a header that grows wider and narrower over the RPM band to optimize harmonics? |
aka Trombone? Slide whistle?
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Do you have any links that further explain your length calculations? |
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For extra thread info, this is what the dyno chart looks like for the Metro's G10 engine. I pulled the torque info from the BSFC chart we have in the wiki for the G10 and then calculated horsepower in excel and plotted both on the graph.
http://ecomodder.com/forum/attachmen...1&d=1448295332 As we can see from this graph, at my cruising rpm of ~2200 (45 mph), I have on tap roughly 24 horsepower. This is more than enough on flat ground, and almost always enough to climb the hills on the way home. In winter I do loose a few mph while maintaining peak BSFC at around 75% load (calculated via the BSFC info we have in the wiki). If I end up making the header, I'll do an A-B test to get a before and after shot of how the header effects the torque curve. |
That is a lot of torque (%) down to 1000rpm. How low do you figure you could get the engine at cruise and not have adverse effects?
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The torque curve on Honda's 3 cylinder looks very similar. I suspect they tuned it to peak a little higher up since there's electric assist, but overall I bet it feels a lot like the geo engine.
http://www.insightcentral.net/_images/enperformance.jpg I cruise at 1000rpm no problem. I try to accelerate between 1700 and 2300rpm, but it cruises nicely down nearly to idle RPM. |
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