my miata's back... slower :( AVO beats BEGI
 

So I got 'round to finishing changing out the cracked 40k-mile AVO turbo manifold (my fault, long story) and downpipe with the new BEGI set. I expected it to spool up more quickly, because of BEGI's better, divorced downpipe and "pulse directed manifold", but alas, the opposite happened. :( The AVO manifold has much better flow, because the exhaust pulses go through shallower turns before reaching the turbine.

No wonder my wee turbo (GT2554), chosen for its lightning spoolup speed, made 240 dynojet hp @10psi, beating many FM turbo setups despite a larger turbo (GT2560). And the older FM manifolds were inferior to the new BEGI that I have. There was another guy, forgot his name, back in 2001 who had a '99 and emulated my setup (AVO kit, GT2554, TEC2), who made even slightly more power than I did, owing to a better exhaust.

The AVO intercooler setup is also better than some of the old FM intercoolers - the AVO has 2.5 psi of pressure loss at 240 whp, while some of the old FM i/c's show 4 psi at just 220 whp.

Oh well.... at least the BEGI manifold is now very easy to mount compared to the AVO.

-- more --

I did check for leaks in the new setup. Note my AVO was leaking when I took it off..it didn't seem to affect performance. I used to get 5 psi at 2000 rpm, now it's ~2150 rpm.
The car doesn't feel as responsive in daily driving at around 3000 rpm.

I spent several minutes comparing the 2 manifolds. The issue IMO is not "pulse tuning" (i.e. equal length). The issue is the # of turns each exhaust pulse encounters after exiting the exhaust ports, before it reaches the turbo. The AVO mounted the turbo lower, so the turbine entry was almost level with the exhaust ports. The FM/BEGI all mount the turbo 1.5" or so higher, and the gases have a sharp up-turn near the turbine entrance. The AVO doesn't. The Greddy I used to have was horrible in this regard (mounts turbo not only even higher, but the turbine entrance points up, and its spoolup was terrible.

So I think the lesson is... the best design for a log manifold is not one that attempt equal lengths, but which tries to make each pulse lose the least energy on its way to the turbine.

That ETD racing "shorty" turbo manifold is looking mighty nice.......

Do you have any datalogs comparing the two?

Jason did you take photos of both exhaust setups off the car by any chance?

What are all the components you replaced? Mani, DP, what else?

btw, I told Joey that stripes is an OK guy to buy a turbo from ;)

I know the AVO kit is good. CSR made 267whp @ 15psi with the kit on a stock 1.8 and Link ecu. When researching intercoolers, he'd stated that his AVO intercooler wasn't showing more than a 4c rise from the carousel and down the front straight of roebling rd.. That's starting out in third and on to fifth @ ~12psi.

what's their manifold look like?

Yes, but how does the top-end compare?

I only replaced the mani and d/p for now, no other changes. Still running the AVO i/c and piping, only needed to shorten the compressor outlet pipe by 1.5".

Topend feels better with the AVO too... witness the dyno results of the AVO vs FM of old. No datalogs yet. If the car wants less fuel that would prove my butt dyno.

In theory making the exhaust lose energy on the way to the turbine will reduce spool AND topend ... it will increase backpressure that the exhaust stroke sees.

Sorry I didn't take pix side by side, but I can post pics of the AVO mani. It's nearly a straight shot for #2 and #3 exhaust valves to the turbine. In the FM and BEGI they need to turn up, then sideways again. :(

yeah neither the begi or FM has gas flowing into the turbo. they flow over by it and then are crammed in. if you could cast some sort of collector where all the gas was flowing +/-10° on axis into the impeller then I bet it'd show significant improvement.

it's interesting to note that begi claims the divider in their mani is an improvement over the FM's non-divider version. at high RPM though, the oncoming gas flow is just about a solid divider wall isn't it?

http://flyinmiata.com/projects/turbo...manifold-2.jpg

http://bellengineering.net/Images/ExhaustManifold_3.JPG

can I design the next one?

