I've already got a cat, so I'm planning to boost my car.

(Kinda) useless details about it :


2003 NB SE, called MX-5 Twins
Sport Brakes/Braces
5spd 4.1
Torsen T2 LSD
D2 Coilovers



Kinda more useful info about it :

1.8 VVT EUDM engine, it's got the squaretop intake manifold afaik
It originally was a 1.6 car, and during the swap we already tapped into the oil pan for oil drain.
MS3 Mini w/ Innovate wideband
52mm alu ebay radiator with silicone hoses
I'm putting a 6spd before boosting

Parts I've already got :

ACT 6puck sprung disc
Used FMIC setup, 2.5" coldside, 2" hotside, intercooler the size of the miata's mouth, routed straight front and down the radiator. Will require cutting the finish panel
Audi S3 mk1 bov
Maxpeedingrods GT2871 turbo
Used genuine rx-8 yellows

Parts I've planned on getting :

custom shop-built 70mm turboback with two big resonators
ebay cast iron t2 manifold
custom strengthened oem pressure plate
mac ebc valve (probably genuine, but are ebay ones worth it?)
ebay replica boost, water temp, oil temp, exhaust temp gauges to get a vague reading
Kemso/Walbro uprated fuel pump


Goal : Taking the stock motor to its limits, reasonably. It'll be a street cruiser, with the occasional drag race, occasional skid. No track time, or heavy abuse. No money wasted, but I don't want to end up with something totally unreliable either. I want it to be a value for money build. I don't mind some extra turbo lag or 20-30 less hp compared to a far more expensive setup. Would you change something and why?

Thanks

 

While it's apart, and easy to do, I'd go with a better pressure plate, as in a matched set of disc and PP, and ditch the injectors for a matched set from Nigel, and get real, quality gauges for temp and oil pre. just not worth wondering if the numbers you are seeing are accurate or not.

 

Hm, I can get a new ACT heavy duty pressure plate for about double what I'll pay for strengthening the oem one. Still, I'd consider the act one.

Quality gauges would be great, but they can get stupid expensive to the point a single one can cost more than my turbo. I mean I won't be hitting the track with it, and all I want is to know then the car is up to operating temp, and when it gets into danger zones, eh, accuracy aint all that much of a priority

Hm, what about the injectors? Am I going to run into fueling problems? Won't 425cc be enough for couple horsepower under 300? I am gonna send them to get cleaned and flow tested

 

Just found this while googling :

A quick trip to the injector calculator shows that at 250 crank hp you are needing about 430 cc @90%. so you are probably maxed out.

Oh well. I need to research some more on injectors or decide to stay at 250hp.

 

Nigel, at Flowforceinjectors, will set you up with modern, EV 14 style (off the top of my head) injectors that will have a better spray pattern, and all 4 will be closely matched for flow. I'd recommend the 640 cc set for you power plans, and added bonus is the improved idle they will bring. I have used AutoMeter gauges on a lot of project cars, and find them to be accurate, and reasonable in cost. Cheap Ebay gauges will probably not be any more accurate than the stock dash, so no benefit in my mind. The important ones are, of course, oil pre., but specific to a Miata, the coolant temp., as it's easy to cook a head while a shitty gauge is getting around to telling you about temps.

 

Just checked the flowforce injectors out, I'll shoot him a message, thanks.
Good points indeed. I may opt for used genuine gauges.

 

430cc injectors won't get you to your power goals.

I strongly recommend flow force 640cc. They're awesome, and on my setup got me to 309whp

 

Already contacted Nigel, I'm selling the yellows and getting the 640s!

 

My initial plan was to retain my current custom 60mm exhaust (two big mufflers on it) and create a custom 70mm (2.75in) downpipe that will connect with a reducer to the current exhaust's middle muffler.

What if I do that, with the exception of a vacuum actuated cutout right before the middle muffler?

