I can't seem to find a consistent answer with how much boost you can run with the stock 550cc injectors. I've heard anywhere from 8-12psi. I'm in the process of buying a boost controller and would look to crank it up a little to 10 (with a walbro pump) but I don't want to throw a seal in the process. So can anyone give me a clear answer on the max duty cycle on our stock injectors?

Thanks,
~Ant

 

Keep it under 10 psi. Without a wideband, you will have absolutely no idea if you're running lean.

Do it the right way, and get a pair of 720cc injectors and some sort of fuel control before running 10-12 psi.

 

I'm glad I found this thread, I have a question that's kind of similar. I am looking into buying an S5 TII and it currently doesn't have an aftermarket exhaust but he is selling it with a 3 inch custom downpipe so I plan on most likely getting a much more free flowing exhaust soon after I buy it.

Basically I've read a couple threads about blowing engines with boost creep if the exhaust flows too well and you don't upgrade the fuel system/port the wastegate. And I was just wondering what the safest mods would be to do to keep the boost predictable and where it should be.

I like to play it safe so I would like to take extra precautions even if I do have to spend a bit more.

 

Rtek 1.7 is the least you should be doin if you wanna go up to 10psi. on the stock turbo 10+ and you are just blowing hot air. Porting you wastegate is ideal but almost a requirement on an S4 with a higher flowing exhaust.

 

3" downpipe and you will need to port even an s5 wastegate. I had an s5 wastegate ported to the edge of the stock flapper and it still creeped bad, with a 2.5" straight through exhaust (big street ported engine).

 

I figured that, porting the wg has been my plan all along basically, I was wondering more about upgrading the fuel system/fuel management because I really have no idea about that, my previous car was N/A and never really needed fuel management unless you were turboing it or going for a crazy N/A build which I never got around to doing either.

 

You shouldn't have too much of a problem running 10 PSI if you play it safe with no boost creep. I'd recommend a fuel pump rewire regardless.

No way? You sure about that? I mean, absolutely sure? He couldn't even read the plugs after a few days of driving to determine the A/F ratio? Or use an EGT monitor? Or hack it with the narrowband?

So the only way to ever know that a car is running lean is with a wideband? I guess I learn something new every day.

</sarcasm>

No fuel pump eh?

 

The reason you can't find a clear cut answer is because more goes into it than just PSI vs. injector size. The condition of many other components play an important role in how much boost is safe with a given injector size.

The most important thing to do is actually tune the car up to the point where your happy with the power it is making and your comfortable that it is running safely. Don't just turn up the boost controller and hope for the best. As others have said, you should be fine at 10PSI AS LONG AS all the supporting systems are up to par. Doing it right the first time can prevent expensive repairs.

 

Haha Aaron always takes the cake!

 

Aaron Cake, you said to rewire the fuel pump? I've never heard this before, I have a walbro pump and only 26k miles on my injectors so do u think I should still look into this? or could you explain that concept a little more...

 

Anybody who reads teh internet knows that a wideband is to only way ever invented to determine your air/fuel ratio. In fact, no turbocharged sports cars existed prior to the invention of the wideband O2 sensor in 2001. Prior to that everybody drove non-turbo Yugos because there was no way to know if they were running lean.


https://www.rx7club.com/2nd-generation-specific-1986-1992-17/fuel-pump-rewire-per-1300cc-com-directions-84533/

 

how does installing a walbro pump compare to a rewire? Well, I already bought the pump but I'd like to know anyway