I believe Markp helped convince corky to add the wall. I wonder if backwards compatability wasn't a concern if it would be the same? There has to be a reason for the tubular design of the S4...

i'm sure the wall doesn't hurt, but i'd love to see a back to back test of the same setup with the wall removed via grinder.

i almost bought the one he had leftover...would have been interesting.

7-11* is generally best for flow. I agree with you one that one, but I still love my BEGi manifold :)

How can AVO design a manifold >8 years ago, that outperforms the 2nd gen designs of the "top 2" US miata tuners?

That wall in theory will prevent #1 exhaust pulse from banging into #4's closed exhaust valve, which is the same problem as FM's current mani... what it does for power, I don't know. AVO has the same "problem", but the flow from all cylinders see smoother turns.

Because backwards compatibility was an issue. That is the #1 reason. I am impressed that the AVO manifold was superior. Having not seen one I can imagine that making the exhaust pulses turn upwards then downwards is part of the issue.

Yes, it's true I suggested the port wall to Corky. If that causes flow to go down, I'll take the beating on that one!

Mark

I have the avo log manifold, spool is fast, but I never had any other one so I can't compare. I can take some pictures of it if interested.

C'mon Jason, everyone said the BEGI manifolds were the best thing since sliced bread. Stephanie has touted their "superiority". I've said in a few threads, TEST THE MANIFOLD TO OTHERS on a dyno and datalog before you claim victory. Seems like a simple premise to me.

Too many BEGI lovers here.

I don't care about the math behind the design of a part, I want to see the results on a dyno.

Frank

I never bought mine because of the "best manifold ever" claim. I bought it cause it was on sale $299, and i got them to make me a custom DP for my turbo when I was in a pinch. I also was dealing with a cracked logstyle manifold, so I wanted something I knew wouldn't do that same.

I was able to achieve the exact same rwhp with my log style as the begi with no additional tuning.

Rusman- shoot some pics. Would be nice to see a visual comparison. :bigtu:

I don't see anything wrong with loving a shop - it's more any issue with the "everything else is crap" attitude. I'm impressed that both FM and BEGI hand out professional advice on a regular basis. I've spent only a little dough with FM, yet they're service has been extensive and stellar. - rob

I too do not remember what the AVO manifold looks like. Best photo I could find was this
http://www.avoturboworld.com/news/miata_a4_small.pdf

http://www.avoturbo.com/avo_guides/d...2/DSCN3378.jpg
http://www.avoturbo.com/avo_guides/d...2/DSCN3383.jpg
http://www.avoturbo.com/avo_guides/d...2/DSCN3388.jpg

LOL, I wonder why people love them. Maybe it's the fact that they genuinely care about their customers. While Stephanie is certainly learning alot and coming into her own, I don't think that you need to target her. You should aim your criticism at Corky, as he is the one who believes his manifold is better than the competition. Stephanie is merely the person we see in public on a more common basis.

So here we have a manifold that flows better than the BEGi one. Good enough for me. I do think the BEGi manifold is better than the FM manifold. I suspect that I will lose some power from my Ghettocharger manifold to the BEGi one, I would be surprised if I didn't. I do expect to gain a factor of reliability though. Jason got a manifold that was easier to install. Does that count towards superiority? Perhaps not, but it is something to consider as well.

There is one other possibility, although I am sure Jason has already looked at this. The new manifold may benefit from different tuning and that could be playing a factor in the way the turbo and manifold are performing. Either way, it looks like the AVO manifold might be the better manifold.

Mark

i wonder how long that Copper RTV will last?

28 seconds, haha.

Anyway, that's the same manifold I have. It mounts the turbo a lot lower than begi or any other manifold I've seen. I can confirm that it is a b*tch to install, the bottom bolts are impossible to reach and I had to replace the nuts twice because I stripped them both times I was taking it off. I cannot comment on the flow because I never had another manifold

Maybe the reason for the AVO's superiority is that the passages are narrower... keeps velocity thus kinetic energy up.

