3" exhaust or reroute
 

I have a T3b turbo, MS3X, LS2 truck coils, and custom intercooler piping on a stock 1.8 engine and I have a little bit of money to spend on the car. I'm trying to decide between changing my crappy 2.5" exhaust with a diy 3" mandrel bent exhaust or a coolant reroute . Right now my cars spools really slow. I'm sure changing the exhaust would improve my spool a good bit. Here is a screenshot of my spool.
Attachment 104350

Just wanted some opinions on if I should go with exhaust or reroute. I will be keeping boost at 8 psi for at least another year and am leaning to the exhaust.

Here is a pic of my engine bay as it sits.


https://www.miataturbo.net/attachmen...ine=1393302099

That's a really really bad datalog.

Maybe it's just me, but i can't see anything from that.

Also, i doubt 2.5" exhaust is slowing your spool that much.

Do you have cooling issues? If not i would advise trying to fix that spool issue. I do doubt that the 2.5" downpipe is causing the issue but im sure a 3" would spool faster and make more power anyways. Tune time is likely what you need.

Brainy wants your spool data.

Post your spool there for comparison.

Is your wastegate adjusted properly?

Boost leak?


We just had a thread almost exactly like this a few week ago.

Are you tapping your gas pedal foot to a song or something?

Where are you getting your M/EBC wastegate signal from? If it's not from directly below that hideous blue 90* coupler off the throttle body, change that first than come back.

I'm running a tial 35mm wastegate and don't believe they have any adjustments except changing springs.

Curly, you are right I had that on one of my to do lists and just forgot it, thanks for the reminder. I will also swap out that terrible 90 with a black one.

If these changes don't improve spool I will perform a leak test on the intercooler piping.

Thanks for the suggestions.

Make sure you have a bit of preload (spring pressure holding the wastegate flapper closed) with that Tial. If it's cracked open at rest, exhaust is bypassing the turbine.

I removed my Tial Bov a couple of months age and need to check and see if the oring got put back on. I will let you guys know if that is my problem. I appreciate all the ideas on what is wrong.

BOV and wastegate actuator are two different things. ??

I understand the difference in a bov and wastegate. I have a tial bov that was removed and I think I'm missing an oring between the flange and bov that may be causing a boost leak.

Also make sure you have the firing ring in your tial gate. Its like a metal o-ring that goes between the flange and the gate, without it you might aswell have the gate open all the time.

I was correct there is no oring on the bov. Could this cause a big enough boost leak to account for my late boost. Guess I will hit eBay up for one tomorrow.

^^^^ This!

Early gate opening symptoms. You'd need to have a MAJOR boost leak to spool that slow, and you would hear it for sure.

You definitely don't need 3" exhaust at 8 psi. I'm running 15-17 PSI (depending on weather) and making ~300 whp through 2.5" exhaust and see no reason to go bigger at this power level. Hell I made 235 whp on 12 psi through the STOCK exhaust.

Thanks for the reply. I didn't think a boost leak would slow my spool this much. I will check the wastegate but I'm pretty sure the firing ring is in there. It never hurts to double check.

Installed new bov flange oring and took the car for a drive. The datalog shows better spool, but after looking at the old logs they show I was only at partial throtlle (50%). Here is a pic of the datalog. This is a 3rd gear pull.
https://www.miataturbo.net/attachmen...ine=1394037224

Do you guys think that this is reasonable spool for my setup. Let me know if you want me to load any other information.

That looks much more reasonable.

Why part throttle? Were you really part throttle or do you need to calibrate your TPS? Being part throttle hurts spool (obviously).

Hornetball you may be correct that my tps calibration was incorrect and it was actually full throttle. I did have my tps wired incorrectly at one point but I'm not sure if I fixed it before or after the previous spool data.

How much spool could I possible gain from changing from a crush bent exhaust to a 3" mandrell bent exhaust?

Why do you keep wanting to spend money on your car when it's not needed?
Fix the tune. It's free, and easy.
Find the problem. Fix the problem.

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.