Won't that allow for more top end hp and less noise during cruising compared to a 70mm turbo-back with just a muffler on the end of it?


Also, people say rods are good for X tq. If you gain tq up top due to a freeer flowing exhaust, will the rods still endure more abuse, or are you just getting free torque that would otherwise be lost due to exhaust backpressure?

 

Cylinder pressure kills rods. Those numbers are averaged guestimates from years of engine failures. Nothing scientific is involved in arriving at them.

Cut outs require tuning for them. If it always opens at WOT you can maybe tune for it, if you are lucky. If it is a sometimes thing it will make the tune rich or lean in boost and can cause it to detonate and destroy the engine.

 

https://loudvalves.com/collections/b...nt=32909551436

That's the ideal cutout solution IMO. It should eliminate the potential tuning issue.

 

That makes an absolute lot of sense.

It'll be just like the one Spartan linked, it will be vacuum actuated, it'll have a wastegate on it, so as long as the vacuum hose remains intact and it's tuned correctly, it should be fairly fine.

In fact, why not put my oem exhaust back on, and buy a cutout that opens up with positive manifold pressure? Off boost it should sound even more quiet than stock, it'll have a cat on so it won't be smelly and it should offer reasonable backpressure to allow for some more fuel eco.

And when map exceeds -3psi for instance, boom it'll open up and go fast.

 

Just get a 2.75-3" free flowing exhaust with the huge magna flow muffler that me and everyone here runs.
It's a fairly quiet and great deep sounding exhaust, quiet while cruising and deep but not loud at WOT.

With the cutout it will be crazy loud and attract every cop in a 1 mile radius every time you press the happy pedal.

 

I don't really mind the noise, I'll mostly Hoon in cop free areas, and my Miata will look totally stock.

I put my foglights back on, oem chrome badge, traded my front blacked out headlights for stock ones and I'm putting oem 15" enkeis back on. It'll look cutesy and stock so I ain't very scared lol.

I mostly need to figure out the technicalities

 

You want a full 3" exhaust.

 

I guess I do. But why?

Now in theory :

1) I'll get an exhaust valve with a -3psi actuator, or something that opens up during positive manifold pressure.
2) Said valve will work properly
3) Car will be tuned correctly and will not be tuned to the "limit"
4) I won't get into trouble with the law
5) The ecu will have AFR limit fail-safes tuned correctly so that even in case something goes wrong, power will be cut, my motor will be given a second chance.

Now I'm a newbie, these are all just my theories, I ain't buying exhaust parts yet and not willing to until I fully understand what I actually should do, can you explain why said plan is a bad idea and I need a full 3" system?

 

Because anything smaller then 3" leaves mid range spool and torque on the table for exactly zero difference in cost. This is something we learned over a decade ago by doing back to back testing.

I am not saying you can't have a cut out or anything like that. Just that you want to up to 3" as soon as possible in the exhaust.

 

Changing to a 3" downpipe then.

What if after the donwpipe, there's a Y pipe, where on one end there's a 3" cutout that opens up past -3psi of boost pressure, and on the other there's my stock exhaust or my current 2.4" system with two straight through mufflers?

 

Why do you want a cutout so bad? I mean, a turbo miata is already a cop magnet.

 

It's going to allow me to use my stock exhaust (silent, looks stock from the back cause it is, not smelly)

It's going to be really loud and exciting when I want and can thrash it

It'll essentially be a 3" straight through system with minimal backpressure when I need the flow

It'll be damn cheap, im saving up a considerable chunk of money if I do it this way, compared to a full 3" system with a big magnaflow and a resonator.

Now, what I'm wondering is, except for the noise, what downsides can such a system have assuming everything works out the way I intend it to?

Could it for instance significantly hurt my fuel economy due to excessive cruise backpressure for instance?

Boost buildup shouldn't be a problem as the exhaust will open up as soon as I go wot, where it should be even better than a proper full 3" system