Secrets of the Mirage

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Secrets of the Mirage

Postby Loren » Thu May 31, 2018 4:10 pm

It just got through customs yesterday. I don't expect to see it for another week.
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Postby CaptainSquirts » Thu May 31, 2018 4:20 pm

Ah, I missed the part about it being in Los Angeles.
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Postby Loren » Fri Jun 01, 2018 3:25 pm

Unexpected knock on my door this afternoon. USPS gets an A+ for timely delivery. C- for having updated delivery information.

No box, but very well cocooned in many layers of bubble wrap, paper and tape. :thumbwink:
Image

Looks good enough. If it fits as good as it looks, I'll be very pleased!
Image

6 bolts and two O2 sensors. I may go ahead and install it tomorrow.
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Postby Loren » Fri Jun 01, 2018 3:32 pm

I really wanted some good baseline measurements, but it just doesn't seem to be in the cards. The Torque app on my phone proved to be pretty useless. It's just too inconsistent. Peak HP and Torque numbers are all over the place. 0-60 I didn't even bother with because I don't have a good place to do it. (Mexico is closed during the daytime) But, even if I did, it requires a launch and two shifts to reach 60. That's a lot of variables unrelated to actual power. The most consistent thing I came up with was 0-30 acceleration. Even that requires a launch and one shift! But, I could pretty consistently find a peak of 4.2-4.4 seconds. That's a reasonable baseline figure.

I was able to get plenty of baseline sound level data the other day. Suffice it to say, the stock exhaust is quiet. Redline acceleration in 1st and 2nd is 83db inside the car. Revving to 6k is 85db 10 feet behind the car. That's as loud as it gets!
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Postby Native » Fri Jun 01, 2018 5:00 pm

Rolling start. 5 mph up to whatever - maybe 1st gear fuel cut? Fairly easy to to hold 5 and floor it. Decent indication of torque.
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Postby Loren » Fri Jun 01, 2018 5:29 pm

Yeah. I guess I could accomplish that with video. I was thinking I needed somebody with a stopwatch, and didn't have anyone handy.
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Postby twistedwankel » Fri Jun 01, 2018 9:49 pm

Loren wrote:Image
Those usually come in pairs :lol:
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Postby Loren » Fri Jun 01, 2018 10:29 pm

If I had two, I could run a dual exhaust and make some real power!
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Postby Loren » Sat Jun 02, 2018 1:01 am

Header Overview and Dimensions

Yes, the quality is very good. Welds are very nice. Not "show car perfect", but very good TIG welds. The tubes are double-welded to the flange, a bead on the outside and one on the inside. There is a slight ridge around the inside of one of the holes of the flange. If I had a half-round file, it would take 30 seconds to get rid of it. I'm not going to bother. Otherwise, there's a pretty healthy set of gouges/scratches on the underside of one of the tubes near the flange. I'm not "that guy", I don't care. But, I know people (we all do) who would lose their mind over such a thing. They are significantly deep scratches. I didn't measure, but they're probably half the thickness of the tube material, and half-inch or so long. I don't think it will be a problem.

The design is interesting. And imperfect. Nice, small diameter primary tubes and slightly larger collector tube. The imperfect part is that it's nowhere near an equal-length header. It's hard to measure a header tube, of course. But, two of the tubes are approximately 11.5" long, and the one with the O2 sensor in it is 8". Significant difference. Given that it's a 3-cylinder and not something like a "tri-y" design or anything complicated like that... I don't think it will matter much. Another intersting thing is that the collector necks down at the flange. I ran across something like this last week while reading about headers somewhere. This is a feature called "anti-reversion". And pressure wave that is reflected back from the exhaust is going to be interrupted by the abrupt change in diameter flowing in the reverse direction. It's a smoother change in diameter flowing in the correct direction. You can Google "anti-reversion chamber" if you want to know more. The way this is built, there would be benefit to making the first section of pipe after the header flange fairly large in diameter to have the desired effect.

Measurements:
Tubing Thickness = .045" (19 GA) (note that this is what I could measure at the collector end, the primary tubes could be thicker)
Primary Tubing = 1.5" OD
Primary Length = 11.5" / 11.5" / 8.0"
Collector Tubing = 1.75" OD
Collector Length (including flex joint) = 8.0"
Anti-Reversion Tip = 1.5" OD
Weight = 5 lb 8.8 oz (5.55 lbs) (kitchen scales are great for not-too-heavy parts!)
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Postby Jamie » Sat Jun 02, 2018 1:27 pm

Loren wrote:If I had two, I could run a dual exhaust and make some real power!
Engines?
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Postby Loren » Mon Jun 04, 2018 5:37 pm

Initial feedback on the header. Seemed pretty subtle at first. And with the rain and all, I can't say that the car felt notably faster yesterday. It felt really good all around, though. But, driving around town today... it's definitely got more torque. I'm wondering if may the long term spark and fuel trims are adapting to it? It feels better than it did on the first drive.

I took sound measurements today, too. I'll spare you all of the details that I put on the Mirage forum. Suffice it to say that it didn't make any difference at idle, maybe 1-2 db in the mid-range, and 3-4 db at the high end. That's inside the car. Outside the car, I was very surprised that at 10 feet, 6000 rpm went from 87 to 94 db! But, at 50 feet, there was no perceptible difference.

