Carloverx

Ah! Very true! Fingers crossed replacing the cat maintains most of the performance I saw with the cat removed.

The current axle back setup (in theory) should be pretty free flowing.

18psi

iTrader: (76)

Didn't read the whole thread closely, but here are some observations that will hopefully help:

1) turbo/hotside is terribly sized for the rest of the setup. spool is horrendous
2) the fm bits and 2.5 exhaust is definitely hurting your spool as well, in addition to the stock muffler
3) that "recovery" you reference past 6300 is a very common glitch In the VD software. I really doubt your power actually jumps up past 6300. as you can see in the 2nd plot it noses over hard
4) your tune sucks

my conclusion is I don't think your engine is the issue. I think everything else is terribly matched. no offense

Just outa curiosity: did you select each part yourself or just bought a random pile of parts?

Carloverx

"everything else is terribly matached" is quite a stretch. I'd argue the only mismatch at this point is the turbo, particularly the hot side. And even that I wouldn't call "terrible", considering how it SHOULD be running. Was there something else you specifically had in mind?

Additionally, I'm under the impression the AR .64 vs .86 on this turbo is only good for about 500rpm quicker spool on most setups. I'll take a little more top end over that.

I do not have a stock muffler.

As for parts selection, it was slowly picking parts here and there over the past two years whenever deals arrived. E.g turbo was used from a 240sx.

All fhat said, I still have high hopes for the setup after I get the cat and tune squared away 🙂

18psi

iTrader: (76)

Maybe I came off way too harsh, my apologies. 370hp is still quite a lot of power

I'm just really shocked at how laggy this setup is. I mean, passing 200tq at 4600 is really late. I think the .86 in your case is doing you zero favors over the .64, but costing you a whole lot of spool/response. The log mani is exacerbating the issue as well. 2.5 exhaust has been proven many times on our cars to reduce spool/response, and as you've learned, the cat is hurting it that much more.

I mis-understood some posts and thought you were on stock axleback, my mistake. (although with it spooling so slow, that would have made sense)

Can you show me a plot where a .86 hotside clearly makes significant power over the .64 on a Miata? I've seen this on other cars no doubt, but have yet to see it on a Miata.
Can you also show me a plot of a Miata performing well with this setup, or as it should? Only other similar setup I can think of is codrus and vtekkiller

codrus

I suspect the cat is hurting you more than the 2.5" exhaust. That said, 3" is definitely better, and there's no reason not to run one that size.

What gear are you doing the Virtual Dyno runs in? IME, 2nd or 3rd is going to give you a very poor estimation of the spool capabilities of the engine. To measure spool, put it in the 1:1 gear and and do a pull from 2000 RPM until it hits full boost (or higher, but going to redline will probably be 120+ in that gear).

IMHO, virtual dyno is a lousy way to tune spark, it's much too sensitive to variables that are too hard to control. A proper dyno is the right answer.

My car is a .72 ATP exhaust housing with EWG V-band, not a .86. I've also got a GTX2863, so it's a slightly smaller compressor.

--Ian

Carloverx

No worries! You may be 100% right, as I have no idea what I'm doing, lol That said, I WISH the problem was 370hp - hell, I'd be completely smitten with 330hp! The problem is, as you mentioned, spool is horrific, and power is poor relative to my expectations for the psi/setup (all things considered). With the midpipe still installed, reaching 290whp was like pulling teeth! At the heart of all this is: this car started a casual weekend toy. "Pffff. Certainly I'll never need more than a 2.5 inch exhaust or a cast log manifold" I said, lol. And yet here we are :(

Regarding providing evidence for the .86 vs .64 on a miata: I have none. 500rpm is my rough estimate based on old dyno graphs from unrelated setups, littered about the internet. (though it does fall in line with the .64 GT2871 ebay charger I previously had on the car). The .86 is NOT helping, I agree. But it just seems like there's a bigger issue in play.

Outside of the anecdotally poor spool and power, the other reason I feel the actual setup could do better (even with the mismatch of parts), is due to the seemingly major increase in power I experienced after removing the midpipe/cat. Hence why I'm headed down the path of swapping out the cat. Fingers crossed

p.s. more details of my nonsense can be found here in my build thread


I'm running VD in 3rd gear. Unfortunately I can't find a local strip of flat road long enough for a clean 4th gear pulls (damn New Jersey).
I agree the VD is not ideal and had done all it could for me at this point. I recently visited a great shop (ProFab - Chasis & Custom Cars) just a few miles away to setup dyno time. BUT, I haven't made an appointment yet b/c I still felt the car wasn't healthy enough.

I genuinely think that after this cat swap, the car will be ready for dyno time.

patsmx5

iTrader: (16)

I tried a .86 and .63 on the same turbo on my car. From seat of the pants, .63 spooled WAYYY faster and got to boost a lot quicker. Logs showed the same. Power, eh, about the same. I'm sure the .86 probably made a few more HP, but doesn't' matter, car was way faster when making full boost sooner with the .63 AR. Surprised me, I expected the .86 to be a lot better. I'm going to swap back to the .63 next time I have a reason to pull the turbo off. But my turbo doesn't choke with a .63, I just figured the .86 would make more power so I tried it. I like testing things to see what works and what doesn't. I drive my car on the street mostly, so I'll take the spool over any potential small gain in power from the larger a/r.

Carloverx

Update:

1. Below is a spool comparison between:
   (Old Cat / 3rd Gear Pull) vs. (New Cat / 4th Gear Pull)
   Looks promising. I'll now be shifting my focus back to the tune.
2. I've concluded I need another column between 5,200 and 6,000RPM to get a better grip on timing. (That may have been obvious to others).
   Previously if I got knock in that area, I'd adjust both my 5,200 and 6K RPM columns, and make both worse for it - when my problem is really in the 5,500 RPM range.
3. I've made great strides in cleaning up my fuel map as well. Including taking pdexta 's advice with those extra rich/lean areas.

New cat (welded to two reducer pipes with slip fittings):

ridethecliche

iTrader: (2)

New boost curve looks way better, but I'm not sure they're directly comparable given that the gear was different. i.e. different load.
I'm sure that you can tell the difference though.