mauimoon

I have a nearly stock 94 R2 except for full 3" exhaust (DP, HF cat, RP cat back), RP cold air intake and PowerFC. The car runs great except for a little boost problem that I'm working on at the moment (different thread).

As long as the UIM etc. is off solving the boost problem not only am I upgrading the vacuum pressure lines with Viton I thought I might as well upgrade the injectors and replace the fuel pulsation dampner (a known weak point).

My tuner has suggested going from 550x850 to 850x1300 injectors. 1300cc's for the secondaries makes sense to improve the high end and prepare for future upgrades. I'm planning on sending my existing 850's to RC Engineering to be bored out.

However, I'm not sure about his advice going from 550's to 850's on the primaries using lower fuel rate settings / duty cycle for low rpms. He claims it will allow him to provide better tuning in the mid-range including the 4500rpm transition and providing quicker throttle response after shifts. I haven't been able to contact his references as yet to validate. Does anyone here have any experience to back up or debunk these claims? If a good thing, is it worth the $250 for new 850cc injectors or is it more a case of splitting hairs?

Jon

ErnieT

iTrader: (2)

You don't need the 850primaries especially if your still stock twins. I run 10's on 550primaries, so I know there OK for you. The 1300cc secondaries are a good idea. And don't waste your money on new injectors if your sending them to RC anyhow.

jspecracer7

Agreed. You won't need them. If your planning to go single, that's not a bad route to go...

duboisr

The car will idle as well with the 850 s Stay with 550-1300 with twins

Flyrx7

iTrader: (1)

Vancouver, Wa.
who's your tuner?
Pineapple is right across the Columbia from you, have you talked to him?

Frank

mauimoon

Pineapple/Rob is excellent for motors and race chassis design but he does not have a dyno nor a solid background in ECU's. He and the rest of us use Ralph Friends at Xcessive-Motorsports in Aloha for dyno-tuning. Ralph is crack at both PowerFC's and Haltech. If you have a lamda sensor tapped into your cat-back he'll even do road-tuning as well.

Jon

Flyrx7

iTrader: (1)

From what I've heard, Ralph is very knowledgable. So is he the tuner you are doubting? I would think that he knows very well what he suggests. But of course, by the sounds of things from other forum members it may not be necessary, but if Ralph says it will work fine, just think of all the extra headroom you would have.

Frank

GoodfellaFD3S

iTrader: (213)

Usually people with the stock twins go either route-850sx4 (like my bud alan) or 550s/1300s like i did.

Chris Ott at RP is of the opinion that taking apart the injectors (like RC Eng does) isn't the best thing for reliability. He recommends just going with 4 stock 850s. Tuning isn't a problem....Steve Kan tuned alan's car at idle with the 850s at idle very easily.

Alot of it depends on your ultimate goals.

Use this link to access RP's FD specific fuel calculator:

http://www.rx7.com/cgi-local/3catalog.cgi?cat=11

According to it, with my setup I'm good until about 475 motor horsepower at 85% injector duty. I'm tuned rich enough that I consistently see 80-83% toward redline.

Are you ever planning on going single and making big power? If so, I say listen to your tuner .

mauimoon

The goal for this car is sleeper stock (or at least the visual appearance of stock...think Concours de' Elegance in another 7 years after the body is brought up to show quality). Driveability and reliabitliy is as important as overall road performance.

I will stay twin and won't do anything special with the motor until he next time it needs to be rebuld (it's a Mazda reman under warranty with only only 2K miles on it now and it's a very nice running motor). However, I do need to be sure I beat the socks off the occasional challenger. Ideally I'll find the place the original engineers had intended for the FD before the priorities of federalization and warranties were applied.

I started out thinking 850x4 as Ralph has done with other cars. However, Ralph's thinking this week is he can more tune for a multi-use car better on larger capacity injectors because the lower duty cycles allow for more precise metering of fuel under all conditions. He told me this just befor leaving town (SEMA in Las Vegas). This is the main reason I bouncing stuff off the forum instead of just talking to Ralph about it because I'm not sure I really need the 850 primaries (and $250 is $250).

As far as any issues with RC's 1300's...Ralph says they are fine for except for sustained race conditions. If your going to race get a new fuel rail and top feed 1600's.