So, clearly it's done something. Exhaust gasses are flowing more freely. Can't wait to open up the rest of the exhaust a little more. Who ever thought 4 horsepower would be so exciting?
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Postby Loren » Tue Jun 05, 2018 4:51 am

Well, I did my second round of acceleration testing today. In analyzing it, I realized that I really should have done the video in slow motion (60 fps rather than 30 fps). Doing it in standard 30 fps, the granularity of my data is .033 seconds. With each 500 rpm segment being about a second, that means I can only see change in about 3.3% increments. Fortunately, the improvement is generally more than 3.5%, so it does readily show on the graph. But, I wouldn't call it accurate.

I'll go ahead and redo the data at 60 fps before I do the rest of the exhaust. I'm not going to redo my baseline, but at least that final comparison with the full exhaust can be more accurate.

All that being said, here it is. Clear 3.5-4.5% improvement in acceleration across the board up to 5500 rpm. I can't explain why there's actually a DECREASE at 6000 rpm, but it was very definitely and repeatably there. I had 3 runs before and 4 runs after, and all of the data, while not exactly the same, was very close and always showed the same trends. It definitely drops off at the last data point.

But, just look at that torque curve! It's brilliant! I think opening up the rest of the exhaust will raise the torque curve a little bit more, and very likely bring the high end up significantly.

I'm thinking seriously about cutting out the 1.5" pinch point at the end of the header. I think that's limiting the total CFM that the header can flow, and thus limiting peak HP to near stock levels.
Mirage Header.png
Mirage Header.png (25.5 KiB) Viewed 797 times
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Postby blacksheep-1 » Tue Jun 05, 2018 5:26 pm

I have some experience with anti reversion cones back in the 70s, they were a very big deal...for a little while. They actually speeded up the airflow, like a carburetor jet would, (this would also add some torque) however, like a carb jet, it was also a restriction, as the HP and RPM number went up, it became clear that ultimate flow was more important than anti reversion, also, big cams came along with a lot of overlap, this only worked at higher RPMs and allowed the cam to "evacuate" the cylinder (a disaster in terms of low rpm torque though), for this to work, you needed an unrestricted exhaust. IT sort of showed up on some turbo engines back in the mechanical pop off valve days, again, to try and get rid of turbo lag and keep the exhaust speed up, but with the advent of electronic boost controls it went away. Remarkably, you see it more in foreign car circles than anything else these days, I'm not sure why since the little motors spin pretty high, but I guess it's an attempt to salvage some torque out of the engine. It's an interesting concept with some merit.
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Postby Loren » Tue Jun 05, 2018 5:52 pm

:notworthy:
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Postby Loren » Sun Jul 15, 2018 12:53 am

Joe and I did the full exhaust on the car a couple weeks ago. Added a bit more power. Sounds nice. Slightly louder, but not so much that anyone other than me notices it. It just has a nicer tone.

I did some more acceleration testing and found that the torque is very slightly more down low, significantly more from about 4000-5500, and is LESS at the very top up to 6000. Overall, maybe another .3 seconds quicker to 60. What's most amazing is that the acceleration time in the 4000-5500 range is improved from stock by about 15%! That's not 15% everywhere... but, very definitely in that range. This little 3-cylinder seems to actually have some tuning potential if a person wanted to mess with it that much!

Last night, I ordered a "tuning" gizmo. It's not a full "flash tuning" setup, it doesn't give me access to fully do a custom tune on the car. But, what it does do is modify the long term fuel and spark trims (I assume) in the ECU. You tell it what minor modifications you've done (intake, exhaust, header, running higher octane fuel, etc), and it makes the appropriate changes. It won't be as effective as a full custom tune, but I did fine reviews and evaluations of the product that indicate that it actually DOES work. For the price of about $130, I couldn't pass it up. It simply plugs into the OBD. If it adds anything at all, it's worth $130.

Stay tuned for results from that. Hopefully, it will show up this week!
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Postby jbrannon7 » Sun Jul 15, 2018 7:50 am

I still think you should drop the pipe at the header and try to expand that cone with your pipe expander.
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Postby Loren » Sun Jul 15, 2018 10:19 am

jbrannon7 wrote:I still think you should drop the pipe at the header and try to expand that cone with your pipe expander.
Yeah, that's on my list. So many little things to do, so little motivation.
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Postby Loren » Mon Jul 30, 2018 11:47 pm

Did I mention that I bought a $130 "tuner" gizmo? I did. It's not a real flash tuner, but it plugs into the OBDII, and has to stay plugged in to work. I'm pretty sure what it does is modifies the short term fuel, spark and throttle trims. Still experimenting with it.

But, so far, it DOES do something. It is at least advancing timing. And it was enough to decrease my 2nd gear 1500-6000 acceleration time by .25 seconds. So, well worth $130. It's got some other settings that could improve throttle response, and maybe also net more power. Just gotta find time to play with it and to some testing.

End of the season, though. Can't complain. I managed to squeak out an M4 win with it.
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Postby aw614 » Tue Jul 31, 2018 8:40 am

It lets you increase timing while still being able to use 87 octane or are you using 93?
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Postby Native » Tue Jul 31, 2018 9:39 am

The car does feel more peppy, and the exhaust sound is cool...a touch Subaru-like.
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