my miata's back... slower :( AVO beats BEGI - Page 3 - Miata Turbo Forum - Boost cars, acquire cats.

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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 07-03-2007, 05:58 PM   #41
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hell if they're custom making something, see if they'll put the flange parallel to the head flange.
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Old 07-03-2007, 06:14 PM   #42
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remove backpressure

here's their mani w/ a seperate wg, visually replace the flange and external wg for a turbo flange and turbo. might have to do a little trimming, but imo would be worth it

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Old 07-03-2007, 06:48 PM   #43
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Quote:
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hell if they're custom making something, see if they'll put the flange parallel to the head flange.
That would require the gases to turn more sharply into the turbine..........
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Old 07-04-2007, 12:31 AM   #44
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Quote:
Originally Posted by JasonC SBB View Post
Yes the AVO mounts a lot lower and there's a nearly straight shot from #3 into the turbine (funny the turbo mounts rearward despite lack of space for the downpipe). It also appears that the curves for #1 and #4 are gentler. On the BEGI the runners come out from the ports a bit before turning sharply, to make room for wrenches. On the AVO they begin curving immediately, thus the gentler radius. There is also a slight turn-in into the turbine for #1 and #4... but of course #1 and #4 still "look" into each other.
As you noted there is more to the Manifold than just good flow. I see the current BEGi manifold as a compromise, it compromises flow for backwards compatibility and ease of installation. I agree that for some these compromises make little sense to the hard core power junkie.

As for JasonC's dilema, I think that the ETD Manifold is a sharp design and 1.25" schedule 40 is the smart choice for the runners. It will make for a very nice collector. It's too bad that the BEGi apparently does not perform as well as the AVO, but I am not surprised. I do believe that the divider is an improvement over the previous design though and with some creative port work it could even be better.

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Old 07-04-2007, 10:35 AM   #45
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Quote:
Originally Posted by JasonC SBB View Post
Maybe the reason for the AVO's superiority is that the passages are narrower... keeps velocity thus kinetic energy up.
And that's where I think FM have an advantage with their manifold. The runners are separate until the exit and the area is similar to the exhaust posts. I know Mark thinks there's an issue with 1 and 4 facing each other, but no-ones commented on the fact 2 and 3 are about half the length, facing directly into the turbine and could actually help the pulses from 1 and 4 turn the corner. BEGi on the other hand have the gases expanding into a fairly large area before getting squeezed through the outlet.

Jason - 170kpa at 3000rpm. AVO, MoTeC, GT2560R! http://www.performance5.com/images/d...TeC11.5psi.pdf Interestingly, I also thought the AVO turbine outlet was a bad design, it looked very restrictive. May be the back end doesn't make that much difference......

Phil
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Old 07-04-2007, 02:27 PM   #46
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I may have to take back what I said about the topend being weak.
The torque seems to flag off less going from 5500 to 7000 rpm with the BEGI than the AVO. It may actually make more power at 6500 rpm or so. This may be due to the downpipe. I agree the AVO turbine discharge looks restrictive.

Phil -
FM vs BEGI - The BEGI design almost looks like there's a plenum before the turbine inlet, as opposed to the FM mani (which you described).

I've seen 1 other AVO+GT2560 plot that shows the same incredible spoolup as your plot. It seems the AVO+GT2554 has the advantage below 2700 rpm or so, and perhaps response in the 3000-3500 rpm range.

Last edited by JasonC SBB; 07-05-2007 at 07:24 PM.
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Old 07-04-2007, 10:12 PM   #47
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That's why my BEGi manifold is separated all the way to the turbine inlet (which is a divided inlet.) I rather think that forming a plenum may be detrimental, I would have extended it further and flowed it to find the best terminal shape.

It is possible that once the gases have sufficient velocity it may be that the BEGi makes up for some of it's deficits. I am looking forward to comparing it with the Ebay tubular manifold that I was using, which really was not a bad unit in concept.

Mark
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Old 07-05-2007, 07:16 PM   #48
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Exported the datalog from AEMLog to Excel.
Here are graphs of the datalogs; 2nd gear spoolup, punching it at 1500 rpm.
Attached Thumbnails
my miata's back... slower :(  AVO beats BEGI-avo_begi_spoolup.gif  
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Old 07-05-2007, 10:09 PM   #49
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So have you re-tuned your boost controller to account for the changes? It appears you had worked at dialing in quite a nice boost "curve" with the old setup.
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Old 07-06-2007, 01:12 PM   #50
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I haven't retuned it yet.. it only oscillates in cooler weather, and it's been hot since.
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Old 07-07-2007, 02:17 AM   #51
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Quote:
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I think that the ETD Manifold is a sharp design and 1.25" schedule 40 is the smart choice for the runners.
In lieu of measuring my cylinder head's ports I looke at the matching ports on my AVO manifold which closely matched the cylinder head. The holes are an oval, 1.25" x 2.0" across. As near as I can tell, the circumference would be close to that of a 1.75" pipe. IOW if you bash or shape a 1.75" pipe you can make it match the ports. It seems to me that a 1.25" pipe will be too narrow to match the ports. Comments?
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Old 07-07-2007, 11:44 AM   #52
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flow area should be kept constant. remember when you smoosh a pipe to be a 1.25 x 2 oval your flow area becomes [pi*(1.25^2)/4 + .75*1.25] or 2.16sqin which is closer to the flow area of a 1.65" ID pipe.

You'd probably be ok decreasing diameter as long as the oval-round transition is smooth and long enough to prevent turbulence.
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Old 07-09-2007, 03:01 PM   #53
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Ah but you're using the equation for an ellipse. The ports are move like an oval race-track - it's got straights.

The '99 exhaust valves are 28mm diameter, for a total x-section area of 1.91 in^2. That's the area of a single pipe, 1.56" in diameter. Still says 1.25" is
too small.
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Old 07-09-2007, 03:38 PM   #54
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that was the area of an oval with straight sides... area of 1/2 circle plus half circle = area of circle (pi R squared or pi D squared over 4) plus area of rectangle between halves. D x (W-D). though maybe my math is wrong.

What's ETD use by default?
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Old 07-10-2007, 02:24 AM   #55
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FWIW look how nice a cast manifold can be. This one is for a Honda:

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Old 07-10-2007, 11:15 AM   #56
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you know the honda's port spacing is the same as ours, right?
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Old 07-10-2007, 11:26 AM   #57
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Is that an hks manifold? The 1.6 miata hks manifold looks similar. The 1.8 HKS manifold is not quite as nice in my opinion, but I think it's still a good design for the money.
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Old 07-10-2007, 11:59 AM   #58
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Unfortunately the cast honda manifolds always have contoured flanges that don't allow for redrilling or altering to fit the B exhaust bolt pattern.
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Old 07-10-2007, 12:28 PM   #59
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yeah i thought of that. not feasible to re-flange it either.

contoured? you mean that pattern of triangles?
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Old 07-10-2007, 01:50 PM   #60
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re: 1.25" vs 1.5" piping.
y8s points out that the real i.d. of 1.25" schedule 40 piping is 1.38", 1.5" is more like 1.6".

That out of the way ...

Just got off the phone from ETD. They said

a) 1.5" piping is way more difficult to merge at the collector for a T25 flange. They use 1.5" for T3 flanges

b) They expand the 1.25" pipe at the exhaust ports as much as they can to match up with the ports

Now I wish there were a not-overpriced ball-bearing T3 turbo sized between a GT2554 and a GT2560.
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