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