RX-7 Pilot

Just wanted opinions on combinations of injector sizes to run on my apex single. I have 1200cc secondaries now but was considering 4-850cc or possibly 550 primaries with 1600cc secondaries. What do you guys think?
thanks
Kelvin

spyfish007

Well I'm eventually going with the same setup . . . but my injectors will be 850 and 1300 ... sounds like overkill which it is..sort of, but you will also never run out of fuel! Another factor is that XS has maps for this very setup. I will get my PFC programmed by them and then fine tune on a dyno. Hope that helps.

4cefed7

why bother with such large primaries? are you planning on hitting full boost that low in the rpm range? and why waste money on 1300cc when you could go ahead with 1500 or 1600 and save yourself the trouble if you ever wanted to go with a bigger turbo?.

RX-7 Pilot

Heh..I also called XS to see what size injectors they would recommend with my set-up and they said:

850cc primaries
1300cc secondaries

And yep they do have a good map for that set-up.

RX-7 Pilot

lol....ordered my new injectors & waiting to get my PFC reprogrammed by XS. Do I need to get a fuel regulator too??

spyfish007

The apex kit makes a lot more power between 2k and 4.5k than most turbos. It is the and up when it starts loosing ground on bigger turbos. The HP peak is at/around 6.5k to 7k. It is a really nice turbo for street, 1/8 mile, and autocross because it spools really fast, as fast as the stock twins, but really out flows the stock setup. That is the reason for big primaries. The turbo is rated up to 450 RWHP .... but I think that is a real long shot. I think Max Cooper is going after that .... and these injectors sizes would equal that rating ... so there is never a real need to go beyond that and if you do this setup then you don't have to modify the stock fuel rail.

HWO

1600cc injectors have horrible spray patterns if you want a car tweaked well around the 0-5psi range then you'll see better results with smaller secondaries

I personally am going for 4 x 800cc secondaries and either a pair of 550 or 720's for primaries

if you intend on running big HP or boost or whatever then too much fuel on tap is something you want, its better to be oversafe than sorry

maxcooper

I am running 550 primaries and 1300 secondaries with an XS map in my PowerFC and the RX6 turbo. I've only driven the car for 50 miles, but it seems to work pretty well. No major activity on the J&S even with some boost spikes up to 18 psi (still sorting out the boost controller setup).

I actually own a secondary rail with 1600s, but I opted to enlarge the secondaries instead so that I could more easily switch back to "emissions test" mode if and when I need to. And I feel better about running stock-like injectors for some reason. Their position and flow pattern has already been engineered into the system and I don't have to cut the wiring harness and use resistors. Enlarged stock injectors just seem like a safer bet.

I might add a regulator and up the base pressure to 45 or 50 psi if my current setup proves inadequate. The next step after that is big primaries, but I don't expect to need to go there. If you haven't seen it yet, I made a web page that helps you figure out what different fuel system configurations will support:
http://www.maxcooper.com/rx7/how-to/...tem/calcs.html

-Max

Cheuk in Seoul

I am running 550 / 1200 and I am running out of fuel. I need to get back on the dyno but I think that I'm maxing out at around 17 psi and approximately 450 RWHP. Remember, I put down 443 RWHP uncorrected at 15 psi. I think that either approach is fine... larger primaries to 850 or going with 550 / 1600.

When Matt the "HITman" is back in town I think I will replace the stock fuel pressure regulator and try for more boost.

RX-7 Pilot

thanks for the info guys!!

RX-7 Pilot

I'm still waiting for my injectors and PFC reprogramming. Does anyone here run 850cc primaries and 1300cc secondaries? I wanted to know how does it feel on street driving? Overly rich idle or a slight bog on full throttle? My mechanic thinks these injectors are too large for the street. He recommends 4 850cc injectors instead. Any comments?

enzo250

Yeah i think that if the car is to be used mainly for street you should not have big primaries.. You will only need big secondaries. You want small primaries so that you have a good spray pattern. Then when boost hits is when the secordaries come into play.

