A/F Ratios and Air Restrictions
 

Hello all, this is my second post, but I've lurked for a while now, and I even used the magic search button. I just got my 90 miata with BEGi Shanghai turbo/ megasquirt PNP/Intercooled, dyno'd. The tuner maxed out my stock injectors and made 158 HP 169 lb/ft at 10 psi. After talking to both FM and BEGi they both think that is dreadfully low, and BEGi thinks it might be a restriction in the air flow. I was running rich (around 11-13 A/F) for about 8/9 months before I could tune it. I may have fried my cat; I won't know I can take it off and look (Sunday afternoon).

My question is since the tuner tuned it with that (potential) restriction what will happen if I 1: Gut the cat for the mean time, 2: Replace it with a new working/non blocked cat?

11:1 AFR is rich. 13:1 AFR is motor-failure lean.

If you have an exhaust restriction, and you remove it, the car will run leaner than it did before.

Who tuned your car?

I had this same problem and peaked at 180whp. I then installed a Walbro 255 and now it will make over 300whp.

It sounds to me like you've been running at 13:1 AFR which means your ---- is burnt.

Well if you are adding all the fuel to get the right ratio and just not making the power with it I would say you are lacking in the spark advance or engine compression department. If you're not getting all the power you should while getting the same air flow and fuel then there is something happening in the combo chamber that isnt up to snuff.

Those numbers don't seem right. I thought Stoichiometric for gas was 14.7 A/F

I was running the base map for 8 months, but I had it tuned at Church's Dyno in LA, CA.

Which ---- is burnt??? The cat? Something in the engine?? Also I was told (by Flyin Miata) that the stock pump is usually good for something like 250whp. Maybe I misunderstood? I will be ordering either 550 Injectors from BEGi or 700 Injectors from Flyin Miata on Monday. Any one here tried either on a Megasquirt PNP??

I had my engine check recently before the dyno tuning by Rocky @ Rocky's Miatomotive, and he said I had really good compression. So I don't know.

I won't have time until Sunday afternoon to take the cat off and see if it is toast. If it isn't anyone know how to check for restrictions in the cat back? I have a Borala dual exhaust.

Accidental double post

Stoich is 14.7, but awesome chemical properties and laws of physics push us to make peak output around 11.5:1 in most scenarios. Running at 14.7:1 in boost will create too much heat for steel valves, most pistons, and most rings. Fancy, modern engines with exotic metals can run stoich in boost at reasonable power levels, we can't. You have a 30-year old engine design, welcome to vintage racing.

I'll help you out since you're new:

1. buy EV14 injectors if you're going to spend the money, but you need to convert to sequential fuel. If you aren't going to convert to sequential fuel, then you're pretty-much stuck running ---- injectors.
2. many people say the stock fuel pump is fine, mine was not. The pump is 23-years old, changing it isn't the worst idea I've ever heard.
3. Yes, we all use those injector sizes. I have 550cc EV1s in my car and they work but kind of suck compared to the level of awesome that is modern fuel injectors.

I understand, I was never in boost at 13 A/F. I was around 11 A/F or close, I was referring to most other conditions other than deceleration of course. You recommend those EV14 injectors over the Denso 550cc? or the Deatschwerks 700cc injectors from FM?

yes. ev14>ev6>ev1

What does ev14, ev6, ev1 mean?? Is it Evolutions? Also do the Densos and Deatschwerks fall into this somehow? If they do what are they?

Estradiol Valerate

I have no idea what that means.... :confused:

more bettah.

its the spray pattern/efficiency to atomize the fuel.

Thanks! Is it the best injector out there for the miata?

No one has said anything about the 550 Denso's and the 700 Deatschwerks from Flyin Miata.. do the EV14's just blow them out of the water??

Yes. I plan to get a set from TSE one day when I have money again.

Do you have a link for TSE? I don't know this distributor. I found these but don't know if they are correct: Fuel Injector Clinic injectors - MiataRoadster - High-performance customer service...and parts for Roadsters

bosch makes the EV14, aftermarket companies "tune" them...

injector dynamic is prob the best.

Trackspeed Engineering
I think TSE does the 750cc injectors cheaper, and they're Injector Dynamics instead of Chinese or whatever. Isn't Miata Roadster guy is the guy who left this forum because of me?

Aren't you still on batch-fuel?

The link you attached is for the 1000cc injectors aren't they? Wouldn't that be too big for 10 psi? I only have stock internals on a 1.6 short nose. I have no idea about the miata roadster guy. and if batch-fuel is pump gas then yes. I'm running premium here in CA so 91 octane.

No batch fire is how your injectors are wired up. They fire 1 and 4 at the same time and 2 and 3. So Each cylinder gets fuel sent to it by the injector when the intake valve is open and also when closed.