It's quite possible. Getting heat and velocity in there is key to making it spool. We often used smaller diameter header pipes because they spooled much more nicely than the large pipes and we lost no real power from them (sub 300 RWHP.)

Mark

Can you buy the AVO manifold by itself in case you're planning on a DIY kit?

http://www.avoroadster.com/avo/html/mazda/mazda.html

Yep 1.6 mani is for sale... (aus dollar)

US$594.88 for the 1.6 AVO manifold, based on AU$700

Got some proper spoolup datalogs done, with some numbers with the AVO. 2nd gear, flooring it at 1500 rpm, same flat road, ambient within 6°C of each other. Full boost is 170 kPa.

Remember this is 2nd gear, it takes all of ~4sec to go from 2000 to 6000 RPM

RPM AVOkpa BEGIkpa
2000 117 112
2500 136 128
3000 161 145
3277 170 159
3450 175 170

Huge difference around 3000 rpm - 2psi - this is why the car feels much soggier shifting at 3000 rpm. On a bad day the AVO never felt this laggy. :(

Ouch, I was hoping for something closer to the price of the BEGi manifold. Say around $400? I also like the fact that BEGi will put a custom flange on the manifold for you too.

US$ has been dropping like a rock. In 2000, I got my whole AVO kit for US$2000. Gotta thank the Federal Reserve, the gov't, and the war for that one.

finnally i found the fabled avo site. anyone know the conversion for kwh to hp. Edit damn only 200 whp at 13 psi what is wrong with there car?

I made 210whp at 9-10psi, so their car is messed up I think.

No comments on my HARD data?

THIS looks like a nice homemade turbo header.
Note how the pulses would flow INTO the turbo.

http://us1.webpublications.com.au/st...6/2658_8lo.jpg

does the AVO hold the turbo down a little lower? That would result in a straighter, and possibly slighly larger diameter, downpipe. I've always thought that the restriction after the turbo, not before, was the primary concern.

Ben

I think the main problem when you look at the BEGi vs. the AVO is that the AVO in the least slightly angles the pulses into the turbine....the BEGi even with it's "directed pulse" wall, still has 1 & 4 pointed towards each other....not even ever so slightly into the turbine. Hitting the pulse wall will angle it in, but then that's another 90° the pulses have to travel.

I'm confident that Corky, if backwards compatibility wasn't a concern, even with a cast manifold, would have designed it slightly different.

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.

I keep looking at this ETD shorty manifold and getting a woody. Look how beautiful the flow is into the turbine:

http://www.etdracing.com/products/manifolds/miata1.jpg

I called them and for an add'l $100 they can custom build one in 3 weeks using 1.25" tubing (inst. of 1.5", for spoolup), with a T25 flange. The extra $100 is because the runners need to neck down more for the T25's narrower entry.

They said they plan to stop making it at some point because it's less profitable than their other stuff. :(

I visited the muffler guy who built my custom exhaust and he can modify my BEGI downpipe to work with the new manifold for $120 to $300 depending on actual time, and ~2 days.

So............ should I leap in?

hell if they're custom making something, see if they'll put the flange parallel to the head flange.

:werd: 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

http://www.etdracing.com/products/manifolds/miata2.jpg

That would require the gases to turn more sharply into the turbine..........

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.

Mark

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

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.

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

Exported the datalog from AEMLog to Excel.
Here are graphs of the datalogs; 2nd gear spoolup, punching it at 1500 rpm.

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.

I haven't retuned it yet.. it only oscillates in cooler weather, and it's been hot since.

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?

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.

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.

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?

FWIW look how nice a cast manifold can be. This one is for a Honda:

http://www.streetrays.com/catalog/im...o_manifold.jpg

you know the honda's port spacing is the same as ours, right?

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.

Unfortunately the cast honda manifolds always have contoured flanges that don't allow for redrilling or altering to fit the B exhaust bolt pattern.

yeah i thought of that. not feasible to re-flange it either.

contoured? you mean that pattern of triangles?

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.