gkane

Hi guys

I've done a bit of research and had a look at other people's setups, but i'm still a bit confused. I'd appreciate any suggestions!

My target power is between 350-400 at the flywheel. My turbo will be HKS T04E, external wastegate and a PowerFC. Stock engine ports.

According to the formulas i found, i'll need 350 * 0.6 = 210 lb/hr fuel

If i use 800cc secondaries, and assume 85% duty I work that out to be

(550cc * 2 * 0.85) + (800cc * 2 * 0.85) / 10.5 = 218 lb/hr

Talking to other people, they say thats not nearly enough, and recommend running 1680cc secondaries.

Why such a big difference in size? What would you guys recommend in your experience?

Thanks

87 t-66

iTrader: (133)

i would run 720/1600's if you are using a power fc. better to have too much fuel than not enough.

eage8

iTrader: (9)

+1

720s are good for primaries so you don't run out of injector before you stage (I think with a power FC you have to keep the stock 3800 rpm staging trigger)

the secondaries don't really have to idle, so there isn't much reason no to go with 1680s. it does make tuning staging a chore though (again, I don't know how the power FC handles that though). you could just get 1000cc or 1300cc injectors though and probably be fine.

if you do go with 1680s, I would get them from injector.com. if you get the "import" style injectors you don't have to modify your fuel rail.

j9fd3s

iTrader: (3)

the PFC has limits as to how big of an injector will idle ok, so that is a factor. the FD guys try to run 850 primaries and they idle really rich, and at a higher rpm, cause they can't turn the 850's down enough... anyways

the 1600's vary like 10% per injector, you could have one that's 1440, and the other that's 1760, unless you buy matched.

yawpower has these nice new designed 1000cc injectors that drop in. 4x1000 is 650cc short of the 720/1600 combo. much faster injector too

to go any further you need to think about how much power you're going to want later, vs running like 40% duty cycle now...

if it was MINE, id run the 4x1000 or 720x1200, cause i know i'm happy with 350-400hp

Demonsniper1

iTrader: (2)

Well I really dont have anything really to add to this topic, but here have fun playing around with this 2nd Gen Fuel Calculator that I found while searching about a year ago. It should help you find that right injector size.

Evil Aviator

Explanation of that formula:
350 hp * 0.60 lb/(hp*hr) Brake Specific Fuel Consumption (BSFC) = 210 lb/hr

Why your number is too low:
1) You specified 350-400hp in your thread, but only used 350hp in the formula. Always use your highest planned horsepower number as a target, which would be 400hp.
2) BSFC is fuel efficiency as defined as Fuel Consumption / Power. This number depends a lot on the type of engine and how it is tuned. As you may know, rotary engines suck at fuel efficiency. Also, if you are the typical tightwad RX-7 owner who refuses to pay a professional to tune the engine, you plan on running a lot of boost, retarding the timing, running a silly-rich mixture while chasing a wideband AFR meter reading, you buy cheap Chinese Ebay parts, etc., then that also hurts the fuel efficiency. I would plan on 0.70 BSFC unless you have a pro tune the engine, in which case 0.62 is probably more accurate. If you manage to get .60 or better, then that's great. If you plan on 0.60 and run out of fuel, then you will need to buy bigger injectors and/or upgrade other components of your fuel system, which is not fun.
3) You did not compensate for the fuel injector duty cycle. The fuel injectors will burn up if you run them full-open. The rule of thumb is to give them at least 20% rest time, which results in a 80% duty cycle.
4) You did not compensate for fuel pressure. Most (not all) aftermarket fuel injectors are flow rated at 3bar (43.5psi) pressure. The stock RX-7 only runs about 34-40psi pressure. As you may imagine, a fuel injector will not flow as much at 34-40psi as it will at 43.5psi. If you plan on using an aftermarket fuel pressure regulator and increasing the pressure to 43.5psi, then you do not need to compensate for fuel pressure in your planning. A higher pressure will inject more fuel than the injector is rated, and you can push most fuel injectors up to about 4bar (58psi) before they hit a brick wall. The pressure conversion equation is: Revised Pressure cc/min = Original cc/min * sqrt(Revised Pressure / Original Pressure).
5) There are many other factors, but the above are the most significant.