If this car is going to see high boost you got to upgrade the FUEL SYSTEM not just injectors. You should get a fuel cell(or add a sump to stock tank), at least -8 fuel lines, fuel pressure reg, external pump, and filter...

Styk33

What Max and HWO recommends is the best for you situation. I would just be repeating what they said, but all is great info.

As far as what Enzo says, he obviously has tons of cash to burn. You can make 600+RWHP with the stock fuel lines, stock fuel tank. Changing out the injectors, FPR and fuel pump is the most you will really need to do. Change the fuel tank only if it is a requirement for the series you are racing in (make sure it is DOT approved).

RX-7 Pilot

Thanks guys, maybe I will not put in the 850cc primaries and run the 1300cc secondaries with the stock 550cc primaries and see if this set-up is adequate. I wonder why XS would recommend the bigger primaries? Max HP?

RX-7 Pilot

Hey Max
please keep me updated on how your car is running since my set-up is very close to yours!!!
thanks

enzo250

hey i don't have ton's of money but i make sure i spend it correctly because if it's not right the first time and i run out of fuel it could get a lot more expensive.

By the way 600hp with stock fuel lines, Your pushing your luck.

enzo250

Thats a good setup

Jedon

I thought the PowerFC only supported up to 1300cc injectors?

RX-7 Pilot

Will the 850cc injectors seat well in the primary injector location? I think they are different lengths. Also can you max out the 550cc primaries with a large secondary injector set-up? Or is the primaries not the limiting factor?

Jedon

From what i've read, you just need some extra gaskets to mount the 850's for primaries. They won't max out until the secondaries do so make the secondaries big :-)

maxcooper

The max size you can set in the PowerFC is 1500 cc/min, but running bigger injectors is equivalent to running more fuel pressure, so it is possible to run bigger injectors with the PowerFC. The PowerFC just doesn't know their true size.

The max size you can bore the stock secondaries to is 1300 cc/min. That is what RC told me when I asked that they make them as big as possible.

Some people have their primaries enlarged to 850 cc/min, much like having your 850 primaries enlarged to 1300 cc/min. That will ensure a good fit.

The 550/1300 setup is good to about 400 RWHP at the stock fuel pressure. That assumes BSFC 0.62, 85% duty cycle, 13.5% drivetrain losses. At 45 and 50 psi base fuel pressure, that setup is good to about 425 or 450 RWHP. This is sufficient for most setups that people are going to use on the street.

850/1300 is good to about 465 RWHP at the stock fuel pressure and 495 or 525 at 45 or 50 psi base fuel pressure, respectively.

550/1600 is good to about 465, 495, or 525, also.

850/1600 is good to about 530, 560, or 590 RWHP at the various fuel pressures.

Play with the numbers youself here:
http://www.maxcooper.com/rx7/how-to/...tem/calcs.html

-Max

RX-7 Pilot

Hey Max
Do you find any kind of bog when the secondaries come online? How is the power delivery? Hey let me know what kind of numbers you put down? Thanks you been a lot of help.
Kelvin

sorry for all the questions.....

RX-7 Pilot

On a side note: Jedon I really like those fm5s you got there how much did you get them for?

Max---what color was your 850cc "plastic top" red??? I have a couple of extra injectors and wanted to make sure they are 850s

RX-7 Pilot

Okay I finally talk to someone at XS who explained the whole injector thing. Hope I understood him right. XS recommends the 850cc and 1300cc injectors for single turbos who want big HP while running the Apexi pfc. This is not necessarily the best size to run for smaller turbos like mine. They said if I was looking to run "only" high 300 or 400 RWHP with good drivability then 550cc and 1300cc injectors would be preferred. Larger single turbos with higher flow capabilities looking for max HP should use the larger primaries. This recommendation was given for use with the Apexi power FC, due to the fact that they reprogram this computer. Max Cooper's fuel requirements worksheet says pretty much the same thing. There is always an exception to the rule but this is a general guideline. Hope this helps!