FxF

I will install 2x550cc RC Eng primaries and 2x720cc Denso secondaries.
No fuel pump upgrade. Stock ECU. The car is going to be running 15% richer.
Planning to remove both cats (70mm pipe) and do the TID mod.
Max Cooper's fuel calculation page has troubled me. http://maxcooper.com/rx7/how-to/fuel_system/calcs.html

According to the calcs I did, I am good for about 221fwhp.
Is this fuel setup going to be enough or do I have to install a Wallbro 255lph fuel pump?
Info about the car in the sig.

-Fanis

Bukwild

yeah you need the fuel pump first. Stocker won't be able to keep up with the 720's

Turbonut

iTrader: (1)

Ditto the above. Get a fuel pump upgrade ASAP!

FxF

Will I need an FCD too?
I am also going to check if the pump get its normal voltage(wiring).
Is there something else I should do?

-Fanis

NZConvertible

Why are you even upgrading the injectors? From your mods list you're making about stock power.

FxF

My stock injectors were FUBARed and I am planning to mod the car, so I said why the hell not.
Check my thread. https://www.rx7club.com/2nd-generation-specific-1986-1992-17/bad-fuel-injector-problem-313589/

-Fanis

NZConvertible

If you simply throw bigger injectors in with no form of control, it'll run worse than before. You'll lose power and chew through fuel unnecesarily. You need to get a fuel controller, which will not only allow you to run bigger injectors without these problems, but will also let you lean out the conservatively rich factory mixtures. More power, less fuel.

BTW, your fuel calcs above are way off. With the correct pressure and proper control, the stock injectors can support ~300hp. With the 720cc/min secondaries that goes up to ~340hp. Note that the stock pump will run out of steam well before the injectors do.

FxF

I know that if I install bigger injectors with no control (ECU or piggyback), I 'l just throw in more fuel. But I am planning to upgrade to a Haltech in the future, so with the bigger injectors I am laying the foundation for further mods.
My fuel calcs were made with 38psi fuel pressure, 2x550cc + 2x720cc injectors, max duty cycle for stock ECU 63%, result 221fwhp. If I insert 50psi fuel pressure and 85% duty cycle I get 342fwhp. I think this is the number you are referring to.

The bad thing is that I didn't know that I would a bigger fuel pump even if I installed the bigger injectors, so if order a Wallbro now it couldn't be here on time.
:mad

-Fanis

NZConvertible

15% extra fuel is a huge amount and will really take the edge off your engine's performance, not to mention the extra cost. Unless your Haltech is coming real soon, I'd seriously consider option options in the mean time. But that's just me...
That 63% "max" duty cycle is a load of BS. The ECU will happily drive the injctors to 100% if you're silly enough to let it. My numbers are based on not exceeding 85% duty cycle.

FxF

I may have to consider the Apexi AFC to tune the extra fuel.

I was referring to the 63% max duty cycle the stock ECU has without tampering with it in any way (reprogrammed ECU, parallel fuel comp, stand alone)
Can the stock ECU without any exterior interference go above the 63% duty cycle?

-Fanis

ilike2eatricers

Also I think it should be added that the 720cc denso injectors are really rated at 700 (I think) and are labeled 720cc because they assume you will have an upgraded fuel pump raising the fuel pressure. Someone correct me if I am wrong.

FxF

I am nut sure about the injectors, but I am going to upgrade the fuel pump too.
Thinking of a Bosch 310lph that I found at a good price. So I got it covered in the fuel pump dept too.

-Fanis

NZConvertible

Like I said, this is a myth. There is no duty cycle limit. If there was, every modified TII would be dead by now, since the injector duty cycle gets up to ~60% when the car's stock. We know you can run 9-10psi boost on a completely stock fuel system, so the peak duty cycle must be higher or the engine would run lean and pop. The AFM is simply measuring the higher airflow and the ECU is calculating fuel requirements accordingly.

FxF

I see.
Does the ECU calculate the fuel requirements only by the AFM? How about the O2 sensor?

-Fanis

ilike2eatricers

The o2 sensor should only affect fuel consumption at cruising speeds.

HAILERS

Can the stock ECU without any exterior interference go above the 63% duty cycle?


I've posted jpgs of my Fluke showing 91 percent duty cycle on this forum. And as we all know, I'm as about as stock as they come........except for a couple of variations.

And although you probably know it.......when hitting boost of 10 psi the stock fpr will raise the fuel rail pressure to approx 50 psi. I do this with a stock fuel pump and have afr in the 11's and lowest 12's. Fuel pump rewire in my own fashion has been done so I get the 13 plus volts at night/lights on/ac on etc. I'm even foolish enough to have REMOVED fuel with the SAFC. No waldo for me right now.

FxF

In my case with the 720cc secondary inj. how will the fuel consumption be? Worse, the same? Will the O2 sensor notice the bigger fuel flow?

Having an Apexi SAFC is considered an exterior interference with the ECU so you are not stock.
I didn't know the info about the fuel pump. Did you measure your afr with a wideband?

-Fanis

NZConvertible

Unless you're cruising over ~85mph you're not even using the secondaries. If you are, it's probably within the ECU's capabilities to compensate, but I wouldn't put money on it. In open-loop driving, any time you're over 3800rpm you'll be using ~15% more fuel than normal.

HAILERS

Got two SAFC, but unlike the multitude out there, I'm REMOVING the fuel, NOT adding it. Wideband? Yes, I have two widebands from TechEdge. And I drive uphill when going full throttle to put a load on the car and viewing the wideband. I consider it fairly stock, oxidized paint and all (well, one car has a hybrid turbo, but my post applies to the car prior to the hybrid). Does a manual boost controller count? Probably. But.....

HAILERS

I probably missed the point trying to be made about the SAFC. So.....the 90percent duty cycle was recorded prior to my ownership of any SAFC. Just put your meter on a primary injector and nail the car going up a long steep grade/hill. You'll see ninty percent or your car/engine is flawed. 68percent duty cycle may be the most desirable duty cycle for the injectors, but any RX worth it's salt hits ninty percent at full throttle.