Assuming that you will run 43.5psi fuel rail pressure, I think the following is a little more realistic. I wrote out the equation so you can recalculate with different numbers as needed.

(400hp * 0.70 BSFC) / 80% duty cycle = 280/0.80 = 350 lb/hr * 10.5 = 3675cc/min

Therefore, 720/1200 or 4x1000 should work fine, or you could go with 720/1000 if you tune better, run a higher fuel rail pressure, and/or shoot closer to the 350hp number as opposed to the 400hp number.

RHDturboII

iTrader: (4)

I am having the same problem. I am thinking of using 4X1000cc sard injectors too with the fc that I am building. I have everything ready to be installed and the only thing that is missing are the injectors. I will use a parallel fuel system with AN fittings and SS hoses, aeromotive FPR and fuel filter, on S4 rails for my 91 Jspec TII.

I am between the yaw power injectors and the sard injectors. The sard injectors are a direct drop in the S4 rails and are low imp so I need to wire resistors in order to use them with my ap eng. Power Fc. The yaw injectors are high imp. so there is no need to wire resistors but I do not know if they fit with the S4 rails. Is anybody using either of the above injectors with an S5 TII that can help?

The turbo that I am using is Aspec's GT3574 T4 sitting on a custom RHD long runner turblown divided manifold with tial 44mm external.

Thanks

RHDturboII

iTrader: (4)

Here is a pic of everything that turblown built for me one year ago. 3.5 downpipe, Heat shield, divided manifold, oil and water lines. The only thing that is different is the turbo on that pic. Mine is the Aspec GT3574. Elliot from turblown sent me this pic before he sent me everything.

gkane

awesome, that explanation makes a lot more sense now, thanks.

I'll be getting my car mapped by a professional tuner, as much as I want to learn about tuning, i just dont know enough yet, so im not taking any risks or cutting corners

2a+RoN

Here is an injector calculator that takes everything into account for the injector dynamics (yawpower) injectors. This has been found to be very accurate.. http://www.injectordynamics.com/hors...alculator.html

Note: setup as 2-stroke sequential for rotary.

arghx

iTrader: (3)

The HKS T04E is not a big turbo by rx7 standards. I believe it's the T04E 57 trim compressor wheel, which is significantly lower flowing than a GT35 for example. 550/1680 will be just fine. It will prevent any possible hassle with idle mixture, and with an adjustable FPR you'll never run out of fuel with that turbo.

The injector staging in the Power FC is duty-cycle based, not rpm or boost based. You configure a target duty cycle and some other settings and the PFC will smoothly blend the two injectors together, ramping up the secondaries and ramping down the primary's. It doesn't even require a whole lot of tuning really. With 550/1680 just use the injector staging settings that everybody else uses and it should be fine. The injector staging is great once you get it set up right.

The side feed FD 850's seem to cause the worst problems with the rich idle, but there are workarounds for it. My 2nd gen with Power FC, 720/1680 and 40psi base pressure idles around 13:1 with a large streetport, no workarounds needed to achieve that. The increased fuel consumption from the porting may help to lean the mixture out.

Also, your choice of plugs can have a big effect on the idle. I used to use aftermarket plugs but now I just run the four BUR9EQ's and it idles fine while boosting with no detonation or spark blowout issues (I use HKS twinpower ignition upgrade).

Turblown

iTrader: (12)

Go with the YawPower Units, don't use anything that needs resistors with that ECU.
I believe they have adapters for the top and bottom of the injectors so they will be identical to the bosch style injectors. However to get the bosch units to drop right in you usually have to grind the tops of them a little bit. I would email Paul over at Yawpower.

Glad to hear your project is coming along.