FastX7

I need new secondary injectors for my car. Can I upgrade them to 1300cc or something bigger on the stock computer? What can I upgrade to on the stock fuel rail? I tried to search around for this, but I didn't find anything.

rxrotary2_7

https://www.rx7club.com/forum/showth...threadid=21519

i have a "stock based" ecu and you can not according to this hread, and NOT ONE PERSON ON HERE (to date) can answer my last question aout uing fuel that is unused already to allow for more boost past 14.7lb

maxcooper

Okay, I answered your question. Primary and secondary injectors run at the same duty cycle after the transition to primary+secondary operation.

Running larger injectors with a stock-style ECU is bad news. Don't do it.

-Max

FastX7

ok, that's the most definite answer that i think i'll get

Want2race

hmm I would say you COULD do it with an afc or some other system like that... that whay you could pull out fuel!

ttpowerd

I would not try it...."play safe" :p

Mahjik

iTrader: (1)

Max, you got me curious...

If the ECU thinks it's running on stock injector size, will larger injectors actually get utilized (I'm not a mechanic, but learning)?

What would happen in a situation like this?

FastX7

From what I've gather, the secondaries are 850cc, so say at 50% they're flowing 425cc worth of fuel. As far as the computer knows, that's what you need. If you put in like 1200cc injectors, the computer doesn't know that. So, at 50% they'll be flowing 600cc worth of fuel when the computer thinks it's flowing 425cc worth. Someone correct me if I'm wrong.

Want2race

Basically. teh stock ecu says it needs 10% injector duty..

So for the 850cc thats 85cc/minute.
If you change those to 1300ccs then 10 % is 130cc/minute...

See the difference ? the stock ecu doesnt know the injectors are larger so it just pumps in more fuel... Notusually a good thing...

rxrotary2_7

it was explained very well in this thread why you can NOT do it this way. read wade's posts.

https://www.rx7club.com/forum/showth...&threadid=21519

maxcooper

You got it. The ECU just blindly uses the values from the fuel map, which are essentially duty cycle values like 10% (they are really pulse widths, but that is just a different representation of the same information). If you double the size of the injectors, you will get double the fuel.

It is possible to get the car running (but never running well) with bigger injectors and electronic gizmos piggy-backed onto the stock ECU, but I just think that is a big waste of time. You'll spend lots of time tuning and it will never be right. Your car will have bad drivability and you'll hate it. These cars are complicated enough to get running correctly that it just doesn't make any sense to me to hobble together a Rube-Goldberg engine control system. You'll never be happy with it that way, so save yourself the trouble and just get a PowerFC, Haltech, or AEM computer to begin with.

Or if you aren't shooting for 360+ RWHP and want to save some cash, keep using the stock injectors and buy a used "purple box" from someone. You can even up the fuel pressure a bit without any problems if you think you will be pushing the limit of the stock injectors.

-Max

Rx7aholic

iTrader: (22)

Ok then how about less cc injectors like 900 cc, shane racing sells these injectors. Can these be used without any porblems?maxcooper, I know it's not goona dump alot of fuel because it's only 50 cc more? btw I am not shooting for high hp. khris

rynberg

why would you bother only adding 50 cc? You don't need larger injectors if you haven't modified your car to the point where you REQUIRE an aftermarket ecu. Why are you trying to spend lots of money on something you don't need yet?

Besides, once you add larger injectors, you also need a higher flowing fuel pump and possibly other things (rising rate pressure regulator). You are not at that upgrading stage yet.

Do intake, downpipe, exhaust, ecu, fuel pump, intercooler, limit to 12 psi. THEN, consider upgrading your fuel injection system.

RotaryKnight

Also running rich too rich on the car will damage it.

maxcooper

Increasing the fuel pressure would be a better option, because at least you won't screw up the primary:secondary ratio that way.

But you are correct, running secondaries that are only slightly larger will only **** your engine control system up a little, rather than ******* it up a lot.

-Max

rynberg

my bad, I just realized that you have to replace the injectors anyway.

if you are not shooting for high horsepower, stick with the 850cc, you can always get them bored out larger later.

Zoomspeed

really, how so?

maxcooper

Too much fuel washes the oil away, and you get increased wear. Carbon deposits raise compression and create hot spots that can lead to detonation.

-Max

Zoomspeed

I see, thanks. I had no idea that running rich would do that.

RotaryKnight

Yup been there done that......damnit!

RX794

You can solve your problem by utilizing additional injectors instead, just my 2 cents.

3rdGen7

Some time ago someone posted a place to get the blue top Bosch 850 cc primaries and 1600 cc secondaries for less than what RP is selling them for. K2RD has them as well but someone told me that you can get them at any GM parts dealer because they are OE injectors on some GM car/truck and they only sell for $70 or $80 bucks each v.s the $150 and $300+ that others are selling them for.

If any of you guys have info on this one please re-post all the details on this one ..when, where, who and how much.

Thanks a mil,
3rdGen7