I understand that my tune is not completed and I need to work on it. I don't get to work on my tune as much as I would like since I'm very busy. I work on it a little every week or 2 and it is slowly getting better. I was just asking a question. I won't be changing any parts on my car till I get my tune dialed in, but would like to fix my exhaust that is restrictive and hits my tunnel in several spots while driving.

2.5" is not restrictive. Not yet anyway.

Unless i missed somewhere that you said it's smaller.

+1 on tuning.

You have to be at a certain power level before you'll start seeing a real difference between a 2.5" vs. 3" exhaust. OTOH, your crush bends might be a lot more restrictive than you expect.

Here's a comparison from my Silver car to whet your appetite:

Blue:
1. Stock Greddy DP.
2. OEM header pipe from triangle flange to cat. (I am NOT going to miss that damn triangle).
3. High-flow metallic cat.
4. Cobalt exhaust system (62mm + resonator + chambered muffler). 62mm is about 2.4".

Red:
1. BEGI Greddy replacement DP with SG pipe for the wastegate and 2.5" termination. (thank you Kotomile and FRTFun -- I'm the 3rd owner)
2. 2.5" test pipe.
3. Enthuza 2.5" turbo racer exhaust with Borla straight-through muffler.

https://www.miataturbo.net/attachmen...1&d=1380248952

I LOVE how flat my torque curve is from 3500 up. Awesome for track use.

Well here are my spool numbers.
rpm psi
2007 1.1
2256 2
2515 2.7
2754 3.4
3012 3.8
3254 4.5
3511 5.4
3755 6.7
3897 7.2

I think I'm going to use some 2.5 mandrel bends from a buddies VW to replace crush bends and adjust the exhaust to keep it from hitting the tunnel. This should improve flow and eliminate alot of vibrations that are driving me crazy while only costing me time. I will do this over my break along with alot of tuning.

Are you running on Wastegate spring alone?

If so, that's likely part of your problem. Soft gate springs, 8 psi and lower, will start to crack open the gate at a much lower psi than the rated pressure. Typically the gate is already starting to open at 2-3 psi on an 8 psi spring. As soon as the gate cracks even a tiny bit, you're loosing energy out the exhaust that should be spooling your turbo.

This is the reason most quality EBCs apply zero pressure to the Wastegate, until you've reached your desired boost set-point. There's actually a setting to denote at what PSI the gate begins to crack open. Setting this properly will improve spool drastically.

Since you don't have an EBC, I'm assuming. You can run a cheapish MBC, or put a stiffer spring in and raise the boost a little and it should help spool.

Why only 8 psi? You can handle quite a bit more than that.

Wow. I think I'm at 12psi (my target) by the low 3000s. If I'm not mistaken, you should be at 7.2psi (if that's your target) just as early. Like, mid 2000s even.

ESPECIALLY WITH THE 1.8 YOUR SIG SAYS YOU HAVE. HOLY FUCK.

Yes, I am currently running on wastegate spring alone. I do have an EBC that I will be using, but was trying to get everything dialed in before adding another variable. I'm not really sure how much boost the stock motor can handle before sending a rod through the block with a t3/t4b.

Hornetball, your numbers look pretty good. But you might want to take a look at your VE table. Your AFRs need to be much richer when the turbo fully spools, around 11.5 or so, and you can taper it off towards the top end, I usually like to end around 11.85-11.9.

Cylinder pressure is at it's highest right when the turbo spools and you need the extra fuel for knock protection. Set your AFR to around 11.5 there and you should be able to run around 17-18 degrees of timing at that boost level when the turbo spools. Then taper fuel off and increase timing. You should have around 22-23 degrees by redline at that boost level. This is assuming 93 octane fuel, or 98 RON if you're across the pond. 91 octane should subtract 2 or so degrees from those timing numbers.

Looking at this setup which has a 2.0 engine, larger exhaust, EBC, and very similar turbo I feel like my spool is not that bad. Its about 300 rpm behind m2cupcars.

Damn, that torque curve looks a lot like my M45 running 9.5 psi of boost! I bet that is pretty sweet on the track :bigtu:

Keith

Well I redid the downpipe with 2.5" mandrel bends that I got for free, which eliminated all my rattles but not sure if it helped spool. I have not had time to check since I have been really busy with school and getting ready for my 2nd child to be born. Hopefully, tomorrow I can go out for a ride and datalog a pull before switching to EBC.