The only real technical catch for upgrading the primaries to 850 is for apply an interim map to the PowerFC so the car will at least run tolerably until I can get to the head of his queue (generally weeks and you have to be ready to go at a moments notice). Ralph says he'll fax me a map to use.

Jon

SleepR1

I'm having my injectors replaced due to possible cracks in the stock injectors. I'm thinking of upgrading the injectors (I think they're the primaries?).

Anyhow, what's the right size to use with Anfini Twin Turbos that I plan to use with a new KDR "secret sauce" motor, HMIC, CAI, and Apex PFC? Will I need to upgrade the fuel pump as well?

I plan to run no more than 10.8 psi max!

mauimoon

My thinking is that in order to provide maximum flexibility for tuning you should go 850 primary x1300 secondary. I believe keeping the approx 1.5:1 ration of secondary to primary is important to keep the duty cycle and injection pulse timing symmetrical (at least for a PFC). Even if you don't the headroom the injectors will be more precisely and run cooler with lower duty cycles (i.e. reliability). In any case with a PFC you'll either need a professional tuner with the Apexi Excel tools or the Datalogit plus an air/fuel meter (preferably with an add-on 4 point Lamda sensor in your exhaust system) in order to get your setup running to it's full potential.

I took my stock 850's and sent them RC Engineering for conversion to 1300's ($350 plus shipping) and bought new 850's for the primaries ($250 plus shipping from RX7Trix.com). Once I programmed my PFC with new baseline injector information the car started right up and is running pretty well. I havent' been to the tuner yet.

Jon

M104-AMG

iTrader: (8)

Can I get a copy of that temporary map ?

Thanks,
:-) neil

RecKleSs

There is a lot of great info on this thread for you. I strongly recommend you NOT to bore out the injectors. I sent out my injectors to RC to have them bored and they failed on me within a few thousand miles. Luckily it didn't destroy my engine.

HDP

iTrader: (2)

Regardless of how many miles on them? 115K mile 850's + RC Engineering = like-new 1300's?

cloud9

iTrader: (4)

I listened to Chris at RP and went with the 850X4 route, the car idles without any problems at all and I now have the fuel to support more power than I will ever want

Ball joint

iTrader: (6)

do any of you know how much it costs to just have RC clean the 850's?

BoOsTin FD

28.98 per injector... 10% if you mention rx7club.com

I just got mine back from them.... however there is another shop i guess that does it a lot cheaper...

Amel

Ball joint

iTrader: (6)

what number do I call or.... whats the procedure?

Bad_Karma7

Do a search for Witchhunter...he does an excellent job and for much cheaper price. $15 per injector.

sevensheaven

iTrader: (1)

Man,

I just got mine back from RC, but I didn't know about the 10% discount. Just the same I wouldn't have sent mine to someone that couldn't possible have all the equipment to do the job right. Russ Collins is very reputable, go to the page and read all of it. They supply some pretty big customers. I can remember watching that guy run multiple engine drag bikes at orange county drag strip in southern California back in the 70s. My 2cents.

Terry7

sevensheaven

iTrader: (1)

Forgot, they provide brand new o rings with theirs too! See how much Mazda charges for those!

Beast From The East

using a Wolf 3d and twin Cosmo pumps. The challenge for your tuner is to get the fuel pressure and injector settings just right, since the 850s drip gas on startup. You need enough fp to get the gas to atomize, but not too much. I have found that you have to run ~2K rpm for the first 15 or 20 seconds on cold start before you can let off the throttle and have it idle, at least when it is less than 50 F ambient, and I run ~ 40 psi base fp. When the temps are higher than 50 F, only about 5 to 10 secs of 2K rpm is needed before idle sets in nicely.

Needless to say, I have all the fuel I need......

Beast

GoodfellaFD3S

iTrader: (213)

I have 850cc primaries, and my FD starts right up and idles at 900 rpm without problems, even in these NJ winters when my coolant temps are around 0 degrees upon startup.

HDP

iTrader: (2)

Anyone?

Tom93R1

iTrader: (2)

I am going with 4x850. I have heard too many people with failed 850 bored to 1300 injectors. To me just one problem is too many for something this vital and I have heard alot more than 1 injector stuck. Unless I was going for some crazy HP numbers that is what I would recommend, and if that isnt enough fuel go with 1600cc aftermarket injectors.