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Old 11-21-2015, 02:26 PM   #31 (permalink)
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Quote:
Originally Posted by Old Tele man View Post
Looks to me like positioning the three pipes side-by-side ( ooo ) -- rather than in a triangle bundle ( ▲ ) -- all the way back to just past the rear axle is called for. There, the three pipes could triangulated & transitioned directly into a flat muffler, with the "collector" being their transition into the muffler.
I definitely agree that is ideal from a design perspective. I also see that being harder and more costly to fabricate. Engineering is all about trade offs.

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Old 11-21-2015, 04:03 PM   #32 (permalink)
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Three straight pipes, each with a small SuperTrapp™ motorcycle muffler?

SuperTrapp: Performance Exhaust
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Old 11-21-2015, 07:00 PM   #33 (permalink)
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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?
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Old 11-22-2015, 07:03 PM   #34 (permalink)
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aka Trombone? Slide whistle?
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Old 11-23-2015, 11:51 AM   #35 (permalink)
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Quote:
Originally Posted by Old Tele man View Post
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.
My daily travel is mostly around 45 mph and that puts me at 2200 rpm.

Do you have any links that further explain your length calculations?
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Old 11-23-2015, 12:50 PM   #36 (permalink)
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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.



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.
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Old 11-23-2015, 02:50 PM   #37 (permalink)
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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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Old 11-23-2015, 03:36 PM   #38 (permalink)
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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.



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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Old 11-23-2015, 03:40 PM   #39 (permalink)
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Quote:
Originally Posted by ksa8907 View Post
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?
I'm not sure what you're asking. How low can I get the engine what at cruise?
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Old 11-23-2015, 06:05 PM   #40 (permalink)
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Quote:
Originally Posted by Daox View Post
I'm not sure what you're asking. How low can I get the engine what at cruise?
Sorry, rpm. I've never driven a geo before, in fact the least powerful car i have ever driven was an '85 vw golf 5 speed, about 85 hp if i remember right.

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